US3625861A

US3625861A - Regeneration of zinc halide catalyst used in the hydrocracking of polynuclear hydrocarbons

Info

Publication number: US3625861A
Application number: US884855A
Authority: US
Inventors: Everett Gorin; Robert T Struck; Clyde W Zielke
Original assignee: CLYDE W ZIELKE; ROBERT T STRUCK
Current assignee: CLYDE W ZIELKE; ROBERT T STRUCK
Priority date: 1969-12-15
Filing date: 1969-12-15
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07

Abstract

Spent zinc halide cracking catalyst, prior to oxidation to remove impurities, is heated to carbonize organic residue to drive off volatiles, and to decompose zinc halide-NH3 complex and drive off NH3.

Description

United States Patent Everett Gorin 439 Austin Ave., Pittsburgh, Pa. 15216; Robert T. Struck, 2347 Morton Road, Pittsburgh, Pa. 15241; Clyde W. Zielke, 195 Dell Ave., Pittsburgh, Pa. 15216 Appl. No. 884;855

Filed Dec. 15, 1969 Patented Dec. 7, 1971 Inventors REGENERATION OF ZINC HALIDE CATALYST USED IN THE HYDROCRACKING OF POLYNUCLEAR HYDROCARBONS 10 Claims, 2 Drawing Figs.

U.S. Cl 252/416, 23/97, 23/100, 23/193, 23/288, 208/10, 252/418, 252/419 Int. Cl B0lj 11/80, B01 j 1 1/04 Field of Search 252/416,

[56] References Cited UNITED STATES PATENTS 3,355,376 11/1967 Gorin et al 208/10 3,371,049 2/1968 Gorin et al.... 208/10 2,780,587 2/1957 Watkins 208/125 2,285,573 6/1942 Dubs 23/97 I FOREIGN PATENTS 1,095,851 12/1967 Great Britain 252/416 Primary Examiner-Daniel E. Wyman Assistant Examiner-P. E. Konopka Attorneys-Ernest S. Cohen and M. Howard Silverstein ABSTRACT: Spent zinc halide cracking catalyst, prior to oxidation to remove impurities, is heated to carbonize organic residue to drive off volatiles, and to decompose zinc halide- NH complex and drive off NH FEED P RETREATM ENT ZONE I GARBONIZATION TAR AND GASES PRETREATMENT ZONE 11 NH RECOVERY /5 AIR COMBUSTOR PRODUCT RECOVERY ZONE REGENERATED ZnC I ZnO INVENTORS ROBERT r. STRUCK 0L r05 w. z/surs ATTORNEYS REGENERATION F ZINC HALIDE CATALYST USED IN THE HYDROCRACKING OF POLYNUCLEAR HYDROCARBONS This invention relates to the regeneration of molten zinc halide catalysts used in hydrocracking predominantly polynuclear aromatic hydrocarbonaceous materials; and more particularly, in the conversion to gasoline of substantially nondistillable, high-molecular weight, predominantly polynuclear aromatic hydrocarbonaceous feedstocks which contain nitrogen, oxygen and sulfur compounds.

A process for utilizing molten zinc halide catalysts in such a type of catalytic hydrocracking is described in British Pat. No. 1,095,851. As set forth in that patent, it was found that polynuclear hydrocarbons, even those which are nondistillable, may be readily converted in the presence of a large quantity of molten zinc halide to low-boiling liquids suitable for fuels such as gasoline. The amount of zinc halide which serves as catalyst must be at least weight percent of the inventory of hydrocarbonaceous material in the hydrocracking zone. To this amount of zinc halidemust be added, in the case of nitrogenand sulfur-containing feedstock, sufficient zinc halide to remove reactive nitrogen and sulfur compounds in the feedstock, in accordance normally with the following equations, wherein zinc chloride is used as an example of the catalyst:

1n the case of a feedstock consisting of coal extract containing, for example, 1.5 percent N and 2 percent S, the amount of zinc chloride required to react stoichiometrically with the nitrogen and sulfur compounds would be 23 percent by weight of the feedstock. A successful commercial process utilizing a molten zinc halide catalyst must therefore provide for. the regeneration of the catalyst.

An improvement in the process described above is disclosed and claimed in British Pat. No. 1,095,852 (counterpart of U.S. Pat. No. 3,355,376). in accordance with that improvement, zinc oxide is mixed with the zinc halide, e.g. zinc chloride, in the hydrocracking zone in a mol ratio of at least 10 parts chloride to one part oxide, to thereby remove hydrogen chloride as set forth in the following equation:

4. ZnO-l-HC1=ZnCl +l-l O By virtue of the use of zinc oxide, loss of HCl from the system is minimized and corrosion by HCl is controlled. The use of zinc oxide also effectively eliminates the reaction expressed in equation (3) above, thus making it unnecessary to regenerate ZnC1 -NHB4C1.

The same U.S. Pat., i.e. US. Pat. No. 1,095,852, describes two of regenerating the spent melt, both involving oxidation of the impurities, one in liquid phase and one in vapor phase. The reactions occurring in such oxidative regeneration processes as applied to ZnCl are as follows:

It will be seen from equation 6 that ammonia is destroyed. Such destruction is obviously undesirable since ammonia is a commercially valuable commodity.

We have now developed a new and improved regeneration process wherein ammonia can be recovered as a byproduct. Basically, the invention comprises subjecting spent catalyst to thermal pretreatment in the liquid phase, prior to oxidation treatment, under conditions such that zinc halide is retained in the liquid phase along with the nonvolatile impurities while ammonia and carbonaceous volatile matter are recovered as valuable byproducts, thereafter subjecting said catalyst, now substantially free of nitrogen compounds, to oxidation to effect combustion of the organic residue and ZnS, and recovering zinc halide and zinc oxide.

It is therefore an object of the present invention to remove nitrogen compounds from the spent catalyst prior to its oxidation to provide substantially pure zinc halide catalyst for recycle to the hydrocracking zone.

Another object is to provide ammonia and hydrocarbon byproducts during regeneration.

Other objects and advantages will be obvious from the following more detailed description of the invention in conjunction with the drawings in which:

FIG. 1 is a schematic flowsheet of the novel regeneration process, in its broadest aspects, for removing organic residue, sulfur and nitrogen compounds from the spent zinc halide catalyst; and

FIG. 2 is a preferred embodiment, schematically illustrated, of the regeneration process generally shown in FIG. 1.

In the practice of the present invention, the feed is spent molten zinc halide catalyst withdrawn from a hydrocracking zone (not shown), fully described as stated above in British Pat. No. 1,095,852. The spent zinc halide catalyst contains (in addition to the zinc halide) zinc sulfide (see reaction (1) above), zinc halide Nl-l (see reaction (2) above), organic residue, and generally some unreacted zinc oxide. If the amount of organic residue present is significant, that is, greater than 6 percent of the feed, then it is generally advisable to remove as much as possible of the organic residue by extraction with an aromatic solvent before attempting to regenerate the catalyst.

Referring to FIG. 1, the spent catalyst is fed to a pretreatment zone I designated by the numeral 10. In this zone, the spent catalyst is subjected to carbonization to effect coking of the organic residue. The molten catalyst is stirred and maintained at a temperature between about 1,0000 and l,200 F whereby fine particles of coke are formed and volatile tar and gases are evolved which are discharged through a conduit 11. The zinc compounds are substantially nonvolatile at these temperatures.

The carbonized catalyst is transferred to a second pretreatment zone ll designated by the numeral 12. In this zone 11, ammonia is evolved from the melt by heating it to a higher temperature, viz, about 1,250 to 1,350 F. and even higher if the operation is conducted under pressure. At these temperatures, the zinc halide-ammonia complex decomposes to yield ammonia which is discharged through a conduit 13. 'T he thus pretreated catalyst now is substantially free of nitrogen compounds and gaseous or low-boiling hydrocarbons.

The pretreated catalyst is oxidized in a combustor designated by the numeral 14. The oxidation may be conducted in either a liquid phase process or a vapor phase process as illustrated by FIGS. 3 and 4 respectively, of the aforementioned British Pat. No. 1,095,852. The particular process employed to oxidize the pretreated catalyst is not relevant to the process of the present invention. Accordingly, the oxidation process of FlGswill be described in general terms only. Air is introduced into the combustor 14 through a conduit 15. In liquid phase oxidation wherein the zinc halide is maintained in a molten state, the temperature and pressure are regulated to maintain the oxidative reactions set forth above in equations 8 through 10 inclusive. ln vapor phase oxidation, the pretreated spent catalyst is incinerated at high temperatures, by combustion of the carbon and sulfur components, as well as any ammonia that may have remained. ln vapor phase combustion, and to some extent in liquid phase combustion, the zinc halide is vaporized. The products from the combustor are separately and suitably treated by condensation, absorption or filtration, as may be required in a product recovery zone generally indicated by the block designated 16. The gases are shown as being separately recovered through a conduit 17, while the regenerated zinc halide catalyst and the HCl acceptor ZnO are separately recovered through a conduit 18 free of contaminants.

A preferred embodiment of the invention is shown in F IG. 2 of the accompanying drawings. In this embodiment, two pretreatment zones, 22 and 24 respectively, and two liquid hase combustion zones, 26 and 28 respectively, are housed in a vessel 20 in vertically spaced relationship. The feed is introduced through a conduit 30 into the first pretreatment zone 22, and thence downwardly in succession through the other three zones. The feed contains the following components: ZnCl ZnCl,-NI-l ZnS, ZnO, organic residue and ash (derived from the coal). The temperature in the descending zones increases continuously from I ,025-l ,125" F. in the first pretreatment zone 22 to l,225-l,325 F. in the first combustion zone 26. Heat is supplied to the upper zones principally by condensing ZnCl vapor and by reabsorption of part of the NH;,. The second and final combustion zone is at a still higher temperature, i.e. l,275l,375 F. The temperature levels are set primarily by the operating pressure. The lower limits of temperature correspond to operation at one atmosphere total pressure; the upper limits to approximately four atmospheres total pressure.

In the first pretreatment zone 22, carbonization of the organic residue is the principal operation. The zone is stirred by a stirrer 32. To assist in holding the temperature constant in this zone, a portion of the molten catalyst is pumped through a heat exchanger 34 in a recirculatory conduit 36. Tar and the effluent gases from the lower zones are discharged through a conduit 38 to a condenser-absorber system 40 for separation and recovery of steam, tar and noncondensable gases. In the condenser-absorber 40, the temperature is maintained between 600 and 700 F. Steam, tar and noncondensable gases may be conveniently recovered as overhead from the condenser-absorber. The zinc chloride vapors condense, and some react with the ammonia to form ZnCI Some of the latter react with any HCl present to from ZnClfl'flCl. The ZnClfi'" and any ZnCl,- C1 are conducted to a separate NH Cl neutralization zone 41. In this zone, the ZnCl -NH Cl is reacted with ZnO introduced through a conduit 42. The reaction is as follows:

1 l. ZnO+2ZnC1 NH Cl=2ZnCl b.NI-I +ZnCl +l-l O The product is then conducted to an ammonia recovery zone 43 which is maintained at a temperature of about 900 F. to effect the decomposition of ZnCl NH and flash off the ammonia. The ZnCl is recycled through a conduit 44 back to the first pretreatment zone 22.

The liquid catalyst, now containing dispersed particles of coke instead of organic residue, overflows into a downwardly extending channel 46 which leads to the second pretreatment zone 24. In this zone, ZnCl -NH is decomposed to ZnCl and NH;,; and any incompletely carbonized organic residue is carbonized to yield more tar. The ammonia and tar, together with the gases from the oxidation zones, are circulated upwardly through the first pretreatment zone 22. The substantially ammonia-free catalyst overflows into a downwardly extending channel 48 which leads to the first combustion zone 26.

There are two combustion zones in the preferred embodiment in order to recover the gaseous products of oxidation in two separate categories, that is, products of oxidation of carbon and products of oxidation of zinc sulfide. Both zones are liquid phase. The first zone 26 is operated to favor selective oxidation of the coke particles to CO Air is introduced through a conduit 50 into the liquid in the first zone. The hot effluent gases containing principally CO and nitrogen are circulated upwardly into the second pretreatment zone 24. The liquid in the first combustion zone 26 is permitted to overflow into a downwardly extending channel 52 which leads to the second combustion zone 28. Oxidation of ZnS to ZnO and S is effected in this zone. The oxidation of ZnS occurs at a much faster rate than does the oxidation of ZnC 1 so that little or no conversion of ZnCl is observed. Air is introduced through conduit 54 into thesecond combustion zone. The gaseous products of oxidation, principally S0 are not circulated into the upper combustion zone, but instead are discharged through a conduit 56 to a condenser 58 wherein any steam and vaporized ZnCl, are condensed and separately recovered through

conduits

60 and 62 respectively. A stream of SO,-rich gas is discharged from the condenser through a conduit 64. he condensed ZnCl is In part recycled through conduit 66 to the second combustion zone 28 and, in part, discharged through a conduit 68 to the main outlet conduit 70 which conducts regenerated ZnCland ZnO from the second combustion zone 28.

What is claimed is:

1. In a process for regenerating molten spent zinc halide cracking catalyst which has been employed in a process for hydrocracking polynuclear aromatic hydrocarbonaceous materials, wherein said spent catalyst, which contains zinc halide, ZnS, organic residue and a complex of zinc halide and NH,-,, is oxidized to drive off impurities, heating said spent catalyst, to a temperature of about l,000-l ,200 F. to drive off volatile matter from said organic residue, and to convert said residue to coke particles; subsequently heating said spent catalyst, prior to said oxidation step, to a temperature of at least 1,250 F. to decompose said zinc halide-Nl-l complex to zinc halide and NH and to drive ofi said NH oxidizing said coke particles in a first oxidation step, and subsequently oxidizing said ZnS to ZnO and S0 in a second oxidation step; zinc halide being retained substantially in a liquid state throughout said steps.

2. The process of claim I wherein said spent catalyst includes unreacted ZnO acceptor.

3. The process of claim 1 wherein said heating is serially carried out in two zones; wherein in the first zone in said series said spent catalyst is heated to effect carbonization of said organic residue to thereby drive off volatile tars and gases, and to form fine particles of coke; and wherein in the second zone in said series the spent catalyst is heated still further to decompose said complex, and to drive off said ammonia.

4. The process of claim 1 wherein said organic residue comprises no more than 6 percent by weight of said spent catalyst.

5. The process of claim 3 wherein said spent catalyst includes unreacted ZnO acceptor.

6. The process of claim 5 wherein said organic residue comprises no more than 6 percent by weight of said spent catalyst.

7. The process of claim 5 wherein, at the pressure in said zones is l to 4 atmospheres absolute.

8. The process of claim 5 wherein said first heating zone is above said second heating zone; wherein oxidation occurs in two zones below said second heating zone, wherein the first oxidation zone is above the second oxidation zone; wherein molten catalyst passes by gravity through said heating and oxidation zones; wherein molten catalyst is heated in said first and second heating zones by hot gases from lower zones of said heating and oxidation zones; wherein said coke particles in said catalyst are oxidized in said first oxidation zone; wherein said ZnS is oxidized to ZnO and SO: in said second oxidation zone, and wherein said 50 is then separated out of said heating and oxidation zones.

9. The process of claim 8 wherein the temperature increases continuously from l,O25-l,l25 F. in said first heating zone to l,275l ,375 F. in said second oxidation zone.

10. The process of claim 9 wherein said organic residue comprises no more than 6 percent by weight of said spent catalyst.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIGN 3.625.861 I Dated December 7. 1971 Inventor(s) Everett Gorin, et. al.

It is certified that error appears in the above-identified patent and that, said Letters Patent are hereby corrected as shown below:

Column 1, line 27, "ZnCl +H S=ZnS+HCl" should read ZnC1 +H S=ZnS+2HCl line 28, "ZnCl +NH =ZnCl NH should read ZnCl +NH =ZnCl .NH line 50, "ZnCl2.NHB4Cl" should read ZnCl .NI-I C l line '51, "The same U. S. Pat., i.e.,

. U. S. Pat. No." should read The same patent, i.e.,' No.

line 52, after "two", insert methods line 56, "ZnCl .NH -ZnCl NH should read ZnCl .NH =ZnCl +NH Column 2, line k33, "1,0000" should read 1,000 line 54, "FIG." should read FIG. 1 Column 3, lines 30-32 should read some react with ammonia to form ZnC1 .NH

Some of the latter reactwith any HCl present to form ZnC1 .NH Cl. The ZnCl .NH and any ZnCl .NH Cl are conducted to a separate line 36, "2znCl b.NH should read 3 5 Column 4, line 20, before "heating" insert comprising Signed and sealedthis l'2th day of December 1972.

(SEAL) Attest:

EDWARD M.F-LETCHER,JR. ROBERT GOT'ISCHALK v Attesting Officer I 1 a Commissioner of Patents FORM PO-105O (10-69) I USCOMM-DC 60376-P69 fi' U.S. GOVERNMENT PRINTING OFFICE: I969 0-368-334,

Claims

2. The process of claim 1 wherein said spent catalyst includes unreacted ZnO acceptor.
3. The process of claim 1 wherein said heating is serially carried out in two zones; wherein in the first zone in said series said spent catalyst is heated to effect carbonization of said organic residue to thereby drive off volatile tars and gases, and to form fine particles of coke; and wherein in the second zone in said series the spent catalYst is heated still further to decompose said complex, and to drive off said ammonia.
4. The process of claim 1 wherein said organic residue comprises no more than 6 percent by weight of said spent catalyst.
5. The process of claim 3 wherein said spent catalyst includes unreacted ZnO acceptor.
6. The process of claim 5 wherein said organic residue comprises no more than 6 percent by weight of said spent catalyst.
7. The process of claim 5 wherein, at the pressure in said zones is 1 to 4 atmospheres absolute.
8. The process of claim 5 wherein said first heating zone is above said second heating zone; wherein oxidation occurs in two zones below said second heating zone, wherein the first oxidation zone is above the second oxidation zone; wherein molten catalyst passes by gravity through said heating and oxidation zones; wherein molten catalyst is heated in said first and second heating zones by hot gases from lower zones of said heating and oxidation zones; wherein said coke particles in said catalyst are oxidized in said first oxidation zone; wherein said ZnS is oxidized to ZnO and SO2 in said second oxidation zone, and wherein said SO2 is then separated out of said heating and oxidation zones.
9. The process of claim 8 wherein the temperature increases continuously from 1,025*-1,125* F. in said first heating zone to 1,275*-1,375* F. in said second oxidation zone.
10. The process of claim 9 wherein said organic residue comprises no more than 6 percent by weight of said spent catalyst.