US2885337A

US2885337A - Coal hydrogenation

Info

Publication number: US2885337A
Application number: US349589A
Authority: US
Inventors: Percival C Keith; Ringer Friedrich
Original assignee: Hydrocarbon Research Inc
Current assignee: Hydrocarbon Research Inc
Priority date: 1953-04-20
Filing date: 1953-04-20
Publication date: 1959-05-05
Anticipated expiration: 1976-05-05

Description

May 5, 1959 P. C. KEITH AL COAL HYDROGENATION Filed April 2O, 1953 United States Patent() COAL HYDROGENATION Percival lC. Keith, Peapack, and Friedrich Ringer, Upper Montclair, NJ., -assignors to-Hydrocarlion Research, Inc., New York, NX., acorporation' of New'Jersey Application April20, 1953, yS'eriaLNo.r `349,58)

Claims. (/Cl. 2082-8) This invention relates= to a. processv for. hydrogenating. coal to` yield liquidv products, and morev particularly. to. a. processfor. hydrogenating bituminous coal and. for cracking the products of hydrogenation ina fluidized bed in the presence of hydrogen.

NumerousV prior proposals have been made for the production of gasoline. and other liquid products.. by hydrogenating coal. However, these proposalshave beenhandicapped by technical complexity andhigh operating cost. For example, one of the diicultprobl'ems encountered in prior processes is. the separation of. the liquid hydrogenation products from the solid. residue which remains after theicoalhas. been hydrogenated.. Another troublesome 4diiiiculty is that the4 last` stages of coal.. hydrogenation proceedv very slowlyA so. that the hydro genation apparatus hasv aV low overall throughput. Wh a high yield of liquid productsk is desired.

. A principal object. of this invention. is to. provide. an.

improved process for recovering liquid products from.

coal, which comprises partial hydrogenation of'. the. coal, followed by cracking the mixture. of liquidlhydrogenation.

subsequent. cracking of the mixture. of liquid productsand. solid residue. inthe presence of hydrogen.

Another important. object. is to provide` a coal hydro-- genation process. in which` the hydrogen is economically generated under: elevated pressures from the carbonaceous.

residue formed in cracking the mixture of.' liquid hydro genation products and solid residue. resulting from the. partial hydrogenation` of. coal.

- Additionalr objects. and advantages: of. the invention will'r be apparent from the description which follows.

Brieiiy,y the invention comprises conductingthel partial.

hydrogenationl of coalv while suspended in ahyd'rocarbon.

oil to.l converti a major portion of the` carbonl therein to liquid and gaseous products, and then` introducing, aV mixture ofv liquid products andi solidV residue. obtained.. from. the partial hydrogenationofL coal. intoy a cracking:`

zone whereinV the mixture is,4 converted` at elevated tem.- perature and. pressure conditions and inthe presence. of. hydrogenv to lower-boiling-` products and. acarbonaceous residue; theca'rbonaceous residue isgasitled with oxygen.

r' ice step; The conditions for hydrogenatingcoal while sus-V pended in oil are well known and may be used in the: partial hydrogenation step of this invention. For' instance, a temperature of about 600 to 1000 F. and a. pressure of about. 1,000 to 12,000 p.s.i.g (pounds per square inch gauge) maybe used. The reaction time is governed by the chosen conditions. under which the.y coal hydrogenation is conducted but is. limited to give the desired conversion in the range of about 60 to 85%. of the carbon content of the coal. As is known, coal` hydrogenation is advantageously carried outwith the. aid of catalysts such as iron oxide and tin compounds: and such catalysts are contemplatedfor. use in the partial coal hydrogenation step of thisv invention.

Desirably, a Vapor product is removed from the.`v partially hydrogenated mass, comprising unreactedl hydrogen, product gases such as NH3, HZS, CH4, and. normally liquid lower boiling compounds. The remaining mixture of liquid hydrogenation products and. solid; residue is subjected to` cracking in an atmosphere of: hydrogen.

The cracking operation. is conducted. at. an elevated. temperature in the range of 900 to l400 F., preferably 1200 to 1300 F., and at apressurey in the range of about 150 to 800 p.s.i.g., preferably 250 to 650 p.s.i.g. It has been found that. the suppression of coke formation during cracking is achieved to a material extent'. when theV partial pressure of hydrogen within the cracking zone isv at least 35' p.s.i; and preferably in the range of about y to 150 p;s.i. It is curious to note that maximum benefits from the presence of hydrogenr occur at hydrogen partial pressures not exceeding about 200`-p.s.i. so that there. is little justification in seeking a hydrogen partial pressure greater than about 200 p.s.i. Asv a preferred mode of operation, the cracking is carried. out yby injecting the mixture of`liquid products and solid residue from the partial hydrogenating step into a, fluidized mass of. the solid residue from the coal used in the. process. Where a hydrogenation catalyst like iron oxide is employed in the partial. hydrogenation step, the fluidized mass inthe cracking' zone will also contain. the hydrogenation catalyst. Other particulate solids such". as bauxite may be added to the uidized mass in the. cracking zone to make the mass more easily fluidzable. With. the aid. of hydrogen owing through. the cracking zone, the injected hydrogenation mixture.

V is: converted. to a. gasiform: effluent. and a substantially dry carbonaceous residue. The gasiform effluent, which is readily.` separable from` the; dry carbonaceous residue, is. removed' for recovery of its. constituents.. by conventional'. methods, such' as rectitication. The. substantially carbonaceous. residue in admixture` with the contact material' iswithdrav/n fromthe cracking zone and passed total gasifying or. regenerating zone where a regenerating gas` consisting of aipreponderancel of steam and a minor proportion of high-purity oxygen. gasities the carbon under: conditions: favoring the production of hydrogen. and'` carbon monoxide; Steam-toeoxygen molar ratios in; the'. range of' about 13.5211 to; 5::1. arefgenerally satisfactoryf for maintaining. the gasifying temperaturel in the desirable range: of about. 1600 to 2500 F. Steamftoroxygen, molar ratios of.l about'. 2::1, to 3:1 audf. gasifying temperatures of about' 1'7-00. to 20`00 F. arev preferred. The gasifyingzone operatesv at substantially the same pressure maintained inthe cracking zone. The high-v purity oxygen .may suitably be the product of air lique- .faction andf rectication containing at least by conducted in` the `same vessel. .,The contact material volume of oxygen, `preferably at least `Like thev cracking operation, thte gasifyingl may be4 done under fluidizing conditions, the two preferablyy being circulates through the cracking and gasifying zones, and at least part of the hydrogen-containing products of the gasifying step, hereinafter termed regeneration product gas, flows through the cracking zone. Large quantities of hydrogen are produced in the gasifying operation, and more hydrogen can be made from the carbon monoxide in the regeneration product gas and excess steam therein by the water-gas shift reaction: CO-l-H2O- CO2{H2. Thus, by suitable treatment, a stream of high-purity hydrogen may be recovered from the regeneration product gas and this recovery of hydrogen may be accomplished at substantially the pressure in the cracking and gasifying zones. The amount of hydrogen produced depends on the quantity of carbonaceous residue remaining from the cracking operation and this residue is in turn a yfunction of the carbon conversion in the preceding step of partial hydrogenation. Large quantities of hydrogen are consumed in coal hydrogenation, but substantially all, i.e., over 80%, of the requisite hydrogen is supplied by the regeneration product gas even for a hydrogenation conversion of about 85% of the carbon content of the coal to liquid and gaseous products. A hydrogenation conversion of about 75 to 80% ultimately results in enough carbonaceous residue for the gasifying operation to allow recovery of 100% of the requisite hydrogen from the regeneration product gas.

For further clarification of the invention, reference is now made to the accompanying drawing which schematically illustrates an arrangement of apparatus suitable for carrying out the process of this invention.

Coal from a feed 11, a pasting hydrocarbon oil from line 12 and a catalyst if desired enter mixer 13 wherein they are intermixed to form a paste which ilows through line 14. A pump 15 pressurizes the paste to the operating pressure of the partial hydrogenation step, e.g., 1000 to 12,000 p.s.i.g. Pressurized hydrogen from line 17 and paste from line 14 enter hydrogenator 16 wherein Ia temperature of about 600 to 1000 F. is maintained. The hydrogenation reaction per se and the equipment necessary for hydrogenation are known to the art, exemplary reference being made to the article Liquid Fuel from Coal in Industrial and Engineering Chemistry, May 1949 (vol. 41), pages 870 to 885. Suice it to say that the hydrogenation reaction is carried out in hydrogenator 16 to convert between about 60 and 85% of the carbon content of the coal to liquid and gaseous products. A preferred set of hydrogenating cond-itions is approximately 10,000 p.s.i.g., 875 F. and 75% conversion.

The hydrogenated paste is removed from hydrogenator 16, optionally cooled in heat exchanger 18 and passed to separator 19. Unreacted hydrogen, H2S, NH3, water vapor, hydrocarbon gases and low boiling normally liquid organic compounds are removed in vapor phase through line 20. The normally liquid components of the vapor are condensed out in stripper unit 21 for recovery of gas and liquid products which 'are withdrawn through

lines

22 and 23, respectively. If desired, a hydrogencontaining gas may be separated and recycled from unit 21 to hydrogenator 16. The temperature at which vapors are separated from the hydrogenated paste may vary widely. In general, a separation temperature in the range of about 400 to 600 F. is preferred. Separation at below 400 F. will retain more of the lower boiling liquid products in the hydrogenated paste, advantageously increasing its fluidity but also increasing the volume of material which must subsequently pass through the cracking zone. Separation at above 600 F. will remove substantially all lower boiling liquid products from the hydrogenated Ipaste as well as some of the higher boiling liquid products which should advantageously be converted to lower boiling products in the subsequent cracking step.

After the vapors are separated from the hydrogenated paste, the remaining mixture of liquid hydrogenation be a section packed with Raschig rings or the like, into freely uidized gasifying zone 30. A transport gas, such as steam, from` line 39 carries contact material through upflow tube 33 back into cracking zone 28. The mixture of liquid hydrogenation products and solid residue entering cracking zone 28 is converted therein to vapors and a substantially dry carbonaceous residue at a temperature in the range of about 900 to l400 F., preferably 1200 to 1300 F., and in the presence of hydrogencontaining regeneration product gas. The carbonaceous residue becomes part of the uidized bed of contact material passing down through thermal barrier 31 into gasifying zone 30v where it is gasiied at a temperature in the range of 1600 to 2500" F. by oxygen and steam introduced near the bottom of zone 30 from line 29. Ash having a carbon content of a few percent by weight or less is Withdrawn through line 35 at a rate which maintains a substantially constant solids inventory in vessel 27. The regeneration product gas consisting predominanely of hydrogen, carbon monoxide and excess steam uidizes the contact material while passing up from zone 30 through thermal barrier 31 and cracking zone 28, thus providing at the same time the desired hydrogencontaining atmosphere in cracking zone 28. Regeneration product gas and the gasiform products of cracking are withdrawn overhead from cracking zone 28 through line 45 and passed into fractionating tower 46. Tower 46 may be operated to pass overhead through line 47 all gases and liquid products, including gasoline hydrocarbons, boiling up to 400 F. Higher boiling liquids such as diesel oil may be withdrawn by way of line 49 while a heavy bottoms `fraction discharged through line 48 is desirably recycled through line 12 to mixer 13 as pasting oil.

Advantageously, the pasting oil requirements are made up by taking all the bottoms fraction from tower 46 and supplementing it with suicient oil drawn from separator 19 by line 24 to provide the necessary balance. It is to be understood, however, that an extraneous pasting hydrocarbon oil may be substituted for either or both of these products of the process. When oil is drawn from separator 19 through line 24, it is preferable to decrease the content of solids suspended therein by settling, centrifuging or like operation; obviously, the portion of oil flowing through line 25 to cracking zone 28 will then have a higher concentration of solids.

The gases and low boiling products removed from tower 46 through line 47 are cooled in heat exchanger 50 and passed into separator 51 from which the condensed liquid products rich in gasoline hydrocarbons are removed through line 53 and the gases through line 52. These gases may be passed through line 38 into gas treatment plant 37 where such components as HZS, NH3, CO2 and CH4 are separated to leave a residual gas comprising essentially hydrogen and carbon monoxide. By the water-gas shift reaction, the carbon monoxide of the residual gas may be converted to additional hydrogen and carbon dioxide which may be readily eliminated to yield high-purity hydrogen, ie., at least about by volume of hydrogen.

A desirable expedient which allows a more facile recovery of high-purity hydrogen involves removing a side stream of regeneration product Igas from gasifying zone 30 without becoming admixed with the cracked products in zone 28. A partition or barrier 34 is placed in the upper portion of vessel 27, extending from the top of vessel 27 to a level below packed section 31. Barrier 34 splits the upowing regeneration product gas so that part assass passes into cracking zone 28 to be removed with the products of cracking, While the rest simply passes up through zone 30a and discharges through line 36, sub-v stantially undiluted with hydrocarbons. This side stream of'regeneration product gas can be passed through line 38 into gas treatment plant 37. Taking olf a side stream through line 36 advantageously reduces the load on the eluent recovery system comprising tower 46 and separator 51. Moreover, the treatment of side stream 36 to produce high-purity hydrogen is simpler than the treatment of the gas from line 52 because regeneration product gas contains substantially only H2, CO, CO2 and H2O. In` any event, hydrogen of over about 90% by volume purity and at substantially the elevated pressure of the cracking operation is recovered from gas treatment plant 37. This hydrogen is further pressurized by compressor 42 and fed by line 17 to hydrogenator 16. Additional' hydrogen, for instance, the hydrogen-containing gas in line 22, may be added by way of line 43, with or without any intervening treatment of the gas. While the gas from line 22 may be separately treated, it maybe added to the gas in line 38 and passed through treatment plant 37.

Gaseous products of the process may be Withdrawn through line 52a and/ or recovered as a by-product stream 40 from gas treatment plant 37, as Well as from line 22. From these gas streams, an LPG (liquefied petroleum gas) productl may be obtained. The gases also contain quantities of H2S, NH3- and CO2 which may be removed to leave a valuable fuel gas of high heating value.

The primary liquid product of the process comprises gasoline hydrocarbons (boiling up to 400 F.). A minor portion of this gasoline is produced in the hydrogenation operation and removed from stripper 21 through line 23. The major portion of the gasoline is produced in cracking zone 28, recovered in separator 51 and removed through line 53.

In a typical operation of the process, in which all quantities of` materials are given on an hourly basis, 100 tonsof coal having 40% by weight of volatile matter and 5% by Weight of ash on a moisture-freebasis is pasted with 150 tons of hydrocarbon oil in mixer 13. The oil is made up of 26 tons of bottom fraction (line 48) and 124 tons of recycle oil (line 24.). An additional 30 tons of solids contained in the recycle oil are returned to mixer 1-3. The paste is hydrogenated at 10,000 p.s.i.g. and 875 F. and with a residence time of 30 minutes. 'I he hydrogen gas` input is 2.25 M s.c.f. (million standard cubic feet) of` 911%l byvolume purity. Approximately 75% of the carbon in the coal is converted to liquid and gaseous hydrogenation products.

The hydrogenated paste is cooled to 500 F. and a1- lowed to settle in separator 19, vapors and gases being removed overhead through line 20. The settled paste is split into the recycle stream of 124 tons of pasting oil containing 30 tons of solids and a thicker stream of 75 tons of liquid hydrogenation products 4containing 29 tons of solids. The gasiform effluent leaving separator 19 by way of line is cooled and separated into:

6.4 tons gasoline (not including C2 hydrocarbons) 4.0 tons H2S and NH3 10.0 tons water After condensation of liquid products and removal of H2S and NH3, there remains 0.88 M s.c.f. of gas having the following composition (on volume basis):

Percent H2 60 CO 10 CO2 2 CH4 19 C2 hydrocarbons 5 C3 hydrocarbons 4 The hydrogen actually consumed in the hydrogenation amounts to about 1.5 M s.c.f`

6. `The thicker stream (line 25) of hydrogenated paste totaling 104 tous of vliquid and solids is fed into cracking zone 28' along with 0.23 M s.c.f. of transport gas. Vessel 27 operates at'a pressure of 400 p.s.i.g. and with a temperature of l200 F. in cracking zone 28. Gasifying zone 30 is supplied with 46.5 tons of oxygen and 52 tons' of steam suitably preheated. The temperature in gasify ing zone 30 is about 1750 F.

The fluidized mass in vessel 27 is the nely divided ash of` the' coal undergoingy treatment. About 5 tons of this ash' is Withdrawn through line 35 from gasifying zone 30 where the carbonv content of the ash does not exceed about 1% by Weight.

A hydrogen-rich (32% by volume of hydrogen) side streamk of 3.88 M s.c.f. of regeneration product gas is' removedV through line 36 and scrubbed to remove steamk anddcarbon dioxide: 'Ilhe previously mentioned transport gas (0.23 i s.c;f.) is` taken from this scrubbed gas stream and the rest is shifted in' the presence of added steamto convert its carbon monoxide content to additional hydrogen and carbon dioxide. After a further condensing and scrubbing operation,.the shifted gas has 91% by volume of hydrogen and is compresedand fed to hydrogenator 16.

The total gasiform efuent removed from cracking zonel 28through line 45 is separated into about 0.80 M s.c.f. (dry basis) of gas, 23.3 tons of gasoline (91-93 CFRR clear octane number) and 26 tons of hydrocarbons boiling above 400L7 F. All of the hydrocarbons boiling above 400 are recycled to hydrogenator 16 as pasting oil. The approximate composition of the gas product in S.c.f.

and minor quantities` of N2, NH3 and H25.

By depropanizing the. gases leaving separator 51 and` stripper 21, an LPG product amounting to 4.3 tons is obtained. A total of 29.7 tons of gasoline is recovered from 100. tons of coal containing 5 tons of ash.

l Various modications of the invention will occur to those skilled in the art upon consideration of the disclosure herein. For instance, While in most cases the ash of the coal and the hydrogenation catalyst, if any is used, will suffice as the contact material maintained in a iluidized state in vessel 27, extraneous materials like bauxite, alumina, and quartz may be used. Such extraneous contact material may be introduced with the fuid flowing through line 26 at a rate to compensate for the quantity removed from vessel 27 in admixture with the ash discharging by Way of line 35. Accordingly, in view of the modifications which may be made without departing from the spirit or scope of the invention, only such limitations should be imposed as are indicated by the appended claims.

What is claimed is:

1. In the hydrogenation of coal involving the treatmen-t With hydrogen of said coal in powdered form While suspending in a hydrocarbon oil, the improvement which comprises terminating said treatment when a major portion not exceeding about of the carbon content of said coal has been converted to liquid and gaseous hydrogenation products, subjecting a mixture of liquid hydrogenation products and solid residue resulting from said treatment to vapor-phase cracking by injecting said mixture into a uidized mass of contact material maintained in the presence of hydrogen at elevated temperature and pressure whereby said mixture is converted to a substantially dry carbonaceous residue and a gasiform stream rich in gasoline hydrocarbons, aind separating said gasiform stream from said dry residue by withdrawing said gasiform stream from the top of said fluidized mass.

2. In the hydrogenation of coal involving the treatment with hydrogen of said coal in powdered form while suspended in a hydrocarbon oil, the improvement which comprises subjecting a mixture of liquid hydrogenation products and solid residue resulting from said treatment to vapor-phase cracking by injecting said mixture into a uidized mass of contact material maintained in the presence of hydrogen at elevated temperature whereby said mixture is converted to a gasiform efuent and a substantially dry carbonaceous residue, separating said gasiform eliiuent from said carbonaceous residue by withdrawing said gasiform eluent from the top of said uidized mass, gasifying said carbonaceous residue with steam and oxygen to produce a hydrogen-rich gas, and supplying from said hydrogen-rich gas substantially all the hydrogen required in said treatment and in said vapor phase cracking.

3. A process for treating coal which comprises hydrogenating a mixture of hydrocarbon oil and coal at an elevated pressure and temperature until about 60 to 85% of the carbon content of said coal has been converted to liquid and gaseous hydrogenation products, converting the mixture of liquid hydrogenation products and solid residue resulting from the hydrogenation to gasiform products and substantially dry carbonaceous residue by injecting said mixture into a uidized mass of contact material in a vapor-phase cracking zone at an elevated ternperature and pressure and in the presence of hydrogen.

containing gas exerting a hydrogen partial pressure of at least 35 p.s.i. in said cracking zone, gasifying said dry residue with steam and oxygen at a temperature of 1600 to 2500 F. to form said hydrogen-containing gas, separating said gasiform products in admixture with said hydrogen-containing gas from said dry residue by Withdrawing the admixture from the top of said uidized mass, separating high-purity hydrogen from the withdrawn admixture, and feeding said high-purity hydrogen to said hydrogenation.

4. The process of claim 3 in which a portion of the liquid hydrogenation products is mixed with coal and recycled to said hydrogenation.

5. The process of claim 4 in which said portion of the liquid hydrogenation products is supplemented with high boiling hydrocarbons recovered from t-he admixture Withdrawn from the cracking zone.

6. The process of claim 3 in which the uidized mass 8 of contact material comprising said dry residue is maintained in circulation through said cracking zone and a lower zone wherein said dry'residue is gasified, and hydrogen-containing gas formed in said lower zone discharges into said cracking zone.

7. The process of claim 3 in which hydrogen is recovered from the liquid and gaseous hydrogenation products and recycled to said hydrogenation.

8. A coal treating process comprising the steps of admixing coal with hydrocarbon oil to form a paste, hydrogenating said paste at a pressure in excess of 1000 p.s.i.g. and at a temperature in excess of 600 F. until about 60 to of the carbon content of said coal is converted to liquid and gaseous hydrogenation products, removing from the hydrogenated paste a vapor phase of unreacted hydrogen and products of hydrogenation boiling below about 400 F., injecting the residual paste into the upper portion of a uidized mass of contact material maintained at a pressure in excess of 200 p.s.i.g. and at a temperature of about 900 to 1300 F. thereby converting said residual paste to gasiform products rich in gasoline hydrocarbons and =a substantially dry carbonaceous residue, gasifying said dry residue with oxygen and steam in the lower portion of said uidized mass to produce hydrogen-containing gas, said hydrogen-containing gas exerting a hydrogen partial pressure of at least about 75 p.s.i. in said fluidized mass, withdrawing from the top of said uidized mass said gasiform products in adrnixture with said hydrogen-containing gas, recovering highpurity hydrogen directly from the gasification of said dry residue, and utilizing said high-purity hydrogen in hydrogenating said paste.

9. The process of claim 8 in which said dry residue is gasied with steam and oxygen of at least by volume purity supplied in a steamtooxygen molar ratio in the range of about 1.5:1 to 5:1.

l0. The process of claim 8 in which said hydrocarbon oil is obtained in part from said liquid hydrogenation products and in part from said gasiform products.

References Cited in the ile of this patent UNITED STATES PATENTS 1,984,596 Pier et al. Dec. 18, 1934 2,450,753 Guyer Oct. 5, 1948 2,634,286 Elliott et al Apr. 7, 1953 2,658,861 Pevere et al Nov. 10, 1953 2,738,311 Frese et al. Mar. 13, 1956 2,756,194 Mayland July 24, 1956

Claims

1. IN THE HYDROGENATION OF COAL INVOLVING THE TREATMENT WITH HYDROGEN OF SAID COAL IN POWDERED FROM WHILE SUSPENDING IN A HYDROCARBON OIL, THE IMPROVEMENT WHICH COMPRISES TERMINATING SAID TREATMENT WHEN A MAJOR PORTION NOT EXCEEDING ABOUT 85% OF THE CARBON CONTENT OF SAID COAL HAS BEEN CONVERTED TO LIQUID AND GASEOUS HYDROGENATION PRODUCTS, SUBJECTING A MIXTURE OF LIQUID HYDROGENERATION PRODUCTS AND SOLID RESIDUE RESULTING FROM SAID TREATMENT TO VAPOR-PHASE CRACKING BY INJECTING SAID MIXTURE INTO A FLUIDIZED MASS OF CONTACT MATERIAL MAINTAINED IN THE PRESENCE OF HYDROGEN AT ELEVATED TEMPERATURE AND PRESSURE WHEREBY SAID MIXTURE IS CONVERTED TO A SUBSTANTIALLY DRY CARBONACEOUS RESIDUE AND A GASIFORM STREAM RICH IN GASOLINE HYDROCARBON, AIND SEPARATING SAID GASIFORM STREAM FROM SAID DRY RESIDUE BY WITHDRAWING SAID GASIFORM STREAM FROM THE TOP OF SAID FLUIDIZED MASS.