EP2802637A1

EP2802637A1 - Method for providing a purified crude gaseous c4 fraction as an input stream for an extractive distillation using a selective solvent

Info

Publication number: EP2802637A1
Application number: EP13700159.0A
Authority: EP
Inventors: Bernd Heida; Randolf Hugo
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2012-01-11
Filing date: 2013-01-10
Publication date: 2014-11-19
Anticipated expiration: 2033-01-10
Also published as: JP6067748B2; EP2802637B1; JP2015508409A; WO2013104692A1; CN104053752B; KR102049312B1; CN104053752A; KR20140120329A

Abstract

The invention relates to a method for providing a purified crude gaseous C₄ fraction (2) as an input stream for an extractive distillation using a selective solvent in order to obtain crude 1,3-butadiene on the basis of a liquid crude C₄-fraction (1) as a feed stream, containing C₃ hydrocarbons, C₄ oligomers, C₄ polymers, and C₅₊ hydrocarbons together with butanes, butenes, and 1,3-butadiene. The method has the steps of 1) separating the C₄ oligomers, C₄ polymers, and C₅₊ hydrocarbons up to the respective residual content previously specified for the purified crude gaseous C₄ fraction and 2) evaporating the liquid crude C₄ fraction in an evaporator tank (VK). The invention is characterized in that the evaporator tank (VK) is associated with a stripping column (K) with one or more separating stages, the liquid C₄ fraction (1) being fed to the stripping column in the upper region of the stripping column. The stripping column directly exchanges gas and liquid with the evaporator tank (VK) in the lower region of the stripping column, and the purified crude gaseous C₄ fraction (2) is drawn off from the stripping column in the upper region. The stripping column (K) is operated without a condenser at the column head.

Description

A process for providing a vaporized purified R0h-C4 cut as feed stream for extractive distillation with a selective solvent

description

The invention relates to a method for providing a vaporized purified R0h- C4- Schnitte.es as feed stream for an extractive distillation with a selective solvent. The term C _{4 cut} denotes mixtures of hydrocarbons having predominantly 4 carbon atoms per molecule. C ₄ cuts are obtained, for example, in the production of ethylene and / or propylene by thermal cracking, usually in steam crackers, especially naphtha crackers or fluidized catalytic cracking (FCC) crackers of a petroleum fraction, such as liquefied petroleum gas, light gasoline or gas oil. Furthermore, C ₄ cuts are obtained in the catalytic dehydrogenation of n-butane and / or n-butene. C ₄ cuts generally contain butanes, butenes, 1,3-butadiene, small amounts of C ₃ and C ₄ acetylenes, 1,2-butadiene and C ₅₊ hydrocarbons. The separation of C ₄ cuts is a complicated distillation problem because of the small differences in the relative volatilities of the components. Therefore, the separation is carried out by a so-called extractive distillation, ie a distillation with the addition of a selective solvent (also referred to as extractant), which has a higher boiling point than the mixture to be separated and which increases the differences in the relative volatilities of the components to be separated.

There are a variety of methods for the separation of C ₄ cuts by means of extractive distillation using selective solvents known. They have in common that by countercurrent flow of the C4- section to be cut in vapor form with the liquid selective solvent at suitable thermodynamic conditions, usually at low temperatures, often in the range of 20 to 80 ° C and at moderate pressures, often at Normal pressure up to 6 bar, which charges selective solvent with the components from the C _{4 cut} , to which it has a higher affinity, whereas the components to which the selective solvent has a lower affinity remain in the vapor phase and are withdrawn as overhead , From the loaded solvent stream, the components are then fractionally released from the selective solvent under suitable thermodynamic conditions, ie at higher temperature and / or lower pressure compared to the first process step, in one or more further process steps. Crude C ₄ sections contain impurities which would lead to problems in the extractive distillation, in particular foaming of the solvent and apparatus fouling, so that they must be separated just before the supply of R0h- C4- section for extractive distillation to a ensure reliable operation of the extractive distillation.

Impurities leading to the above problems are particularly high relative to 1,3-butadiene higher boiling components, especially C ₅₊ hydrocarbons (predominantly hydrocarbons having 5 or more carbon atoms per molecule, isoprene, C ₄ oligomers and polymers, ie Oligomers and optionally polymers of butadiene of the formula (C ₄ H ₆ ) n, where n is greater than or equal to 2. The proportion of C ₅₊ hydrocarbons in C ₄ cuts is dependent in particular on the operating conditions during thermal cracking and is up to to 1000 ppm by weight or even up to 5000 ppm by weight, in individual cases up to 1 wt .-%, based on the total weight of R0h-C4-Schnitt.es. the C ₄ oligomers and polymers are formed in particular by storage and transport, their proportion is therefore largely dependent on the storage and transport conditions, in particular temperature, duration, inerting of the atmosphere under which the storage and / or transport takes place.

In addition, C ₃ hydrocarbons, ie hydrocarbons having three carbon atoms per molecule, the extractive distillation can cause problems; These are in particular methylacetylene, which has a similar affinity to the commonly used selective solvents such as 1, 3-butadiene. The proportion of C ₃ hydrocarbons should therefore be limited in the feed stream for extractive distillation to a maximum of 50 ppm by weight, based on the total weight of the feed stream. The above objects for the pre-purification of the feed stream for extractive distillation of crude C ₄ cuts have so far been solved in different ways: according to a known procedure, in a distillation column upstream of the distillation column C ₃ hydrocarbons are removed overhead and the remaining components are withdrawn through the bottom. The bottom stream is then fed to an evaporator vessel for the purpose of separating the high-boiling components from 1,3-butadiene, ie an apparatus with a single separation stage. In the evaporator vessel, the depleted with C ₃ components crude C ₄ stream is almost completely evaporated, and indeed flow controlled, so that compared to 1, 3-butadiene high-boiling components in the remaining liquid content not above 5 wt .-%, in particular not above 1 wt .-%, or even not more than 0.1 wt .-%, based on the total weight of the crude boiler supplied to the evaporator C ₄ - Schnittes lie. The liquid stream remaining in the evaporator vessel is discharged as purge stream. The disadvantage here, however, that high levels of recyclables, C ₄ hydrocarbons are discharged via the purge stream together with the high boilers.

It was accordingly an object of the invention to provide a process according to which the secondary components interfering with the extractive distillation can be separated into crude C ₄ sections in a technically simple manner with low investment and energy costs, thereby increasing the service life of the extractive distillation column ,

This object is achieved by a method of providing a vapor purified crude C ₄ fraction as a feed stream for an extractive distillation using a selective solvent, starting from a crude liquid C ₄ fraction as a feed stream containing, in addition butanes, butenes and 1, 3 Butadiene C ₃ hydrocarbons, C ₄ oligomers and polymers, and C ₅₊ hydrocarbons, wherein the purified crude vapor C ₄ - cut less than two-thirds of the C ₅₊ hydrocarbons contained in the feed stream and less than 5 wt .-% of the feed stream contained in the C ₄ oligomers and polymers containing the process steps

1) separation of the C ₄ oligomers and polymers and the C ₅₊ hydrocarbons, each except for the above-mentioned for the crude crude C ₄ -purified purified residual contents, and

2) evaporating the liquid crude C _{4 cut} in an evaporator vessel which is characterized in that the evaporator vessel is associated with a stripping column with one or more separation stages, the liquid C _{4 cut is} supplied in the upper region thereof, in the lower region the same is in direct gas and liquid exchange with the evaporator vessel and from the upper in the same of the vapor cleaned crude C _{4 cut is} withdrawn, the stripping column is operated without a condenser at the top of the column.

It has been found that it is possible to increase the high-boiler separation in the evaporator vessel in a technically simple and energy-consuming manner and at the same time to reduce the loss of C ₄ hydrocarbons via the purge stream from the evaporator vessel by assigning a stripping column to the evaporator vessel. It is possible, in particular for the construction of new plants, to set up the stripping column on the evaporator vessel, that is to integrate the evaporator vessel and stripping column in a single apparatus.

In another embodiment, in particular for existing plants, it is also possible to arrange a stripping column to the evaporator boiler, that is to provide evaporator boiler and stripping column as separate apparatuses.

Evaporator boilers are known in the process engineering simple apparatus. They usually include a boiler, in which a gas phase can separate from a liquid phase, and a heat exchanger, which is located inside or outside the boiler.

According to the invention, a stripping column is assigned to the evaporator vessel. Since the stripping column and the evaporator boiler is intended only for depletion of high boilers, it is possible to operate the stripping column in a simple manner, without a condenser at the top of the column.

A typical crude C _{4 cut} from a naphtha cracker has the following composition in weight percent:

Propane 0 - 0.5

Propene 0 - 0.5

Propadien 0 - 0,5

Propin 0 - 0.5

n-butane 3 - 10

i-butane 1 - 3

1-butts 10 - 20

i-butene 10 - 30

trans-2-butene 2 - 8

cis-2-butene 2 - 6 1,3-butadiene 35-65

1, 2-butadiene 0.1 - 1

Ethyl acetylene 0.1-2

Vinylacetylene 0.1-3

C5 0 - 0.5

Raw C ₄ cuts from naphtha crackers thus contain predominantly butanes, butenes and 1, 3-butadiene. In addition, small amounts of other hydrocarbons are included. C ₄ -acetylenes are frequently present in a proportion of 5% by weight or even up to 2% by weight.

For the extractive distillation initially defined, suitable substances generally include substances or mixtures which have a higher boiling point than the mixture to be separated and a greater affinity for conjugated double bonds and triple bonds than simple double bonds and single bonds, preferably dipolar, particularly preferably dipolar, aprotic solvents , For technical reasons, less or non-corrosive substances are preferred. Suitable selective solvents for the process according to the invention are, for example, butyrolactone, nitriles such as acetonitrile, propionitrile, methoxypropionitrile, ketones such as acetone, furfurol, N-alkyl-substituted lower aliphatic acid amides such as dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, N-formylmorpholine, N-alkyl-substituted cydic acid amides (Lactams) such as N-alkylpyrrolidones, in particular N-methylpyrrolidone. Generally, N-alkyl substituted lower aliphatic acid amides or N-alkyl substituted cydic acid amides are used. Particularly advantageous are dimethylformamide, acetonitrile, furfurol and in particular N-methylpyrrolidone. However, it is also possible to use mixtures of these solvents with one another, for example N-methylpyrrolidone with acetonitrile, mixtures of these solvents with cosolvents such as water and / or tert-butyl ether, for example methyl tert-butyl ether, ethyl tert-butyl ether, propyl tert-butyl ether, n- or iso-butyl tert-butyl ether can be used.

Particularly suitable is N-methylpyrrolidone, preferably in aqueous solution, in particular with 8 to 10 wt .-% water, particularly preferably with 8.3 wt .-% water. To avoid problems in the extractive distillation, it should be fed as a feed stream, a purified vaporized crude C _{4 cut} less than 50 Ppm by weight of C ₃ hydrocarbons, based on the total weight of the purified vaporous R0h-C4 cut, less than two-thirds of the C ₅₊ hydrocarbons contained in the feed stream and less than 5% by weight of the C contained in the feed stream ₄ -oligomers and polymers.

It has been found that it is possible to improve the Hochsiederabtrennung in a simple manner by the evaporator vessel is assigned a stripping column.

In addition, in the process according to the invention, the separation of high-boiling components from the C _{4 cut} with respect to 1,3-butadiene is possible with substantially less loss of desired product, C ₄ hydrocarbons.

Preferably, the C ₃ hydrocarbons in the gaseous purified crude C ₄ - cut to less than 10 ppm by weight, based on the total weight of the gaseous purified R0h- C4- Schnitte.es, or even more preferably less than 4 wt. -ppm, depleted in a distillation column upstream of the evaporator boiler.

More preferably, the C ₅₊ hydrocarbons are depleted in the gaseous purified crude C _{4 cut} to less than half of the C ₅₊ hydrocarbons present in the feed stream.

The stripping column is preferably operated at a top pressure in the range of 3 to 7 bar absolute, more preferably at a top pressure in the range of 4.5 to 5.5 bar absolute.

The stripping column has in particular 1 to 15 theoretical plates.

The invention is explained in more detail below with a drawing and exemplary embodiments.

The drawings show in detail

1 is a schematic representation of the evaporator boiler with attached stripping column and

Fig. 2 is a schematic representation of an evaporator boiler with associated stripping column. The schematic representation in Fig. 1 shows an evaporator vessel, VK, at the upper end of which a stripping column K connects, such that the Evaporator VK and the stripping column K form a single apparatus. At the lower end of the evaporator vessel VK a sump evaporator is provided.

The stripping column K is supplied in the upper region thereof the liquid crude C _{4 cut} as stream 1, and at the top of the stripping column K, the purified crude C ₄ - cut, stream 2, deducted.

Fig. 2 shows the schematic representation of a further preferred embodiment, in which the evaporator vessel VK and the stripping column K are formed as separate apparatus, and wherein a direct gas and liquid exchange at the upper end of the evaporator vessel VK is provided with the stripping column K.

The evaporator boiler VK is equipped with a sump evaporator S.

The stripping column K is fed in the upper region thereof the liquid C _{4 cut} as stream 1 and withdrawn as overhead stream of the vaporized purified crude C _{4 cut} , stream 2.

embodiments

The starting point is a crude liquid C _{4 cut} as feed stream for a 100 kt / year plant containing 200 ppm of propane, 400 ppm of propene, 300 ppm of propadiene, 400 ppm of propyne, 2.0% of n-butane, 6.0 % isobutane, 19.0% n-butene, 28.3% isobutene, 5.5% trans-2-butene, 4.4% cis-2-butene, 39.0% butadiene-1, 3 , 0.2% butadiene-1, 2, 1200 ppm butyn-1, 4500 ppm vinyl acetylene and 1000 ppm iso-pentane, 3-methylbutene-1 and 2-methylbutene-2, in each case based on the total weight of the feed stream. Depending on the storage and transport conditions, C ₄ oligomers and polymers can be contained in the% range. In order to be used as feed stream in an extractive distillation, the above crude C _{4 cut is} subjected to a pre-purification, for comparison in a plant with a distillation column in which the C ₃ hydrocarbons are removed overhead and the remaining components are withdrawn via the bottom whereupon the bottoms stream is fed to an evaporator vessel for separation of the high boiling components relative to 1,3-butadiene, ie a single separation apparatus. In the evaporator vessel, the crude C ₄ stream depleted in C ₃ components is virtually completely vaporized and discharged under flow control, so that the C ₅ components which boil over 1, 3-butadiene in the remaining liquid fraction do not exceed 5% by weight, based on the total weight of the R0h- C4-Schnitten.es supplied to the evaporator vessel, lie to the loss of C ₄ components in liquid residue to keep small. The proportion of oligomers and polymers contained in the liquid residue is significantly greater because of the lower vapor pressure. The liquid stream remaining in the evaporator vessel is discharged as purge stream.

In the example according to the invention, the same crude C _{4 cut is} fed as feed stream to an evaporator vessel VK, on which a stripping column K is set up with 5 theoretical plates, to which the liquid C _{4 cut} 1 is fed in the upper region and from the top End of the same is withdrawn from the gaseous purified crude C _{4 cut} 2, wherein the stripping column K is operated without a condenser at the top of the column. Such a system is shown schematically in FIG.

According to the state of the art, less than 5% of the C ₅ components contained in the C ₄ cut are separated off via the residue stream (= purgestream), while according to the inventive process more than one third of the C _{5 +} hydrocarbons contained in the feed stream and more 95% by weight of the C ₄ oligomers and polymers present in the feed stream are discharged via the bottoms in the residue stream. The residue stream (from the evaporator vessel) is according to the prior art 160 kg / h, with a proportion of 1, 3-butadiene of 38.6 wt .-%.

In contrast, although the residue stream (bottom stream) from the distillation column by the process according to the invention was likewise 160 kg / h, but with only 23 wt .-% 1, 3-butadiene. The yield of 1,3-butadiene in the pre-distillation (1,3-butadiene in the purified C _{4 cut} based on 1,3-butadiene in the crude C _{4 cut} ) was 99.29% in the prior art 99.49% according to the example of the invention. That is, according to the inventive method, a higher yield of desired product 1, 3-butadiene is achieved.

As a further advantage, a purified crude C _{4 cut} with a higher degree of purity, compared to the method of the prior art is separated by the novel process. At 32 t / h of crude C ₄ feed with a total of 3000% by weight of ppm C ₅ components (additional proportions of C ₆ components as well as oligomers and polymers, which are not taken into consideration here, may be used) 94.16 kg / h C ₅ - fed components according to the prior art extractive distillation. In the case according to the invention, on the other hand, only 55.1 kg / h of C ₅ components of the extractive distillation are fed in. Since fewer C ₅ components are fed from the pre-distillation of the extractive distillation, the loss of 1,3-butadiene also correspondingly decreases in the extractive distillation or the subsequent purifying distillation. Based on the pure product (pure 1, 3-butadiene) from the entire Extractive distillation including predistillation is the yield of 1, 3-butadiene (calculated as 100% 1, 3-butadiene) according to the prior art 96.47% and in the case of the invention 96.66%.

In a large-scale plant of 100 kt / a given above, the loss of desired product 1, 3-butadiene is thus greater by about 192 t / year in the process according to the prior art than in the process according to the invention. By virtue of the solvent forming a closed circuit, the previous separation of interfering components and impurities keeps the same clean, thereby minimizing the regeneration effort. At the same time, the contamination of the extractive distillation unit (fouling of the beds in the columns) and foaming are kept low. As a result, less antifoam is required with correspondingly lower costs. Reduced fouling reduces the cleaning effort for a shutdown. Each shutdown means a production loss of about 2 weeks; this adds to the cleaning effort. This leads to costs in the 7-digit range.

Claims

claims

1 . Process for the preparation of a vaporous purified R0h- C4- section (2) as feed stream for an extractive distillation with a selective

Solvent for the production of crude 1,3-butadiene, starting from a liquid crude C ₄ fraction (1) as feed stream, comprising, in addition to butanes, butenes and 1,3-butadiene, C ₃ -hydrocarbons, C ₄ -oligomers and Polymers, and C ₅₊ hydrocarbons, wherein the purified crude vapor C _{4 cut contains} less than two thirds of the C ₅₊ hydrocarbons contained in the feed stream and less than 5 wt% of the C ₄ oligomers contained in the feed stream and Contains polymers, with the process steps

1) separation of the C ₄ oligomers and polymers and the C ₅₊ hydrocarbons, in each case except for the residual contents indicated above for the crude crude C ₄ -cut purified by steam, and 2) evaporation of the liquid R 0h -C 4 cut in an evaporator vessel

(VK), characterized in that the evaporator vessel (VK) is a stripping column (K) with one or more

Is associated with separation stages, the liquid C _{4 cut} (1) is supplied in the upper region of the same, in the lower part of the same in direct gas and liquid communication with the evaporator vessel (VK) and from the top of the same gaseous purified Roh C _{4 cut} (2) is withdrawn, wherein the stripping column (K) without capacitor on

Column head is operated.

2. The method according to claim 1, characterized in that the stripping column (K) is placed on the evaporator vessel. A method according to claim 1, characterized in that the stripping column (K) is assigned to the evaporator vessel (VK) as a separate apparatus.

Method according to one of claims 1 to 3, characterized in that the C ₃ hydrocarbons in the gaseous purified crude C _{4 cut} to less than 10 ppm by weight, based on the total weight of the gaseous purified crude C _{4 cut} in a distillation column upstream of the evaporator vessel (VK) are depleted.

A method according to claim 4, characterized in that the C ₃ - hydrocarbons in the vaporized purified crude C _{4 cut} to less than 4 ppm by weight, based on the total weight of the gaseous purified crude C _{4 cut} , are depleted.

Method according to one of claims 1 to 5, characterized in that the C ₅₊ hydrocarbons are depleted in the vaporized purified crude C _{4 cut} to less than half of the C ₅₊ hydrocarbons contained in the feed stream.

Method according to one of claims 1 to 6, characterized in that the stripping column (K) is operated at a top pressure in the range of 3 to 7 bar absolute.

A method according to claim 7, characterized in that the stripping column (K) is operated at a top pressure in the range of 4.5 to 5.5 bar absolute.

Method according to one of claims 1 to 8, characterized in that the stripping column (K) has 1 to 15 theoretical plates.