Hydrogenolysis catalysts for the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4-butanediol

Abstract

Hydrogenolysis catalysts for the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4-butanediol The specification describes a process for the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4-butanediol, comprising the step of carrying out hydrogenolysis of the dialkyl maleate or dialkyl succinate in the presence of a heterogeneous catalyst, wherein the catalyst in its oxidic form comprises: 5-50 wt% CuO; and 0.5-20 wt% Mn3O4; on an alumina support. Also described is a catalyst for the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4-butanediol, wherein the catalyst in its oxidic form comprises: 5-50 wt% CuO; and 0.5-20 wt% Mn3O4; on an alumina support.

Description

[0001]P102174 1 Hydrogenolysis catalysts for the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4-butanediol Field of the Invention The present invention relates to hydrogenolysis catalysts and their use in the hydrogenolysis of dialkyl maleate or dialkyl succinate to 1,4-butanediol. Background Catalytic hydrogenolysis of dialkyl maleate or dialkyl succinate to 1,4-butanediol is a commercially important reaction. The hydrogenolysis reaction is: The reaction can produce 1,4-butanediol, gamma-butyrolactone and tetrahydrofuran. It is sometimes advantageous to produce all three products but there are circumstances in which it is desirable to maximise the 1,4-butanediol production. For example, 1,4-butanediol can be used in the production polybutylsuccinate (PBS), which is a biodegradable polymer. Typically, in a PBS plant the 1,4-butanediol production should desirably make as much 1,4- butanediol as possible since that is the feedstock needed for the downstream PBS production. The hydrogenolysis of dialkyl maleate or dialkyl succinate to 1,4-butanediol has previously been carried out using catalysts containing CuO and MnO2. However, there is a need for further, improved, hydrogenolysis catalysts. In particular, there is a need for hydrogenolysis catalysts that are effective for producing 1,4-butanediol with good activity and reduced by- product make. The present invention relates to a catalyst having a good balance of the above properties, and a process of using the catalyst in the hydrogenolysis of dialkyl maleate or dialkyl succinate to 1,4-butanediol. P102174 2 Figure 1 is a plot showing tetrahydrofuran make as a function of dimethyl succinate conversion for catalysts comprising Mn3O4 and catalysts comprising MnO2; and Figure 2 is a column chart of by-product formation for catalysts comprising Mn3O4 and catalysts comprising MnO2. of Invention The present inventors have now found that a catalyst containing CuO and Mn3O4 on an alumina support provides a catalyst having advantageously low by-product production in the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4-butanediol. In a first aspect the invention relates to a process for the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4-butanediol, comprising the step of carrying out hydrogenolysis of the dialkyl maleate or dialkyl succinate in the presence of a heterogeneous catalyst, wherein the catalyst in its oxidic form comprises: 5-50 wt% CuO; and 0.5-20 wt% Mn3O4; on an alumina support. Preferably the total content of elements other than Cu, Mn, Al and O is ≤ 1 wt%. Preferably substantially all, such as greater than 80 wt%, preferably greater than 90 wt%, more preferably greater than 95 wt% of the Mn is present as Mn3O4. The applicant has found that catalysts comprising Mn3O4advantageously produce less tetrahydrofuran than catalysts comprising MnO2. While catalysts comprising Mn3O4can produce a little more gamma- butyrolactone than catalysts comprising MnO2, they also tend to produce fewer other by- products (i.e., other than tetrahydrofuran and gamma-butyrolactone) and so overall by- product formation is advantageously reduced. The Mn3O4content is measured by XRF. As will be appreciated, the XRF measures how much Mn is present. The phase is confirmed by XRD. Once the quantity of Mn and the phase are both known, the Mn3O4content can be calculated using the known total mass of the catalyst, the molar content of Mn and the known molecular mass of Mn3O4. The CuO content is also measured by XRF in an analogous way. P102174 3 The catalyst is supplied in its oxidic form and reduced before use in the reaction. Activation may be achieved by flowing hydrogen, for example in nitrogen, over the catalyst. For example, the catalyst may be activated by flowing a blend of, for example less than 5%, such as 1%, for example 0.5 to 1.5%, H2 in N2 while ramping temperatures from ambient, such as not more than 25°C, to at least 170°C, for example over a period of 4 hours. The skilled person will appreciate that the compositional analysis is typically carried out on the oxidic form of the catalyst and thus it is appropriate to define the catalyst composition in relation to its oxidic form even though it is reduced before use in the reaction. Without wishing to be bound by theory, it is believed that the CuO is reduced to Cu while the Mn3O4 remains as Mn3O4 in the reduced catalyst, which results in the advantageous lower tetrahydrofuran production. In some embodiments the catalyst in its oxidic form comprises: 5-20 wt% CuO; and 0.5-20 wt% Mn3O4; on an alumina support. In preferred embodiments the dialkyl maleate or dialkyl succinate is dimethyl maleate or dimethyl succinate. Preferably the conversion of dialkyl maleate of dialkyl succinate is greater than 90 mol%, more preferably greater than 95 mol%. The catalyst of the invention may advantageously permit high conversions while still producing low levels of by-products compared to previous catalysts, in particular those containing MnO2. In some embodiments the heterogeneous catalyst is provided in a first catalyst bed upstream of a second catalyst bed. The first catalyst bed may be a guard bed, in that it contains a catalyst tolerant of harsh conditions that protects a less tolerant catalyst in the second bed. Thus, the second catalyst bed may comprise a second heterogeneous catalyst, different to the heterogenous catalyst. For example, the first catalyst bed may contain the catalyst of the invention and the second catalyst bed may contain a catalyst comprising MnO2and preferably a catalyst comprising CuO, MnO2and an alumina support. Such a catalyst may be a previously known catalyst for the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4-butanediol. However, it may be advantageous for the second catalyst bed to comprise the heterogeneous catalyst. In that way, the full advantages of using the heterogeneous catalyst are obtained and it may be possible to replace the first P102174 4 catalyst bed more frequently, while the lifetime of the second catalyst bed is extended, or to use different conditions in the two catalyst beds. In a second aspect the invention relates to a catalyst for the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4-butanediol, wherein the catalyst in its oxidic form comprises: 5-50 wt% CuO; and 0.5-20 wt% Mn3O4; on an alumina support. Preferably the total content of elements other than Cu, Mn, Al and O is ≤ 1 wt%. Preferably substantially all, such as greater than 80 wt%, preferably greater than 90 wt%, more preferably greater than 95 wt% of the Mn is present as Mn3O4. The CuO and Mn3O4 contents are measured on the catalyst by the method described above and in the examples section. It will be appreciated that any features described in relation to the first aspect may be applied to the second aspect, and vice versa. Detailed Description Any sub-headings are for convenience only and are not intended to limit the invention. Any aspect described as being preferred in connection with the catalyst also applies to the catalyst used in the process of the first aspect. Catalyst The catalyst comprises 5-50 wt% CuO. In some embodiments the catalyst comprises 5- 20wt% CuO. A low content of copper is preferred from a cost perspective provided sufficient activity is obtained. The catalyst comprises 0.5-20 wt% Mn3O4. The presence of Mn3O4reduces the production of tetrahydrofuran and also of other (i.e., other than tetrahydrofuran or gamma- butyrolactone) by-products. A little more gamma-butyrolactone can be produced, but overall the by-product formation is advantageously reduced. P102174 5 The total content of elements other than Cu, Mn, Al and O in the catalyst is preferably ≤ 1 wt%. The content of elements can be determined by inductively coupled plasma mass spectrometry (ICP) or by X-ray fluorescence (XRF). The CuO and Mn3O4 are supported on an alumina support. As used herein, the term “alumina” is not intended to encompass silica-aluminas. The silicon content of the alumina used herein is ≤ 5 wt%, preferably ≤ 2 wt%, such as ≤ 1 wt%. Alumina takes on various different forms depending on the temperature to which it has been calcined. The support is preferably α-alumina, γ-alumina, δ-alumina or θ-alumina, or a mixture thereof. The alumina may be a single form or a mixture of different forms. In a preferred embodiment the alumina support is γ-alumina. It is preferred that the catalyst is in the form of granules, spheres or multi-lobe shapes such as trilobes. Such catalysts can be prepared by impregnating an alumina support in the form of granules, spheres or multi-lobe shapes such as trilobes. It is preferred that the support (and the catalyst) is in the form of trilobes. Manufacture of the catalyst The catalysts described herein may be prepared by impregnation of an alumina support. The catalysts may be manufactured by sequential impregnation of a particulate alumina support with a solution of a soluble manganese salt and a solution of a soluble copper salt. These are preferably manganese nitrate in demineralised water and copper carbonate in ammonium hydroxide. Decomposition of each salt occurs in between impregnation by thermal treatment between 300-1000°C to afford the desired manganese and copper phase. Hydrogenolysis process The catalysts described herein are suitable for the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4-butanediol. Preferred substrates are dimethyl maleate or dimethyl succinate. Examples Catalyst testing procedure P102174 6 The equipment used to test the catalysts briefly consists of a gas feed, liquid feed, preheater, vapouriser, reactor and liquid product collection vessel. 5 mL of each catalyst sample was charged to the reactor unit of the catalyst screening equipment. The units were leak tested using N2, then activated using a blend of 1% H2 in N2 (10 L / Hr) ramping temperatures from ambient to 170°C over 4 hours. The catalysts were tested at the following conditions: Reactor temperature, 190-220 °C; Preheater temperature, 190-220 °C; Reactor pressure, 290-809 psig; LHSV (based on ester only), 0.34-0.50 h-1; H2:Ester mol ratio, 350:1 Feed, 15wt% dialkyl succinate in methanol Test work was performed until 3 stable data points were obtained for each of the operating conditions. The product from the testing rig was analysed 4 hourly, with the product stream being analysed by Karl Fisher coulometric titration and gas chromatography (DB-160m x 0.32mm x 5.00µm column). Comparative Example – Cu and MnO2 catalyst (C1) 15.9 g of manganese nitrate hexahydrate was dissolved in demineralised water to a volume of 40 ml. This was used to impregnate 50 g of the γ-Al2O3support EXTRAL 25 to 100 % incipient wetness before undergoing drying at 120°C and calcination at 400°C. A copper solution was prepared by dissolving 259 g of basic copper carbonate and 211 g of ammonium carbonate in 800 mL of ammonium hydroxide.20 ml of this solution was mixed with 7 ml of demineralised water and used to impregnate 35 g of the manganese impregnated alumina to 100 % incipient wetness. The impregnated material was dried at 120°C and calcined at 300°C to afford a catalyst containing 7.63 wt.% Cu and 4.87 wt.% Mn with the phase of manganese being MnO2 (Pyrolusite, XRD literature reflection PDF 04- 003-1024). Comparative Example – Cu and MnO2catalyst (C2) A catalyst was prepared as per comparative example one using sufficient manganese nitrate hexahydrate and copper carbonate to afford a catalyst with 13.42 wt.% Cu and 2.79 P102174 7 wt.% Mn with the phase of manganese being MnO2 (Pyrolusite, XRD literature reflection PDF 04-003-1024). Example 1 – Cu and Mn3O4 on alumina (E1) 155.8 g of manganese nitrate hexahydrate was dissolved in demineralised water to a volume of 201 ml. This was used to impregnate 250 g of the γ-Al2O3 support EXTRAL 25 to 100 % incipient wetness before undergoing drying at 120°C and calcination at 975°C. A copper solution was prepared by dissolving 259 g of basic copper carbonate and 211 g of ammonium carbonate in 800 ml of ammonium hydroxide.23 ml of this solution was used to impregnate 35 g of the manganese impregnated alumina to 100 % incipient wetness. The impregnated material was dried at 120°C before undergoing a subsequent impregnation with 17 ml of the copper solution. This was then dried at 120°C and calcined at 300°C to afford a catalyst containing 13.82 wt.% Cu and 8.24 wt.% Mn with the phase of manganese being Mn3O4 (Hausmannite, XRD literature reflection PDF 04-007-9639). Example 2 – Cu and Mn3O4 on alumina (E2) A catalyst was prepared as per example one using sufficient manganese nitrate hexahydrate and copper carbonate to afford a catalyst with 12.95 wt.% Cu and 5.48 wt.% Mn with the phase of manganese being Mn3O4 (Hausmannite, XRD literature reflection PDF 04-007-9639). Example 3 – Cu and Mn3O4 on alumina (E3) A catalyst was prepared as per example one using sufficient manganese nitrate hexahydrate and copper carbonate to afford a catalyst with 11.8 wt.% Cu and 8.58 wt.% Mn with the phase of manganese being Mn3O4(Hausmannite, XRD literature reflection PDF 04-007-9639). C1 C2 E1 E2 E3Support Al2O3 Al2O3 Al2O3 Al2O3 Al2O3 Cu (wt%) 7.63 13.42 13.82 12.95 11.8 P102174 8 Mn (wt%) 4.87 2.79 8.24 5.48 8.58 DMS conversion* 97.9 98.2 94.5 94.0 90.9 (mol%) 1,4-butanediol 38.2 51.3 71.9 70.8 70.1 selectivity (%) THF: 37.2 THF: 21.5 THF: 2.3 THF: 2.1 THF: 2.2 GBL: 10.9 GBL: 15.6 GBL: 20.7 GBL: 22.8 GBL: 23.3 By-products* BuOH: 0.7 BuOH: 1.0 BuOH: 0.6 BuOH: 0.6 BuOH: 0.6 (product selectivity, %) Water: 10.5 Water: 6.7 Water: 2.3 Water: 2.3 Water: 2.5 Other (sum): Other (sum): Other (sum): Other (sum): Other (sum): 2.6 3.9 2.2 1.4 1.4 *Data from operation conditions of 190°C, 809 psig, LHSV 0.34h-1It can be seen that the overall by-product make is lower for E1-3 than C1-2. Figure 1 shows THF production as a function of DMS conversion for a range of Mn3O4containing catalysts according to the invention and comparative MnO2containing catalysts. The THF production is consistently lower across all DMS conversions, and particularly at conversions above about 90 mol%. Figure 2 shows by-product make for 3 Mn3O4 containing catalysts according to the invention and 2 comparative MnO2 containing catalysts. While GBL make is higher for the catalysts according to the invention, the THF make is substantially lower, as is the make of other by- products. Overall, therefore, the catalysts according to the invention produce fewer by- products than the comparative catalysts. While not wishing to be bound by theory, the applicant believes that the improved by-product performance is due to the significant reduction in acid sites and significant increase in basic sites in the Mn3O4 containing catalysts according to the invention compared to the previous MnO2 containing catalysts. Mn3O4 is advantageously also more thermally stable that MnO2. P102174 9 Mn phase Melting point Tamman Huttig (°C) temperature (°C) temperature (°C) MnO2 535 268 161 Mn3O4 1567 784 470 Catalysts comprising Mn3O4according to the invention may therefore be particularly suitable for use in guard beds where temperatures may be higher.

Claims

P102174 10 Claims 1. A process for the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4- butanediol, comprising the step of carrying out hydrogenolysis of the dialkyl maleate or dialkyl succinate in the presence of a heterogeneous catalyst, wherein the catalyst in its oxidic form comprises: 5-50 wt% CuO; and 0.5-20 wt% Mn3O4; on an alumina support.

2. A process according to claim 1 wherein the total content of elements other than Cu, Mn, Al and O is ≤ 1 wt%.

3. A process according to claim 1 or claim 2, wherein the alumina support is α-alumina, γ- alumina, δ-alumina or θ-alumina or a mixture thereof.

4. A process according to any of claims 1 to 3, wherein the alumina is Al2O4.

5. A process according to any of claims 1 to 4, wherein the alumina support is in the form of granules, spheres or multi-lobe shapes.

6. A process according to any of claims 1 to 5, wherein the alumina support is in the form of trilobes.

7. A process according to any of claims 1 to 6, wherein the dialkyl maleate or dialkyl succinate is dimethyl maleate or dimethyl succinate.

8. A process according to any of claims 1 to 7 wherein the conversion of dialkyl maleate of dialkyl succinate is greater than 90 mol%.

9. A process according to any of claims 1 to 8, wherein the heterogeneous catalyst is provided in a first catalyst bed upstream of a second catalyst bed.

10. A process according to claim 9, wherein the second catalyst bed also comprises the heterogeneous catalyst.

11. A process according to claim 10, wherein the second catalyst bed comprises a second heterogeneous catalyst, different to the heterogenous catalyst.P102174 11 12. A catalyst for the hydrogenolysis of a dialkyl maleate or dialkyl succinate to 1,4- butanediol, wherein the catalyst in its oxidic form comprises: 5-50 wt% CuO; and 0.5-20 wt% Mn3O4; on an alumina support.

13. A catalyst according to claim 12 wherein the total content of elements other than Cu, Mn, Al and O is ≤ 1 wt%.

14. A catalyst according to claim 12 or claim 13, wherein the alumina support is α-alumina, γ-alumina, δ-alumina or θ-alumina or a mixture thereof.

15. A catalyst according to any of claims 12 to 14, wherein the alumina is Al2O4.

16. A catalyst according to any of claims 12 to 15, wherein the alumina support is in the form of granules, spheres or multi-lobe shapes.

17. A catalyst according to any of claims 12 to 15, wherein the alumina support is in the form of trilobes.

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