US3844928A

US3844928A - Hydrocracking heavy hydrocarbonaceous materials in molten zinc iodide

Info

Publication number: US3844928A
Application number: US00359159A
Authority: US
Inventors: D Geymer
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1973-05-10
Filing date: 1973-05-10
Publication date: 1974-10-29
Anticipated expiration: 1991-10-29

Abstract

High boiling and normally solid nitrogeneous hydrocarbonaceous materials are hydrocracked in a continuous phase molten salt mixture predominating in zinc iodide. The mol ratio of ammonia to zinc iodide is maintained at a value of from about 0.25 to about 0.75 in the hydrocracking zone. Ammonia, which is formed from the nitrogen of the feed stock, is continuously stripped from a slipstream of the salt mixture taken from the hydrocracking zone and a portion of the stripped ammonia is recycled to the hydrocracking zone to maintain the indicated ratio of ammonia to zinc iodide.

Description

Geymer HYDROCRACKING HEAVY HYDROCARBONACEOUS MATERIALS IN MOLTEN ZENC IODIDE Primary ExaminerVeronica OKeefe [75] Inventor: Douglas 0. Geymer, Houston, Tex. [73] Assignee: Shell Oil Company, Houston, Tex. [57] ABSTRACT [22] Fikad: May 10 1973 High boiling and normally solid nitrogeneous hydrocarbonaceous materials are hydrocracked 1n a contin- [21] Appl. No.: 359,159 uous phase molten salt mixture predominating in zinc iodide. The mol ratio of ammonia to zinc iodide is 52 l maintained at a value of from about 0.25 to about E K 8 208/10 fig gg 0.75 in the hydrocrackmg zone. Ammonia, WhlCh 18 58 Field o'r'iilllllll1.1111111111111111?b'/s, 10, 10s F f is ously stripped from a slip-stream of the salt mixture [561 Ree'mescied 122 52553211 312.5%? is fi e /5,31%? 3 33332205; 5 UNITED STATES PATENTS zone to maintain the indicated ratioof ammonia to 3,6 7,108 4/1972 Kiousky 208/ Zinc iodide 3,677,932 7/1972 Hardesty et a1 208/108 3,790,468 2/1974 Loth 208/10 5 Claims, 1 Drawing Figure NH3 33 23 l L NH3 13 To PRODUCT 34 RECOVERY [VH3 7 H20 11 5 6 32 2/11 12 E ZnIg FEED STOCK Zn(NH3) I 84 T NH4ZnI3 56 NH4I r0 PRODUCT H7 EEOVERY H2 52 27, 22 INERTS I2 r I A CHAR. 87 43/ i ASH W ZnS L Zru'z CHAR, ASH, s

MOLTEN ZnIZ RECYCLE 2/1974 Loth et al. 208/10 HYDROCRACKING HEAVY HYDROCARBONACEOUS MATERIALS IN MOLTEN ZINC IODIDE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the hydrocracking of coal I and heavy nitrogeneous hydrocarbonaceous oils in a molten catalyst system comprising predominately zinc iodide.

2. Description of the Prior Art An extensive amount of research and development work has been done by a number of workers on the conversion of coal to liquid hydrocarbon products. Much work has been carried out on the hydrocracking of coal in the presence of a continuous phase of molten zinc chloride by workers at Consolidation Coal Company, under the sponsorship of the Office of Coal Research, U.S. Department of the Interior. Many publications have been based upon this work, including a number of patents, e.g., US. Pat. Nos. 3,355,376; 3,371,049; 3,594,329; 3,625,861 and British Pat. No. 1,095,851. Others have also been active in the field. US. Pat. No. 3,543,665 is directed to a similar process involving the use of various molten metal halides. Still further, U.S. Pat. Nos. 3,657,108 and 3,685,962 are directed to the regeneration of metal halides--ammonium halide complexes or mixed'salts which are formed in the use of certain molten metal halides, including zinc iodide, in the hydrocracking of coal. It has also been disclosed in US. Pat. No. 3,667,932, in the use of molten zinc halides (chloride, bromide and iodide), in the hydrocracking of heavy oil fractions, that various advantages are obtained by the addition of various melting point depressants, such as the corresponding alkali metal halide to the molten zinc halide system.

The complexity of the reaction system (the variety of reactions taking place) in the hydrocracking of coal, coal extracts and heavy petroleum fractions, due in part to the presence of relatively high contents of bound nitrogen and sulfur, has been well recognized and discussed in considerable detail in the prior art. For instance, bound sulfur in the coal is converted to hydrogen sulfide, which in turn reacts with the metal halide, particularly zinc halide, to form metal sulfide, thereby tending to deplete the system of the catalytic metal halide. Also, bound nitrogen in the coal is converted to ammonia, which can give rise to a number of changes in the system. For example, ammonia can complex with zinc to form a zinc-ammonia complex consequently altering the catalytic activity of the zinc. It can also react with hydrogen iodide, resulting from the zinc iodide reaction with hydrogen sulfide, to form ammonium iodide, thereby changing the character of the iodide in the system. Ammonium iodide, in turn can interact with zinc iodide to form a complex or mixed ammonium zinc iodide.

SUMMARY OF THE INVENTION It has now been found, and this is the basis for the present invention, that the hydrocracking of coal and heavy nitrogeneous carbonaceous materials in a molten salt mixture comprising predominately zinc iodide containing a suitable melting point depressant is improved by maintaining in the hydrocracking zone, throughout the time that the feed stock is subjected to hydrocracking conditions, a mol ratio of ammonia to zinc iodide of from about 0.25 to about0l75. The mols of ammonia for purposes of this ratio are calculated as the NH;, content varying ammonia and zinc ammonia iodide complex, while the mols of zinc iodide are calculated as the Znl content of all the zinc iodide-containing salt. While ammonia in high concentrations will poison many metal halide catalysts, it has been found that the molten zinc iodide system is not substantially adversely affected by the presence of ammonia in aforesaid high concentrations, and in fact, a higher total conversion of feed, such as coal to volatile hydrocarbon products, is obtained. Furthermore, selectivity is improved in that a smaller amount of hydrogen is consumed in making gaseous hydrocarbons. In fact, by varyingg the ammonia concentration within the previously described limits, it is possible to exercise considerable control over product distribution, high ammonia concentrations favoring the production of fuel oil range products while lower ammonia concentrations favor the production of lighter products, e.g., gasoline. Moreover, ammonia and complexed ammonia also serve to lower the melting point of the molten salt catalyst in the hydrocracking zone.

The desired ratio of ammonia to zinc iodide is preferably maintained in the hydrocracking zone by continuously stripping the free and combined ammonia from a portion of the molten catalyst system withdrawn from the hydrocracking zone as a slip-stream, and recycling a portion of the recovered ammonia, directly orindirectly, 'to the hyrocracking zone as hereinafter explained.

THE DRAWING PREFERRED EMBODIMENT OF THE INVENTION Referring to the drawing, the selected feed stock and zinc iodide, in the desired proportions, as already indicated in the prior art, are suitably mixed in a mixing zone 14 and the mixture then subjected to hydrocracking under hydrocracking conditions in the presence of added hydrogen in a hydrocracking zone 16. The feed stock and zinc iodide may be passed separately and directly to the hydrocracking zone.'The hydrocracking is effective at a temperature of about 3005,00.C under a hydrogen partial pressure of from about SOD-5,000 psig. A molten body of the zinc iodide is maintained in the hydrocracking zone, at a-high level, with a vapor space above the molten mass. Vaporous material including unused hydrogen is removed overhead from the hydrocracking zone. Hydrogen is separated from the product in separation zone 31' and is recycled to the hydrocracking zone. Molten catalyst, containing char, ash, and zinc sulfide, is continuously withdrawn and flashed to a relatively low pressure in a suitable flash zone 41 with resulting coolingto a temperature of about 250300C. A portion of the resulting molten mass is recycled, directly or indirectly, to the hydrocracking zone. The other portion is processed for the separation of solids from the molten phase in separation zone 51. The separated molten phase is heated to about 375-425C, typically 400410C and then stripped in stripping zone 61 to remove ammonia and water (water having been formed from bound oxygen in the feed). The ammonia and water are separated in a suitable separation zone 71, and a selected portion of the ammonia is recycled to the hydrocracking zone. This portion may be recycled in whole or in part to the initial zinc iodide introduced into the mixing zone, or to a portion of the zinc iodide which is fed directly to the hydrocracking zone, or to the recycle hydrogen stream recovered from the overhead stream from the hydrocracking zone. In order-to insure adequate removal of ammonium iodide from the molten mixture in the stripping zone 61, a portion of the bottoms product therefrom is mixed with air to convert a portion of the zinc iodide content to zinc oxide and free iodine. The zinc oxide, after separation from the iodine, is returned in the molten stream to the stripping zone where it displaces ammonia' from ammonium iodide in the molten mass.

For a better understanding of the practice of the invention, as applied to the preferred feed stock, namely coal, a more detailed description thereof with reference to the drawing is given below. I

Ground and dried coal is delivered through line to mixing zone 14, wherein it is slurried with at least about 7 proportions by weight of a molten mass predominating in zinc iodide supplied by line 11 and recycle line 21. The slurry in mixing zone 14 is maintained at a tem perature of about 250300C. When utilizing liquid feed stocks, both the zinc iodide and the feed stock may bypass the mixing zone and go directly as indicated to the hydrocracking zone. The zinc iodide (normal melting point 449C) is maintained in a molten state under these conditions with the use of suitable melting point depressants such as alkali and alkaline earth metal iodides and/or the ammonia entering through line 11, via

lines

24 and 25. Alkali metal iodides are particularly useful for this purpose and once incorporated in the circulating molten salt system remain therein. The coal slurry is pumped through line 15, with a suitable pump, to a pressure of from about 500 to 5,000 psig, e.g., 2,500 psig, into hydrocracking zone 16. Hydrogen is supplied by line 17, recycled hydrogen being added to line 17 from line 32. The hydrocracking is a highly exothermic reaction so that the desired elevated temperature, e.g., 400-420C is easily obtained. Excess heat is removed by various suitble means, such as by sensible heat in the vapor stream withdrawn overhead from the hydrocracking zone and by heat of vaporization in flash zone 41. The overhead stream from the hydrocracking zone is passed to separation zone 31 wherein the unused hydrogen, ammonia and water and hydrocarbon product are separately recovered, e.g., by condensation. The hydrogen-is recycled to the hydrocracking zone via line 32, while the ammonia and water are passed through line 33 to separating zone 71. The hydrocarbon product stream passes through line 34 to product recovery to be separated into suitable products by means well known to the art and not shown in the drawing.

Because of contamination of the molten salt catalyst system by char, ash, tars and zinc sulfide, in addition to water, ammonia, ammonia complexes and salts, it is necessary to provide a means for continuous regeneration. This is done by withdrawing a side stream of the molten mass from the hydrocracking zone through line 35 and passing it through heat exchanger 28 and a suitable reducing device, such as a valve 36 or an expansion turbine, to flash zone 41. The pressure is reduced on the order of 20-60 psig with a reduction in temperature to about 250300C. A product stream is recovered via line 42 while a portion of the resulting cooled molten salt mass, including contaminants, is recycled through

lines

43 and 21 to line 11 and mixing zone 14. A portion of the molten salt mass may be recycled directly to the hydrocracking zone through

lines

44 and 22. In general, from about to 90 percent of the molten salt mixture in the flash zone is recycled directly without further purification. The remainder of the molten salt mixture in the flash zone is passed by line 45 to a suitable solids separation zone 51, which may be a pressure filter or centrifugual separator, wherein contaminating solids are separated from the molten salt mixture. The separated molten salt, at a temperature of about 250-300C, is heated in heat exchanger 52 or other equivalent heating device to a temperature of from about 375 to 425C and passed through line 54 to stripping zone 61 wherein it is countercurrently stripped by the use of an inert gas such as nitrogen delivered by line 62. The stripping gas and stripped ammonia and water are removed overhead through line 64 to a suitable separation zone 71, which may be a fractionating zone wherein inert gas (nitrogen), ammonia, and water are separated. The separated inert gas in line 72 is recycled to the stripping zone. Water is withdrawn from separation zone 71 through line 76. The ammonia is withdrawn through line 74, with a selected portion, as required, being passed by line 75 back to the hydrocracking zone. The recycle of the selected portion of ammonia may be accomplished completely through

lines

24 and 25 to line, 11 wherein it is mixed with the zinc iodide going to the mixing zone, or all or part of it may be passed by

lines

26 and 13 directly to the hydrocracking zone, or all or part of it may be passed by line 27 to join with the recycled hydrogen in line 32 and thence to line 17 and the hydrocracking zone. The amount of ammonia thus recycled to the hydrocracking zone is adjusted to provide a mol ratio of ammonia to zinc iodide of from about 0.25 to about 0.75 in the hydrocracking zone. In order to insure that ammonia is present in the required proportions with the molten zinc iodide catalyst throughout the time the coal is subjected to hydrocracking, it is preferred to incorporate the required amount of recycled ammonia into the feed stock, or mixture of feed stock and zinc iodide while they are still under non-cracking conditions.

As hereinbefore described, substantially complete stripping of the ammonia from the molten salt mixture in stripping zone 61 is effected by treating the molten salt mixture with zinc oxide which reacts with ammonium iodide converting it to zinc iodide with the release of ammonia. The zinc oxide required for this reaction is produced by oxidizing a portion of the stripped zinc iodide (withdrawn from stripping zone 61 through

lines

79 and 80).with air which is introduced into line 80 via line 81. Oxidation of the zinc iodide with air results in its partial conversion to zinc oxide and free iodine which are separated in separation zone 82. The amount of zinc oxide required to effect regeneration of ammonium iodide is an essentially stoichiometric equivalent to the ammonium iodide in the molten salt going to the stripping zone; this requires a stoichiometric amount of oxygen (in the air).

The free iodine liberated by the air oxidation of a portion of the zinc iodide is taken overhead from separation zone 82 in line .83, and suitably recovered as desired. Preferably, the liberated iodine is suitably passed by line 84 to conversion and recovery zone 91 wherein it reacts with the zinc sulfide content of the solids separated in separation zone 51, to form zinc iodide and free sulfur. The thus formed zinc iodide may be suitably separated from the solid materials present and returned by line 95 to the line 79 carrying the stripped molten salt recovered from stripping zone 61. Any inerts present in recovery zone 91 are withdrawn through line 92. The stripped molten salt withdrawn in line 79 and the recovered zinc iodide from conversion zone 91, are recycled to the coal slurrying zone (mixing zone 14) via

lines

21 and 11. If desired, a portion of the regenerated molten zinc iodide may be bypassed through valved line 22 to line 13 and the hydrocracking zone. Incidentally, since the amount of ammonium iodide is essentially stoichiometric to the zinc sulfide, the amount of free iodine formed in producing the zinc oxide for ammonium iodide regeneration is essentially stoichiometric to the zinc sulfide, thereby giving an essentially balanced requirement.

EXAMPLES The advantage resulting from the addition of ammonia to the molten zinc iodide hydrocracking system in accordance with the invention is demonstrated by the results of comparative runs on the hydrocracking of coal, in one case no ammonia having been added, while in the other case a specified amount of ammonia was added to the system. In the two runs. a simulated steady state catalyst composition was heated with coal at 250C for 28 minutes, then the mixture subjected to bydrocracking at 420C and 2000 psig for 34 minutes. Experience from much experimentation has indicated that. with the particular coal being processed, the equilibrium catalyst system contained Z1113, NHJ and ZnS in the relative weight proportions of 21 1:21:69, respectively. In the runs, thirty parts by weight of the coal was mixed with 238.9 parts by weight of the simulated equilibrium catalyst mixture. The results of the two runs are given in Table 1 (all parts by weight are in the same units):

(Moisture and ash-free To further demonstrate the benefits of the invention, four further runs were conducted to show the effect of progressive increases in ammonia concentration on the molten zinc iodide hydrocracking system. The composition of the simulated equilibrium catalyst mixture, concentration of ammonia, reaction conditions and product yield for these runs are presented in the follow ing table.

Table 11 Run No. 3 4 5 6 Znl .g 211 211 199 186 NH ,g 0.0 5.2 7.5 10.6 NH l,g 21.0 21.0 19.8 18.5 ZnS.g 6.9 6.9 6.5 2.3 Coal, g 30 3O 30 30 Catalyst volume, ml/ coal 210 235 233 235 Catalyst melting point, 400 300 190 200 Reaction temperature, C 420 420 420 420 Pressure, psi 2000 2000 2000 2000 Reaction time, minutes 30 30 30 32 H consumption. g/IOOg Mmmm g MAF coal 7.5 6.0 5.7 5.3 Nit /2M molerafto 0.00 0.47 0.71 1.07 NH partial pressure, psi 16 6 9 19 Yield of volatile hydrocarbons.

basis of feed C 4 1.0 0.7 0.6 0.8 z a' a a 8.7 6.0 5.0 4.7 i-CJ-I 9.3 6.0 4.4 2.5 n-C,H -C H l 1.7 7.9 6.0 3.4 Methylcyclopentane-C boilin g range hydracar'boiis 21.4 18.5 "17. 7 13.3 160-216C boiling range hydrocarbons 5.6 9 8 9.5 6.5 2l627lC boiling range hydrocarbons 2.5 8.3 8.8 6.6 Hydrocarbons boiling WMMWA above 271C 0 I 4 15,9 20.8 21.4 1.7 2.0" 2.0 1.7

Totals 66.2 75.1 74.8 60.9

"' in every case the catalyst is saturated with ZnS. since the solubility of ZnS is low.

I The above results conversion of coalto hydrocarbons is substantially increased by operating in accordance with the invention (Runs 4 and 5) and then falls off as the mol ratio of NH to Znl is increased sent'ially of zinc iodide containing a compatible melting point depressant, wherein (1) the feedstock is contacted with the molten salt mixture in the presence of hydrogen at a partial pressure of from about 500 to about 5,000 psig and at a temperature of from about 300C to about 500C, (2) oil products are separated from the molten salt catalyst system, (3) resulting spent catalyst is withdrawn from the hydrocracking zone and is separately regenerated whereby ammonia complexed with zinc iodide is removed therefrom, and wherein (4) the regenerated zinc iodide is returned to the hydrocracking zone, the improvement which comprises:

maintaining a mol ratio of ammonia to zinc iodide of from about 0.25 to about 0.75 in the catalyst system in the hydrocracking z one,fthe mols of ammonia calculated as the NH;, content of ammonia and ammonia iodi de cdrnpl exfand warriors zinc iodide calculated as the Znl content of all zinc iodide-containing salt. 2. The process of claim 1 wherein the ammonia content, including complexed ammonia and ammonia bound as ammonium iodide, of the portion of the spent 4. The process of claim 1 wherein the coal feed stock is supplied to the hydrocracking zone as a slurry of finely divided coal in a molten salt mixture predominating in zinc iodide.

v 5. The process of claim 4 wherein ammonia is incorporated in the coal-molten salt slurry under substantially non-cracking conditions to provide the specified ammonia to zinc iodide mol ratio when the slurry is fed to the hydrocracking zone.

Claims

1. IN A CONTINUOUS PROCESS OF HYDROCRACKING COAL IN A HYDROCRACKING ZONE CONTAINING A CONTINUOUS PHASE CATALYST SYSTEM OF A MOLTEN SALT MIXTURE CONSISTING ESSENTIALLY OF ZINC IODIDE CONTAINING A COMPATIBLE MELTING POINT DEPRESS AND, WHEREIN (1) THE FEEDSTOCK IS CONTACTED WITH THE MOLTEN SALT MIXTURE IN THE PRESENCE OF HYDROGEN AT A PARTIAL PRESSURE OF FROM ABOUT 500 TO ABOUT 5,000 PSIG AND A TEMPERATURE OF FROM ABOUT 300*C TO ABOUT 500*C, (2) OIL PRODUCTS ARE SEPARATED FROM THE MOLTEN SALT CATALYST SYSTEM, (3) RESULTING SPENT CATALYST IS WITHDRAWN FROM THE HYDROCRACKING ZONE AND ITS SEPARATELY REGENERATED WHEREBY AMMONIA COMPLEXED WITH ZINC IODIDE IS RREMOVED THEREFROM, AND WHEREIN (4) THE REGENERATED ZINC IODIDE IS RETURNED TO THE HYDROCRACKING ZONE, THE IMPROVEMENT WHICH COMPRISES: MAINTAINING A MOL RATIO AMMONIA TO ZINC IODIDE OF FROM ABOUT 0.25 TO ABOUT 0.75 IN THE CATALYST SYSTEM IN THE HYDROCRACKING ZONE, THE MOLS OF AMMONIA CALCULATED AS THE NH3 CONTENT OF AMMONIA AND ZINC AMMONIA IODIDE COMPLEX, AND THE MOLS OF ZINC IODIDE CLACULATED AS THE ZNL2 CONTENT OF ALL ZINC IODIDE-CONTAINING SALT.

2. The process of claim 1 wherein the ammonia content, including complexed ammonia and ammonia bound as ammonium iodide, of the portion of the spent catalyst withdrawn and regenerated, is removed as ammonia from the zinc iodide, and a portion of the removed ammonia is returned to the hydrocracking zone to maintain the specified ratio of ammonia to zinc iodide.

3. The process of claim 1 wherein ammonia is incorporated in a mixture of the feed stock and the zinc iodide under substantially non-cracking conditions sufficient to provide the specified ammonia to zinc iodide mol ratio when the mixture is initially subjected to hydrocracking conditions.

4. The process of claim 1 wherein the coal feed stock is supplied to the hydrocracking zone as a slurry of finely divided coal in a molten salt mixture predominating in zinc iodide.

5. The process of claim 4 wherein ammonia is incorporated in the coal-molten salt slurry under substantially non-cracking conditions to provide the specified ammonia to zinc iodide mol ratio when the slurry is fed to the hydrocracking zone.