DE2461759B2 - METHOD OF PURIFYING CRUDE METHANE - Google Patents

Description

The invention relates to a method for removing impurities present in crude methane Water, carbon dioxide and hydrocarbons by changing adiabatic adsorption Pressing according to the preceding claims.

There is a need in the chemical industry for cheap, high-purity methane. Such a methane is used in the production of ethylene oxide, fluorocarbons, carbon disulfide and Hydrocyanic acid. So far, purified methane has been obtained from natural gas through a multi-stage process to which a Washing with oil and a subsequent chemisorption belonged, for example, in a bed of a Contact mass made of copper at elevated temperature. The process is expensive and difficult to regulate. As a result, the use of methane purified by this process is costly severely limited. Purified mettian can also be obtained by cryogenic processes, below Use of a distillation column in which a methane-rich fraction of the starting gas is added an end product consisting of pure methane is refined. This latter method can be economical be carried out when large quantities are processed and when other pure end products be obtained as methane, for example hydrogen or carbon dioxide. For obtaining smaller ones or moderate amounts of methane, this process is costly and difficult to perform.

It is known to separate hydrocarbons by adsorption. Usually natural gas is treated in such a way that the water is separated off and that the so-called condensable components, for example coals Hydrogen with 3 or more carbon atoms in the molecule can be obtained. Activated carbon, silica gel and Aluminum oxide are the usual adsorbents for this purpose. But this is a raw one Process that cannot be called cleaning. The end products were not very pure required and there was no need to completely isolate any components in one of the factions. After adsorption, the fraction consisting of condensable components becomes further refined and separated. The natural gas freed from condensable components is used as fuel used, a precise regulation of the composition is not necessary if only the condensable components are removed to below the dew point and freezing point, which corresponds to the temperatures in which this residual gas is used.

In the aforementioned known adsorption systems for the treatment of natural gas are changing Pressures applied. A closed regeneration with a heater / um is usually used Desorbing the beds at an elevated temperature. Downstream of the desorbing bed it will Gas is cooled to remove the heavy hydrocarbons by condensation, whereupon the gas is returned to the heater. The condensed hydrocarbons are main

those with three or more carbon atoms in the molecule, and a large proportion of the components with two Carbon atoms in the molecule get into the end product together with the methane.

In a few cases attempts have been made to obtain the To separate components with two carbon atoms in the molecule from the methane, but with the purpose that To obtain components with two carbon atoms in the MoL-kül, not to obtain purified Methane. In this trial, a two-step process was used, in which first one Fraction from components with one and two carbon atoms in the molecule was obtained, which subsequently was separated in a second process step.

Systems for adiabatic adsorption under changing pressures are known for separation of gas mixtures with selectively adsorbable components. One such system is in U.S. Patent 34 30418. After this, the gaseous end product becomes unadsorbed or less strong adsorbed constituents withdrawn under practically the same pressure under which it is introduced. According to the aforementioned US-PS at least four separate adsorbent beds are required by Lines are connected in parallel. Each of these beds goes through four different process steps:

(1) Adsorption at constant feed pressure.

(2) Extraction of what is located in the interstices Gas,

(3) Rejection of the adsorbed components,

(4) Increase the pressure again.

Adsorption at constant feed pressure is achieved by flowing the freshly introduced gas through the adsorbent bed and by simultaneously withdrawing the end product from the bed at practically the feed pressure. the Extraction of the gas located in the interstices is carried out in cocurrent Reduction of the pressure over the bed, as described in US Pat. No. 3,176,444. The very pure from the The gas obtained from the interstices is used for increasing the pressure in a second flushed bed and also for flushing a third bed under increased pressure. That Separation of the adsorbate is carried out in cocurrent by reducing the pressure above the Bed and then by countercurrent purging at low pressure with one of the interstices recovered gas of high purity. The increase in pressure is carried out with a gas from which the adsorbate is completely or almost completely removed. The required gas will partially run out recovered from a bed which has been placed under reduced pressure in cocurrent, d. H. with a gas extracted from the interstices. and partly from another bed during the Adsorption, d. H. the gaseous end product. The four different process steps preferably require the same length of time. As I said, at least four beds are required to have a continuous To achieve flow of the imported gas and the end product. The system according to the US-PS 34 40 418 allows the recovery of the constituents of the end product that are in the bed after adsorption are located. Some of these constituents can also be adsorbed together with the preferably adsorbed constituents of the supplied gas. The rest

remains in the gas phase within the bed, i.e. H. in the interstices. For effective use of the system according to US-PS 34 40 418, it is essential that the adsorbent bed in cocurrent supplied gas to reduce the pressure at the moment when this gas enters from another Bed can be pulled off. An improvement of the system according to US-PS 34 30 418 is in US-PS 35 64 816. According to this, after completion of the adsorption under constant pressure, the pressure in equated two stages in order to extract the gas from the interstices; at first with one already partially pressurized bed and then with another bed just below that has been purged at the lowest pressure applied in the process.

If the final product is to be used at pressures well below the supply pressure of the gas, recovery of the gas from the interstices can be carried out in three tanks using a method described in US Pat. No. 3,636,679. In this process for recovering the end product under low pressure, compressed feed gas and gaseous end product are introduced simultaneously at opposite ends of a previously purged adsorbent bed in order to partially increase the pressure. This is followed by a further increase in pressure, all with fresh gas, whereupon the end product is withdrawn. Simultaneously with the increase in pressure by supplying the gas from both sides, part of the gas freed from a constituent is released from the bed, which is under reduced pressure in cocurrent, as the end product obtained under reduced pressure. These measures make it possible to carry out all critical process steps which are necessary in order to achieve an effective separation of the gas fed in and in order to avoid an intolerable interruption and changes in the pressure of the gas fed in and of the end product.

Another adiabatic adsorption process using alternating pressures, which is particularly suitable for the use of two adsorbent beds, is described in US Pat. No. 3,738,087. The improvement according to this process consists in particular in the fact that the pressure of the gas introduced into the adsorption zone, which is partially under lower pressure, is higher than the aforementioned intermediate pressure. One constituent is selectively adsorbed and at the same time the gas freed from one constituent is withdrawn at the outlet end of the zone. The introduction of the fresh gas, the adsorption of one component and the removal of the gas freed from a component are carried out at such relative speeds that the pressure in the adsorption zone is brought from the intermediate pressure during this process step to a higher pressure at this step. In other words, during the increase in pressure in the adsorption step, the total molar ratio of the rate of gas intake to the adsorption zone is greater than the molar rate of adsorption of the gas on the bed. The term "total molar feed rate dcv gas" means the rate at which the make-up gas is introduced minus the rate at which gas is withdrawn from the bed.

The expression "molar rate of adsorption" is the rate at which components of the supplied gas are transferred from the gas phase to the adsorbed phase, minus the rate at which components of the supplied gas are displaced or otherwise removed from the adsorbed phase. If the molar rate of gas supply is higher than the molar rate of gas adsorption, the adsorption pressure increases. This can be achieved by throttling the withdrawal of the constituent gas relative to the supply of fresh gas.

An object of the invention is an improved adiabatic adsorption process under alternating conditions Pressures for the extraction of high purity methane in small or moderate amounts from cheap easy available raw materials such as natural gas. In this context, methane of high purity means a methane with a purity of at least 99 percent by volume, which is only traces of water, less than 1.0% hydrocarbons with two or more carbon atoms in the molecule and less than 100 ppm carbon dioxide. Most of the The nitrogen, hydrogen, and noble gases in the crude methane are also included in the final product. These latter ingredients do not interfere with the known uses of high purity methane.

The invention relates to an adiabatic method using alternating pressures for selective Adsorbing impurities such as water, hydrocarbons with two to five carbon atoms in the Molecule. Carbon dioxide and hydrocarbons with six or more carbon atoms in the molecule raw methane for the production of purified methane.

In the method according to the invention, the methane impurities can consist of less than 15 percent by volume of hydrocarbons with two to five carbon atoms in the molecule, less than 5 percent by volume of carbon dioxide and less than 1 percent by volume of hydrocarbons with six or more carbon atoms in the molecule. Natural gas is the most common source of methane with these levels of contaminants. In natural gas, the hydrocarbons present as impurities are mainly saturated hydrocarbons such as ethane and propane. According to the method, the crude methane is introduced under the highest pressure at the inlet end. The contaminants are selectively adsorbed in each of at least two sequentially operated adsorption zones. The contaminated methane is withdrawn from the adsorption zone such that the adsorption front of the contaminants is formed in the zone at the inlet end and progressively moves towards the outlet end for the purified methane. The gas flow ceases when the adsorption front of the contaminants is between the inlet end and the outlet end of the zone. The methane freed from impurities is then withdrawn at the outlet end of the adsorption zone, the pressure in the adsorption zone being lowered in cocurrent. The impurities are flushed away from the zone under reduced pressure by introducing part of the methane freed from the impurities in countercurrent from another adsorption zone through the outlet end into the adsorption zone under reduced pressure and withdrawing it from the inlet end, and in that the zone flushed in this way is placed under an at least partially higher pressure by introducing another part of the pressure; from the contaminants liberated methane from Ainet

s another adsorption zone before the re-introduction of crude methane into this adsorption zone.

The inventive method is characterized in that as an adsorbent in dei Adsorption zone used silica gel, and that one the

ίο carries out selective adsorption at 10 to 66 ⁰ C under an absolute pressure of 6.3 to 25.5 kp / cm ² .

The selective adsorption is preferably carried out at 21 to 38 ° C and / or preferably it is carried out under an absolute pressure of 8.05 to 16.80 kp / cm ·

is done. Because the procedure is adiabatic. get all process steps carried out practically at the same temperature as the adsorption, where eir slight cooling of the zone during flushing due to the heat of desorption is neglected

ίο can. The information to be in the DC reduction de: pressure and the purging be carried out at significantly lower pressures, usually nui slightly above atmospheric pressure, / .. B. at an absolute pressure of 1.75 kgf / cm ^2.

2 <i In this description, the during dei Purified methane withdrawn by adsorption and then passed through in cocurrent during the following led depressurization designate withdrawn methane as purged methane;

ίο Both can be used at least !: 'Partial reduction of the pressure in the flushed! Adsorption zone. In certain embodiments dei invention, for example, in the preferred exporting approximate shape with four zones according to the F i g. 8, can dr

is purified methane, which is un'ei during adsorption constant pressure is withdrawn, very few! Contain impurities than the gas. this in Direct current is used to reduce the pressure, for example only 1/100 of these impurities.

The method according to the invention can be used in any adiabatic method Use of alternating pressures with the features described above. /. B. in systems with viei Adsorption zones according to US-PS 34 30418 11 nt

4s 35 64 816, with three adsorption zones according to US-I '. ¹ : 36 36 679 and with two adsorption units according to US Pat. No. 3,738,087. The method according to the invention is particularly described and shown in connection with these systems with two, three and much

so adsorption zones.

The following description makes it clear that this process completely achieves the object of the invention and that a methane of high purity can be obtained from natural gas by an inexpensive adiabatic process using alternating pressures.

De drawings illustrate some embodiments of the invention.

F1 g. 1 shows breakthrough curves for raw methane be

no use of three selective adsorbents Activated carbon, aluminum oxide and silica gel;

F i g. 2, 3 and 4 show the self-cleaning behavior for the impurities carbon dioxide and ethane from activated carbon, aluminum oxide and silica gel;

fts F i g. 5 shows the relationship between the purity of the methane obtained as the end product and the yield when using different pressures with silica gel as adsorbent:

F i g. Fig. 6 shows the relationship between the purity of the final product methane and the pressure over the silica gel serving as adsorbent at a constant yield from the crude methane;

F i g. 7 shows a program for the circulation and the times for the various process steps in Use of four adsorbent beds made of silica gel in a preferred embodiment of FIG Invention;

F i g. 8 schematically shows a flow diagram in a device which is used for the method according to FIG. 7 can be used using four idsorbing beds with pebble urchins;

F i g. 9 shows another program for the process steps and the time periods in a device according to FIG. 8th:

Fig. 10 schematically shows a flow chart of a Device using three adsorbent beds with silica gel;

F i g. FIG. 1 shows a suitable program for the method steps and the time periods in a device with three adsorbing barks according to FIG. 10;

Fig. 12 shows a suitable program for the method steps and the time periods using a device according to FIG. K) with three adsorbing At th;

I- ig. 13 schematically shows a flow diagram of a device to carry out the invention using two adsorbent beds with Kicselgel;

Fig. 14 shows a suitable routine for the procedural steps and the durations of use a device according to FIG. 13 with two adsorbing Beds.

It was generally believed that Kicselgel. Activated carbon and alumina are equivalent in the recovery of Ciasolinfraktionen au ¹ - F.rdgas by thermal ;; Adsorp on using varying pressures. However, commercially available pebble urchins are used for the process according to the invention. / .. B. Davidson Grade 40 from Grace Chemical Company, useful as an adsorbent alone. This is surprising since activated carbon and aluminum oxide have always been used as adsorbents / in order to separate gases containing natural gas and similar hydrocarbons. It is also known that activated carbon is suitable for the adsorption of carbon dioxide using alternating pressures and for the adsorption of hydrocarbons from hydrogen. Using this latter method, an exceptionally high purity hydrogen, greater than 99.999%, can be obtained. be won.

The uniqueness of silica gel for the implementation The method according to the invention is based on three special properties under adiabatic work conditions using alternating pressures. These characteristics are: (1) A high differential Loading capacity for all impurities that are to be removed from the methane, (2) a good one Enrichment of the exhaust gas in impurities, and (3) light cleaning of the bed with a purge gas low pressure. The high loading capacity allows a relatively small adsorbent bed to be added use, the cost of which is cheap and which does not need to be desorbed frequently, whereby less end product is lost. The accumulation of impurities in the exhaust reflects this Extent of severance, again, that can be achieved with this procedure, and is important to come with

to remove the impurities with as little loss of end product as possible. The easy cleaning or desorption allows a high purity methane to be obtained as the end product using from only small amounts of purge gas. All of these three qualities are important in obtaining one High purity methane in high yield

The first of these characteristic advantages of silica gel, the high differential loading capacity, is shown in FIG. 1. This figure shows the breakthrough of impurities in activated carbon (curve A) in aluminum oxide (curve β 1 'and in silica gel (curve C) were obtained using a bed of each adsorbent that had previously been cleaned of all impurities, CO :, hydrocarbons with two and three carbon atoms in the molecule, then heated uniformly to 24 C and then with pure methane to an absolute pressure of 11.5 kp / ^cm. was brought at the start of the experiment, a gas mixture of known composition containing the mentioned impurities was passed at 24 C under a pressure of ll.Skp / cm ² with a measured speed of 1870 1 / hr the therethrough flowed through the fielt Gas was analyzed at known time intervals after the start of the experiment.

In such an attempt initially no impurities are found in the gas which has passed through, and a purified end product is withdrawn. After the formation of an adsorption front for each impurity, the time within which an adsorption stream of the impurities reaches the end of the bed is determined at a constant measured feed rate of the fresh gas end product free of impurities. In the fig. 1, the abscissa is the time from the start of de: adsorption, and the ordinate is the concentration C of the impurity in the passed Ga 'at the time; at. in relation to the concentrator Co of the impurity in the supplied gas. At a point in time t , a lower value for da means the ratio C / Q ·,. that the adsorption front for the respective impurity has not yet broken through. That in the experiments according to Fi g. 1 supplied Ga! contained 96.5% by volume of CH ₄ . 0.30 Vol. - ¹ Vo C ₂ H _n . 0.05 Vol- ⁰ A C ₃ Hs and 2.40 Vol .-% CO ₂ . Obviously there are three curves for each impurity, one for C; H _h . one for C ₃ Hs and one for CO ₂ . The F i g. Fig. 1 shows the curves for the former of these impurities.

Activated carbon absorbs the impurities in the following order: CO ₂ , C ₂ H ₆ and C ₃ H ₈ . Curve A is di <breakthrough _{curve for CO 2} . the concentration in the gas that had flowed through reached after 10 minutes the value of 0.5 for C / C6 aluminum oxide holds the impurities firmly in the sequence C ₂ He. C ₃ H and CO ₂ .

The curve B therefore relates to C ₂ H6 and the value for the ratio OG of 0.5 is reached after 7 minutes. Silica gel holds the impurities in the order C ₂ H ₆ , CO ₂ and C ₃ H ₈ . The curve (thus relates to C ₂ H ₆ , and the value for the C / Co ratio of 0.5 is reached after 15 minutes! It can be seen that silica gel enables two more pure end products to be obtained than the other adsorbents before a breakthrough of any of the impurities occurs.

ίο

The experiment described shows the movement of the absorption fronts of the impurities in beds when operating the method according to the invention not again. In this process, the adsorption fronts may only move up to a ■■ Feet in the middle of the bed and are not allowed to move break through. However, the test results shown explain the behavior of the three adsorbents Under operating conditions and are therefore suitable for comparison purposes. κ

The second characteristic of the advantageous (Properties of silica gel, the accumulation of impurities was shown at identical beds each adsorbent through which suppressing the 11.5 to 3.15 kgf / ^cm: exchanged \ ~, a gas with 96 , 5 _{vol-% CH 4} , 2.40 vol-% CO ;, 0.04 vol- ⁰ Zo N:, 0.30 vol-% C ₂ H ₀ and 0.05 vol- ⁰ Zo CjHi The following process steps were carried out one after the other:

Traversing step

Pressure kp / cm- Elapsed time in minutes
at the end of each process step

(1) Adsorption 11.5 3.0

12) Reduction of 11.5 to 3.15 5.5
Pressure in direct current

(3) flush in 3.15 9.5
Cegenstrom

(4) Re-increase 3.15 to 11.5 11.1
of pressure with

Kl ethan

At the beginning of procedure step 3, as soon as the pressure above the bed had dropped to 3.15 kp / cm ^: and purging began, the gas that had passed through the bed was analyzed _{for CO 2} and C ₂ H _0. The enrichment factor ε for an impurity was calculated as the ratio of the maximum Ieη concentration of this impurity in the gas used in the countercurrent to reduce the pressure to its concentration in the supplied Cas. The results of these tests are given in Table I.

Tabel
factor

Adsorbents

Carbon alumina silica gel

E. CO:
Real,

1.0

1.1

3.0 to 4.0
2.0

2.5

1.7 to 1.8

These values show that practically no separation of CO ₂ or C ₂ He was achieved on activated carbon by adsorption at changing pressures. The enrichment factors E of or about 1.0 mean that each impurity was released in about the same concentration as it was in the fresh gas Eugefühn. This means that an unusually large amount of the final methane would be required to remove the contaminant from the bed and therefore the yield of the final product would be uneconomically low.

In contrast, there were good enrichment facts Lorries observed with aluminum oxide and silica gel. The higher values for alumina indicate that the ability of aluminum oxide to give off impurities is superior to that of silica gel gen isi, when using relatively small amounts of rinsing gel. But as will be shown below, Although high enrichment factors can help remove the bulk of the contamination mean, but they don't mean that the pollutants graze completely removed. Careful cleaning is important to an end product of high purity / u win.

The third advantageous characteristic ligament of silica gel is the easy self-cleaning: it wiirdi shown in the experiments to determine the enrichment factor. A self-cleaning comes out through a stable adsorption front of the impurity, dii does not progress to the end of the indentation, not even with numerous repetitions. When the bed fell cannot clean itself with regard to a contamination, this contamination may occur 11 the gas which has flowed through it, and with repeated work its concentration in the end product increases dukt gradually. In the tests described, the ability to clean itself was measured by analyzing the gas which has flowed through after process step 2, d. H. just before dii Removal of the contamination began. Such analyzes were carried out when the circulation was repeated several times carried out. A gradual increase in the concentration of the contamination until it is unacceptable! Lot showed that a self-cleaning ability not available. A decrease in the concentration of the impurity or a constant below it maximum portable amount showed that a satisfactory self-cleaning was present. A continued decrease me the concentration of the impurity to amounti far below the required upper limit in the The end product is evidence of overcleaning and shows that the yield can be increased Reduction in the amount of gas required for purging.

The F i g. 2 shows the results of the experiments on dii Self-cleaning coal, the F i g. 3 the voi aluminum oxide and FIG. 4 those of silica gel. Dii F i g. 2 shows that a breakthrough is the impurity egg from the bed of coal usually immediately after the repetition begins, which agrees with the Enrichment factor determined above in the sewing

by Ί.Ο. The curve A for CO ₂ runs smoothly at a concentration of the supplied gas of 2.4 ° ö. Dii curve B for C ₂ H _C shows that self-cleaning for dii

- 50 pollution is reached, but that in the The end product still contains a significant amount of this contaminant. For this attempt there was Fresh gas in an amount of 2090 l / h. supplied, unc the ratio of the gas used for purging to the gas supplied was 0.45.

Fig. 3 for aluminum oxide shows that CO _{2 is} better retained (curve A). but that considerable amounts of C ₂ He get into the end product (curve < B). The abrupt discontinuities in the curves correspond to efforts to reverse the adsorption fronters of the contaminants in the bed by very strong purging. Curve A for CO corresponds to the very strong flushing at lower concentrations in the withdrawn gas. The breakthrough _{front for C 2} H ₆ (curve / ^ reappears almost immediately on the outflow side of the bed. The experiment was started with a supply before 990 l / h and a ratio of purge gas and fresh

supplied gas of 0.50. In the final ties Attempt were only 610 1 / hour. I mixed gas supplied, and the ratio of purge gas and fresh gas became aiii 0.55 increased without a satisfactory cleaning ties Adsorpiionsmiuels on the projecting end of the bed> egg was enough.

The 1Ί g. 4 for silica gel shows an excellent Il-it I er nc η of CO: (curve A) and C; H _b (curve B). At the beginning of the experiment, a ratio of purge gas to supplied gas of 0.59 was used. it is clear that

labile 11

under these conditions silica gel versus COj was not self-cleaning. But the adsorption front for COj responded well. if after 25 cycles the ratio was increased to 0.63. The adsorption front was apparently driven back and only small residues remained in the outlet end of the bed.

The results of these experiments are summarized in Table II. Only the stabilized graze are shown Levels and impurities in the final product at about the end of each run.

/ uhihniMi'x ratio winding

^ esi'liw inilisikeil giis / ziipcfuhries
I ¹ Si. G; is

Content; in impurities in the withdrawn gas. ppi.i

CC): r: llh

Coal Aluminiuüioxvd Kicseigcl coal .- \ luminiunu> \ ul

510 0.55 100 110 680 0.41 300 990 0.50 510 0.55 110 680 0.41 100 990 0.50 24,000 300 2080 0.4 5 690 0.63

A commercially available silica gel manufactured and sold by the Davison Division of WR Grace Company was used in all of the experiments described. The adsorbent is granular, has a surface area of about 740 m ² / g, an average pore diameter of 22 Å and a pore volume of 0.43 cm ¹ Zg. The silica gel had a particle diameter of between 14 and 3.4 mm with an average particle diameter of 2.2 mm . This is the adsorbent which is preferably used when carrying out the method according to the invention. Another pebble urchin (Davison 0.3) was also tested, which otherwise corresponded to the one described, but had a particle diameter of more than 2.4 mm with an average particle diameter of 3.8 mm. The experimental results are not conclusive but support the belief that limited transfer of mass occurs in the process and that smaller particles with diameters less than .5.3 mm are preferred. The thickness of the particles is a dimension which represents the maximum diffusion path of the gas from the surface of the particles to the most distant pores. For cylindrical or spherical particles this maximum path is the radius and the thickness corresponds to the diameter. For tubular particles, the thickness is the difference between the outer and inner radius. For even platelets it is the cross-section and for non-uniform platelets it is the maximum size of the cross-section.

Both silica gels mentioned have porosities of 46 to 49 ¹ Vn and are preferably used according to the invention. The term "porosity" denotes the actual porosity of the silica gel: it does not include the spaces between the particles in a bed of particles.

The pressure in the process of the invention must be kept within the limits of 6.3 to 25.5 kp'cm ² in order to obtain a sufficient yield of methane of high fiO

1000

! 00

1100
1000
2000

1 100

30th

required

Achieve purity and get one
To achieve self-cleaning of the bed.

The F i g. 5 shows the sensitivity of the adsorption by the Kicseigel at high pressures, for example above 22 kp / cm ² . The hatched area, designated curve A , shows the change in the purity of the end product as a function of the methane yield for a specific starting gas, a specific feed rate and a specific bed size. The actual position of given working conditions within the belt depends on the adsorption pressure within the u - s range of 11.5 to 22 kp / cm ² . In general;] lower pressures are near the lower limit of the band and higher pressures are near the upper limit. For a given methane yield, increasing the adsorption pressure shifts the behavior vertically through the band until the upper limit is reached at around 22 kp / cm ² . A further increase in this pressure causes conditions under which self-cleaning does not take place, and a large sudden increase in the end product ar hydrocarbons with two or more carbon atoms in the molecule. Tests at pressures of 25.5 and 29 kp / cm ² fall on curve B. It should be noted that the ethane content in the end product was not stabilized but increased continuously as the values were determined.

The values for Figure 5 were obtained at temperatures within the preferred range of 21 to 38 ° C. Working at higher temperatures of 38 to 66 ° C makes it easier to clean the bed and flush it with gas. At a given value for the methane yield, the transition from purification to non-purification takes place at significantly higher pressures than at 22 kp / cm ² , as shown in FIG. it shows. The extent of the pressure increase due to the use of higher temperatures is limited, as will be explained later, because at temperature

above 38 ° C other circumstances result in greater losses of the end product with s:; h. Even if higher temperatures contribute to cleaning, the pressures should not exceed ^{25.5 kp / cm 2} , otherwise the yield is seriously impaired.

For a given methane yield, when the pressure is reduced below 22 kp / cm ^2, an end product of greater purity is obtained that contains fewer hydrocarbons with two or more carbon atoms in the molecule . If, however, the adsorption pressure is reduced compared to the Durchspüldruck, so the differential of the loading of the adsorbent and decreases the extent of the bed must be increased or the time for one cycle must be shortened. This results in greater losses of end product through purging and purging, and the methane yield is reduced. If the yield is kept constant, the gas to purge through is absent and the purity of the end product is deteriorated. The F i g. 6 shows that at lower adsorption pressures with a constant yield, the content of the end product of hydrocarbons with two or more carbon atoms in the molecule increases, just as the content of impurities increases at high pressures. It is clear that the adsorption pressure must be above 6.3, preferably above 8.05 kp / cm ^2. in order to keep the level of impurities in the methane produced as an end product low.

FIGS. 5 and 6 relate to given working conditions, for example to the composition of the introduced gas, the feed rate, the dimensions of the bed and the Temperature. Other working conditions produce their own characteristic band for a satisfactory one Operation of Fig. 5, and this band does not necessarily coincide with the hatched one Area in Fig. 5. Even so, the upper and lower limits apply to the pressures at a given one Value for the yield of methane, and these limits correspond to a different range of impurities from hydrocarbons with two or more carbon atoms in the molecule in the final product.

Since the curves of FIG. 5 and 6 can move vertically when the working conditions change, are not values for the ordinate in FIG. 6 specified. If the working conditions are like that correspond to FIG. 5, the lower point of the curve is at about 100 ppm of impurities Hydrocarbons with two or more carbon atoms in the molecule.

The pressure at which the adsorbed constituents are expelled from the adsorbent beds should be between 1.1 and 3.9, preferably between 1.6 and 2.1 kp / em ² . Flushing pressures below 1.1 kp / cm ² are undesirable in order to avoid lines and valves that are too long and to avoid the use of vacuum pumps

Tabel

to make exhaust gas evacuation unnecessary. A low pressure slightly above atmospheric pressure is best suited for embodiments in which the exhaust gas is discarded. The exhaust gas , however, usually has a value either as a fuel or as a raw material for the production of hydrocarbons with two carbon atoms in the molecule. A pressure approximately above atmospheric is therefore desirable in order to supply the gas to the point of consumption. A pressure of the exhaust gas near the lower limit of the preferred range usually means that the gas must be compressed slightly before it is subsequently used. In order to ensure an even flow and to maintain an even pressure of the compressor, an air chamber is desirable. A pressure drop of around 0.35 kp / cm ² through the air chamber is usually sufficient. In a fluid pressure of 1.6 ko / crn ² and a pressure drop 0.35 kg / cm ² through the air chamber is sufficient positive suction pressure of 0.21 kD / crn ² for the compressor. Exhaust gas pressures in the vicinity of the upper limit of the preferred range are often sufficient to conduct the gas as heating fuel or some other non-compression use.

The purging pressure should ^{not exceed 39 kp / cm 2 in} order to achieve a sufficient ratio of the pressures for adsorption and desorption to enable high differential loadings of the bed and to clean the bed well with moderate amounts of purging gas. The flushing pressure timer should preferably be 2.1 kp / cm ² . One of the advantages of the process according to the invention is that the pressures for adsorption and purging are in relatively low ranges compared to the pressures which are usually used in the work-up of hydrocarbons by adsorption.

The sensitivity of the process according to the invention to the temperature of generally 10 to 66 "C. Preferably 21 to 38 ^: C has been shown by tests in a plant with four beds under alternating pressures. At an adsorption pressure of 20 to 22 kp / cm ² and one Minimize the flushing pressure of 2.2 kp / cm ² , cm gas was processed, the 1.0 mol% N ₂ , 91.5 mol% Cl _4. \ 0 MoI- ¹ Vn C _: 1! ". 1.4 mol% (JjHs and 1.0 mole - "/ n of hydrocarbons with four or more carbon atoms in the molecule. A five-step process used four-times cycles, as shown in FIG. 7 in US Pat. No. 3,564,816. Each bed of adsorbent had a diameter of 16.2 cm, a length of 366 cm and contained 75 liters of a granular gravel with particle diameters between 1.4 and 3.4 mm, an average bulk density of 0.75 g / cm ³ , a mean pore diameter of 22 Å and a mean surface area of 740 m ² / g. Table III shows the results of this r attempts.

Test period I.

average values him a Tesi mim K) SuJ.

/ ami
Si

value

Wim i

Sl.

/ c

Si

WtM!

Yield of (I Ι · ι, "■ '<>
MMiere I emner; iliir. (

4 1

Continuation

factor

Test period

average values in a test of lOStd.

Time St.

value

Time St.

value

Time St.

value

Content of the end product of hydrocarbons with two or more
Carbon atoms in the molecule, ppm

74

The ever-increasing levels of impurities from hydrocarbons having two or more carbon atoms in the molecule in the final product in the test periods 2, 3 and 4, while dtrer was carried out below the lower limit of 1O ⁰ C, are an indication of a lack of self-cleaning with a progression the adsorption fronts to the outlet end of the bed. Shortly before test periods 2 and 4, the outlet ends of the beds were carefully cleaned by rinsing for several hours with 100% of the end product used for this purpose. This explains the low values for these impurities at time zero.

In other test periods, the same test plant was operated with the same starting material ^{being fed in under an adsorption pressure of 11 kp / cm 2} , a flushing pressure of 1.5 kp / cm ² and with an aso yield of methane of 44 to 46%. This Period ·: extended over 24 hours, during which the decreased Tsmperatur of the supplied gas of 18 C ^r to 5.5 ^r C, and then increased again to 17 ° C. During this test period the following temperatures and purities of the final product were observed.

Temperature. C.

18th
5.5

10

17th

Älhan in the end product (ppm)

69
227
176
116

In another test period, the same test facility was operated with the same fresh gas at an adsorption pressure of 15 kp / cm ² with a methane yield of 46%. This period extended over 6 hours, during which the temperature of the fresh gas rose from 21 to over 32 C. The following temperatures and levels of impurities in the end product were observed;

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113
142
134
155

3
5.5

131
228 363 482

0.9 2.3 2.8

4.8

<66

162

192

247

when working at temperatures above 10 "C., preferably above 2TC. If, however, the temperatures are increased above 38 ^C. , the behavior no longer improves, but begins to deteriorate. It would be expected that the loading capacity of the adsorbent decreases at higher temperatures, but that would not adversely affect the yield of methane. Nevertheless, the yield of methane decreases increasingly at higher temperatures above 38 ° C. so that the invention can no longer be used successfully at temperatures of about 66 ° C. This is primarily because the difference in impurity loading capacity between adsorption and desorption is smaller at high temperatures, and therefore a larger amount of adsorbent is needed to separate a given amount of the end product to increase the size of the bed and reduce the loss of end product Reduction of the pressure in the countercurrent will be higher. The selectivity of the silica gel for hydrocarbons with two or more carbon atoms in the molecule probably also decreases at higher temperatures, i.e. the adsorbed phase becomes relatively richer in methane with the result that more end product is lost when the pressure is reduced in countercurrent and when flushing.

The general effect of temperature on behavior in this process is the same as that of the Pressure. This can be seen from a comparison according to FIG. 6, when the abscissa the Temperature. For a given yield, the purity changes with temperature, and a The minimum content of impurities is achieved at temperatures between 10 and 38 ° C.

It can be seen from this that higher temperatures and higher pressures both have beneficial and detrimental effects on performance, but in opposite directions. Higher temperatures improve self-cleaning and reduce the loading capacity of the adsorbent, while higher pressures increase the loading capacity of the adsorbent, making self-cleaning more difficult. The detrimental effects of increasing either the temperature or the pressure cancel each other out by the beneficial effects of increasing one unistamy or the other, so that higher values of one factor are best applied with high values of the other factor. If, on the contrary, “ta, πι bet the invention-appropriate YcI. Their relatively low temperatures or ί> low temperatures, then the ι other i-ictor \ or / ngsweiH · η iod nc <-em but inside de *, respected ¹ ) Hvreu Iu * netUM

The inventive method is preferably carried out in a system with four beds for Adsorption at changing pressures, as shown in FIG. 8 it doesn't matter. Here, those process stages for adsorption and desorption are in the cycle The four-bed system applied as shown in FIG. 7 it shows. In the four bed system and the cycle three process steps of co-current pressure reduction are used, two of them are associated with the pressure increase in other beds and another is associated with the Flushing another bed.

Figures 7 and 8 show the preferred system and its operation. Four beds of silica gel ( AD) are arranged in parallel between a manifold 10 for the gas supplied and a manifold ίΐ for the end product. The feeding and removal of the case from the beds are regulated by the automatic valves ΙΛ-D and 2,4-D. The equalization of high pressure differences is facilitated by the connection lines 15 and 16 with the automatic valves 4.4ß and 4CD. The pressure reduction for flushing with direct current is brought about by the collecting lines 17 and 18 with the automatic valves 5/1-ß and 5C-D together with the crossed lines 20 with the manual valve 22. The compensation of the low pressure differences occurs through the connecting line 21 with the automatic valve | 9, which also connects the collecting lines 17 and 18. The flow of gas from the beds to the exhaust gas distribution line 12 is regulated by the automatic valves 3A-D. The end product for restoring the pressure in the beds flows through line 7 with control valves 23 and 28, then through manifold 29 for restoring pressure with control valves 30 and 31 and actually through one of manifolds 32 and 33 the automatic valves 6/4-ß and 6C-D.

The whole cycle is written here for bed A , and is typical for all beds. The pressures and times are only given as examples. It is assumed that bed A is pressurized and that the valves associated with it are originally closed. The valves 1-4 and 2A are opened and a fresh gas at a pressure of 11 kp / cm ² and the conditions described above flows from the manifold 10 into the bed, while the end product flows from the bed into the manifold U. The flow is continued under constant pressure for 5 minutes. Now the valves 1-4 and 2Λ are closed and the valve 4 / 4ß opened, whereby a flow between the bed A and the bed B ♦ nt is, which the latter has been put under partially increased pressure and originally under a pressure of 2.1 kp / cm ² stand. The pressure in both beds is equalized at 6.8 kgf / cm ² in 0.75 minutes. Then valve 4AB is closed and valves 5A, 5C, iC and 26 are opened to allow gas flow between the hay 4 and the bed (through manifold 20. In bed C "a blow has just taken place in the (and it is now flushed through by the one from the bed .4. whose drink is throttled through the valve 22 , ml about 1h kp / cm- '. The flushing is set for 3.5 minutes, whereby the pressure in the hatchet .4 is reduced ~? kp-cnv 'sinks. The pressure is set by a pressure switch PS-C. which closes valve JC and opens valve 19. The sfomuiiü from your bed 4 / around bed ( set / l continues.

The outlet from bed C is closed, however, so that a combined pressure of 2.1 kp / cm ^{2 is established} in 0.75 minutes. The valves 5.4, 5C, 19 and 26 are closed and the valve 3Λ is opened so that the excess pressure in bed .4 in the Geger.strom is drained through the manifold 12 for the exhaust gas. The final pressure of 1.6 kp / cm ² is set by a control valve, not shown, downstream in line 12 for the exhaust gas, from which the gas reaches its point of combustion. The valve 26 is more of a resistance valve than a shut-off valve. When it is closed, the flow in bed A is throttled. A countercurrent pressure release is completed in 0.75 minutes at which time valves 26, 5-4 and 5D are opened. This causes the purge gas to flow from bed D through manifold 20 to bed .4 at a pressure of about 1.6 kgf / cm- '. and then through manifold 12 for the exhaust gas. Rinsing takes 3.5 minutes.

The adsorption phase in bed -4 is now complete, as is the extraction of the L-nd product and the desorption phase. It is now ready for a pressure increase in three stages. The valve 3.4 is closed and the inflow from bed D is continued, with the outflow from bed 4 being closed. so that a pressure of 2.1 kp cm ² is established in 0.75 minutes. The valve 6.4 is opened so that at the same time the end product flows back from the collecting line 11 through the valves 23 and 28 into the bed 4 . Now the valves 5.4 and 5D are closed and the valve 4-40 opened. This connects to bed B, which was originally under the feed pressure of 11 kgf / cm ² , and both beds reached a pressure of 6.8 kg / cm ² in 0.75 minutes. Finally, the valve 4-4S is closed so that only end product from the collecting device 11 flows to the bed A. The pressure in bed A rises to practically the feed pressure of 11 kp / cm ² in 4.25 minutes .

The entire cycle for bed .4 takes 20 minutes, after which it can now begin adsorption; this is done by closing valve 6Λ and opening valves 1-4 and 2A. The cycle for bed A is typical of all beds A - D, and the beds adsorb one after the other during an 'Ades cycle so that the supply of fresh gas and the discharge of the end product are continuous. The order of the beds according to F i g. 8 in adsorption goes from A to D to ßto C.

The described embodiment according to FIG. 7 with a device according to FIG. 8 contains four beds and a cycle of five steps, two steps serving to equalize the pressure. However, the process can also be carried out in a system with four beds and with cycles of four process steps, a single process step being required to equalize the pressure. This is shown in the program for the cycle and the duration according to Fig. *? with a device according to Fig. H. In this Ausfiihrungsfonn the manifold 21 may be omitted lur niedngen pressure to the valve 19, but the other components operate in the manner described. The pressure switch /'.S- .4, Il (and /> now cause a pressure of 4.2 kp / cm- 'When actuated, they stop the reduction of the pressure in the cocurrent flow and prevent the decrease in the pressure in the countercurrent flow.

The method according to the invention can also be carried out

eir lat on There

ent de * Γ.Ρ. Dr bra

are performed in systems with three beds according to LiS-PS 36 36 679, using the device according to Fig. 10. A single process step in the cycle for equalizing the pressure un.1 the program for this purpose are shown in FIG. 11, a program for the cycle with two process steps for adjustment of the pressure is shown in FIG. 12th

Figure 10 shows three adsorbent beds .4. B and C, which are connected in parallel between the manifold 111 for the supplied gas and the manifold 112 for the impurity-depleted methane, the manifold 113 for the purge gas and the manifold 114 for the exhaust gas. Automatic valves 115.4. 115ß and 115C respectively carry the fresh gas into the first bed A, into the second bed and into the third bed C. Automatic valves 116.4. 116ßund U6C conduct the gas from these beds in the ^Collected: tung 112. The manifold !! 3 connect the purge gas! the pollutant-depleted methane manifold 112 to the outlet end of the three beds, and the purge gas is countercurrently fed into beds A, B and C through the automatic valves 17, 4, 117 and 117 C. The automatic valves 118.4. 118B and U8C connect the exhaust gas collection line 114 to the inlet end of the respective beds for the discharge of the countercurrently introduced gases to reduce the pressure and the purge gas. Valves 119A, 119B and 119C at the vent end upstream of valves 116.4. 116B and 116C for the final product are manually operated to regulate gas flow as the pressure is equalized.

The F i g. 11 shows the timing for a system after Fig. 10, with six particular process steps may be used, each of which entails the onset or termination of currents. the Flows into and from the three beds in the system are indicated by vertical lines in the manifold

111 for the supplied gas and in the manifold

112 for the impurity-depleted methane. The gas supply manifold 111 is horizontally connected to each of the three adsorbing beds, and these in turn are horizontally connected to the impurity-depleted methane manifold 112. The process steps for ^re-r production of pressure and for flushing using a portion of the depleted impurities methane are horizontally connected to these steps, ie, with the pressure increase in the direct current, and with the surge, including depleted impurities Metnan is used. All gas flows between the beds are shown in the figure.

It can be seen from FIG. 11 that at any point in time one of the adsorbing beds leads an end product under continuously decreasing pressure into line 112 for the impurity-depleted methane as follows: Bed C for 0-40 seconds, bed A for 40-40 seconds. 50 seconds, the bed, 4 at 50-80 seconds and the riding I) at 80-120 seconds. Accordingly, the end product will continuously / u the consumption tax! deducted.

At this particular / cycle. If all of them are on a single bed, one needs ¹ Zt of the entire cycle to restore the pressure, the removal of the end product and the simultaneous equalization of the pressure or the reduction in pressure in cocurrent need ¹ Zt of the entire cycle. and countercurrent pressure depressurization and purging

! eastern third of the cycle. Using the Pressure equalization within the system and the reduction of the pressure in the co-current are indicated by horizontal lines. Every step in the process for equalizing the pressure is horizontal combined with an increase in pressure in another bed, which has already been flushed through, and everyone Process step for reducing the pressure in cocurrent is connected to a horizontally Step to flush another bed, in which the pressure is being reduced in countercurrent is.

Each process step in the cycle of component 4 should now be made with these components of FIG. 10 in Connection can be set, which participate in the cycle. Examples of pressures are also given here for this method of purifying methane using Kicselgel as an adsorbent specified.

Time 0-0.5: Bed 4 is pressurized, bed B is depressurized in countercurrent and in bed C the pressure is equalized. The valves 115.4 and 116.4 are open and the valves 117.4 and 118.4 are closed. Fresh gas is supplied to bed A at its inlet end from manifold 111 and impurity-depleted methane from manifold 112 is simultaneously introduced into bed 4 through the outlet end. This latter comes out of bed C through valves 119C 116C and continues to flow through valves 116.4 and valve 119 / \ into bed A. Bed C is co-pressurized during this period and the flow continues. until the pressures in beds, 4 and C are practically balanced ^{at about 7.4 kp / cm:} During this period, another portion of the gas from the bed of CaI's end product is vented into manifold 112.

Time 0.5-3.0: The valve 116 / A is now closed and only fresh gas is passed into bed A until a final pressure of 11.5 kgf / cm ^{2 is} reached. This completes the period for pressurizing the bed 4. During this pressurization, the adsorption front for the contaminant sets up near the inlet end of bed A and then progresses towards the outlet end. So much fresh gas is used in relation to the impurity-depleted methane to restore the pressure that there is a certain length of the unloaded bed between the adsorption front and the outlet end when the pressure is restored.

Time 3.0-3.5: The pressure equilibrium for bed, 4 begins with closing valve 115Λ and opening valves 116.4 and 1160, with cocurrent pressure in bed A decreasing by releasing gas from the outlet end . This gas flows through the unbonded part of the bed, whereby the impurities are adsorbed and that of the impurities: methane is used in two parts. The methane! ^ Standing final product passes through the control valve 121 in the manifold 112 to do ^one 'Verbraucherleiiung downstream from dom valve 121. Since ^ valve 121 is self-regulating and maintains the pressure in de-Veri-.ilungsleiiung 112 via a Miniuni \ on for example 1.75 kgf / cm ² . what is enough to lead the!.! egg product into the customer line. The remainder and large part of the methane freed from impurities flows through the valves I!

Outlet end of bed B in order to partially increase the pressure there again. The adsorbates have previously been flushed away from bed B and it is initially under the lowest pressure of the entire system of about 1.75 kp / cm ² . This flow of de-contaminated methane from bed 4 to bed B takes about 0.5 minutes until the two beds are under practically the same pressure, e.g. 7.4 kgf / cm ² .

Time 3.5 - 6.0: Additional methane, freed from impurities, comes out of the discharge end of bed 4 to further reduce the pressure in cocurrent, a portion being introduced into the discharge end of the bed ("by closing valve 1 16 /? And opening of the automatic valve 117C in the manifold for the purge gas to purge the adsorbate from bed C at a pressure slightly above 1.75 kg ^{/ cm 2.} Valves 123 and 124 throttle the pressure of the purge gas to practically 1.75 kg / cm ² and keep the flow rate of the purge gas constant. This also keeps the total amount of purge gas constant, because the process step of purging preferably only lasts a certain time. The flow rate is regulated to a fixed value by setting the valve 123. which adjusts the pressure between the keeps both valves 123 and 124 constant. the exhaust gas from the inlet end of the bed Cströmt through the automatic valve 1 18C into the manifold 114 for the exhaust gas and is drained through the automatic drain valve 125. This latter valve only throttles the drain rate and does not close completely. When it closes, it throttles the flow into the manifold 114 for the exhaust gas, whereby the pressure reduction is slowed down to such a value that abrasion of the adsorbent particles takes place. However, the valve 125 is open to discharge the purge gas, so that the flow rate regulated by the valves 123 and 124 is not reduced. Another part of the additional methane impurities from bed A is withdrawn as the end product. During this process step, the pressure in bed A and in manifold 112 decreases until a value of about 2.45 kgf / cm ^{2 is} reached, which happens after an additional 2.5 minutes (6 minutes in the cycle to ² Ii of the entire cycle ). The pressure in bed A should not fall below a certain lower limit for the depressurization in cocurrent, ie below 2.45 kg / cm ² , since this pressure corresponds to the impending breakthrough of the adsorption front at the outlet end of the bed. The phase for obtaining the end product for bed A is thus ended.

Time 6.0—6.5: The desorption phase now begins in bed Λ by closing valves 116/4 and 117C and opening valve 118/4. Additional gas is vented from the inlet end of bed A for the countercurrent depressurization through manifold 114 for the exhaust gas and outlet valve 125. The latter valve is "closed" for this process step in order to restrict the gas flow in order to avoid excessive flow velocities from the Avoid bed. This process step takes about 0.50 minutes until the lowest pressure of 1.75 kp / cm ² prevails in bed .4.

Time 6.5 - 9.0: residual adsorbate is washed away by opening the valves 1174 and 125 from bed A. Additional contaminated methane flows down the outlet end of bed B

through the manifold 1 12. through the valves 123 uric 124 and through the manifold 113 for the purge gas then through the valve 1174 to the outlet end of the bed A. The purge gas flowing out of the bed 1 valve 184 and is discharged durcl the valve 125. the flushing takes 2.5 minutes worau the entire cycle of 9 minutes is complete. Since ¹ bed 4 is now ready to increase the pressure in it in the manner described above.

In beds B and C , the process steps described are carried out one after the other, if the fresh gas is introduced into bed B at the same time, the pressure is equalized in bed 4 for 3.0 to 3.5 minutes with the methane freed from impurities,! N that Bed C steps there at the same time; Fresh gas on, while at 6.0 to 6.5 minutes in Bet! A in countercurrent by means of the methane freed of impurities, the pressure is lowered. The necessary change in the valve for these process steps can be seen in FIGS. 10 and 11 and FIG. previous description. F. A regulation of the 2-cycle system is necessary in order to coordinate this setting of the valves. For example, the cycle controller may receive a signal from the pressure sensor 126 in the final product manifold.

It is clear that changes to the timing program shown in FIG. 11 can also be considered. For example, it is not necessary for the duration of the flushing to coincide exactly with the duration of the pressure reduction in the cocurrent flow of the bed by means of the flushing gas. Flushing the bed Λ can be stopped shortly before completion ;; the cocurrent depressurization in bed B. and the flushed bed 4 can be isolated for this short period of time before a repressurization is started. Accordingly, all of the cocurrent depressurization gas is withdrawn from Bed B as an end product while Bed .4 is isolated and none is used.

The fig. FIG. 12 shows a preferred embodiment of the three bed system that can be implemented with an apparatus of FIG. The time table according to FIG. 11 is modified so that two process steps are necessary to equalize the pressure at part of a process step during the reduction of the pressure in each bed. This results in a higher yield of end product with the same purity. A comparison of the individual steps according to FIG. 12 with those according to FIG. 11 (for example bed A) shows. since the total duration of the cycles is identical at 9 minutes, but that the phase for restoring the pressure for each bed according to FIG. 12 takes place in three stages, while according to FIG. 11 only two levels are necessary. The F i g. 12 shows that for the bed 4 of the additional compensation of the pressure (8.5 to 9.0 minutes], the first step that the second step, the increase of the pressure through the gas mixture with the contaminants depleted gas ^(: up to 0.5 minuter of FIG. 11) and that the third step obtained wire, the increase in pressure by the gas state is (0.5 to 3.0 minuter of FIG. 11). the time period for the additional compensation of the pressure at low pressure by shortening the Time for flushing. / B. from 2.5 minutes (6.5 to 9.0 minutes according to Fig. 11) to 2.0 minutes (b.5 to 8.5 minutes after

Fig. 12). A treatment for the flushing time means not necessarily, dall the conditioner accordingly is worsened. The flow rate of the Purge gas can be increased by an appropriate F. Including valves 123 and 124.

The setting of the valves for the passage of an additional procedural step to equalize the pressure results from the careful description of FIG. 11. After flushing, one bed is first brought under increased pressure by pressure equalization with another bed of relatively low pressure. This flow / to equalize the pressure is passed through the manifold for the end product in the same way as in the single process step for equalizing the pressure according to 1 i g. 11. During the line from 8.5 to 9.0 minutes according to FIG. 12 receives the bed .4 that during the pressure equalization at low pressure through the open valves 116.4 and tlbö with closed valves 115.4 and 115 / J. A subsequent setting of the valves for bed A is the same as according to FIG. 11 IiLr the time NuIlI during the pressure reduction in cocurrent (5.5 minutes). The gas passes from the belt .4 into bed C during the pressure equalization at low pressure through the open valves 116.4 and 116C. The further settings of the valves for bed .4 are the same as in I i g. 11 for the process steps of pressure reduction in countercurrent and flushing. The pressures for the process of Figure 12 are higher than for the Pig process. II and II correspond to the preferred combination of two cycles / um pressure equalization with higher pressures, and the preferred combination of a single cycle for pressure equalization with lower pressures.

The process according to FIGS. 7 and 12 consists of cycles with five process steps, two of which Process steps for equalizing the pressure are. In a preferred embodiment the gas flows during the second step to equalize the pressure under low pressure of one Drain end to the other drain end of the two beds. This reduces the possibility that Impurities enter the neat end product at the outlet end of the receiving bed when sometimes a breakthrough takes place in one bed. But if there is a precise regulation to prevent it such a breakthrough is provided or if an end product of very high purity is not required is then the gas flow during the second process step to equalize the pressure under low pressure from the outlet end of one bed to the inlet end of the other bed. Changes in flow for performing this process in a four bed system as shown in FIG. 8th are in the F 1 g. 2 of US Pat. No. 3,514,816. Changes in flow for the implementation of the Procedures in a three bed system as shown in Fig. 10 are shown in Fig. 3 of U.S. Patent 37 38 087.

The method according to the invention can also be carried out are in a system with two beds For the continuous recovery of methane, being preferred a device and a program for the cycles and times according to FIGS. 1 and 2 of the US-PS 37 38 087 can be used.

13 shows the adsorbing beds A and B connected in parallel between the manifold 211 for

the supplied gas, the manifold 212 for the impurity-depleted methane, the manifold 213 for the purge gas and the manifold 214 for the exhaust gas. The automatic valves 215,4 and 215 / i lead the gas flow accordingly into the first at A and the second bed ß. The automatic valves 216,4 and 216ß lead the gas directly from these two beds into the manifold 212. The manifold 213 for the purge gas connects the manifold 212 for the contaminated methane to the outlet end of the two beds, and purge gas is through the automatic Valves 217.4 and 217Ö are supplied in countercurrent to the direction of flow of the gas introduced. The automatic valves 218.4 and 218ß connect the exhaust manifold 214 to the inlet ends of the respective beds for admitting the gas for countercurrent depressurization and purging. Valves 219.4 and 219B at the outlet ends upstream of final product valves 216A and 216S can be manually adjusted to restrict the flow of gas used for pressure equalization. Supplied gas under a suitable pressure reaches the collecting line 211, and the gaseous end product flows through the control valve 221 into the collecting line 212 and into the line for consumption. The valves 223 and 224 throttle the pressure of the purge gas to the lowest desired level, and also keep the flow rate of the purge gas constant. As a result, the total amount of purging gas is also kept constant, since purging preferably takes place during a certain period of time. The flow rate is kept at a certain value by adjusting the valve 223, which keeps the pressure between the two valves 223 and 224 constant. The exhaust gas in the manifold 214 is discharged through the automatic drain valve 225. The latter only throttles and cannot be completely shut off. When "closed" it restricts the flow into manifold 214 for the exhaust gas, thereby reducing the rate of pressure decrease to a level such that the particles of the adsorbent do not wear off. However, valve 225 is fully open to let off the purging gas, since the flow rate is already limited by valves 223 and 224.

14 shows the timing for the operation of a Device according to FIG. 13, with eight individual process steps may be applied, including the beginning or the end of the flow. Supplied Gas and the end product flow through the system with two beds and are indicated by vertical beds Lines, i.e. by flows in the manifold for the supplied gas 211 and in the manifold 212 for the contaminated methane. The manifold 211 for the supplied gas connects horizontally the two adsorbing beds, and these in turn are horizontally connected to the collecting line 212 for the contaminated methane. Restoring the pressure and that Flushing using some of the contaminated methane is horizontal associated with the process steps of pressure equalization and restoring the pressure below Use of the contaminated methane. The process step is correspondingly Restoration of the pressure horizontally connected to the manifold for the fresh gas, which also has the

609 54? '475

Gas ran for this period of time. All streams / wipe the hatchets are in the I i g. 14 shown.

One sees from Fig. 14. el a 1.1 at any point in time one of the adsorbing beds releases gas into the collecting line 212 for the methane freed from impurities at constantly changing pressure, namely as follows: bed B during the period 0-1 , 0 minutes. Bed A during the period 1.0-4.0 minutes and Bed B during the period 4.0-6.0 minutes. Accordingly, the flow of the end product into the acceptance line is continuous.

each process step in the bed A cycle will now be described in connection with those parts of Figure 13 involved in changing the cycle. The pressures for this process for purifying methane using silica gel as adsorbent are also not given as final pressures.

Lowest pressure
Lowest intermediate pressure
Equalizing pressure
Higher intermediate pressure
Highest intermediate pressure
Highest pressure

1.75 kgf / cm ²
4.20 kg / cm ²
5.60 kg / cm ²
6.65 kg / cm ²
7.35 kg / cm ²
8.05 kg / cm ²

Time 0-0.5: In bed A the pressure is increased from the lowest pressure in the process of about 1.75 kp / cm ^: Iu to the equalization pressure of 5.60 kp / cm ² . and in bed B the pressure is equalized. The valve 215.4 is open and the valves 217.4 and 218.4 are closed. Fresh gas is introduced into bed 4 through its inlet end from manifold 211 through valve 215Λ, and contaminated methane from manifold 212 is simultaneously introduced dl through valve 216/4 into the outlet end of bed A. The latter gas originates from bed B by pressure equalization through valve 2195, valve 216S and then flows through valves 216.4 and valve 219.4 into bed A. In bed B , the pressure is depressurized cocurrently during this period and the flow continues about 0.5 minutes is balanced Iraq table until the pressure between the ßptten a and B (at about 5,60 kp / cm ^2. During this time, a part of the discharged gas from the bed B as the end product in the collecting line 212th

Time 0.5-1.0: The valve 216.4 is now closed and the fresh gps enters bed A for a further 0.5 minutes, where a higher intermittent pressure of about 6.65 kp / cm ^{2 is} set. Simultaneously, the depressurization in bed B continues in cocurrent and all of the methane freed from impurities is discharged as end product into the manifold 212. During this period the pressure in bed B increases from 5.60 kp / cm ² (pressure equalization) to 4.20 kp / cm ² (lowest intermediate pressure). During the pressure equalization and the pressure reduction in cocurrent in bed B , the adsorption front of the impurities migrates towards the outlet end of the bed and at this point has reached the outlet end, so that a breakthrough threatens. As a result, gaseous pure end product is no longer allowed to reach the manifold 212 and the valve 216ß is closed. In order not to interrupt the flow of the gaseous end product, gaseous end product must come from bed A , and pass from this latter during the remainder of the period for the pressurization.

Line 1.0-1.5: The valve 2 <6.4 is opened again and the end product flows out of the Ben 4 into the collecting line 212. This is the first part of the process step for adsorption under increasing pressure in the bed .4. the pressure there from 6.65 kp / cm ² (higher intermediate pressure) to 7.35 kp / cm- '(highest intermediate pressure) increases. At the same time, the valve 218 'is opened, the discharge valve 225 for the exhaust gas is closed and the pressure in the bed is reduced by the outlet end to about 1.75 kg / cm ^2, the lowest pressure during the process.

Time 1.5-3.0: Here, adsorption takes place in the remaining part of bed A under increasing pressure, the pressure in the bed from 7.35 kp / cm ² (highest intermediate pressure) to 8.05 kp / cm ² (highest pressure ) increases. The valves 217Ö and 225 are open. and some of the contaminated gas from bed A passes through valves 223, 224 and 217 for purging into bed B.

At the beginning of the pressure increase in the Ben .4 at 0 - 0.5 An adsorption front of the impurities arises for minutes through the inlet end and the outlet end any contamination near the inlet end. This front is progressively moving against that Discharge ends for the remainder of the 0.5 minute period and during the subsequent increase of pressure for the first 3.0 minutes of the cycle. At the end of this period there remains an unloaded remainder of the Bed between the adsorption front and the outlet end.

Time 3.0-3.5: The valve 215.4 is closed and the valve 216ß opened, and the pressure equalization now begins in bed A , while end product continues to flow out of bed B. Bed .4 is depressurized cocurrently by venting gas from the outlet end. There"; Gas flows through the unloaded part of the bed where the contaminating components are adsorbed. The emerging gas, which has been freed from impurities, is used in two parts. The methane as the end product flows through the manifold 212 to the consumer line downstream of the valve 221 at such a rate that a suitable low pressure of, for example, 1.60 kp / cm ² prevails in the consumer line. Most of the remainder of the contaminated gas flows through valves 216 and 219 to the outlet end of bed B in order to at least partially increase the pressure there. The adsorbates have previously been flushed away from bed B and the lowest pressure of the process prevails in it. This flow of the gas, freed from impurities, from bed A into bed B takes about 0.5 minutes until practically the same equilibrium pressure of 5.6 kp / cm ² prevails in both beds. During this process step, the valve 215 is open and at the same time the pressure in the bed B is increased through the outlet end by means of fresh gas from the manifold 211.

Time 3.5-4.0: Valve 216ß is closed and additional de-contaminated gas is vented from the outlet end of Bed A to depressurize cocurrently to about 4.20 kgf / cm ² (lower intermittent pressure), the entire Amount of this gas is withdrawn from bed A as the end product. Simultaneously, the supply of fresh gas continues through the inlet end into bed B , the pressure in that bed being from

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5, bO kgf / cm ^{J increases} to 6.65 ^{kg / cm 2} .

Time 4.0-4.5: In bed A , the pressure is now reduced in countercurrent to the lowest pressure of the process by closing valves 215.4 and 216.4. Open the valve 218.4 and close the valve 225. s so that the desorbate is drained through the collecting line 214 for the exhaust gas. At the same time the valve 2nd /? opened and contaminated gas passes from the discharge end of the bed / JaI's end product into the manifold 212 through valve 221. This is the first part of the process step for adsorption under increasing pressure in bed S, the pressure in bed 6, 65 kp / cm ^{3 increases} to 7.35 kp / cm ² , while the fresh gas flows through the bed with adsorption of the impurities.

4.3-6.0 Time: The valves 217.4 and 225 are opened and a portion of the impurities-gas from the bed B, the valves 223 and 224 back through the manifold 212 and as a purge gas through the outlet in the bed A. This cast flows in countercurrent to the fresh gas through the bed .4 and desorbs the remaining adsorbent. The resulting exhaust gas is discharged through the valve 218.4 and the collecting line 214. Simultaneously with the flushing of bed A , the process step for adsorption is continued under increasing pressure in bed B until a pressure of 8.05 kp'cm- is reached in the bed. the highest pressure of the process. At this point in time, the valves 217.4 and 218.4 are closed, and the pressure can now begin to increase in the flushed bed .4 as described.

For example, in the process according to the invention, a fresh gas can also be used which contains water below the saturation threshold at the temperatures and pressures of adsorption. For further safety the supplied gas can also be overheated with regard to its water content, so that the dew point or the saturation temperature at the supply pressure is at least about 10 ^c C below the adsorption temperature. The reason for this is that silica gel structurally disintegrates on contact with liquid water, and that by limiting the moisture content it is ensured that the adsorbing silica gel does not lose its structure at the inlet end. An adsorbent other than silica gel can also be used at the inlet end of each adsorbent vessel for further protection against water damage. It is particularly suitable to use a small amount of, for example, 5% by weight of the total amount of the adsorbents of another adsorbent, such as calcium zeolite A (5A Molecular Sieve). Alternatively, aluminum oxide can be provided at the inlet end to protect against moisture.

It has already been pointed out that during the desorption process step in this process removes the impurities from the fresh gas washed out of the bed of silica gel in the following order: first ethane, then carbon dioxide and finally propane. Those are those three impurities that are usually found in larger quantities found in mixtures with methane gas. It follows that in the construction and operation of a Stystems. at which the adsorption front for ethane during the depressurization in cocurrent is kept within the bed, the adsorption fronts of the other impurities necessarily as well must be inside the bed. Experience has shown that this assumption is correct is when impurities from hydrocarbons with four or more carbon atoms in the molecule only a small part of the total impurities from hydrocarbons with two or more carbon atoms form in the molecule. Such a composition seems to be characteristic of what is available Fresh gas as a starting material for the production of methane of high purity, since hydrocarbons with four and more carbon atoms in the molecule are usually removed down to small residues on the gas surface will.

Experiments with isothermal adsorption have shown. that activated alumina equivalent to that Silica gel is useful in removing hydrocarbons with four or more carbon atoms in the molecule from methane. Indeed, alumina may have certain advantages over silica gel in terms of removal of hydrocarbons with four or more carbon atoms in the molecule, because fewer pronounced effects of heat in adsorption and desorption occur. As a result, at the method according to the invention also beds are used, which at the inlet end Aiuminiumowd contain for the adsorption of components from hydrocarbons with four or more carbon atoms in the molecule, while the section with .lern silica gel at the projection end which is not made up of hydrocarbons existing impurities and the compounds with two to three carbon atoms in the molecule removed. The amount of aluminum oxide provided for this purpose can be determined by experiments and is dependent on the content of the fresh gas in hydrocarbons with four or more Carbon atoms in the molecule, the allowable amount of such hydrocarbons in the final product, and the respective pressures and temperatures. The section with the aluminum oxide shouldn't Make up more than 1/3 of the entire length of the bed the section with the silica gel should be at least - i the entire length of the bed, because otherwise the ability of the process to remove hydrocarbons with two carbon atoms is irr Molecule is deteriorated.

If calcium zeolite A and aluminum oxide are used at the same time, the latter should be used be attached downstream of the calcium zeolite at the inlet end.

According to the invention, the fresh gas is at a temperature of 10 to 66 ° C, preferably of 21 bi 38 ° C introduced. In practice it may be necessary to provide means to adjust this temperature and to regulate, especially in cold climatic conditions. The F i g. 8 shows such suitable centers like a heat exchanger 40 in the line 10 fi> the fresh gas, which by a suitable external source can be heated, e.g. B. by steam or eil hot combustion gas. Also a thermal insulation tion 41 can be arranged on the line 10 for the fresh gas and to the inlet valves M-ID Insulation against a cold outside temperature. Not Corresponding thermal insulation for the discharge end of the manifolds 11. 15-18, 2C are shown 21, 27. 29, 32 and 33. When the adsorption vessels kiei are with a relatively large ratio of surface to content and if the outside temperature ren are very low, it may be desirable to have a

Hermetic insulation also to attach the adsorption vessels to the lerum.

According to a further embodiment of the method according to the invention, the flushing can also be effected by part of the methane obtained as an end product from a bed during adsorption instead of reducing the pressure by means of methane freed from impurities, as described above. In order to obtain a good yield of de-contaminated methane in such a system, it is advantageous to employ two steps to equalize the pressure in order to effectively use the gas used in cocurrent to depressurize, as shown in FIGS. 7 it describes. According to the F i g. 7 and 8, the methane obtained as the end product can be branched off practically the supply pressure from the collecting line 11 through the line 27 with the valves 23 and 28 into the line 29 to increase the pressure.

The manifold 20 for the purge gas is then fed with gas from the manifold 29 for the Restoring the pressure using e.ner n.ch; iba-formed line, which the two collecting lines 20 and 29 connects. Also the valve 22 to reduce the gas pressure to the low to

The pressure would then be required by the flushing

'Collecting line 20 in the new connection path be moved.

In a further embodiment, the flushed adsorbent beds at least

, o are partially put under higher pressure by means of before. Impurities liberated methane, which is introduced at the inlet end of the bed in place of the Discharge end as described above. the necessary changes in the currents h.er for sine

, s clear to a professional. It should be noted that the increase the pressure from the end of the end is not enough for whom an end product of the highest possible purity is to be obtained. One can do this procedure use if methane of lower purity is present

> o For example 99% is sufficient.

For this 1? Sheet drawings

Claims (4)

Patent claims: 1. Process for the purification of crude methane, the impurities of which are water, less than 15 percent by volume of hydrocarbons with 2 to 5 carbon atoms in the molecule, less than 5 percent by volume of carbon dioxide and less than 1 percent by volume of hydrocarbons with 6 or more carbon atoms in the molecule, by an adiabatic process under alternating pressures, with the crude methane being fed through the inlet under the highest pressure, the impurities are selectively adsorbed in at least two successively operated adsorption zones ", and the methane freed from the impurities is then withdrawn in such a way that the impurities in adsorption fronts of the zone at the inlet end, which move progressively towards the outlet end for the purified methane, the supply of the gas being terminated when the adsorption fronts of the impurities are midway between the inlet end and the outlet end of the zone, with the evacuation of the vo In the methane freed from the impurities, the pressure in the adsorption zone is reduced at the same time, the impurities are flushed away from the zone under reduced pressure in that part of the methane released from the impurities is countercurrently from another adsorption zone through the outlet end into the below reduced pressure adsorption zone is introduced and withdrawn from the inlet end, and that the thus purged zone is pressurized at least partially by introducing another portion of the contaminated methane from another adsorption zone prior to re-introducing crude methane into this adsorption zone , characterized in that silica gel is used as the adsorbent in the adsorption zone and that the selective adsorption is carried out at 10 to 66 ⁰ C under an absolute pressure of 6.3 to 25.5 kp / cm ² . 2. The method according to claim 1, characterized in that the selective adsorption is carried out at 21 to 38 ° C and under an absolute pressure of 8.05 to 16.80 kp / cm ² . 3. The method according to any one of claims 1 and 2, characterized in that a silica gel with a surface area of about 740 m ² / g, an average pore diameter of 22 Å, a porosity of 46 to 49% and a particle diameter of less than 3 , 3 mm used. 4. Modification of the method according to claim 1, characterized in that at high Water content of the starting gas as an adsorbent for water Calcium Zeolite A in an amount ♦ on ctw.i 5 percent by weight, based on the fcesamtgewichi of the silica gel and the Calciumzeo-Ullis A. \ iTwendet. ^r ). Modification of the process according to Claim 1, characterized in that such an amount of aluminum oxide is used in addition to the silica gel to selectively remove hydrocarbons with 4 or more carbon atoms in the molecule. that it. starting from the inlet end of each adsorion / nne up to / 11 a third of the bed of the Adsorbent occupies, with the silica gel at least two-thirds of each adsorption zone up to occupies towards the outlet end.