Hydrogenation of Maleic Anhydride and Intermediates by Nickel-Rhenium Catalyst Supported on Kieselguhr*

by Junichi Kanetaka**, Seiichi Kiryu***, Taisuke Asano** and Shinobu Masamune***

Summary: A kineticstudy of the hydrogenationof maleicanhydride and intermediatesusing nickel-rheniumcatalyst supported on kieselguhrhas beencarried out in orderto investigate the activity of this catalyst on each reactionstep and its effect on the reactionmechanism. It has beenshown that this catalyst not only resists corrorsionby the organic acids suchas maleic acid, succinicacid, propionicacid and butyric acid under the co-existenceof water, but also directly promotes hydrogenationof maleic anhydride to tetrahydrofuran. The kineticstudies weredone for each of the reactionsteps involvedin thisprocess, and the orders and the rate of constantsof thesereaction steps were obtained. Especially,from the kineticstudy of hydrogenationof succinicanhydride to y-butyrolactoneit is clearlynoted that succinicacid and water are the strong inhibitors.

There are three main reaction paths in this process as follows: "via γ-butyrolactone">"via

polyester"》"via succinic acid".

water. Thus, the conventional catalyst has the 1 Introduction disadvantage in that its catalytic activity is greatly reduced during the course of the reaction. The attempt to obtain tetrahydrofuran(THF) andγ-butyrolactone(γ-BL)by the hydrogenation Realizing this point, since 1963, a study of this of maleic anhydride was first described in the U. S. subject was commenced and it was found that the metallic solid solution catalyst consisting of nickel patents1)～3)proposed by E.I. du Pon't de Nemours & Co. in 1956. Thereafter, some examina- and rhenium supported on kieselguhr shows tions4)～6)were carried out by various companies, peculiar property not normally found in the con- but their investigations resulted only in obtaining ventional hydrogenation catalysts, that is, this

γ-BL and not THF. The catalysts described in catalyst not only resists corrorsion by organic acids these literatures were mixed catalysts consisted under the co-existence of water, but also directly of nickel-molybdenum oxide and cobalt-molyb- promotes the hydrogenation of maleic anhydride denum oxide1), Raney nickel2), Raney cobalt2), to THF. nickel-molybdenum oxide3), supported nickel4), The main reaction steps could be considered copper-chromium oxide5), supported palladium6), to consist of the following consecutive reactions. etc. However, none of these catalysts was found to be adequate for industrial use. In the direct hydrogenation of dicarboxylic anhydride such as maleic anhydride, the reaction must proceed under the existence of dicarboxylic acid such as maleic acid and succinic acid, which are the by-products of the hydrogenation reaction in the presence of

* Received October 30 We name this path"via γ-BL". , 1969. A part of this paper was lectured at the 158th As the study progressed, succinic acid, 1, 4- ACS National Meeting-New York. butanediol and a polyester were found as inter- ** Mitsubishi Petrochemical Co . Ltd., Central Re- mediates in addition to γ-BL. search Laboratory (1315 Wakaguri, Ami-machi Thereupon, these intermediates as well as maleic Inashiki-gun, Ibaragi) *** Mitsubishi Petrochemical Co . Ltd., Yokkaichi anhydride and succinic anhydride were also Factory, Research and Development Department subjected to hydrogenation in order to investigate (1 Toho-cho, Yokkaichi, Mie) the reaction mechanism.

Volume 12-May 1970 90 Kanetaka, Kiryu, Asano and Masamune: Hydrogenation of Maleic Anhydride

2 Experimental Procedure graphy or nuclear magnetic resonance spectra. THF, γ-BL, n-propanol, n-butanol, propionic The catalyst was prepared as follows: acid and butyric acid were analyzed by GC, 100g of finely powdered kieselguhr were added while maleic anhydride, succinic anhydride, into 500g of nickel nitrate [Ni(NO3)2 6H2O] succinic acid and polyester were analyzed by the dissolved in 400g of distilled water. The result- NMR. ing mixture was kneaded for one hour by a kneader to give a slurry-like product of dark-greenish 3 Result and Discussion color. 200g of ammonium carbonate [(NH4)2 CO3] dissolved in 200g of distilledwater was 3.1 Hydrogenation of Maleic Anhydride to Succinic Anhydride slowly added to the slurry-like product while Since the rate of reaction of this step was fast, stirring to give a yellowish green precipitate, which estimate was difficult to make. Consequently, was then filtered off. the data were obtained by using lower reaction The solid collected was washed with distilled temperatures, lower reaction pressure and lower water twice. After washing, the solid was dried concentration of catalyst than those used on the at temperature of 110℃ for 24 hours. 1g of other steps. Moreover, when this reaction was rhenium heptoxide in the form of an aqueous carried out under high concentration of catalyst solution was added to a 30g portion of this dried and at a reaction temperature above 250℃, solid which was basic nickel carbonate supported decomposition occurred rapidly accompanied by on kieselguhr and then the resulting mixture was a remarkable generation of heat and a pitch-like kneaded and dried at the temperature of 110℃ product was obtained. Therefore, the following for 12 hours. The reduction of this powder was reaction conditions were adopted on this step. done at temperature of 150℃ for 2 hours and then The range of reaction temperature was from 150 at increased temperature of 450℃ for another to 200℃, the reaction pressure was 60kg/cm2 and 3 hours. The catalyst thus reduced was then concentration of catalyst was 0.1wt% for the cooled to 150℃ and hydrogen stream was switch- reaction temperature of 150℃ and 0.05wt% for ed over to carbon dioxide stream. The catalyst the others. then allowed to stand over night. Result of Any other reaction product, except succinic chemical analysis on this catalyst as prepared anhydride was not detected. Under these con- above showed a proportion of nickel component ditions, only the carbon-carbon double bond of to kieselguhr of 2:3. maleic anhydride was hydrogenated. The reaction procedure and analysis were done The experimental results are shown in Fig. 1 as follows: A conventional 300ml autoclave as yield of succinic anhydride vs. the reaction time. provided with an electromagnetic stirrer was used. If the reaction proceeds with first order for a The amount of each reactant used was 100g, and the amount of catalyst was 0.05 or 0.1wt% in the case of maleic anhydride and 5wt% in the case of the others. The range of reaction temperature was from 150 to 280℃. The reaction pressure was 60kg/cm2 for maleic anhydride and 120kg/cm2 for the others. In order to let the reaction proceed as slowly as possible until the prescribed reaction temperature is reached, the autoclave including reactant and catalyst was kept under the condi- tion from 5 to 30kg/cm2 of hydrogen pressure and 50rpm of agitation. The reaction was carried out under constant pressure and 1,000rpm of agitation during the prescribed reaction time. After this time was over, the autoclave was im- mediately cooled down by quenching it in water to stop the subsequent reaction. After separating the catalyst, various components of the reaction Fig. 1 Yield of Succinic anhydride vs. Reaction products were analyzed by either gas-chromato- Time in Hydrogenation of Maleic Anhydride Bulletin of The Japan Petroleum Institute and Intermediates by Nickel-Rhenium Catalyst Supported on Kieselguhr 91 given concentration of maleic anhydride under considered from Fig. 3 and Fig. 4 that THF is constant hydrogen pressure, the equation rate obtained from the successive reaction of γ-BL. may be written as follows Though by-products such as n-propanol and n-butanol are not shown, their yield actually increase with increasing yield of THF. Integrating the above equation, and considering that at t=0, CMAH=CMAH,we obtain euqation (2), In(C°MAH/CMAH)=k1t (2)

where CMAH=concentration of maleic anhydride k1=rate constant t=reaction time The plot obtained by applying the data to Eq. 2 shows the linear dependence as shown in Fig. 2.

Fig. 3 Yield ofγ-BL vs. Reaction Time in Hydro-

genation of Succinic Anhydride

Fig. 2 Test of First Order Reaction Mechanism for Hydrogenation from Maleic Anhydride to Succinic Anhydride

3.2 Hydrogenation of Succinic Anhydride

The range of reaction temperature was from 240to 270℃, the reaction pressure was 120kg/cm2 and the concentration of catalyst was 5wt%. The solid products were not detected at least after 30 minutes. The succinic acid, however, Fig. 4 Yield of THF vs. Reaction Time in Hydro- was detected in the liquid products through their genation of Succinic Anhydride nuclear magnetic resonance spectra. Since succinic anhydride reacts easily with water under The kinetic expression is assumed to be re- room temperature to give succinic acid, the ratio presented by of succinic anhydride to succinic acid in the pro- ceeding reaction could not be determined. The relation between the yield obtained over where CSAH=concentration of succinic anhyd- unit weight of catalyst and reaction time is shown ride respectively for γ-BL and THF in Fig. 3 and Fig. 4. k2'=rate constant The reaction to γ-BL from succinic anhydride CP=concentration of inhibitor com- is extremly fast in the early stage and then gradu- ponent ally becomes slower as reaction time elapsed. K=adsorption coefficient of SAH

If the rate of THF production follows the zero KP'=adsorption coefficient of inhibitor order for the concentration of γ-BL, it can be component

Volume 12-May 1970 92 Kanetaka, Kiryu, Asano and Masamune: Hydrogenation of Maleic Anhydride

Water and succinic acid may be considered as including succinic acid was used as initial reac- the chief inhibitor components in this step . Water tants.

is produced through out the reaction from succinic 3.3 Hydrogenation of γ-BL

anhydride to γ-BL and THF . Furthermore, the , In order to eliminate the inhibition effect of concentration of succinic acid can be propor- succinic acid, reaction (III) and the side reaction tional to the concentration of water . to produce the lower alcohols such as n-propanol Therefore, Eq. 3 becomes and n-butanol were investigated in the hydro-

genation of γ-BL as a starting material.

The range of reaction temperature was from where C°SAH=initial concentration of succinic 240 to 280℃, the reaction pressure was 120kg/cm2 and the concentration of catalyst was 5wt%. anhydride α=nKp,H2O+mKP,SA

n=coefficient correlating with the

concentration of water with the

conversion of succinic anhydride:n=1 for γ-BL, n=2 for THF

m=coefficient associated with the concentration of succinic acid

If KP≫K, and that the term[1+KCSAH]could

be neglected in comparison with the term

[α(C°SAH-CSHA)], the integrated form of the resulting equation is represented as follows

ln(C°SAH/CSAH)-(C°SAH-CSAH)=k2t (5)

where k2=(K/α)k2' The graphical illustration of data using Eq. 5 is shown in Fig. 5. It is obvious from this graph that the above assumption is satisfied. Fig. 6 Conversion of γ-BL vs. Reaction Time in Hydrogenation of γ-BL

In Fig. 6, the conversion of γ-BL vs. reaction time is plotted. It is clear that the rate of this step follows the zero order kinetics as follows

Integrating Eq. 6, the following Eq. 7 is obtained.

where C°γ-BL=initial concentration ofγ-BL

Cγ-BL=concentration of γ-BL at re-

action time, t

k3=k3'/C°γ-BL

The rates of side reaction in the formation of n-propanol and n-butanol are considered as first order kinetics with respect to the concentration of THF. Fig. 5 Test of Eq. 5

From this result, it is difficult to distinguish which is the stronger inhibitor between succinic acid and water. However, it was confirmed that succinic acid is the stronger inhibitor through where CPrOH=concentration of n-propanol the experiment in which succinic anhydride CBuOH=concentration of n-butanol

Bulletin of The Japan Petroleum Institute and Intermediates by Nickel-Rhenium Catalyst Supported on Kieselguhr 93

From the material balance, Eq. 10 is obtained

CTHF=k3C°γ-BLt-(CPrOH+CBuOH) (10)

Since these are mutual parallel reactions, Eq. 11 is obtained from Eq. 8 and Eq. 9.

Replacing Eq. 10 and Eq. 11 into Eq. 8,

Integrating Eq. 12 and noting that, at t=0, CPrOH=0, Eq. 13 is obtained.

Fig. 8 Comparison between Calculated Curves and With similar exercise, the following equation Experimental Points for Conversion to n- pertains to n-butanol is derived. Butanol in Hydrogenation of γ-BL

used in the calculation are shown in Table 1. These values are estimated for a unit time (hr), unit pressure (kg/cm2) and unit amount of catalyst

In Fig. 7 and Fig. 8, the calculated curves and the (g). 3.4 Hydrogenation of Succinic Acid experimental points of the yield for n-propanol In Eq. 4, succinic acid is considered as the main and n-butanol vs. reaction time are shown. The inhibitor component. Therefore, it was examined calculation curves were obtained by the trial and whether this catalyst is capable or not of promoting error method, giving several values to k4 and k5 hydrogenation succinic acid to γ-BL and THF. in Eq. 13 and Eq. 14. The values of k4 and k5 In this reaction step, the reaction temperature Table 1 Values of k4 and k5 Estimated for Several was 260℃, reaction pressure was 120kg/cm2 Reaction Temperatures and the concentration of catalyst was 5wt%.

The conversion of succinic acid vs. reaction time is plotted as shown in Fig. 9.

Fig. 9 Conversion of Succinic Acid vs. Reaction Time

It appears from this figure that zero order kinetics fit the data for the conversion under 70 mole %.

The yield of THF and γ-BL vs. the reaction time Fig. 7 Comparison between Calculated Curves and are plotted as shown in Fig. 10. It may be con- Experimental Points for Conversion to n- Propanol in Hydrogenation of γ-BL cluded from Fig. 10 that succinic acid is adsorbed

Volume 12-May 1970 94 Kanetaka, Kiryu, Asano and Masamune: Hydrogenation of Maleic Anhydride

more strongly than γ-BL. If succinic acid is Fig. 11 showing the relationship between the adsorbed strongly by the catalyst, the rate of reac- conversion of polyester vs. reaction time was tion should obey zero order kinetics with respect made based on the experimental results. As to concentration of succinic acid. It can be seen it was difficult to define clearly the conversion of polyester. the summation of weight percentages from Fig. 10 that the rate of THF production from ユげロ

of the products such as THF,γ-BL,n-Propanol, γ-BL is extremely restrained in compliance with the concentration of succinic acid in the reactor. n-butanol and water was adopted as the conver- Therefore, in order to make the THF production sion of polyester. rate greater, it is necessary to decrease the con- The yield of THF and γ-BL vs. reaction time centration of succinic acid as much as possible. are plotted as shown in Fig. 12.

Fig. 10 Yield of THF or γ-BL vs. Reaction Time

in Hydrogenation of Succinic Acid

3.5 Hydrogenation of Polyesters from Suc- cinic Acid and 1,4-Butanediol Fig. 11 Conversion of Polyester vs. Reaction Time Though a polyester was not detected in the batch type reactions, it was detected in the flow type reactions which were operated in the bench scale and pilot plant. Accordingly, the examination for polyester was carried out. The polyester is one product of succinic acid and 1,4-butanediol through the condensation polymerization. These structures have been confirmed by the analysis of the infrared absorption spectra and the nuclear magnetic resonance spectra. The structures were classified with the combination of terminal groups, that is, carboxyl group and hydroxyl group. No parti- cular difference of the reactivity for the hydrogenation was found among them.

The reaction temperatures were 240, 250 and 260℃,the reaction pressure was 120kg/cm2 and the concentration of catalyst was 5wt%. In order to examine the effect of molecular weight on the reaction rate, the polyester with molecular Fig. 12 Yield of THF orγ-BL vs. Reaction Time weight 1,000 and 2,000 were examined for 260℃. in Hydrogenation ofPolyester

Bulletin of The Japan Petroleum Institute and Intermediates by Nickel-Rhenium Catalyst Supported on Kieselguhr 95

With respect to the effect of molecular weight centration of catalyst of 5wt% are shown in Fig. of polyester, it may be said from Fig. 11 and Fig. 14 representing the conversion of 1,4-butanediol 12 that the reaction rate is diminished a little. vs. reaction time. This reaction step is only Moreover, it may be concluded from Fig. 12 a dehydration and may be considered as being that the hydrogenolysis rate of polyester is greater independent on the conditions of hydrogenation. than its hydrolysis rate because, if hydrogenolysis However, this reaction did not occur without the and hydrolysis occur at the same level, the amounts catalyst and hydrogen. of γ-BL and THF should be almost the same, but the amounts of both products are very diffe- rent as seen in Fig. 12. Though it may not be accurate to use the above- mentioned conversion as the Q values in the rate equation, Fig. 13 in the first order graph was made by using the values of conversion in Fig. 11 as the Q values. It may be considered formally from Fig. 13 that the reaction rate is satisfied with the first order kinetics.

Fig. 14 Conversion of 1,4-Butanediol vs. Reaction Time

Fig. 13 First order Plots for Reaction of Polyester

3.6 Hydrogenation of 1,4-Butanediol 1,4-Butanediol was not detected in the products produced by the flow type reactions. In the batch type reactions, a little amount of 1,4-butanediol was observed in the early reaction time and then rapidly decreased as the reaction time elapsed. However, this amount was only a few per cent. It was seen that the maximum amount of the above Fig. 15 First Order Plots for Reaction of 1,4-Butane- 1,4-butanediol which was obtained through the diol reaction time decreased with the increase of the reaction temperature. The data in Fig. 14 if plotted for the first order The experimental results which were carried kinetics are as shown in Fig. 15. In this figure , out under reaction temperature of 230, 240 and C°BDO is the initial concentration of 1 ,4-butanediol 250℃,reaction pressure of 120kg/cm2 and con- CBDO is the concentration at reaction time , t.

Volume 12-May 1970 96 Kanetaka, Kiryu, Asano and Masamune: Hydrogenation of Maleic Anhydride and Intermediates by Nickel-Rhenium

3.7 Values of Activation Energy and Fre- X→XI→VII

quency Factor It may be seen from Fig. 16 that the following The activation energies and frequency factors several reactions occur simultaneously. for each reaction step are shown in Table 2. (1) hydrogenation for double bond: (I), The frequency factors are estimated for unit time (VIII) (hr), unit pressure (kg/cm2) and unit amount of (2) equilibrium reaction between hydration catalyst (g) as wel as value of k4, k5 shown in and dehydration: (IV), (V) Table 1. The values of k6 and k7 are those (3) hydrogenative dehydration: (II), (III), for the hydrogenation reaction of polyester and (IX) 1,4-butanediol respectively. (4) hydrogenative cyclization: (VI) (5) dehydrative cyclization: (VII) Table 2 Kinetic Data for Each Reaction Step (6) equilibrium reaction between dehydrative condensation polymerization and hydrolysis: (X) (7) hydrocracking of polyester: (XII) The order of the reaction rates to THF of the above mentioned three paths is considered as follows.

"via γ-BL">"via polyester"》"via succinic acid". Therefore, this process should consider the above mentioned several reactions as balancing mutually. 3.8 Reaction Scheme The side reactions produce a small quantity The over all reaction scheme can be shown in of lower organic acids such as propionic acid and Fig. 16. In this figure,"via γ-BL"means that butyric acid beseides lower alcohols. These its reaction proceeds mainly through the following organic acids may be produced from the thermal

steps cracking of dicarboxylic acids and γ-BL. I→II→III or I→II→VI→VII "via succinic acid" is Acknowledgement

IV→VIII→IX→VII The authors wish to express their gratitude to or I→V→IX→VII Mitsubishi Petrochemical Co., Ltd. for permission "via polyester" is to publish this paper. The authors also would like to express their appreciation to Mr. T. Shimodaira, Mr. S. Mori and the other many members of the THF group.

References

1) U.S. 2,772,291 (1956), du Pon't 2) U.S. 2,772,292 (1956), du Pon't 3) U.S. 2,772,293 (1956), du Pon't 4) U.S. 3,312,718 (1967), Petro-Tex 5) U.S. 3,065,242 (1962), Quaker Oats 6) U.S. 3,214,385 (1965), FMC Corp.

Fig. 16 Reaction Scheme

Bulletin of The Japan Petroleum Institute