CA2055444C

CA2055444C - A method for pretreating a catalyst slurry and a method for the continuous partial hydrogenation of a monocyclic aromatic hydrocarbons by using the pretreated catalyst slurry

Info

Publication number: CA2055444C
Application number: CA002055444A
Authority: CA
Inventors: Hajime Nagahara; Koji Nakagawa
Original assignee: Asahi Kasei Kogyo KK
Current assignee: Asahi Kasei Corp
Priority date: 1990-02-14
Filing date: 1991-08-13
Publication date: 1999-04-13
Anticipated expiration: 2011-08-13
Also published as: CA2055444A1; JP3141944B2; JPH03238047A

Abstract

A method for pretreating a slurry containing a ruthenium catalyst for use in the continuous partial hydrogenation of monocyclic aromatic hydrocarbons is disclosed. In this method, the above-mentioned slurry is heat treated at a temperature of from 60 to 180 °C for at least 10 minutes while agitating. By using the pretreated catalyst slurry in the above-mentioned continuous partial hydrogenation, partial hydrogenation reaction products can be efficiently obtained without suffering from the excess mixing of the components of the catalyst slurry into an oil phase containing the partial hydrogenation reaction products, thereby enabling operations and facilities required for separation to be simplified.

Description

2 ~

SPECIFIC~TION
A method for pretreating a catalyst slurry and a method for the continuous partial hydrogenation of monocyclic aromatic hydrocarbons using the pretreated catalyst slurry Technical Field The present invention relates to a me~hod for pretreating a catalyst slurry and a method for the continuous partial hydrogenation of monocyclic aromatic hydrocarbons usiny the pretreated catalyst slurry.
More particularly, the present invention is concerned with a method for pretreating a catalyst slurry in which a slurry containing a ruthenium catalyst is heat-treated, and a method in which the partial hydrog-enation of monocyclic aromatic hydrocarbons is carried out using the pretreated catalyst slurry to thereby efficiently, ,stably and continuously produce and recov-er corresponding cycloolefins, especi.ally cyclohexenes.
Cyclohexenes are hi.ghly valuahle i.n the commerce as intermediates :Eor the manufacture oE organic chemical engineering products, and particularly, they are impor-tant as intermediates for the production of polyamides and lysines.

- 2 - 2 ~

Background Art Various methods have been proposed for producing cyclohexenes using as starting materials monocyclic aromatic hydrocarbons. For example, it has been pro-posed to use (1) a method using water, an alkali agent and a catalyst composition containing a member selected from the Group VIII elements of the Periodic Table [Japanese Patent Publication (Kokoku) No. 5~-22850/1981]. Further, it has been proposed to use (2) a method in which a reaction is carried out in the presence of a ruthenium catalyst and a neutral or an acidic aqueous solution containing a salt of a cation of at least one member selected from the group consist-ing of Group IA and Group IIA metals of the Periodic Table and manganese [Japanese Patent Publication (Kokoku) No. 57-7607/1982~. Still furtherl it has been proposed to use (3) a method in which a reaction is carried out Ln the presence oE a ru(herl.i.um catcllyst dispersed in si.lica gel derived from a hydrolysis product of a si.licon alkoxide, and water [Japanese Pa-tent Publicati.on (Kokoku) No. 60-59215/1985]. Still fur-ther, i-t has been proposed to use (43 a method in which a reaction is carried out in the presence of a ~5 catalyst comprising ruthenium supported on barium - 3 - 2~a4~4 sulfate, water and an additive rJapanese Laid-Open Patent Application (Kokai) No. 61-40226/1986]. Still further, it has been proposed to use (5) a method in which a reaction is carried out in the presence of a catalyst comprising ruthenium supported on a compound containing a rare earth element, water and an alkali agent [Japanese Patent Publication (Kokoku) No. 1-29174/1989]. Still further, it has been proposed to use (6) a method in which a reaction is carried out in the presence of metallic ruthenium particulates, zirco-nium oxide or hafnium oxide, and water [Japanese Laid-Open Patent Application (Kokai) No. 62-81332/1987].
Still further, it has been proposed to use (7) a method in which a reaction is carried out in the presence of a ruthenium catalyst using as a starting material a monocyclic aromatic hydrocarbon which substantially does not contain a sulfur compound [Japanese Laid-Open Patent Application (Kokai) No. 60-255738/1985]. Still further, it has been proposed to use (8) a method in which a reaction is carried out in the presence of a ruthenium catalyst and water in an atmosphere which does not cause iron to be deposited on the catalyst [Japanese Laid-Open Patent Application (Kokai) No. 62-67033/1987~. In all of these methods, catalyst slur-ries prepared by dispersing or dissolving a ruthenium catalyst and various types of additives in water are brought into contact with monocycl.ic aromatic hydrocar-bons and hydrogen by mixing in a liquid phase, thereby obtaining cycloolefins.
When a practical process for continuously produc-ing cycloolefins is designed accorcling to these conven-tional methods, it is requisite to effect complete separation between a catalyst slurry comprised of a ruthenium catalyst and water (hereinbelow frequently referred to simply as "aqueous phase") and an oil phase containing a partial. hydrogenation reaction produc-t and an unreacted monocyclic aromatic hydrocarbon (hereinbe-low frequently referred to simply as "oil phase~).
With such a process, if components of the aqueous phase, for example, excess amounts of a catalyst and/or an additive (such as a solid material, an alkaline material, or an acidic material which is added for improvement and stabilization of reaction performance) get mixed into the oil phase, problems, such a5 clog-ging of process pipes or corrosi.on of conventionally used apparatus materials, would occur due to the mixed components. Such problems can he solved to a certain extent by provid:ing, for example, a :Eiltering device or a washing clevice for removing the mixed components.
l~owever, in the commercial practice, facilities and - 5 ~ a ~ ~ ~

operations therefor are inevitably accompanied with difficulties. Further, in a continuous partial hydrog-enation reaction as well, it is apparent that when excess amounts of a catalyst and/or an additive get mixed, and even when gradually get mixed into the oil phase, and flow away, some measures and facilities must be provided for ~eeping the reaction system stable for a prolonged period of time.
Accordingly, from a commercial viewpoint, means for preventing components of the aqueous phase from excessively getting mixed into the oil phase is strong ly desired.
The term, "excess" used herein means an amount in excess of the solubility of components of the aqueous phase in an oil phase under partial hydrogenation reaction conditions or phase separation conditions (for example, the temperatures employed, and the composition of the oil phase generally comprising a reaction product and an unreacted startlng mater:i.al). As a practical mat:ter, however, probl.ems arise when excess amounts of several times the solubility get mixed.
Therefore, more specifically, the term "excess" used herein means several or more times the solubility. For example, according to the study of the present inven-tors, when a partial hydrogenation reaction of benzene - 6 2~

is conducted at a hydrogen pressure of 50 kg/cm2G and at 150 ~C using as an aqueous phase a catalyst and an 1~ % hy weight agueous ZnSO4-7~2O solution (which is an additive to be added for improvement and stabilization of a reaction yield) to thereby obtain a reaction mixture comprised of 50 mole % of benzene and 50 mole %
of a mixture of cyclohexene and cyclohexane, the solu-bility of water in the oil phase is about 1 ~ by weight, and the solubility of ~nSO4 in the oil phase is 1 ppm or less (the solubility thereof in water dis-solved in the oil phase is 100 ppm or less). In this instance, the meaning of "excess" is several times, for example, two or three times the above-mentioned solu-bility of about 1 % by weight with respect to water and 1 ppm with respect to ZnSO~. In addition, it is noted when the above-mentioned excess mixing of water and ZnSO4 occurs, the mixing of solid components of the aqueous phase into the oil phase is also observed in most cases.
E'rom thi.s viewpoint, a revie~w i.s made of the conventional technologies. For example, with respect to the above--described prior art methods (1) to (6), although there is a description regarding a continuous reaction according to a liquid phase suspension method, only a batch reaction is conducted in the Examples .. : ~ . , - 7 ~

thereof and there is no description regarding an at-tempt to almost completely separate a ca~alyst slurry from an oil phase, which separation is aimed at by the present invention.
Further, the above-described prior art methods (5) to (8) are the methods developed by the present inven-tors themselves. Especially in the methods (7) and (8), the partial hydrogenation reaction of monocyclic aromatic hydrocarbons is continuously carried out using a catalyst slurry comprised of a ruthenium catalyst and water. In the prior art methods (7) and (8), continu-ous reaction was actually performed, and partial hy-drogenation reaction was successfully performed over a period of 100 to 500 hours at relatively stable reac-tion performance. However, there is no description regarding materials having gotten mixed into the col-lected oil phase and the amounts thereof, and no study has been conducted with respect to almost complete separation of the catalyst sl.urry from the oil phase, which separation is aimed at by the present invention.
Disclosure of Invention The present inventors have carried out continuous partial hydrogenation reactions using various types of catalyst slurries with respect to monocyclic aromatic - 8 ~ 2~53~

hydrocarbons which were continuously flowed and fed to a reaction zone, and have made detailed investigations not only on reaction performance but also on the sepa-ration between an aqueous phase and an oil phase. As a result, the present inventors have found that when such a reaction comprising a flow step (flow reaction) is easily started, a portion of the components of the catalyst slurry which should be essentially retained in the aqueous phase gets mixed into the oil phase and flowed away, thereby causing adverse effects on the subsequent process operations and materials. Further, the present inventors have determined that this phenome-non rather generally occurs although the occurrence of this phenomenon depends on the difference of the compo-nents of the catalyst slurry. Still further, it has been found that this phenomenon cannot be recognized by only observing a reaction mixture after conducting an ordinary batch reaction, and that in some cases, this phenomenon is observed in a continuous reaction al-though the oil phase appears to be clearly separated from the aqueous phase after the batch reaction. Still further, the present inventors have found that in order to prevent the phenomenon, it is not sufficient to only provide a stationary separating vessel having a suffi-cient size for separating most of the catalyst slurry _ from the oil phase.
The present inventors have extensively and inten-sively studied with a view toward avoiding such a phenomenon, to thereby complete the present invention.
According to one aspect of the present invention, there is provided a method Eor pretreating a catalyst slurry for use in the continuous partial hydrogenation of monocyclic aromatic hydrocarbons by the reaction with a hydrogen gas, which comprises heat-treating a catalyst slurry comprised mainly of a ruthenium catalyst and water, while agitating, at a temperature of from 60 to 180 ~C for at least lO minutes, prior to the use of the catalyst slurry in the continuous partial hydrogenation of the aromatic hydrocarbon.
]5 In another aspect of the present invention, there is provided a method for the continuous partial hydrog-enation of monocyclic aromatic hydrocarbons, which comprises: (1) continuously feeding a monocyclic aromatic hydrocarbon and a hydrogen gas to a reaction zone to effect a contact thereof with a catalyst slurry comprised mainly of a ruthenium catalyst and w~ter and perform a partial hydrogenation reaction of the aromat-ic hydrocarbon, the catalyst slurry having been heat-treated at a temperature of from 60 to 180 ~C for at least 10 minutes while agitating, thereby obtaining a - l o ~ 3 ~ 4 ~-~

reaction mixture comprising an oil phase comprised mainly of a partial hydrogenation reaction product and the unreacted aromatic hydrocarbon and an aqueous phase comprised of the catalyst slurry and (2) continuously introducing the reaction mixture to an oil phase-aqueous phase separation zone to separate the oil phase from the aqueous phase.
When the pretreatment of the present invention is carried out under suitable conditions, the desired activity and selectivity of the catalyst with respect to the partial hydrogenation reaction of monocyclic aromatic hydrocarbons can be stably obtained as from immediately after the start of the flow reaction.
Further, an improvement of the selectivity itself is sometimes attained.
Hereinbelow, the particular embodiments of the present invention will be described. The catalyst slurry comprised of a ruthenium catalyst and water to be used in the present invention comprises as essential components a ruthenium catalyst and water. ~n addi-tion, the catalyst slurry may further comprise various types of additives, as described hereinbelow.
Examples of ruthenium catalysts include metallic ruthenium particulates and ruthenium supported on various carriers, for example, rare earth element I 1 2 ~

compounds, oxides and hydroxides of Ti, Zr, Hf, Nb, Ta, Cr, Fe, Co, Al, Ga and Si, hydrates of such oxides and hydroxides, and water insoluble salts, such as barium sulfate. The ruthenium catalyst may contain catalyst components other than ruthenium, such as Cu, Fe, Zn and Ag. To improve reaction performance and effect reac-tion stabilization, the following additi~es can be added to the ruthenium catalyst. The additives include a variety of soluble and insoluble materials, such as salts of a Group IA metal, a group IIA metal, Zn and Co, various a]kali agents (reagents for alkalinization, such as NaOH and ammonia), oxides and hydroxides of Ti r Zr, Hf, Nb Ta, Cr, Fe, Co, A1, Ga and Si, hydrates of such oxides and hydroxides, and activated carbon.
Especially, a method in which metallic ruthenium particulates and, as a solid additive, an oxide or a hydroxide of Ti, Zr, Hf, Nb, Ta, Cr, Fe, Co, Al, Ga, Si or a hydrate thereof are used with an aqueous solution of a Zn salt (for example, the above-mentioned prior art method (6)) can be preferably employed because the selectivity and yield are high in the preparation of cycloolefins by partial hydrogenation reaction.
The amount of catalyst to be used depends on the form of the catalyst. When rne-tallic ruthenium particu-lates are used, the catalyst is used in an amount of - 12 ~ 5~

from l x lO-5 to 0.1 part by weight, preferably from l x 10-4 to 5 x 10-2 part by weight, per part by weight of coexisting water. When a catalyst comprised of ruthenium supported on a carrier is used, the catalyst is used in an amount of from 1 x 10-4 to 0.3 part by weight, preferably from 1 x 10-3 to 0.1 part by weight, per part by weight of coexisting water. Further, when a solid additive is used in addition to the catalyst itself, the total amount of the catalyst and the solid additive other than the catalyst, that is, the slurrv concentration, is in the range of from 1 x 10-3 to 0.3 part by weight, preferably from 1 x 10-2 to 0.1 part by weight, per part by weight of coexisting water. When the additive is soluble in water, the amount thereof can be chosen in the range of from several parts per million to solubility.
Examples of monocyclic aromatic hydrocarbons to be fed to a partial hydrogenation reaction zone include benzene, toluene, xylenes, and lower alkylbenzenes w:ith an alkyl group having 2 to 4 carbon atoms. The partial hydrogenation reaction is generally conducted at a temperature of from lO0 to 200 ~C under a hydrogen pressure of from 10 to 100 kg/cm2G. The time for contact of the monocyclic aromatic hydrocarbon with the catalyst is generally in the range of from about 1 _ 13 _ 2~3~

minute to 10 hours. The reaction mixture to be with-drawn as an oil phase i.5 a mixture of a cyclohexene, a cyclohexane and an unreacted starting material. The method for separating the desired reaction product from the unreacted material is not limited, and any one of the conventional methods can be employed. For example, separation can be performed by distillation.
The pretreatment of a catalyst slurry according to the method of the present invention is conducted in a condition such that oil phase components, such as a monocyclic aromatic hydrocarbon as a starting material, are not present. However, a small amount of oil phase components can be present as long as it is soluble in the aqueous phase under pretreatment conditions.
Further, the pretreatment of the present invention is carried out for the catalyst slurry which is for the first time to be used for a partial hydrogenation reaction. The pretreatment according to the present invention is not necessarily required Eor the catalyst slurry which has once been pre~reated and which has already been used in the partial hydrogenation reaction and then cooled for reuse in a partial hydrogenation reaction.
The gaseous phase under which the pretreatment of the present invention is performed may be comprised of 14 ~ 2~t7A~ ~

steam, hydrogen, air or nitrogen. The type of the gas is not especially limited as long as it does not have an adverse effect on the catalyst. Generally, however, a hydrogen or a nitrogen atmosphere is preferred.
Moreover, when the pretreatment is conducted in the presence of hydrogen, that is, in the presence of hydrogen dissolved in the catalyst slurry, the desired activity and selectivity of the catalyst for the par-tial hydrogenation reaction of monocyclic aromatic hydrocarbons can be stably ensured as from immediately after the start of flow reaction, and in some cases an improvement of the selectivity itself is attained.
Therefore, the above-mentioned method for the pretreat~
ment is advantageous. In such a method, the pretreat-ment is conducted at a hydrogen pressure of from 1 to 100 kg/cm2G, preferably under the same pressure as that in the partial hydrogenation reaction.
The pretreating method of the present invention is conducted at a temperature of from 60 to 180 ~C. When the temperature is lower than 60 ~C, an extremely pro].onged period of time is undesirably required for the pretreatment, or the effects aimed at by the present invention cannot be obtained. On the other hand, when the temperature is higher than 180 ~C, denaturi~ation of the catalyst itself sometimes occurs - 15 - 2~

to disadvantages. It is preferred that the pretreat-ment be conducted at a temperature of from 100 to 150 ~C.
In the present invention, it is requisite to conduct the pretreatment for a period of at least 10 minutes under the above-described conditions. A pre-ferred treating period varies depending on the types of components of the catalyst slurry and the treatment temperature. Generally, however, the treating period is at least 10 minutes, generally in the range of from several hours to several days.
The reason why in a continuous partial hydrogena-tion reaction, a complete separation is attained be-tween an aqueous phase (a catalyst aqueous phase) and an oil phase by the pretreatment of the catalyst slurry according to the present invention, so that the compo-nents of the catalyst slurry are inhibited from getting mixed into the oil phase, has not yet been elucidated.
However, it is presumed as follows: Even in a compound generally known as a hydrophll;c compound, a lipophilic surface is partially formed thereon as viewed micro-scopically, which lipophilic surface is likely to cause the compound to get mixed into the oil phase. However, this lipophilic surface would be changed to a hydro-philic surface by the pretreatment of the present _ 16 - 2~A~4 invention.
By virtue of the present invention, a desired partial hydrogenation reaction product can be continu-ously obtained without suffering from the excess mixing of the components of the catalyst slurry into the oil phase and, hence, the operations, facilities and the like which are required for separation can be stream-lined on an industrial scale. The method of the present invention is highly valuable in the commerce.
Best mode for Carrying Out the Invention The present invention will now be further illus-trated in more detail with reference to the following Examples which should not be construed to be limiting the scope of the present invention.
The preparation methods of the catalyst slurries employed in Examples 1, 2 and 4 hereinbelow are the same as those described in the Examples of U.S. Patent No. 4,734,536, and the preparation method of the cata-lyst slurry employed in Example 3 hereinbelow is the same as that described in the Example of U.S. Patent No. 4,678,861.
Example 1 A catalyst slurry comprised of 2.5 g of a metallic ruthenium particulate catalyst (average crystallite size, 55 ~) containing 7.4 % by weight of zinc, which ;. . - . ~.. , , ,........ ,,, ~ .. ..
. . : ,. - :. . :~:- . : .. :
.,, i ~'' ''i:: , : ;,., : ' '' ' .' ,:.,. ., , - ;:,- -. .; ~ , : . -., ~ . . .: . .~ ,, - ;,. . . .:
: ,~
,:: :, ::: , :
.: , , -:: ' , . ' , - 17 - 2055~4 ruthenium catalyst had been obtained by reducing Ru(OH)3 having contained zinc hydroxide, 15 g of ZrO2 powder (average particle size, 0.35 ~), and 1,400 ml of an 18 ~i aqueous solution of ZnSO4-7H2O containing 250 mg of ZnSO4-3Zn(OH)2, was charged into a continuous flow reaction apparatus having an inner capacity of 3 liters which was provided therein with an about 100 ml stationary vessel for oil phase-aqueous phase separa-tion (equipped with an inlet for a reaction mixture, an ~ outlet for an aqueous phase, and an outlet for an oil phase) and had Teflon coating applied at portions to be brought into contact with the liquid.
Next, the gaseous phase was replaced by a hydrogen gas, and the temperature was elevated~to 150 ~C over a period of one hour while~agieating the~catalyst slurry.
Subsequently, hydrogen was introduced to attain a total ineernal pressure of 50 kg/cm2G, which was kept for 20 hours. Thus, pretreatment of the catalyst slurry was performed. Thereafter, benzene~was fed at a rate of 2 liter/hr, and the partial hydrogenation reaction of benzene was continuously carried out while maintaining a temperature of 150 ~C and a hydrogen pressure of 50 kg/cm2G.
The aqueous phase discharged from the stationary vessel for oil phase-aqueous phase separation was -~

. : , , , ,: :, ~. ~, ., - .. : , . - .
., : . , ,, . . . . :
, ~ , : .. , . . . .: ~
- : . , . . i ; .. ... ~, ~
. - -. . . .. .
:.
. ; , . : ~ , : , ~ , :. ," .

- 18 - 2055~

recycled to the reaction system, while the oil phase discharged was cooled and passed through a polypropyl-ene microporous filter. The water contents precipitat-ed from the oil phase due to the occurrence of a super-saturat.ed state caused by the cooling and the compo-nents of the catalyst slurry excessively mixed into the oil phase, were aggreqated and filtered to thereby separate the same from the oil phase. Thus, the oil phase as a reaction product was continuously withdrawn.
On the other hand, the separated and collected water and water-soluble components were appropriately recy-cled to the reaction apparatus. These operations were continuously carried on for 500 hours, thereby obtain-ing a partial hydrogenation reaction mixture comprised of benzene, cyclohexene and cyclohexane.
An aliquot of the separated and collected water was taken out, and the amount of the water-soluble cc onent (ZnS04 and the like) of the catalyot slurry contained in the collected water was analyzed to find that the cohtent of this component was as small as 10 -30 ppm in terms of the amount of Zn by weight relative to the weight of the separated and collected water.
After the completion of flow reaction, ehe microporous filter was taken out, and the deposition of 001id materials thereon was examined. ~he amount of white ; . : .. - : . : ,. .

19 - 2 0 ~

Zr~2 deposited was only of a trace. From the above, it is apparent that the amount of components of the cata-lyst slurry which got mixed into the oil phase during the flow reaction was extremely small, so that substan-tially no material got mixed into the oil phase, except only the water, the amount of which corresponded to the solubility of water in the oil phase at 150 ~C.
Example 2 Substantially the same procedure as in Example 1 was repeated to perform a continuous reaction for 200 hours, except that the pretreatment operation of the catalyst slurry was conducted by elevating the tempera-ture to 80 ~C over a period of 30 minutes, and the pretreatment was continued for 48 hours at the same temperature. The content of Zn in the water separated and collected during the continuous reaction was 10-50 ppm by weight. Further, the amount of white ZrO2 deposited on the microporous filter was of a trace, and the amount of c~ nents of the catalyst getting mixed into the oil phase during the flow reaction was ex-tremely small. From the above, it is apparent that substantially no material got mixed into the oil phase, except the water, the amount of which corresponded to the solubility of water in the oil phase at 150 ~C.
Comparative Example 1 ~ , , . .' ~' ' ' ,' ' .. . . .

..

Substantially the same procedure as in ~xample l was repeated to perform a continuous reaction for 200 hours, except that the pretreatment of the catalyst slurry was not carried out, and that in the process of temperature elevation to 150 ~C, feeding of benzene was started at the time when the temperature reached 100 ~C
by heating for five minutes. The content of Zn in the water separated and collected during the continuous reaction was 80-600 ppm by weight. Abou-t 1.0 g of a mixture of white ZrO2 and the ruthenium catalyst was deposited on the microporous filter. From the above, it is apparent that the components of t:he catalyst slurry excessively got mixed into the oi.l phase.
Example 3 Pretreatment of a catalyst slurry and a partial hydrogenation reaction of benzene were carried out in substantially the same manner as in Example 1, except that a catalyst slurry comprised of 70 g of a hydroge-nating catalyst composed of 1 % of rutheni.um supported on lanthanum hydroxide, 700 mg of z:irlc ox.ide, 35 g of sodium hydroxide and 1400 ml of water used. During the reaction, an aliquot of the separated and collected water was taken out, and the amount of components of the catalyst slurry which was contaLned therein was analyzed. The amount of Na was as small as 30 to 70 - 21 - 205~

ppm by weight, and the amount of Zn was less than 0.2 ppm by weight, relative to the weight of the separated and collected water. After the completion of the flow reaction, the microporous filter was taken out and ex~ ined to determine solid components deposited there-on. Only a trace amount of hydrogenating catalyst was observed.
Comparative Example 2 Substantially the same procedure as in Comparative Example 1 was repeated to perform a continuous reac-tion, except that the same catalyst slurry as used in Example 3 was used. The amount of Na contained in the water separated and collected during the continuous reaction was 150-500 ppm by weight, and the amount of Zn contained therein was 0.5-2 ppm by weight. After the completion of the flow reaction, deposition of about 2.5 g of the hydrogenating catalyst was observed on the microporous filter.
Example 4 Substantially the same procedure as in Example 1 was repeated to perform a continuous reaction, except that the gaseous phase was replaced by nitrogen at atmospheric pressure in the pretreatment of the cata-lyst slurry. The amount of Zn contained in the water separated and collected during the continuous reaction ... . . ~. : :' ' '.

i ~ . ~' , :' , - 22 ~ 5 ~ ~ ~

was 10-60 ppm. Only a trace amount of white ZrO2 was deposited on the microporous filter. From khe above, it is apparent that the amount of components of the c~ta-lyst slurry which got mixed into the oil phase during the flow reaction was extremely small. The selectivity for cyclohoxene immediately after the start of the flow reaction was about 3% lower than that obtained in Example 1.
Industrial Applicability sy virtue of the present invention, the continuous partial hydrogenation of monocyclic aromatic hydrocar-bons can be efficiently attained. In -the present invention, partial hydrogenation reaction products can be efficiently obtained without suffering from the excess mixing of the components of the catalyst slurry into an oil phase containing the partial hydrogenation reaction products, and operations and facilities re-quired for separation can be simplified. The partial hydrogenation products oE monocyclic aromatic hydrocar-bons efficiently obtained by the present inventi.on are highly valuable as i.ntermediates for the manufacture of organochemical industrial products, and par-ticularly, they are important as intermediates for the production of polyamides and lysines.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for pretreating a catalyst slurry for use in the continuous partial hydrogenation of a monocyclic aromatic hydrocarbon by the reaction with a hydrogen gas, which comprises heat-treating a catalyst slurry comprised mainly of a ruthenium catalyst and water, while agitating, at a temperature of from 60 to 180°C for at least 10 minutes, prior to the use of said catalyst slurry in the continuous partial hydrogenation of said aromatichydrocarbon, wherein said heat treatment is conducted substantially in the absence of said monocyclic aromatic hydrocarbon and in the presence of a hydrogen gas dissolved in said catalyst slurry.

2. A method for the continuous partial hydrogenation of a monocyclic aromatic hydrocarbon, which comprises:
(1) continuously feeding a monocyclic aromatic hydrocarbon and a hydrogen gas to a reaction zone to effect a contact thereof with a catalyst slurry comprised mainly of a ruthenium catalyst and water and perform a partial hydrogenation reaction of said monocyclic aromatic hydrocarbon, said catalyst slurry having been heat-treated at a temperature of from 60 to 180°C for at least 10 minutes, while agitating, thereby obtaining a reaction mixture comprising an oil phase comprised mainly of a partial hydrogenation reaction product and the untreated aromatic hydrocarbon and an aqueous phase comprised of the catalyst slurry, wherein said heat treatment has been conducted substantially in the absence of said monocyclic aromatic hydrocarbon and in the presence of a hydrogen gas dissolved in said catalyst slurry; and (2) continuously introducing said reaction mixture to an oil phase-aqueous phase separation zone to separate said oil phase from said aqueous phase.