WO1992004115A1

WO1992004115A1 - Catalyst and treatment thereof

Info

Publication number: WO1992004115A1
Application number: PCT/EP1991/001617
Authority: WO
Inventors: William Mayes; Friedrich Helmut Puls; Kenneth Lloyd Riley
Original assignee: Exxon Chemical Limited; Exxon Chemical Patents Inc.
Priority date: 1990-08-30
Filing date: 1991-08-23
Publication date: 1992-03-19
Also published as: GB9018875D0

Abstract

Solid spent catalyst especially a spent phosphoric acid catalyst is regenerated by mixing into a paste, extruding and calcining. The resulting product is an effective catalyst especially for olefin oligomerization.

Description

"Catalyst and Treatment Thereof"

This invention relates to catalysts, and especially to catalyst treatment. More especially, it is concerned with regeneration of spent catalysts, in particular of solid phosphoric acid catalysts.

It is well known that a catalyst used in hydrocarbon conversion has a limited useful life. During operation, there is a build up in and on the catalyst of polymeric and

carbonaceous by-products of the conversion reaction. This results both in a greater pressure drop across the catalyst bed, with increased operating expense, and lower catalyst activity as a result of the reduced effective surface area of the catalyst.

Depending on the cost of the catalyst, a spent catalyst may be regenerated or discarded. However, it is becoming

increasingly difficult to dispose of spent catalyst in an environmentally acceptable way regardless of the intrinsic value of the material, and accordingly much attention is given to regeneration of catalysts of all types.

Solid phosphoric acid and other solid catalysts are much used in the petrochemical industry to effect numerous

reactions. These include, for example, the oligomerization of olefins, for example propylene, to produce dimers, trimers and tetramers, and the reaction of olefins with aromatic

hydrocarbons or phenols to produce, for example, ethylbenzene, cumene or thymols. A solid phosphoric acid catalyst is normally formed by mixing a phosphorus acid, e.g., ortho-, pyro-, meta-, or poly-phosphoric acid, with a solid carrier to form a paste. The carrier may, for example, be a synthetic or natural porous silica or other oxide-containing material, e.g., keiselguhr, kaolin, infusorial earth, diatomaceous earth, activated clay, a zeolite, or an oxide of aluminium, zirconium, titanium or thorium. The paste may then be calcined and the resulting mass crushed or the paste may be extruded and

pelletized and then calcined to yield uniform catalyst

particles.

The catalyst may contain other components, for example, mineral talc, fuller's earth, and various metals or their oxides, e.g., nickel, copper, cobalt, zinc, manganese and, especially, iron, to modify its physical properties, e.g., thermal conductivity, strength and attrition resistance.

It has been proposed to regenerate solid phosphoric acid catalysts by a variety of treatments.

In Japanese Patent No. 74033750, a procedure is disclosed in which spent catalyst is blended with fresh catalyst, diatomaceous earth, and phosphoric acid, moulded and sintered at 700°C to 1100°C.

Japanese Patent No. 78047800 discloses a process comprising washing the spent catalyst with water, removing fines, boiling with water to remove phosphoric acid, calcining at 700°C to remove carbonaceous deposits, and reimpregnating with

orthophosphoric acid. In Japanese Patent No. 74034313, a spent catalyst is regenerated by coating with phosphoric acid and calcining at 750°C to 1050°C.

In British Specification No. 1500036, the spent catalyst is treated with a hydrocarbon solvent to dissolve polymer and carbonized hydrocarbons.

Some of the prior art proposals amount virtually to

preparing new solid catalyst, while others themselves generate a product with disposal difficulties.

Accordingly there remains a need for a regeneration process that is relatively simple and does not itself generate waste products.

The present invention provides a process for the

regeneration of a spent solid catalyst, especially a phosphoric acid-containing catalyst, which comprises forming an extrusible paste of spent catalyst and an aqueous medium, extruding the paste, and calcining the extrudate. Alternatively, but less preferred, the paste may be calcined without being extruded, and then formed (e.g., by crushing) and/or selected (e.g., by screening) to a desired size range.

The invention also provides the regenerated catalyst made by the process.

The procedure adopted for removing catalyst from reactors, normally drilling from a tubular reactor and digging out from a chamber reactor, exposes fresh surface, but if insufficient fresh surface is thereby exposed, the spent catalyst may be roughly broken up to expose more fresh surface. Advantageously, before being formed into the paste, the spent catalyst is screened to remove fines and lumps. If required or desired screened lumps are or the entire catalyst is ground or crushed to form particles of appropriate size and size range. Advantageously, particles smaller than U.S.

Standard Sieve (ASTM E-11-61) Mesh No. 325 and larger than Mesh No. 20 (0.044 mm and 0.84 mm respectively) are removed. If desired, particles larger than 100 Mesh (0.149 mm) may be removed. Small proportions of particles of size less than Mesh No. 325 may be incorporated in a mixture mainly composed of particles up to Mesh No. 20 size.

The catalyst particles are next mixed with an aqueous medium, to form a paste of viscosity appropriate for extrusion. The aqueous medium is advantageously free of organic solvents and may be water itself, to which reference will be made subsequently for simplicity. It will be understood, however, that the water may contain additives that assist in improving the properties, e.g., the mechanical properties or the

activity, of the regenerated catalyst, for example, in the case of a solid phosphoric acid catalyst, a phosphoric acid may be used in solution, the aqueous medium may also contain a binder for the catalyst such as charcoal, kaolin, silica or mixtures thereof. Suitably, a weight :volume of catalyst:water within the range of from 6:1 to 4:1 grams/cc advantageously about 5:1, is employed. Mixing may be carried out by mulling on a drill press, in a mix-miller, a ribbon blender, or a double cone mixer, to yield a uniform paste. Suitable mixing times using a drill press are from about 10 minutes to about 1 hour,

advantageously for from 15 to 30 minutes, adding more water if the paste is too dry or more catalyst if it is too wet.

The paste is then extruded, advantageously through a die of from about 1/16 to about 1/4 inch (about 1.5 mm to about 7 mm) diameter, if necessary with cooling, and advantageously chopped to a similar length as it exits from the extruder.

Alternatively, the extrudate may be calcined in lengths, employing breakage during transport to site and subsequent grading to give pellets of appropriate size. (It is believed that extrusion itself exposes more fresh surface.)

The extrudate may then be allowed to dry in ambient

temperature air for some-hours and dried, for example, for from 0.5 to 3 hours, for example in a vacuum oven at, for example, from 100°C to 150°C, advantageously at about 120°C, to remove free water.

The dried material is then calcined, for example, at a temperature in the range of from 200°C to 500°C, advantageously from 225 to 450°C, preferably from 250 to 400°C, for a period of, for example, from 30 minutes to 5 hours, advantageously from 1 to 3 hours. The time and temperature regime should in general be sufficient to form a solid product, the silica and phosphoric acid reacting to form silico-phosphates in the case of a solid phosphoric acid catalyst. Heating removes the bound water enabling the reaction to proceed, and the particle bind to provide the regenerated catalyst with sufficient strength. Calcining may be carried out in air. After calcining, the catalyst may be treated with steam, to achieve a desired degree of hydration.

The resulting regenerated material may be used as catalyst for any reactions for which fresh catalyst may be used, for example, in the case of a solid phosphoric acid catalyst, the oligomerization and alkylation reactions mentioned above, the preparation of tertiary olefins from a tertiary ether (e.g., isobutylene from methyl t-butyl ether), the hydrotreating of heavy mineral or shale oil, or other feedstocks, the cracking of mono- or dialkyl dioxolanes to conjugated diolefins (e.g., dimethyl dioxolane to isoprene), the cyclization of

alkenylbenzenes to dialkyltetralins, and dehydrations, e.g., of butanediol to butadiene.

Accordingly, the present invention also provides a process for the treatment of an organic feedstock, especially a hydrocarbon feedstock, and more especially a feedstock

comprising an olefin component, employing the regenerated catalyst, especially a solid phosphoric acid catalyst, of the invention, and the resulting treated feedstock.

The regenerated catalyst of this invention is useful in catalytic condensation, aromatic alkylation, and other types of hydrocarbon conversion processes where solid phosphoric acid catalysts have been known to be useful. When employed in the conversion of olefinic hydrocarbons into polymers, the catalyst formed as heretofore set forth, is preferably employed as a granular layer in a heated reactor which is generally made from steel, and through which the preheated hydrocarbon fraction is directed. Thus, the solid catalyst of this process may be employed for treating mixtures of olefin-containing hydrocarbon vapours to effect olefin polymerization, but the same catalyst may also be used at operating conditions suitable for maintaining liquid phase operation during polymerization of olefinic hydrocarbons, such as butylenes, to produce gasoline fractions.

When used for polymerization normally gaseous olefins, the particles of the catalyst are generally placed in vertical cylindrical treating towers or in fixed beds in reactors or towers and the gases containing olefins are passed downwardly through the reactors or towers at temperatures of 140° to

290°C, and pressures of 6 to 102 atmospheres. These conditions are particularly applicable when dealing with olefin-containing material which may contain from approximately 10 to 50 percent or more of propylene and butylenes. When operating on a mixture comprising essentially propylene and butylenes, this catalyst is effective at temperatures from about 140° to about 250°C, and at a pressure of from about 34 to about 102

atmospheres.

The regenerated catalyst of this invention is also useful in the alkylation of aromatic hydrocarbons with an alkylating agent. The alkylating agent which may be charged to the

alkylation reaction zone may be selected from a group of

diverse materials including monoolefins, diolefins,

polyolefins, acetylenic hydrocarbons, and also alkylhalides, alcohols, ethers, esters, the latter including the alkylsulfates, alkylphosphates, and various esters of carboxylic acids. The preferred olefin-acting compounds are olefinic hydrocarbons which comprise monoolefins containing one double bond per molecule. Monoolefins which may be utilized as olefin-acting compounds in the process of the present invention are either normally gaseous or normally liquid and include ehtylene, propylene, 1-butene, 2-butene, isobutylene, and the higher molecular weight normally liquid olefins such as the various pentenes, hexenes, heptenes, octenes, and mixtures thereof, and still higher molecular weight liquid olefins, the latter including various olefin polymers having from about 9 to about 18 carbon atoms per molecule including propylene trimer, propylene tetramer, propylene pentamer, etc. Cycloolefins such as cyclopentene, methylcyclopentene, cyclohexene,

methylcyclohexene, etc, may also be utilized, although not necessarily with equivalent results. Other hydrocarbons such as paraffins, naphthenes, and the like containing 2 to 18 carbon atoms may also be present in the alkylating agent. When the catalyst of the present invention is used for catalyzing an aromatic alkylation reaction, it is preferred that the

monoolefin contains at least 2 and not more than 14 carbon atoms. More specifically, it is preferred that the monoolefin is propylene.

The aromatic substrate which is charged to the alkylation reaction zone in admixture with the alkylating agent may be selected from a group of aromatic compounds which include individually and in admixture, benzene and monocyclic alkyl- substituted benzene of from 7 to 12 carbon atoms having the structure:

where R is methyl, ethyl or a combination thereof, and n is an integer from 1 to 5. In other words, the aromatic substrate portion of the feedstock may be benzene, and alkylaromatic containing from 1 to 5 methyl and/or ethyl group substituents, and mixtures thereof. Non-limiting examples of such feedstock compounds include benzene, toluene, xylene, ethylbenzene, mesitylene (1,3,5-trimethylbenzene) and mixtures thereof. It is specifically preferred that the aromatic substrate is benzene.

Temperatures which are suitable for use in the alkylation process are those temperatures which initiate a reaction between an aromatic substrate and the particular olefin used to selectively produce the desired monoalkylaromatic compound. Generally, temperatures suitable for use are from about 100º to about 390ºC, especially from about 150º to about 275ºC.

Pressures which are suitable for use herein preferably are above about 1 atmosphere but should not be in excess of about 130 atmospheres. An especially desirable pressure range is from about 10 to about 40 atmospheres; with a liquid hourly space velocity (LHSV) based upon the benzene feed rate of from about 0.5 to about 50 hr^-1, and especially from about 1 to about 10 hr^{- 1}. Additionally, a regulated amount of water is preferably added to the alkylation reaction zone. In order to

substantially prevent loss of water from the catalyst and subsequent decrease in catalyst activities, an amount of water or water vapour such as steam is added to the charge so as to substantially balance the water vapour pressure of the

alkylation catalyst hereinabove described. The amount of water varies from about 0.01 to 6% by volume of the organic material charged to the alkylation reaction zone. The water is then typically removed with the light by-product stream recovered in the first separation zone.

The invention further provides the use of the regenerated catalyst in such an olefin treatment process, and the resulting treated feedstock as well as use for the alkylation of

aromatics.

Although the invention has been primarily described with reference to a spent phosphoric acid catalyst, it is applicable to any solid catalyst that is regarded as spent because of the build up of deposits on the surface, for example, tar and hydrocarbon deposits, rather than through catalyst poisoning.

The following Examples illustrate the invention:

Example 1

300 g of spent solid phosphoric acid catalyst taken from about 1.5 to 3 m from the top of a vertical bed reactor, the catalyst having been used for oligomerization of propylene, was passed through a U.S. Standard Mesh Size 20 sieve (0.84 mm mesh size) and mix-mulled with 60 ml deionized water for 15 minutes. The resulting paste was extruded from a Welding Engineers twin screw extruder with a die having a single orifice of 3/16 inch (about 4.76 mm) diameter, operating at 100 r.p.m. The

resulting extrudate was dried, first in ambient temperature air then in a vacuum oven at 120°C for four hours. The resulting dried extrudate was then calcined for two hours in a flow- through bomb at 250°C under nitrogen. The crush strength of the materials of Examples 1 to 6 was measured using a 0.125 inch (3.175 mm) anvil. The crush strength of the material of this Example was 29.7 lb (13.5 kg), the surface area 5.0 sq. m/g, and the pore volume 0.032 ml/g. The average length of the pellets was 8.74 mm, average diameter 5.60 mm.

Example 2

The procedure of Example 1 was repeated, using material collected from between about 3 and 4.6 m from the top of the reactor. Crush strength 20.8 lb (9.43 kg), surface area

2.5 sq. m/g, pore volume 0.038 ml/g.

Example 3

The procedure of Example 1 was repeated, using material collected from about 6.7 m and more from the top of the

reactor. Crush strength 46.5 lb (21.1 kg), surface area

3.1 sq. m/g, pore volume 0.044 ml/g.

Example 4

The procedure of Example 1 was repeated, except that

calcining was carried out at 400°C. Crush strength 17.2 lb (7.8 kg), surface area 2.4 sq. m/g, pore volume 0.036 ml/g. Example 5

The procedure of Example 2 was repeated, except that calcining was carried out at 400°C. Crush strength 26.5 lb (12.0 kg), surface area 5.8 sq. m/g, pore volume 0.040 ml/g.

Example 6

The procedure of Example 3 was repeated, except that calcining was carried out at 400°C. Crush strength 46.4 lb (21.0 kg), surface area 6.7 sq. m/g, pore volume 0.049 ml/g.

Example 7

The product of Example 1 was used as catalyst for the oligomerization of propylene. A mixed propylene/propane feedstock containing about 45% propylene, more details being given in Table 1 below, was fed at 70 bar to a reactor packed with 178 g of the catalyst, the reaction being continued for 5 days. In this and other examples, the feed composition varied after some time as the supply was replenished. Where this occurs, the new composition of the feed is given also. The results are shown in Table 1 below.

Example 8

Example 7 was repeated, using 182.4 g of the product of Example 2, with the difference that the reaction was continued for 4 days. The results are shown in Table 2 below.

Example 9

Example 8 was repeated, using 224.9 g of the product of Example 3. The results are shown in Table 3 below. Example 10

Example 8 was repeated, using 169.5 g of the product of Example 4. The results are shown in Table 4 below.

Example 11

Example 8 was repeated, using 167.4 g of the product of Example 5. The results are shown in Table 5 below.

Example 12

Example 8 was repeated, using 211.5 g of the product of Example 6. The results are shown in Table 6 below.

Comparative Example A

213.1 g of fresh solid phosphoric acid catalyst, obtained from UOP Inc., and similar to that which constituted the fresh catalyst from which the starting materials of Examples 1 to 6 were formed, was used in this Example. Otherwise the procedure was as described in Example 8. The results are shown in Table 7 below.

The following Table 8 summarizes the results of Examples 1 to 12 and Comparative Example A, and also indicates the packing efficiency of the regenerated catalyst pellets, with the fresh catalyst packing efficiency being 100 by definition. Also indicated is the free P₂O₅ percentage of the regenerated catalysts, this value being uncorrected for carbon loading.

The results show that regenerated catalyst, especially at lower calcining temperatures, give useful conversion rates of propylene into higher olefins, albeit at lower levels than with the fresh catalyst.

Claims

CLAIMS :

1. A process for the regeneration of a spent

phosphoric acid-containing catalyst, which comprises forming an extrusible paste of spent catalyst and an aqueous medium, and either (a) extruding the paste and calcining the extrudate or

(b) calcining unextruded paste and forming or selecting

catalyst of a desired particle size range.

2. A process as claimed in claim 1, wherein the spent catalyst is screened to remove particles outside the range of from 0.044 to 0.84 mm before being formed into the paste.

3. A process as claimed in claim 1 or claim 2, wherein the paste is formed from catalyst and water in a weight :volume ratio of catalyst to water within the range of from 6:1 to 4:1 grams/cc.

4. A process as claimed in claim 3, wherein the ratio is about 5:1.

5. A process as claimed in any one of claims 1 to 4, wherein the paste is formed by milling.

6. A process as claimed in claim 5, wherein mulling is carried out for a period within the range of from 10 minutes to 1 hour.

7. A process as claiired in any one of claims 1 to 6, wherein the paste is extruded through a die of diameter within the range of from 1.5 to 7 mm.

8. A process as claimed in any one of claims 1 to 7, wherein the extrudate is dried in air before being calcined.

9. A process as claimed in any one of claims 1 to 8, wherein the extrudate is calcined at a temperature within the range of from 200°C to 500°C.

10. A process as claimed in claim 9, wherein calcining is carried out at a temperature within the range of from 225 to 450°C.

11. A process as claimed in claim 1, carried out substantially as described in any one of Examples 1 to 6 herein.

12. A solid phosphoric acid catalyst whenever produced by the process of any one of claims 1 to 11.

13. A process for the treatment of an organic

feedstock employing the catalyst of claim 12.

14. A process as claimed in claim 13, wherein the feedstock is a hydrocarbon feedstock.

15. A process as claimed in claim 13, wherein the feedstock is an olefin-containing feedstock.

16. A process for the alkylation of aromatics

employing the catalyst of claim 12.

17. The product of the process of any one of claims 13 to 16.

18. The use of the product claimed in claim 12 as a catalyst in a process for the treatment of an

organic feedstock.

19. The use as claimed in claim 18, wherein the process is as defined in any one of claims 14 to 16.

20. The organic product resulting from the use as claimed in claim 18 or claim 19.

21. A process for the regeneration of a spent solid catalyst, which comprises forming an extrusible paste of spent catalyst and an aqueous medium, and either (a) extruding the paste and calcining the extrudate or

(b) calcining unextruded paste and forming or selecting catalyst of a desired particle size range.