CA1091700A

CA1091700A - Selective hydrogenation process

Info

Publication number: CA1091700A
Application number: CA293,634A
Authority: CA
Inventors: John F. Van De Castle; Rajinder K. Mahendroo; John C. Bonacci
Original assignee: Engelhard Minerals and Chemicals Corp
Current assignee: Engelhard Minerals and Chemicals Corp
Priority date: 1976-12-28
Filing date: 1977-12-21
Publication date: 1980-12-16
Also published as: FR2376100A1; AU516847B2; JPS5382704A; DE2758274A1; IT1093082B; AU3192677A; GB1555270A

Abstract

SELECTIVE HYDROGENATION PROCESS

Abstract of the Disclosure In a process for the selective hydrogenation of unsaturated hydrocarbon components of a feedstock a hydrogenation catalyst is first pre-treated by contact with gaseous ammonia, and thereafter contacted with the feedstock in the presence of hydrogen. The process is found to improve the hydrogenation selectivity of the catalyst, especially in minimizing undesired hydrogenation of aromatic ring compounds.

Description

:
- 1~917~0 i .
1 BACKGP~OUND OF THE INVENTION

2 The present invention relates to the hydrogenation of

3 unsaturated hydrocarbon compounds, and more particularly to the

4 selective hydrogenation of one or more unsaturated compounds, or unsaturated portions of compounas contained in a feedstock.
;6 The use of selective hydrogenation of hydrocarbon 7 compounds to prepare particular products and/or to confer desirable 8I characteristics to various feedstocks is known throughout the I i ~ 9 oil and chemical industry. For example, selective hydrogenation ¦
`~ 10 is utilized to selectively remove olefins and diolefins from .~.
11 aromatic feedstocks to prevent the polymerization of these 12l compounds, and hence avoid contamination of the products of 13'` later treatment of the feedstock. An example of this process - 14 is the hydrogenation of conjugated aliphatic or cyclic diolefins ,,,:, , in naphthastreams that are blended into gasoline products or ~' 16 further processed for extraction of aromatic compounds.
.i . .~ .
17 Selective hydrogenation is also utilized to preferen-18 tially hydrogenate a portion or portions of hydrocarbon com-v 19 pounds while leaving unaltered other unsaturated portions of the same compound. For example, in the preparation of cumene 21 ~ (isopropylbenzene), alpha-methylstyrene is processed so as to 1 -22 hydrogenate the unsaturated aliphatic branch thereof without 23 hydroqenating the aromatic benzene ring. Additionally, in 24 those cumene production processes wherein the alpha-methylstyrene feedstock contains either naturally occurring or recycled cumene, i, 26ll ring saturation must obviously especially be avoided. ¦

27 Catalysts and process conditions have been developed ¦
28 in this field to achieve the preferential hydrogenation re-. . . .
29 quired by the foregoing processes. Typically, catalysts con-taining supported noble metals such as platinum, palladium ;~ - 2 --: . . ~
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. i 1 1 or ruthenium are utilized. I -2 While the foregoing catalysts are generally effective 3 in achieving an acceptable degree of hydrogenation specificity, 4 improvement in this area is consistently sought. For example,

5 il it has been proposed to add certain organic nitrogen compounds

6 ,! to the feedstock in order to improve the selectivity of pro-.;:
~, 7 cesses designed to produce cyclohexenes and substituted cyclo- I
,:, 8 1 hexenes by hydrogenation; see U.S. Patent No. 3,793,383 to - ~ 9 1! J~hnson~ et al.
~: 10 ' Of particular concern in this area is the observation ., ;~
~¦ 11 that catalyst selectivity in hydrogenation processes is poor 12 when virgin or freshly regenerated catalysts are utilized, 13 the selectivity gradually increasing as the catalyst ages on-14 l stream. Thus, undesired aromatic ring hydrogenation occurs ;:; 15 i in the early stages of the process leading to product losses, ;`~~ 16 the need for appropriate separatory e~uipment, and possible ~ 17 li unsafe operation owing to potential temperature runaway 1 18 situations due to the high activity of the catalyst. In the .. l 19 belief that the poor selectivity of fresh catalysts is ~ -; 20 attributable to rapid temperature rises at the start-up of : .
21 the hydrogenation process, it has been proposed to place limits 2~ on the te~perature and amount of hydrogen present at the 23 ¦' start-u~ of the process; see U.S. Patent No. 3,769,358 to Nets, 24 et al. There is a need however, for further improvement in obtaining greater catalytic hydrogenation selectivity.
26 It is accordingly an object of this invention to develop¦
27 11 an improved process for the selective hydrogenation of unsatur-28 ,' ated hydrocarbon compounds.
29 A particular object of this invention is to improve the hydrogenation selectivity of hydrogenation catalysts, especially .": . - ~
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1 virgin or freshly regenerated hydrogenation catalysts.
. 2 1 In accordance with this invention, the hydrogenation ~ 3 ¦ selectivity of catalysts, particularly virgin or freshly regene-4 1 rated catalysts, is improved by a process comprising contacting a .: 5 llydrogenation catalyst with gaseous ammonia for a period of time .. 6 sufficient to increase the hydrogenation selectivity of the : 7 catalyst, and thereafter contacting the catalyst, in the presence : 8 of hydrogen, with a feedstock comprising either (a) at least one : 9 ¦ unsaturated compound for which hydrogenation is intended in the 10 ¦ process and at least one unsaturated compound which is intended ~........... 11 to remain unsaturated, or (b) a compound having a first unsaturate .~ 12 portion which is intended to be hydrogenated in the process, and a .. :. 13 second unsaturated portion which is intended to remain unsaturate .; 14 ~ or (c) a mixture of (b) and an unsaturated compound which is.. 15 intended to remain unsaturated.
16 In a preferred embodiment of this invention, the contact i:
17 of the catalyst with ammonia gas utilized in pre-treating the 18 hydrogenation catalyst is continued during the hydrogenation .-.......... 19 process until the catalyst is found to have a suitable hydrogena-20 j tion selectivity.
21 1¦ Exemplary feedstocks utilized in accordance with this 22 1 invention include, respectively, (a) mixtures, such as naphtha, j 23 containing aromatics and mono- and diolefins, wherein h~drogena-24 tion of such olefins is desired without saturating the aromatic ~!' 25 components of the feedstock or mixtures of, for example, acetylene . 26 and diolefins; (b) alpha-methylstyrene wherein, in the conversion :`.......... 27 ¦ to cumene, it is desired to hydrogenate the unsaturated alkenyl .: 28 side chain of the alpha-methylstyrene without hydrogenating 29 the aromatic ring; and (c) a mixture of alpha-methylstyrene and ; 30 cumeme, wherein saturation of the alkenyl side chain of the alpha-~;, . ~ -4-':
, . i1 methylstyrene is desired without causing saturation of the aromati 2 !¦ ring thereof or the aromatic ring of the cumene.
3 ¦ The process of this invention further comprises in-4 creasing the hydrogenation selectivity of a supported noble metal hydrogenation catalyst, which process comprises contacting the 6 catalyst with ammonia in the vapor phase for a period of time

7 sufficient to increase the hydrogenation selectivity of the

8 catalyst. The catalyst may be contacted with the ammonia in

9 the presence of a feedstock during a hydrogenation process or in the absence of a feedstock.
11 In accordance with more specific aspects of this 12 invention, the catalysts utilized in the present process may be 13 ! any of the well-known hydrogenation catalysts, generally 14 comprised of a supported metal. Suitable metals include particularly the noble metals such as ruthenium, rhodium, 16 palladium and platinum. Suitable supports include natural or 17 treated clays such as kaolin or bentonite, siliceous materials, 18 magnesium oxide, silica gel, alumina gel, natural or synthetic 19 zeolites, and activated carbon and in suitable form, such as 20 ¦ pellets, spheres, extrudates, and the like. Activated aluminas 21 such as alpha-alumina, eta-alumina and gamma-alumina are especiall 22 useful supports. Preferred catalysts comprise platinum or 23 palladium on alumina supports. When utilizing these or other 24 noble metals on a support, the noble metal will typically be present in the range of from about 0.01% to about 5% by 26 weight of the catalytic composition, and preerably in the range 27 of from about 0.2~ to about 2.0~ by weight.
28 ___ 29 ___ ___ ,..' .' ~' ' ,.

i7~3 he duration of time during which the hydrogenation 2 catalyst is contacted with gaseous ammonia is not presently : . , believed to be critical, it being noted that improved selectivity 4 ~ is noted after relatively short contact times, and continues ` 5 li to improve in a fairly regular manner as the duration of pre-` 6i treatment is extended. Where the presence of ammonia is con-; 7 tinued with the flow of hydrocarbon feedstock and hydrogen after . . .
8 pre-treatment, the duration of pre-treatment needed to obtain I' g ~ improved selectivity will generally be shorter than in the case where the presence of ammonia is terminated upon introduction 11 of the feedstock and hydrogen. As will be apparent to those : I
12 skilled in this art, practical considerations such as economics 13 ; may dictate the e~tent of pretreatment, e.g., the degree of 14 l~ improvement in selectivity achieved for each increase in the duration of pretreatment may at some point become so small 16 as to not warrant any longer periodsof pretreatment.
17 i, The pretreatment of the hydrogenation catalyst with 18 ammonia may conveniently be carried out in the hydrogenation 19 reaction vessel. The pretreatment may consist either of continuously flowing ammonia over the catalyst or admitting a 21 predetermined amount of ammonia to the reaction vessel which 22 ~ is thereafter closed off to maintain contact between the 23 ¦I catalyst and ammonia. The conditions utili~ed during this 24 pretreatment may vary widely, subject to the provision that the ammonia be maintained in the gaseous state. Typical tempera-26 tures may range from about 20C to about 200C, preferably 27 11 100C to about 150C, and pressures in the range of from 28 ¦jabout 30 psig. to about 400 psig. The amount of ammonia 29 1 vapor contacted with the hydrogenation catalyst may vary widely . _ _ _ _ '. '.
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1 depending upon the feedstock to be hydrogenated, the de~ree of ....
1 2 selectivity required and other like factors. The ammonia may 3 ibe contacted with the catalyst as pure ammonia vapor or alter-4 natively admixed with a suitable gas such as nitrogen, helium, hydrogen and the like.
6 In a preferred embodiment of this invention, contact 7 of the hydrogenation catalyst with ammonia is maintained during 8 the hydrogenation reaction, i.e., along with the mixture of 9 feedstock and hydrogen. Thus, following a predetermined dura-

10 ¦ tion of pretreatment in the absence of feedstock and hydrogen,

11 ¦the hydrogenation reaction is commenced by introduction of the

12 !feedstock and hydrogen and ammonia vapor. While the ammonia

13 vapor may be introduced as a separate feed stream or as part

14 of the hydrocarbon feedstock, it is preferred to admit it to the reaction vessel in the hydro~en stream. When so doing, 16 the ammonia is maintained in the range of from about 0.15 to 17 about 20~ by volume of the hydrogen stream. For typical hydrogen ~- 18 Ito hydrocarbon molar ratios employed in selective hydrogena-19 ¦Ition~ the a~monia is generally present in the range of from about 0.01% to about 2.0% by weight based on thè liquid feed.
21 It has been found that this ammonia feed durlng hydrogenation 22 nay be terminated at such time that it appears that the desired 23 jdegree of selectivity is achieved.
24 11 Once the deslred degree of pretreatment, i.e., ithe contact of the catalyst with ammonia, is completed, 26 ydrogenation proceeds according to well-known procedures.
27 rhe conditions at which such selectivity hydrogenation 28 s conducted will, of course, vary depending upon the 29 eedstock to be treated and the hydrogenation desired, but ypical processes utilize temperatures in the range of from , , 7~

1 about 60C to about 200C, pressures in the range of from about 2 1 80 psig. to about 1500 psig., and liquid hourly spaCë vèlocities I in the range of from about 0.25 to about 40. The feedstock to 41 be hydrogenated is maintained in the liquid phase and the molar ratio of hydrogen to the unsaturated hydrocarbon to be hydroge-6 nated in the feedstock may be in the range of from about 1:1 to about 5 8 As earlier noted, the hydrogenation reaction is pref-9 erably conducted in the presence of gaseous ammonia.
According to a specific embodiment of the present inven-11 tion, alpha-methylstyrene is converted to cumene by contacting a 12 noble metal catalyst with ammonia vapor in the absence of hydro-13 ¦I carbon feedstock and hydrogen, and thereafter introducing hydrogen 14 ¦ along with the feedstock to selectively hydrogenate the aliphatic

15 I portion of the alpha-methylstyrene without causing hydrogenation

16 I of the aromatic ring.

17 ¦ The following examples are presented to illustrate the

18 ~ process of the present invention.

19¦¦ EXA~PLE I

20 j To a reaction vessel containing a catalyst composition

21 I comprised of 0. 3 wt.% palladium on 1/8 inch diameter cylindrical

22 alumina pellets was added 100~ ammonia vapor at 50 psig. The

23 vessel was closed off and contact of the ammonia with the catalyst

24 was maintained at room temperature for 2 hours. The ammonia was then heated to 140C and contact continued with the catalyst 26 at this temperature for an additional 2 hours. Thereafter, the 27 vessel was cooled and vented.
28 A feedstock of the following composition 29 Alpha-methylstyrene 19.8~ by weight Hydroxyacetone 280 p.p.m.

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~ Benzofuran 110 p.p.m.
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~` Cumene Balance ';r' ~ .
was passed over the pretreated catalyst with hydrogen at 100 psig., a temperature of 80C, a liquid hourly space velocity of 2.0 (lbs feed/lb. catalyst/hr.), and a hydrogen ¦ ~i to alpha-methylstyrene mole ratio of about 3Ø
~ ~ Table I summarizes the results of this hydrogenation - process. The effectiveness of the catalyst selectivity is ,; monitored by measurement of the production of isopropyl cyclohexane which indicates that hydrogenation of both the alkenyl group and the aromatic ring structure has occurred. Despite the decrease in hydrogenation of alpha-. .
, methylstyrene to isopropyl cyclohexane, the hydrogenation to cumene remains high, indicating that selectivity of the r: ~.
r'.`' catalyst is improving.
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TABLE I -Hours on Stream IPCH in Product AMS in Product (after Pretreatment) wt. percent wt. percent :
0.3 - 0.~353 0.71 - 1.8 0.0296 0.12 -~ 1.3 0.0286 0.06 1.8 0.0345 0.05 2.3 0.~373 0.04 2.8 0.0323 0.03 3.3 0.0290 0.03 . 4.8 0.0235 0.03 21.8 0.0090 0.12 24.5 0.0039 0.14 ~ .
28.3 0.002~ 0.13 .,' . ' ' .

- 1 Isopropyl cyclohexane i: 2 Alpha - methylstyrene .. . .

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EXAMPLE II

Utilizing a fresh catalyst sample of the same com-position employed in Example I, 100% ammonia was contacted with the catalyst in a closed reaction vessel at room temperature and 90 psig. for two hours. The vessel was then vented and the catalyst utilized for selective hydro-genation of alpha-methylstyrene employing the same feed and conditions described in Example I with the exception ; that ammonia vapor was added with the hydrogen stream (10%
by volume of hydrogen stream; approximately 0.9% by weight of liquid feed).
The results are summarized ln Table II.

:' TABLE II

Hours on Stream IPCH in Product AMS in Product (after pretreatment) wt. percent wt. percent 0.6 0.0380 .56 1.2 0.0220 .48 1.6 0.0100 1.31 2.1 0.0030 2.22 2.6 < 0.0030 2.89 3.1 < 0.0030 3.36 ' ` ' ` ~
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EXA~PLE III

Over a fresh catalyst sample of the same composition as utilized in the previous examples was passed hydrogen and a feedstock having a composition similar to that in the previous examples (21~ alpha-methylstyrene) at a temperature of 80 C, a pressure of 100 psig., a liquid weight hourly space velocity of 2.0 and a hydrogen to AMS mole ratio of 3.5. No pretreatment with ammonia was provided.
The results of this run are summarized in Table III.
.
TABLE III

;-Hours on Stream IPCH in Product AMS in Product ; _ _ __ wt. percent wt. percent .8 0.1820 0.07 .. .
1.3 0.1560 0.03 1.8 0.1450 0.02 2.3 0.1280 0.02 2.8 0.1260 0.02 3.8 0.1240 0.01 ', 20.6 0.0750 0.02 23.3 0.0660 <.01

25.8 0.0610 ~.01 28.3 0.0550 <.01 44.6 0.0130 <.01 45.6 0.0110 <.01 It will be noted comparing Tables I and III that the pretreatment according to the invention has reduced the ; production of isopropyl cyclohexane substantially while not affecting the hydrogenation of alpha-methylstyrene.

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When expressed in terms of the duration of hydrogenation ¦ reaction elapsed for the level of isopropyl cyclohexane in the product stream to decrease to 100 p.p.m., the process of Example I
4 required about 16 hours; Example IT about 2 hours; and Example III
about 50-60 hours. Both Examples of the process of the invention 6 (I and II) significantly decrease the time ~eriod when off-specification product is made, since in this application of the 8 invention isopropyl cyclohexane is undesirable and must be kept at 9 a low concentration.
The overall effect of a preferred ammonia pretreatment methoc 11 is seen in a high ratio of the rate constant for disappearance of 12 alpha-methylstyrene to the rate constant for appearance of 13 isopropyl-cyclohexane. This ratio defines the selectivity of the ; 14 catalyst and is calculated as follows. The rates of the two reactions can be expressed as:

16 Rate of disappearance of AMS = - ~ = kAMS CAMs (1) 17 Rate of appearance of IPCH = ~ ~ = k (2) . I
1 18 ¦ Where, 1/

19 kAMS = AMS Rate constant, time kIpCH = IPCH Rate constant, Mol %/(time) 21 C = Component concentration, mol %

22 t = Residence time, hrs.
.
23 IThe above expressions must be integrated to calculate the ra~e 24llconstants from the data listed in the Examples, obtaining:
kAMS =-- ln CPMS~o~t) (3)

26 IPCH t [cIpcH(out) ~ CIpcH(in)] = t CIpcH(out) (4) ~, . ' .

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1IjThe selectivity is then conveniently expressed as kAMS/kIpCH by ; 2 ¦1, dividing Eq (3) by Eq (4):
' cA~5(in) r 3i kAMS ln CAMS (out) ; k - (5) , , IPC~ CIPCH(out) . 1 1 4 l The selectivities calculated for Examples I and III are 5Ishown in Eigure 1. It can be seen that the pretreated catalyst of ~"~ 6'Example I is significantly be-tter than the untreate~ catalyst of ~; 7IExample III during the first hours of operation. The pretreated . 8Icatalyst produces less IPCH than the untreated catalyst while s- 9jhydrogenating substantially all the AMS present. Although the ~ 10,selectivity of the catalyst when the hydrogena~ion reaction begins j " ll ls nearly the same for both Examples I and III, the selectivity of i ¦1the catalyst pretreated with ammonia, Example I, improves rapidly 13 and has a clear advantage over the untreated catalyst of Example III.
t 14 5f Example II were plotted on the same graph, it would be expected ¦
51lto appear as a curve lying above that of Example I since a catalysti pretreated with ammonia and then contacted with ammonia during 7lhydrogenation has an even more rapid increase in selectivity than when the catalyst is only pretreated.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the selective hydrogenation of unsaturated hydrocarbon compounds, comprising contacting a virgin or regenerated noble metal hydrogenation catalyst with gaseous ammonia for a period of time sufficient to increase the hydro-genation selectivity of said catalyst, and thereafter contacting said catalyst, in the presence of hydrogen, with a hydrocarbon feedstock in the liquid phase at conditions which effect hydro-genation of the unsaturated compound or portion thereof intended to be hydrogenated, said feedstock comprising (a) at least one unsaturated compound for which hydrogenation is intended in the process and at least one unsaturated compound which is intended to remain unsaturated, or (b) a compound having a first unsatur-ated portion which is intended to be hydrogenated in the process, and a second unsaturated portion which is intended to remain unsaturated, or (c) a mixture of (b) and an unsaturated compound which is intended to remain unsaturated.

2. The process of claim 1 wherein said contacting with gaseous ammonia is at a temperature in the range of from about 20°C to about 200°C and a pressure in the range of from about 30 psig. to about 400 psig.

3. The process of claim 1 wherein the contact of said catalyst with gaseous ammonia is continued along with the contact of feedstock and hydrogen with said catalyst.

4. The process of claim 3 wherein said continued contact with ammonia comprises admixing ammonia with said hydrogen.

5. The process of claim 4 wherein said ammonia is present in an amount in the range of from about 0.15% to about 20% by volume of said hydrogen.

6. The process of claim 1 wherein said compound or a portion thereof which is intended to remain unsaturated comprises an aromatic ring moiety.

7. The process of claim 1 wherein said feedstock comprises a compound containing an aromatic ring portion and an unsaturated aliphatic portion.

8. The process of claim 7 wherein said feedstock comprises a mixture of alpha-methylstyrene and cumene.

9. The process of claim 1 wherein said compound, in said feedstock, intended to be hydrogenated is an unsaturated aliphatic compound, and said feedstock also comprises aromatic compounds intended to remain unsaturated.

10. The process of claim 1 wherein said feedstock and hydrogen are contacted with said catalyst at a temperature in the range of from about 60°C to about 200°C, pressure in the range of from about 80 psig. to about 1500 psiq., and a mol ratio of hydrogen to unsaturated hydrocarbon to be hydrogenated of from about 1:1 to 5:1.

11. The process of claim 1 wherein said hydrogenation catalyst comprises a noble metal selected from the group consisting of palladium, platinum and mixtures thereof.

12. A process for the production of cumene comprising initially contacting a virgin or regenerated noble metal hydrogenation catalyst with ammonia in the absence of hydrocarbon and hydrogen for a time sufficient to improve the hydrogenation selectivity of said catalyst, and thereafter con-tacting said catalyst in a reaction zone with a feedstock com-prised of alphamethylstyrene and cumene in the presence of hydrogen under hydrogenation conditions.

13. The process of claim 12, wherein ammonia is introduced into the hydrogenation reaction zone concurrently with said feedstock and said hydrogen.