Rejuvenation process for olefin polymerization and alkylation catalyst

Abstract

A method of rejuvenating a deactivated molecular sieve catalyst, deactivated by use in an olefin oligomerization or aromatics alkylation process, which method comprises contacting the deactivated catalyst with a stream of rejuvenation gas comprising a hydrocarbon product fraction from the process at an elevated temperature and pressure for a time sufficient to effect an increase in catalytic activity of the deactivated catalyst.

Description

DRAWINGS

FIG. 1 shows a process schematic for the olefin polymerization unit for converting light refinery olefins to motor gasoline with a circuit for catalyst rejuvenation.

FIGS. 2 and 3 are graphs showing the effect of catalyst rejuvenation.

DETAILED DESCRIPTION

The present process is for the conversion of light cracking olefins or the alkylation of aromatics by light cracking olefins to produce higher boiling liquid hydrocarbon products, for example, motor gasoline and other motor fuels such as road diesel blend stock as well as alkylaromatic petrochemical products such as ethylbenzene and cumene. For convenience, the present guard bed regeneration technique will be described below with reference to the olefin polymerization process and the aromatics alkylation processes described in the earlier filed applications cited above but its is more generally applicable, to other similar processes using molecular sieve catalysts and requiring a guard bed to remove contaminants form the feed stream which would otherwise deactivate the catalyst. As described in our previous applications, the olefin conversion process when used to produce gasoline boiling range product, is intended to provide a replacement for the SPA polymerization process, using a molecular sieve catalyst which can be used as a direct replacement for SPA and so enables existing SPA units to be used directly with the new catalyst, so allowing the advantages of the new catalyst and process to be utilized while retaining the economic benefit of existing refinery equipment. The aromatic alkylation process is similar in operation and again, is used to convert light refinery olefins to higher value, higher boiling liquid products.

As described in prior applications, Ser. Nos. 11/362257 and 11/362,139, the gasoline boiling range products can be produced by the polymerization (oligomerization) of a light refinery olefin stream. An alternative to the straightforward polymerization process is an aromatics alkylation process of the type described in Ser. Nos. 11/362,256, 11/362,255, 11/362,139, which may be combined with the polymerization process as described in Ser. No. 11/362,139. Reference is made to these prior applications for descriptions of the basic olefin upgrading processes.

The present guard bed regeneration technique is, as noted, capable of use with other processes using molecular sieve catalysts which are subject to poisoning by contaminants in the feed, including processes for converting olefins into lubricants as described in U.S. Pat. No. 4,956,514 which describes the use of zeolite MCM-22 as an olefin oligomerization catalyst for making lube range materials by the oligomerization of low molecular weight olefins such as propylene and FCC off gas streams. Other processes to which it can be applied are the well-established processes for manufacturing aromatics such as ethylbenzene or cumene, using reactions such as alkylation and transalkylation. The cumene production (alkylation) process is described in U.S. Pat. No. 4,992,606 (Kushnerick et al). Ethylbenzene production processes are described in U.S. Pat. No. 3,751,504 (Keown); U.S. Pat. No. 4,547,605 (Kresge); and U.S. Pat. No. 4,016,218 (Haag); U.S. Pat. Nos. 4,962,256; 4,992,606; 4,954,663; 5,001,295; and 5,043,501 describe alkylation of aromatic compounds with various alkylating agents over catalysts comprising MWW zeolites such as PSH-3 or MCM-22. U.S. Pat. No. 5,334,795 describes the liquid phase synthesis of ethylbenzene with MCM-22. The processes for cumene and ethylbenzene manufacture are well-established commercially and are available under license from vendors such as ExxonMobil Chemical Company and Polimeri Europa.

In their application to the production of hydrocarbon fuels by the processes described in the earlier filed applications, the present olefin upgrading processes utilize light refinery olefins, especially propylene and butane but also ethylene to produce gasoline boiling range liquid hydrocarbon products. When the olefinic refinery stream is used by itself as the sole feed, the product is essentially a light hydrocarbon stream of high octane rating resulting from a high level of branched-chain mono-olefins in the product, principally di-branched octenes. If an aromatic stream such as a reformate is used as a co-feed, the product will be of alkylaroamatic character with the benzene content of the aromatic feed converted to alkylaromatics by reaction of the olefins with benzene and other aromatics from the aromatic feed. In each case, however, the catalyst used in the olefin upgrading process is a solid, porous molecular sieve material. The preferred catalysts are the MWW zeolites such as the MCM-22 family of zeolites (MCM-22, MCM-49, MCM-56) but in certain applications such as the vapor phase olefin/aromatic alkylation process described in U.S. Ser. No. 11/362,255, filed 27 Feb. 2006, “Vapor Phase Aromatics Alkylation Process”, other catalysts may be used, for example, the intermediate pore size zeolites such as ZSM-5, and ZSM-11. Other molecular sieve catalysts which may be used include those based on zeolite Beta, ZSM-22, ZSM-57 as well as large pore size zeolites such as zeolite Y, USY, in forms such as REY, HY and other zeolites such as ZSM-18 or ZSM-20. Thus, in the operation of the present rejuvenation technique, the product generation will be as described in the earlier applications described above, with feeds, catalysts and processing conditions as described in those applications, to which reference is made for a detailed description of them. A metal hydrogenation/dehydrogenation component on the catalyst may be present with potential benefit to the catalyst rejuvenation. Suitable metals may include nickel, cobalt, possibly promoted with molybdenum, chromium or tungsten, or even a noble metal such as platinum or palladium.

The present catalyst rejuvenation process extends the cycle length of the zeolite catalyst. The rejuvenation process for zeolite requires the addition of a stream with minimum or no olefin content (referred to here as a “substantially non-olefinic” stream) at elevated temperature and pressure. Normally, the temperature for the rejuvenation will be from 50 to 300° C. (about 120 to 570° F., although higher temperatures up to about 350 C (660 F) e.g. 315° C. (600° F.) may be used. In most cases, the rejuvenation temperature will be 100° C. (about 210° F.) or more. Pressures will normally be at least 1000 kPag (145 psig) not normally to exceed 8,000 kPag (1160 psig). The optimal combination of temperature and pressure for any given system of catalyst and feed/product may be found by empirical means since the generation of soft coke on the catalyst surfaces will depend upon the selected feed(s), the particular catalyst and the reactions conditions employed. Higher temperature will tend to drive off contaminants and removal of the contaminants will be favored by lower pressures but operation within the ranges of temperature and pressure described will normally be found to yield satisfactory results.

The rejuvenation medium can be nitrogen or paraffinic streams available in the unit or from elsewhere in the refinery. Streams with high aromatic content such as light, intermediate, or full reformate can also be used as the rejuvenation stream. Descriptions of such aromatic streams can be found, for example, in U.S. Ser. Nos. 11/362,256, 11/362,255, and 11/362,139, all filed 27 Feb. 2006, referred to above.

The duration of the rejuvenation treatment can typically vary from 1 hour to 72 hrs, but typically it lasts from 4 to 24 hrs for a reactor containing about 10,000 kg of zeolite catalyst. The rejuvenation stream can have a LHSV between 0.1 to 7 hr⁻¹, typically between 1 to 3 hr⁻¹.

The rejuvenation can be carried out by storing enough of the rejuvenation medium and then passing it through the reactor(s) when catalyst activity is to be restored. If feed storage capacity in the unit is not sufficient for the amount of required rejuvenation feed, the unit can be configured as shown in an illustrative unit configuration in FIG. 1 in which the dotted lines show the needed modifications for a conventional Polygas unit, with the quench circuit omitted for clarity. The reactors can be tubular or chamber type. The number of reactors changes from unit to unit, in this example the configuration has three reactors and this potentially enables the rejuvenation can be practiced in one of the reactors while keeping the others in operation. The feed to be used as the rejuvenation stream is the olefin-depleted stream from the overhead of the fractionation tower. In this configuration, some piping is needed, and an additional pump to boost the recycle stream to the reactor operating pressure; this re-compressor is needed in any event if the recycle is used as quench as described in Ser. No. 11/362257.

FIG. 1 shows an simplified illustrative configuration for an olefin polymerization unit (no aromatic co-feed) which produces a monoolefinic gasoline product (mainly di-branched octenes) by polymerization of the olefins. The scheme shown may however, be used with similar units using an aromatic co-feed to produce alkylaromatic gasoline products. The unit configuration shown is fitted also for regeneration of the guard beds as described in concurrently filed application Serial No. ______, claiming priority from Provisional application Ser. No. 60/834,804, referred to above, entitled “Olefin Upgrading Process with Guard Bed Regeneration”, to which reference is made for a description of the guard bed regeneration technique.

In FIG. 1 the dotted lines show the modifications for a conventional Polygas unit. The reactors can be tubular or chamber type. The number of reactors changes from unit to unit, in this example the configuration has three reactors and this potentially enables the rejuvenation can be practiced in one of the reactors while keeping the others in operation. The feed to be used as the rejuvenation stream is the olefin-depleted stream from the overhead of the fractionation tower. In this configuration, some piping is needed, and an additional pump to boost the recycle stream to the reactor operating pressure; this pump is needed in any event if the recycle is used as quench as described in Ser. No. 11/362257.

A mixed light olefin feed from a catalytic cracking unit is introduced through line 10 and passes through guard bed 11 which operates on a swing reactor system with a matching guard bed 12. The feed then passes to feed drum 13 and on through line 14 to reactors 15A, 15B, 15C. The olefins in the feed are polymerized in reactors 15A, 15B and 15C and effluent from the reactors passes to fractionator 20 by way of manifold line 16. The reactor effluent is fractionated in the fractionator to produce the desired product fractions. The heavy product fraction leaves fractionator 20 through line 23 as product. A portion of the light product fraction together with unreactive paraffins from the feed is removed from the top of the fractionator and passed by way of line 21, pump 22, line 23, pump 24 and line 25 to second guard bed 12 which is in the regeneration phase, desorbing the contaminants which have been removed from the feed. The guard bed vessels are switched alternately between feed treatment and regeneration by means of conventional valving (not shown) which may also direct effluent from the guard bed during the regeneration portion of the cycle to recovery facilities by way of line 27 so as to permit removal of the desorbed contaminants. When desorption of the contaminants from the guard bed in the regeneration phase is complete, the beds can be switched so that bed 11 is in the regeneration phase, receiving product from fractionator 20 to desorb contaminants and bed 12 is put into the feed treatment phase with the feed passing from bed 12 to reactors 15A, 15B and 15C. If the reaction in reactors 15 is the olefin/aromatics alkylation reaction, using a mixed refinery olefin/reformate stream as the feed, the contaminant desorption stream will usually be a light stream with a heavier alkylaromatic fraction going to recovered product.

The guard beds may be operated on the swing cycle with two beds, 11 and 12 as described above. If desired, a purge phase may be added before a regenerated bed is returned to feed treatment although this will not always be necessary since the bed contains at that point only innocuous reaction products which can be recycled to the reaction. A three-bed guard bed system may be used with the two beds used in series for contaminant removal and the third bed on regeneration. With a three guard system used to achieve low contaminant levels by the two-stage series sorption, the beds will pass sequentially through a three-phase cycle of: regeneration, second bed sorption, first bed sorption.

A portion of the light product stream is used as rejuvenation gas for the catalysts in the reactors when rejuvenation is required, at which time, the flow of olefin reactant is stopped and the stream from pump 24 is sent through branch lines 29A, 29B and 29C to reactors 15A, 15B and/or 15C, as necessary, to rejuvenate the catalysts, in accordance with the present invention. Admittance of the rejuvenation stream to the reactors is controlled by appropriate valving of conventional type (not shown). From pump 22, the stream passes to pump 24 before passing on through distributor lines 29A, 29B and/or 29C to the inlets of the three reactors. Reheat may be supplied as necessary to bring the stream up to the requisite temperature for the rejuvenation. If it is desired to carry out the rejuvenation wholly or partly with another stream, e.g. nitrogen, this may be introduced through line 30.

The guard beds may be operated on the swing cycle with two beds, 11 and 12 as described above. If desired, a purge phase may be added before a regenerated bed is returned to feed treatment although this will not always be necessary since the bed contains at that point only innocuous reaction products which can be recycled to the reaction. A three-bed guard bed system may be used with the two beds used in series for contaminant removal and the third bed on regeneration. With a three guard system used to achieve low contaminant levels by the two-stage series sorption, the beds will pass sequentially through a three-phase cycle of: regeneration, second bed sorption, first bed sorption.

Rejuvenation of zeolitic catalyst is performed in-situ, after shutting off the olefinic feed, by means of the stripping action of the light paraffinic stream. The paraffinic stream can be the olefin-depleted LPG quench stream or any other stream containing one or more aliphatic hydrocarbons in the C₁-C₈ range. In the case of the process using an aromatic co-feed, the rejuvenating gas stream may be a light alkylaromatic stream in the C₆ to C₁₀ range such as produced by reaction of benzene with butene. The rejuvenation will normally be performed for a minimum of 1 hr or for a maximum of 3 days, preferentially between 4 to 24 hrs. The rejuvenation process can be performed at pressure between 1000 kPag (145 psig) (or 350 kPag (50 psig) above the stabilizer or feed drum pressure) to 8,000 kPag (1160 psig) preferably between 3,500 to 8,000 kPag (about 510 to 1160 psig) with temperatures from 100 to 310° C. (about 210 to 590° F.), preferentially between 100 and 230° C. (about 210 to 450° F.). The rejuvenation stream can have a LHSV between 0.1 to 7 hr⁻¹, typically between 1 to 3 hr⁻¹.

During the rejuvenation process, some heavy compounds are stripped out from the catalyst, and lowering the reactor pressure will facilitate the removal of these compounds. To utilize these lower pressures the rejuvenation can be performed at a pressure approximately 350 kPa (about 50 psi) above the stabilizer or feed drum pressure. This lower pressure option does not require the additional pump 24 but requires splitting the quench flow and control quench to the feed drum and controlling the rejuvenation stream to the reactor. The outlet of the reactor is blocked in and a line at the reactor outlet(s) installed to one of the following locations: (1) feed drum, (2) stabilizer overhead receiver, or (3) stabilizer feed. Piping to the feed drum is less likely to be disruptive but is the less recommended option. In this low pressure option, procedures would have to be implemented to gradually depressurize and repressurize the reactor so as to avoid perturbing the catalyst bed.

The efficacy of the rejuvenation process is illustrated in FIG. 2, the data for which were obtained in a micro unit fixed bed reactor. In the first run, the selected catalyst was a MCM-22 zeolite catalyst with reduced activity so the effect of the rejuvenation process could be noted during an accelerated deactivation run under typical olefin polymerization conditions. Real refinery LPG feed containing 45% olefins, approximately 2000 ppm dienes and 10 ppm sulfur was used in this experiment. Reactor temperature was adjusted to obtain an olefin conversion of 78%, reactor pressure was maintained at 3800 kPag (550 psig) and an LHSV of 2 hr⁻¹. After the conversion dropped below 25%, the olefinic feed was shut off and catalyst was exposed to nitrogen at 205° C. (400° F.) for 8 hrs. The olefin feed was then reintroduced following this stripping step. Significant recovery in activity is shown in the graph of FIG. 2.

In another experiment, the results of which are illustrated graphically in FIG. 3, the MCM-22 catalyst was tested with the same feed as the previous run. In this case, the feed used for the rejuvenation was a light paraffinic feed containing mainly butane isomers. At around 3300 tonne of product/tonne of catalyst, the paraffinic rejuvenation feed was introduced for around 8 hrs without changing operating conditions. After the initial rejuvenation step, the olefinic refinery feed (LPG) was introduced and around 10 additional days were run without change in the deactivation rate. At this point, another 8 hrs rejuvenation process was performed with an almost identical result to the first one. To test the effect of additional timing, the rejuvenation process was repeated but this time for 24 hrs. The additional time reduced slightly the reactor temperature to get the 78% conversion.

Claims

1. A method of rejuvenating a deactivated molecular sieve catalyst, deactivated by use in an olefin oligomerization or aromatics alkylation process, which method comprises contacting the deactivated catalyst with a stream of rejuvenation gas comprising a hydrocarbon product fraction from the process at an elevated temperature and pressure for a time sufficient to effect an increase in catalytic activity of the deactivated catalyst.

2. A method according to claim 1 in which the contact between the deactivated catalyst and the rejuvenating gas stream is carried out at a pressure from 1000 to 8,000 kPag and at a temperature from 50 to 310° C.

3. A method according to claim 2 in which the contact between the deactivated catalyst and the rejuvenating gas stream is carried out at a pressure from 3,500 to 8,000 kPag and at a temperature from 100 to 230° C.

4. A method according to claims 1 in which the contact between the deactivated catalyst and the rejuvenating gas stream is carried out at a space velocity for the rejuvenating stream of from 0.1 to 7 hr−1 LHSV.

5. A method according to claim 4 in which the contact between the deactivated catalyst and the rejuvenating gas stream is carried out at a space velocity for the rejuvenating stream of from 1 to 3 hr−1 LHSV.

6. A method according to claim 1 in which the rejuvenating gas stream comprises a stream of a light product fraction (C1 to C8) obtained from a product fractionator for the process.

7. A method according to claim 1 in which the rejuvenating gas stream comprises a stream of a light alkylaromatic product fraction (C6 to C10) obtained from a product fractionator for the process.

8. A method according to claim 1 in which the catalyst is a porous solid molecular sieve catalyst deactivated by use in an olefin polymerization process using a light olefinic feed comprising C2 to C4 olefins.

9. A method according to claim 8 in which the catalyst comprises a zeolite of the MWW family.

10. A method according to claim 9 in which the catalyst comprises zeolite MCM-22 or zeolite MCM-49.

11. A process for the production of a gasoline boiling range hydrocarbon product by the oligomerization of a light petroleum refinery olefinic stream comprising C2 to C4 olefins in the presence of a solid, porous, molecular sieve catalyst until the catalyst is deactivated and then rejuvenating the catalyst by contacting the deactivated catalyst with a stream of rejuvenation gas comprising a C3 to C8 hydrocarbon product fraction from the process at an elevated temperature and pressure for a time sufficient to effect an increase in catalytic activity of the deactivated catalyst.

12. A method according to claim 11 in which the contact between the deactivated catalyst and the rejuvenating gas stream is carried out at a pressure from 3,500 to 8,000 kPag and at a temperature from 50 to 230° C.

13. A method according to claim 12 in which the contact between the deactivated catalyst and the rejuvenating gas stream is carried out at a space velocity for the rejuvenating stream of from 1 to 3 hr−1 LHSV.

14. A method according to claim 11 in which the rejuvenating gas stream comprises a stream of a light hydrocarbon product fraction (C1 to C8) obtained from a product fractionator for the process.

15. A method according to claim 14 in which the catalyst comprises zeolite MCM-22 or zeolite MCM-49.

16. A process for the production of a gasoline boiling range hydrocarbon product by the alkylation of an aromatic refinery reformate stream containing benzene with a light refinery stream comprising C2 to C4 olefins in the presence of a solid, porous, molecular sieve catalyst until the catalyst is deactivated and then rejuvenating the catalyst by contacting the deactivated catalyst with a stream of rejuvenation gas comprising a C6 to C10 alkylaromatic hydrocarbon product fraction from the process at an elevated temperature and pressure for a time sufficient to effect an increase in catalytic activity of the deactivated catalyst.

17. A method according to claim 16 in which the contact between the deactivated catalyst and the rejuvenating gas stream is carried out at a pressure from 3,500 to 8,000 kPag and at a temperature from 50 to 230° C.

18. A method according to claim 16 in which the contact between the deactivated catalyst and the rejuvenating gas stream is carried out at a space velocity for the rejuvenating stream of from 1 to 3 hr−1 LHSV.

19. A method according to claim 16 in which the rejuvenating gas stream comprises a stream of a light alkylaromatic product fraction (C6 to C8) obtained from a product fractionator for the process.

20. A method according to claim 16 in which the catalyst comprises zeolite MCM-22 or zeolite MCM-49.