Catalyst, preparation method and application thereof

Abstract

The present invention belongs to the fields of catalysts and petrochemicals, and specifically relates to a catalyst, its preparation method, and its application. The catalyst comprises a composite support and an active metal Ni supported on the composite support. The composite support is composed of a modifier and a natural mineral compound, wherein the modifier comprises zirconium and a rare earth metal. The natural mineral is selected from one or more of diatomaceous earth, sepiolite, halloysite, attapulgite, vermiculite, and molybdenite. The rare earth metal is selected from one or more of yttrium, lanthanum, cerium, neodymium, samarium, europium, gadolinium, and ytterbium. The catalyst of the present invention has good structural stability and exhibits high activity and selectivity in the catalytic production of DMS. The catalyst of the present invention exhibits excellent performance in the hydrogenation of DMM to produce DMS, effectively improving DMS selectivity and reducing the production of GBL, BDO, and THF.

Description

Technical Field

[0001] The present invention belongs to the field of catalysts and petrochemical industry, and in particular relates to a catalyst and a preparation method and application thereof. Background Art

[0002] Currently, the main production method for polybutylene succinate (PBS) is the direct esterification polymerization of succinic acid or succinic anhydride with 1,4-butanediol (BDO). However, the PBS synthesized by this method has a low molecular weight, and its color value, mechanical properties, and processing performance all fail to meet the expected requirements, limiting the promotion and application of PBS. According to a report in the second issue of Volume 36 of Polyester Industry, PBS produced by transesterification polymerization of dimethyl succinate (DMS) with BDO is more likely to produce a high-molecular-weight product, and its physical properties such as terminal carboxyl groups, melt index, and antioxidant properties are more in line with the requirements of downstream products. Therefore, the development of a low-cost, high-quality polymerization-grade DMS production process has broad application prospects and economic benefits.

[0003] Traditional DMS production processes primarily include succinate esterification, catalytic hydrogenation, and electrochemical catalytic conversion. Because succinate esterification and electrochemical catalytic conversion typically utilize highly corrosive catalysts such as concentrated sulfuric acid, acidic resins, or p-toluenesulfonic acid, and because they are slow and produce numerous byproducts, they lack the foundation for large-scale industrial production and have largely been phased out. Currently, the catalytic hydrogenation process holds the greatest promise for industrial application. This process typically uses maleic anhydride as a raw material, initially undergoing an esterification reaction to produce dimethyl maleate (DMM). DMM is then hydrogenated to produce DMS, which is then further processed through light and heavy removal to yield DMS. The key to this process lies in the post-esterification hydrogenation reaction. Since DMS, BDO, tetrahydrofuran (THF), and γ-butyrolactone (GBL) can be converted into each other through reactions such as hydrogenation, hydrogenolysis, or dehydration, and DMS, often a reaction intermediate, is readily and rapidly converted to BDO, GBL, or THF, achieving high yields of DMS is difficult and the conditions for its isolation are limited. Although numerous literature reports describe methods for producing various chemicals via esterification and hydrogenation using maleic anhydride as a raw material, most products are mixtures of BDO, DMS, THF, and GBL. Patent application CN104822650A discloses a method for producing DMS using maleic anhydride and an alkanol over a Pd catalyst. However, the DMS content in the reactants produced by this method is low, at only 30%-55%, making distillation separation difficult. Patent application CN102070448A discloses a method for producing DMS using maleic anhydride as a raw material through a two-step esterification and hydrogenation process over a precious metal catalyst. Only a few publications report on the hydrogenation of DMM. Patent applications CN117380185A and CN103657693A primarily utilize precious metal catalysts such as Pd, Pt, or Ru to produce DMS via DMM hydrogenation. However, these methods are not only costly but also suffer from low conversion rates, numerous side reactions, and the resulting DMS is difficult to purify and cannot reach polymerization grade. Summary of the Invention

[0004] The purpose of the present invention is to provide a catalyst and a preparation method and application thereof.

[0005] In a first aspect of the present invention, a catalyst is provided, comprising a composite carrier and an active metal Ni loaded on the composite carrier, wherein the composite carrier is composed of a modifier and a natural mineral, and the modifier comprises zirconium and a rare earth metal; the natural mineral is selected from one or more of diatomaceous earth, sepiolite, halloysite, attapulgite, vermiculite and molybdenite; and the rare earth metal is selected from one or more of yttrium, lanthanum, cerium, neodymium, samarium, europium, gadolinium and ytterbium.

[0006] In one or more embodiments, the catalyst has one or more of the following characteristics:

[0007] The modifier consists of zirconium and rare earth metals;

[0008] In the modifier, the molar ratio of zirconium to rare earth metal is 1:(0.001-0.5);

[0009] The content of zirconium element is 0.01-30wt% of the natural mineral content;

[0010] The specific surface area of the composite carrier is 150-450m 2 / g;

[0011] The total pore volume of the composite carrier is 0.15-1.5m 3 / g;

[0012] The average pore size of the composite carrier is 5-30 nm;

[0013] In the catalyst, the content of the active metal Ni is 1-40 wt %.

[0014] The second aspect of the present invention provides a method for preparing the catalyst according to the first aspect of the present invention, the method comprising the steps of:

[0015] (1) preparing a modifier by subjecting an aqueous solution containing a zirconium salt and a rare earth metal salt to a high-pressure hydrothermal method;

[0016] (2) allowing the modifier and the natural mineral to form a precipitate in a dispersant, collecting the precipitate by filtration, drying, and calcining to obtain a composite carrier;

[0017] (3) impregnating the composite support in an aqueous solution containing nickel salt, filtering out the solution, drying, and calcining to obtain a catalyst precursor;

[0018] (4) subjecting the catalyst precursor to a reduction reaction in a reducing gas to obtain the catalyst.

[0019] In one or more embodiments, step (1) has one or more of the following features:

[0020] The zirconium salt is selected from one or more of zirconium nitrate, zirconium chloride and zirconium alkoxide;

[0021] The rare earth metal salt is selected from one or more of Gd(NO3)3·6H2O, Yb(NO3)3·5H2O, Y(NO3)3·4H2O, La(NO3)3·xH2O, Ce(NO3)3·6H2O, Nd(NO3)3·6H2O, Sm(NO3)3·6H2O, Eu(NO3)3·5H2O and chlorides of rare earth metals;

[0022] In the aqueous solution, the concentration of the zirconium salt is 2-2.5 mol / L;

[0023] In the aqueous solution, the molar ratio of zirconium to rare earth metal is 1:(0.001-0.5);

[0024] The reaction pressure of the high-pressure hydrothermal method is 1.0-3.0 MPa;

[0025] The reaction temperature of the high-pressure hydrothermal method is 110-150°C;

[0026] The reaction time of the high-pressure hydrothermal method is 3-24 hours.

[0027] In one or more embodiments, step (2) has one or more of the following features:

[0028] The amount of the modifier added is such that the content of zirconium in the modifier is 0.01-30 wt % of the content of the natural mineral;

[0029] The conditions for forming the precipitate are: stirring and dispersing the modifier and the natural mineral under heating conditions, and then allowing them to stand under heating conditions until a precipitate is formed;

[0030] The drying temperature is 100-150°C;

[0031] The drying time is 2-48h;

[0032] The calcination temperature is 150-800°C;

[0033] The calcination time is 0.5-12h;

[0034] Before performing step (2), the natural mineral is subjected to heat treatment and / or chemical treatment.

[0035] In one or more embodiments, step (3) has one or more of the following features:

[0036] The nickel salt is selected from one or more of nickel nitrate, nickel chloride and nickel sulfate;

[0037] The aqueous solution containing nickel salt also includes an organic acid;

[0038] In the aqueous solution containing nickel salt, the concentration of nickel salt is 0.01-2.0 g / mL;

[0039] The dipping time is 20-240 min;

[0040] The drying temperature is 80-120°C;

[0041] The drying time is 2-12 hours;

[0042] The calcination temperature is 150-550°C;

[0043] The calcination time is 0.5-50h.

[0044] In one or more embodiments, step (4) has one or more of the following features:

[0045] The reducing gas includes hydrogen and a protective gas, wherein the protective gas is selected from one or more of nitrogen, helium and argon;

[0046] The temperature of the reduction reaction is 130-650°C;

[0047] Heating the reduction reaction system to a set temperature at a heating rate not exceeding 10°C / h;

[0048] After the temperature of the reduction reaction system reaches the set value, it is maintained for 4-48 hours.

[0049] The third aspect of the present invention provides a method for preparing dimethyl succinate, comprising the step (a): hydrogenating dimethyl maleate with hydrogen under the catalytic action of a catalyst to produce crude dimethyl succinate, wherein the catalyst is the catalyst described in the first aspect of the present invention or the catalyst produced by the method described in the second aspect of the present invention.

[0050] In one or more embodiments, the method further comprises step (b): distilling the crude dimethyl succinate to obtain dimethyl succinate.

[0051] In one or more embodiments, step (a) has one or more of the following features:

[0052] The molar ratio of dimethyl maleate to hydrogen is 1:(100-500);

[0053] The reaction pressure is 1.0-10.0 MPaG;

[0054] The reaction temperature is 110-230°C;

[0055] The gas phase space velocity of the reactor is 20000-30000 h -1 ;

[0056] The conversion rate of dimethyl maleate in step (a) is ≥99.9%;

[0057] The selectivity of dimethyl succinate in step (a) is ≥99%;

[0058] In step (a), the content of γ-butyrolactone in the crude dimethyl succinate is ≤5 wt %.

[0059] A fourth aspect of the present invention provides a method for preparing polybutylene succinate, comprising the steps of:

[0060] (A) providing the catalyst described in the first aspect of the present invention, or providing a catalyst prepared by the method described in the second aspect of the present invention;

[0061] (B) preparing dimethyl succinate by hydrogenating dimethyl maleate with hydrogen under the catalytic action of the catalyst;

[0062] (C) polymerizing the dimethyl succinate obtained in step (B) with 1,4-butanediol to obtain polybutylene succinate.

[0063] The present invention has the following beneficial effects:

[0064] (1) The present invention uses a natural mineral with rich pores as the main catalyst carrier. Taking advantage of the large mesoporous volume, large specific surface area, and excellent adsorption properties of the natural mineral, rare earth metals and zirconium are introduced to modify the natural mineral carrier. The catalyst of the present invention is prepared by loading the active metal Ni on the modified natural mineral carrier.

[0065] While ensuring the stability of the catalyst's pore structure, acidic properties, and mechanical strength, the active metal Ni is uniformly dispersed on the support surface. The catalyst of the present invention exhibits excellent structural stability and high activity and selectivity in the catalytic production of DMS. The catalyst of the present invention demonstrates excellent performance in the hydrogenation of DMM to DMS, effectively improving DMS selectivity and reducing the production of GBL, BDO, and THF.

[0066] (2) The process for preparing DMS of the present invention adopts a fixed-bed cold hydrogen cycle, which can effectively eliminate the hot spot temperature occurring in the hydrogenation reaction, accurately control the bed temperature rise, ensure the stability and safety of the reaction, inhibit the occurrence of side reactions, improve the quality and output of the product, and effectively reduce energy consumption, improve production efficiency, and reduce production costs.

[0067] (3) The method for preparing DMS of the present invention can produce a high-purity, polymer-grade DMS product with a purity ≥99.9% and a color ≤10AHPA. Compared with PBS products prepared using conventional commercially available succinic acid and succinic anhydride as raw materials, the PBS product prepared using the DMS product of the present invention has a higher molecular weight, and its physical properties such as terminal carboxyl groups, melt index, and antioxidant properties are more in line with the requirements of downstream products. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1Schematic diagram of the structure of the fixed bed reactor used in Example 1 of the present invention; wherein 1-reactor, 101-hydrogen inlet, 102-reaction raw material inlet, 103-catalyst, 104-multi-point thermometer, 105-reactant outlet. DETAILED DESCRIPTION

[0069] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0070] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0071] Herein, “comprising,” “including,” “containing” and similar terms encompass the meanings of “consisting essentially of” and “consisting of,” for example, when “A comprises B and C” is disclosed herein, “A consists essentially of B and C” and “A consists of B and C” should be deemed to have been disclosed herein.

[0072] Throughout this document, all features, such as values, amounts, contents, and concentrations, specified in numerical ranges or percentage ranges are provided for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to encompass and specifically disclose all possible subranges and individual values within those ranges (including integers and fractions).

[0073] In this document, unless otherwise specified, percentage refers to mass percentage and ratio refers to mass ratio.

[0074] Herein, when describing embodiments or examples, it should be understood that they are not intended to limit the present invention to these embodiments or examples. On the contrary, all alternatives, modifications and equivalents of the methods and materials described herein are encompassed within the scope defined by the claims.

[0075] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0076] Herein, rare earth metals refer to metals such as scandium, yttrium, and lanthanides in Group IIIB of the periodic table, specifically including scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), preferably one or more of yttrium, lanthanum, cerium, neodymium, samarium, europium, gadolinium, and ytterbium.

[0077] The catalyst of the present invention has the general formula Ni x -Zr y R z P and R represent rare earth metals, P represents natural minerals, x represents the mass fraction of Ni in the catalyst, which is x%, and y and z represent the molar ratio of Zr to R, which is y:z. x -Zr y R z In P, x, y, and z do not represent the content relationship between Ni and Zr, nor do they represent the content relationship between Ni and R.

[0078] As used herein, natural minerals typically contain trace amounts of ions or organic impurities, as the materials are natural. To enhance and stabilize the performance of natural minerals, those skilled in the art typically pre-treat the natural minerals before use. The pre-treatment method for natural minerals may be selected from one or more of sintering, acid treatment, and alkaline treatment. Because natural minerals carry relatively low levels of impurities, the mass loss of the pre-treated natural minerals is negligible.

[0079] The present invention adopts a special reactor structure, which can increase the circulating cold hydrogen to a larger flow rate without increasing the pressure difference of the reactor. Therefore, the present invention provides a reactor used in the method for preparing dimethyl succinate of the present invention. The reactor is a fixed bed reactor. Figure 1 As shown, the reactor 1 is composed of two nested inner and outer layers, the catalyst 103 is loaded in the inner cylinder of the reactor, and the outer cylinder is filled with circulating cold hydrogen. The reaction raw materials enter the inner cylinder filled with the catalyst 103 through the reaction raw material inlet 102. The reaction liquid after the reaction is completed is discharged from the reactor 1 through the reactant outlet 105. Hydrogen enters the outer cylinder structure inside the reactor through the hydrogen inlet 101, and further passes through the catalyst to reach the center of the inner cylinder, and then passes through the entire catalyst bed axially. The structure of the reactor of the present invention allows the hydrogen entering the reactor 1 to be transmitted axially, so that the fluid passing area is much larger than the normal radial area, thereby achieving a large circulating cold hydrogen. The reactor can still maintain a low pressure drop. Preferably, a multi-point thermometer 104 is also provided in the reactor of the present invention. One or more multi-point thermometers 104 are arranged in the inner cylinder of the reactor through the catalyst 103.

[0080] Herein, the reactor bed temperature difference refers to the temperature difference between the reactor top temperature and the bottom discharge temperature. Those skilled in the art can measure the reactor bed temperature difference by inserting a multi-point thermometer (T) from the top of the reactor.

[0081] Herein, the reactor bed pressure drop refers to the difference between the reactor top pressure and the reactor bottom pressure. Those skilled in the art can measure the reactor bed pressure drop using a pressure transmitter installed at the reactor top and a pressure transmitter installed at the bottom discharge.

[0082] The catalyst carrier of the present invention is composed of a composite of a modifier (including zirconium and a rare earth metal) and a natural mineral. When used in the hydrogenation of dimethyl maleate to produce dimethyl succinate, it can produce dimethyl succinate with high yield (high DMS conversion) and high purity (high DMS selectivity). Therefore, the present invention provides a catalyst for catalyzing the reaction of dimethyl maleate with hydrogen to produce dimethyl succinate.

[0083] The catalyst of the present invention includes a composite carrier and active metal Ni loaded on the composite carrier. The composite carrier is composed of a modifier and natural minerals, and the modifier includes zirconium and rare earth metals. The natural minerals are selected from one or more of diatomaceous earth, sepiolite, halloysite, attapulgite, vermiculite and molybdenite. The rare earth metal is selected from one or more of yttrium, lanthanum, cerium, neodymium, samarium, europium, gadolinium and ytterbium.

[0084] In some embodiments, the natural mineral is selected from one or more of diatomaceous earth, sepiolite, halloysite, attapulgite, vermiculite, and molybdenite. Preferably, the natural mineral is selected from one or more of diatomaceous earth and sepiolite. Using the natural mineral of the present invention as a component of the composite support can impart high activity and selectivity to the resulting catalyst in the reaction for catalyzing the production of DMS. This catalyst exhibits excellent performance in the hydrogenation of DMM to produce DMS, effectively improving DMS selectivity and reducing the production of GBL, BDO, and THF.

[0085] In some embodiments, the rare earth metal is selected from one or more of yttrium, lanthanum, cerium, neodymium, samarium, europium, gadolinium, and ytterbium. Preferably, the rare earth metal is selected from one or more of yttrium, lanthanum, and cerium. Modifying natural minerals with a modifier comprising the rare earth metal of the present invention to produce a composite support can result in a catalyst having high activity and selectivity in the catalytic production of DMS. This catalyst exhibits excellent performance in the hydrogenation of DMM to produce DMS, effectively improving DMS selectivity and reducing the production of GBL, BDO, and THF.

[0086] In some embodiments, the modifier comprises zirconium and a rare earth metal. Using the modifier of the present invention to modify natural minerals to produce a composite support can result in a catalyst with high activity and selectivity in the catalytic production of DMS. This catalyst exhibits excellent performance in the hydrogenation of DMM to produce DMS, effectively increasing DMS selectivity and reducing the production of GBL, BDO, and THF.

[0087] In some embodiments, the molar ratio of zirconium to rare earth metal in the modifier is 1:(0.001-0.5), such as 1:0.005, 1:0.008, 1:0.01, 1:0.02, 1:0.05, 1:0.08, 1:0.1, 1:0.2, 1:03, or 1:0.5, preferably 1:(0.001-0.1), 1:(0.001-0.01), or 1:(0.01-0.1). Controlling the molar ratio of zirconium to rare earth metal in the modifier within the range defined herein can result in a catalyst having high activity and selectivity in the reaction for catalyzing the preparation of DMS. The catalyst exhibits excellent performance in the reaction of hydrogenating DMM to prepare DMS, effectively improving DMS selectivity and reducing the production of GBL, BDO, and THF.

[0088] In some embodiments, the zirconium content is 0.01-30 wt % of the natural mineral content, for example, 0.05 wt %, 0.1 wt %, 0.2 wt %, 0.5 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 7 wt %, 9 wt %, 11 wt %, 13 wt %, 15 wt %, or 17 wt %, and preferably 0.5-20 wt %, 1-5 wt %, 5-10 wt %, or 5-20 wt %. Controlling the zirconium content within the range defined in the present invention can result in a catalyst having high activity and selectivity in the reaction of catalyzing the preparation of DMS. The catalyst exhibits excellent performance in the reaction of hydrogenating DMM to prepare DMS, effectively improving DMS selectivity and reducing the production of GBL, BDO, and THF.

[0089] In some embodiments, the active metal Ni content in the catalyst is 1-40 wt%, for example, 2 wt%, 5 wt%, 8 wt%, 10 wt%, 13 wt%, 15 wt%, 18 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%, and preferably 5-25 wt%, 10-20 wt%, or 5-10 wt%. Controlling the Ni content in the catalyst within the range defined in the present invention can make the resulting catalyst highly active and highly selective in the reaction of catalyzing the preparation of DMS. The catalyst exhibits excellent performance in the reaction of hydrogenating DMM to prepare DMS, effectively improving the selectivity of DMS and reducing the production of GBL, BDO, and THF.

[0090] The present invention also provides a composite support comprising a modifier and a natural mineral. The modifier and natural mineral are as described in any embodiment herein. A catalyst prepared using this composite support exhibits good structural stability and high activity and selectivity in the reaction for catalyzing the production of DMS. The catalyst prepared using this composite support exhibits excellent performance in the reaction of hydrogenating DMM to produce DMS, effectively improving DMS selectivity and reducing the production of GBL, BDO, and THF.

[0091] The present invention also provides a method for preparing a composite carrier, the method comprising the steps of:

[0092] (1) preparing a modifier by subjecting an aqueous solution containing a zirconium salt and a rare earth metal salt to a high-pressure hydrothermal method;

[0093] (2) allowing the modifier and the natural mineral to form a precipitate in a dispersant, collecting the precipitate by filtration, drying, and calcining to obtain a composite carrier;

[0094] Step (1) and step (2) are as described in any embodiment of the present invention.

[0095] In some embodiments, the specific surface area of the composite carrier is 150-450 m 2 / g, for example, 155 m 2 / g, 160m 2 / g, 165 m 2 / g, 170 m 2 / g, 175 m 2 / g, 177 m 2 / g, 180 m 2 / g, 185 m 2 / g, 187 m 2 / g, 188 m 2 / g, 200m 2 / g, 220 m2 / g, 250 m 2 / g, 280 m 2 / g, 320 m 2 / g, 350 m 2 / g, 400 m 2 / g, preferably 150-250 m 2 / g, 170-190 m 2 / g, 177-188 m 2 / g. The use of a composite support having a specific surface area defined herein to prepare the catalyst of the present invention can result in the catalyst having high activity and selectivity in the catalytic production of DMS. The catalyst exhibits excellent performance in the hydrogenation of DMM to DMS, effectively improving DMS selectivity and reducing the production of GBL, BDO, and THF.

[0096] In some embodiments, the total pore volume of the composite support is 0.15-1.5 m 3 / g, for example 0.2 m 3 / g, 0.25 m 3 / g, 0.3 m 3 / g, 0.35 m 3 / g, 0.38 m 3 / g, 0.4 m 3 / g, 0.45 m 3 / g, 0.5 m 3 / g, 0.6 m 3 / g, 0.7m 3 / g, 0.8 m 3 / g, 1.0 m 3 / g, 1.3 m 3 / g, preferably 0.3-1.0 m 3 / g, 0.35-0.5 m 3 / g. The use of a composite support having a total pore volume defined herein to prepare the catalyst of the present invention can result in the catalyst having high activity and selectivity in the catalytic production of DMS. The catalyst exhibits excellent performance in the hydrogenation of DMM to DMS, effectively improving DMS selectivity and reducing the production of GBL, BDO, and THF.

[0097] In some embodiments, the composite support has an average pore size of 5-30 nm, for example, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 22 nm, 25 nm, or 28 nm, preferably 8-20 nm, 10-12 nm, or 10-15 nm. The use of a composite support having an average pore size as defined herein to prepare the catalyst of the present invention can result in the catalyst having high activity and selectivity in the catalytic production of DMS. The catalyst exhibits excellent performance in the hydrogenation of DMM to produce DMS, effectively improving DMS selectivity and reducing the production of GBL, BDO, and THF.

[0098] The inventors discovered that natural minerals modified with rare earth metals and zirconium can achieve a suitable specific surface area and pore structure. Using this modified natural mineral as a composite support and loading it with active metal Ni, the resulting catalyst exhibits excellent performance in the hydrogenation of DMM to DMS, demonstrating high catalytic activity and selectivity. This effectively improves DMS selectivity and reduces the production of GBL, BDO, and THF.

[0099] The present invention provides a method for preparing the catalyst of the present invention, the method comprising the steps of:

[0100] (1) preparing a modifier by subjecting an aqueous solution containing a zirconium salt and a rare earth metal salt to a high-pressure hydrothermal method;

[0101] (2) allowing the modifier and the natural mineral to form a precipitate in a dispersant, collecting the precipitate by filtration, drying, and calcining to obtain a composite carrier;

[0102] (3) impregnating the composite support in an aqueous solution containing nickel salt, filtering out the solution, drying, and calcining to obtain a catalyst precursor;

[0103] (4) subjecting the catalyst precursor to a reduction reaction in a reducing gas to obtain the catalyst.

[0104] In some embodiments, in step (1), the zirconium salt is selected from one or more of zirconium nitrates, zirconium chlorides, and zirconium alkoxides. Preferably, the zirconium salt is selected from one or more of ZrOCl2, ZrO(NO3)2, and ZrCl4, such as ZrO(NO3)2.

[0105] In some embodiments, in step (1), the rare earth metal salt is selected from one or more of Gd(NO3)3·6H2O, Yb(NO3)3·5H2O, Y(NO3)3·4H2O, La(NO3)3·6H2O, Ce(NO3)3·6H2O, Nd(NO3)3·6H2O, Sm(NO3)3·6H2O, Eu(NO3)3·5H2O and chloride salts of rare earth metals. Preferably, the rare earth metal salt is selected from one or more of Ce(NO3)3·6H2O, La(NO3)3·6H2O and Y(NO3)3·4H2O.

[0106] The catalyst of the present invention is prepared using the zirconium salt and rare earth metal salt of the present invention, and the prepared catalyst has high activity and high selectivity in the reaction of catalyzing the preparation of DMS. The catalyst exhibits excellent performance in the reaction of hydrogenating DMM to prepare DMS, and can effectively improve the selectivity of DMS and reduce the production of GBL, BDO and THF.

[0107] In some embodiments, in step (1), the concentration of the zirconium salt in the aqueous solution is 2-2.5 mol / L, for example, 2 mol / L, 2.2 mol / L, 2.3 mol / L, 2.5 mol / L.

[0108] In some embodiments, in step (1), the molar ratio of zirconium to rare earth metal in the aqueous solution is 1:(0.001-0.5), for example, 1:0.005, 1:0.008, 1:0.01, 1:0.02, 1:0.05, 1:0.08, 1:0.1, 1:0.2, 1:03, 1:0.5, preferably 1:(0.001-0.1), 1:(0.001-0.01) or 1:(0.01-0.1).

[0109] In some embodiments, in step (1), the reaction pressure of the high-pressure hydrothermal method is 1.0-3.0 MPa, for example, 1.0 MPa, 1.5 MPa, 2.0 MPa, 2.5 MPa, 3.0 MPa, preferably 2.0-3.0 MPa.

[0110] In some embodiments, in step (1), the reaction temperature of the high pressure hydrothermal method is 110-150°C, for example, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, preferably 120-130°C.

[0111] In some embodiments, in step (1), the reaction time of the high-pressure hydrothermal method is 3-24 h, for example, 3 h, 5 h, 6 h, 8 h, 10 h, 15 h, 18 h, 20 h, preferably 6-18 h.

[0112] In step (1), a modifier is prepared using the concentration of zirconium salt in the aqueous solution, the molar ratio of zirconium to rare earth metal in the aqueous solution, the reaction pressure of the high-pressure hydrothermal method, the reaction temperature of the high-pressure hydrothermal method, and the reaction time of the high-pressure hydrothermal method defined in the present invention. The prepared modifier is compounded with natural minerals to obtain a composite support suitable for the catalyst of the present invention. The use of the composite support to prepare the catalyst of the present invention can make the prepared catalyst have high activity and high selectivity in the reaction of catalyzing the preparation of DMS; the catalyst exhibits excellent performance in the reaction of DMM hydrogenation to prepare DMS, can effectively improve the selectivity of DMS, and reduce the formation of GBL, BDO and THF.

[0113] In some embodiments, in step (2), the amount of the modifier added is such that the content of zirconium in the modifier is 0.01-30 wt% of the content of the natural mineral, for example, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 7 wt%, 9 wt%, 11 wt%, 13 wt%, 15 wt%, 17 wt%, preferably 0.5-20 wt%, 1-5 wt%, 5-10 wt%, 5-20 wt%.

[0114] In some embodiments, in step (2), the dispersant is selected from one or more of methanol, ethanol, and water. In some embodiments, the dispersant is a mixture of ethanol and water; preferably, the volume ratio of ethanol to water is (0.1-10):1, for example, 0.1:1, 0.2:1, 0.5:1, 1:1, 3:1, 5:1, 8:1, 10:1.

[0115] In some embodiments, in step (2), 100-500 g of natural minerals are added per liter of dispersant, for example, 100 g, 150 g, 200 g, 250 g, 300 g, 330 g, 350 g, 380 g, 400 g, 450 g, preferably 300-400 g, 330-350 g.

[0116] In step (2), the conditions for forming a precipitate are: stirring and dispersing the modifier and the natural mineral under heating conditions, and then allowing to stand under heating conditions until a precipitate is formed. In some embodiments, the stirring and standing are each independently performed at 50-90°C, preferably at 50-80°C, 60-80°C, or 80-90°C. Preferably, stirring is performed for 2-12 hours, for example, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, or 12 hours. Preferably, standing is performed for 4-48 hours, for example, 8 hours, 12 hours, 18 hours, 24 hours, 30 hours, 35 hours, or 40 hours.

[0117] In some embodiments, the drying temperature is 100-150°C, such as 110°C, 120°C, 130°C, 140°C, 150°C, preferably 100-120°C, 120-130°C, 120-150°C.

[0118] In some embodiments, the drying time is 2-48 h, such as 4 h, 8 h, 12 h, 15 h, 18 h, 24 h, 30 h, 36 h, 42 h, preferably 5-12 h, 2-8 h or 8-24 h.

[0119] In some embodiments, the calcination temperature is 150-800°C, for example, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, preferably 200-650°C, 200-450°C, 450-800°C.

[0120] In some embodiments, the calcination time is 0.5-12 h, such as 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, preferably 1-8 h, 2-4 h, 4-12 h.

[0121] Before performing step (2), the natural mineral is subjected to heat treatment and / or chemical treatment.

[0122] The heat treatment temperature is 300-800° C., preferably 500-600° C. The heat treatment time is 0.5-5 hours, preferably 2-4 hours. The heat treatment is performed in an air environment.

[0123] The chemical treatment is to soak the natural mineral in an acid solution. The acid can be selected from one or more of sulfuric acid, hydrochloric acid and phosphoric acid; preferably sulfuric acid. The concentration of hydrogen ions in the acid solution is 0.1-0.8 mol / L, for example, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L. In some embodiments, the acid solution is an aqueous acid solution. In some embodiments, the content of natural minerals is 1-80 wt%, preferably 1-60 wt%, 30-60 wt%, based on the total mass of the natural minerals and the acid solution. The chemical treatment can be carried out at 30-150°C, preferably 50-120°C. The chemical treatment is carried out for 0.5-24 h, preferably 1-16 h, 5-8 h. Preferably, the natural minerals after chemical treatment are washed to a pH of 6-7. Preferably, the natural minerals after chemical treatment and washing are dried.

[0124] In some embodiments, before performing step (2), the natural mineral is subjected to the above-mentioned heat treatment and chemical treatment in sequence.

[0125] In step (2), the amount of modifier added, the type of dispersant, the amount of natural mineral added, the conditions for forming a precipitate, the drying temperature, the drying time, the calcination temperature, the calcination time, and the heat treatment and / or chemical treatment method of the natural mineral defined in the present invention are used to prepare a composite support. The use of the composite support to prepare the catalyst of the present invention can make the prepared catalyst have high activity and high selectivity in the reaction of catalyzing the preparation of DMS; the catalyst exhibits excellent performance in the reaction of hydrogenating DMM to prepare DMS, can effectively improve the selectivity of DMS, and reduce the production of GBL, BDO and THF.

[0126] In some embodiments, in step (3), the nickel salt is selected from one or more of nickel nitrate, nickel chloride and nickel sulfate, preferably nickel nitrate.

[0127] In some embodiments, in step (3), the aqueous solution containing the nickel salt further comprises an organic acid. The organic acid may be selected from one or more of formic acid, acetic acid, oxalic acid, and citric acid, preferably citric acid. Preferably, the aqueous solution containing the nickel salt contains 0.9-35 vol% of the organic acid, for example, 1 vol%, 2 vol%, 3 vol%, 5 vol%, 7 vol%, 9 vol%, 11 vol%, 15 vol%, 20 vol%, 25 vol%, 30 vol%, preferably 5-20 vol%, 5-10 vol%.

[0128] In some embodiments, the concentration of nickel salt in the aqueous solution containing nickel salt is 0.01-2.0 g / mL, for example, 0.05 g / mL, 0.08 g / mL, 0.1 g / mL, 0.3 g / mL, 0.5 g / mL, 0.8 g / mL, 0.9 g / mL, 1.0 g / mL, 1.3 g / mL, 1.5 g / mL, 1.8 g / mL, preferably 0.5-0.9 g / mL, 0.8-0.9 g / mL.

[0129] In some embodiments, the immersion time is 20-240 min, for example, 20 min, 30 min, 50 min, 80 min, 100 min, 120 min, 150 min, 180 min, 210 min, 230 min, preferably 20-120 min, 50-120 min, 80-120 min.

[0130] In step (3), parameters such as the volume of the solvent used in the impregnation, the content of the nickel salt in the solvent, the content of the organic acid in the impregnation solution, and the amount of the composite support can be adjusted according to the Ni content in the catalyst to be prepared. Those skilled in the art can reasonably design the above parameters based on the mass fraction of Ni in the catalyst to be prepared.

[0131] In some embodiments, the drying temperature is 80-120°C, such as 80°C, 90°C, 100°C, 110°C, 120°C, preferably 100-120°C.

[0132] In some embodiments, the drying time is 2-12 h, for example, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, preferably 4-12 h, 4-8 h.

[0133] In some embodiments, the calcination temperature is 150-550°C, for example, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, preferably 170-550°C, 300-550°C, 500-550°C.

[0134] In some embodiments, the calcination time is 0.5-50 h, for example, 1 h, 2 h, 4 h, 8 h, 12 h, 15 h, 20 h, 24 h, 36 h, 48 h, preferably 1-24 h, 8-24 h, 2-8 h.

[0135] In step (3), a catalyst precursor is prepared using the nickel salt, aqueous solution containing the nickel salt, impregnation time, drying temperature, drying time, calcination temperature, and calcination time defined in the present invention. The catalyst precursor is further reduced to obtain a catalyst of the present invention having high activity and high selectivity in the reaction of catalyzing the preparation of DMS. The catalyst exhibits excellent performance in the reaction of hydrogenating DMM to prepare DMS, can effectively improve the selectivity of DMS, and reduce the production of GBL, BDO, and THF.

[0136] In some embodiments, in step (4), the reducing gas comprises hydrogen and a protective gas. The protective gas is selected from one or more of nitrogen, helium, and argon, preferably nitrogen. In the reducing gas, the molar ratio of the protective gas to hydrogen is 1:(0.01-1), for example, 1:0.01, 1:0.02, 1:0.05, 1:0.08, 1:0.1, 1:0.2, 1:0.3, 1:0.5, 1:0.8, 1:0.9, preferably 1:(0.01-0.1), 1:(0.05-1), or 1:(0.05-0.1).

[0137] In some embodiments, the temperature of the reduction reaction is 130-650°C, for example, 150°C, 200°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C.

[0138] In some embodiments, the reduction reaction system is heated to a set temperature at a heating rate not exceeding 10° C. / h.

[0139] In some embodiments, after the temperature of the reduction reaction system reaches the set value, it is maintained for 4-48 hours, for example, 4 hours, 8 hours, 12 hours, 18 hours, 24 hours, 30 hours, 36 hours, 42 hours, preferably 6-24 hours, 12-30 hours.

[0140] The inventors have found that the catalyst prepared using the method of the present invention exhibits excellent performance in the reaction of DMM hydrogenation to produce DMS, has high catalytic activity and high selectivity, can effectively improve the selectivity of DMS, and reduce the production of GBL, BDO and THF.

[0141] The catalyst of the present invention is prepared using the type of reducing gas, reduction reaction temperature, reduction reaction heating rate, and reduction reaction time defined in the present invention. The prepared catalyst has high activity and high selectivity in the reaction of catalyzing the preparation of DMS. The catalyst exhibits excellent performance in the reaction of hydrogenating DMM to prepare DMS, can effectively improve the selectivity of DMS, and can reduce the production of GBL, BDO, and THF.

[0142] In some embodiments, the catalyst is stored isolated from air under the protection of a protective gas (eg, one or both of nitrogen and argon) or a liquid seal (eg, one or both of water and ethanol).

[0143] The present invention provides a method for preparing dimethyl succinate, which comprises the step (a): under the catalytic action of a catalyst, hydrogenating dimethyl maleate with hydrogen to obtain a crude dimethyl succinate product, wherein the catalyst is the catalyst of the present invention or a catalyst prepared by the method of the present invention.

[0144] In some embodiments, the method further comprises step (b): distilling the crude dimethyl succinate to obtain dimethyl succinate.

[0145] In the present invention, the use Figure 1 The reactor shown for preparing dimethyl succinate can control the reactor bed temperature difference and pressure drop during the reaction. The method of the present invention controls the bed temperature rise by circulating a large flow of cold hydrogen, eliminating hot spots in the catalyst bed, suppressing side reactions, and effectively improving the selectivity and conversion rate of dimethyl succinate.

[0146] In some embodiments, the reactor bed temperature difference (∆t) can be controlled to be ≤1°C, and the lowest can be ≤0.1°C.

[0147] In some embodiments, the reactor bed pressure drop (∆P) can be controlled to ≤0.2 MPa, and the lowest can be ≤0.1 MPa.

[0148] Using the present invention Figure 1 The reactor shown is used to prepare dimethyl succinate, and controlling the reactor bed temperature difference and the reactor bed pressure drop within the range defined herein can inhibit the occurrence of side reactions and effectively improve the selectivity and conversion rate of dimethyl succinate.

[0149] In step (a), the molar ratio of dimethyl maleate to hydrogen is 1:(100-500), for example, 1:100, 1:150, 1:200, 1:250, 1:300, 1:350, 1:400, 1:450, 1:500, preferably 1:(100-300) or 1:(300-500).

[0150] In step (a), the reaction pressure is 1.0-10.0 MpaG, for example, 1.0 MpaG, 2 MpaG, 3 MpaG, 5 MpaG, 8 MpaG, 9 MpaG, preferably 1-5 MpaG, 3-8 MpaG.

[0151] In step (a), the reaction temperature is 110-230°C, for example, 110°C, 120°C, 130°C, 150°C, 170°C, 190°C, 210°C, 230°C, preferably 125-210°C, 110-190°C, 150-230°C, 190-230°C.

[0152] In step (a), the gas phase space velocity of the reactor is 20000-30000 h -1 , for example 21000 h -1 , 22000 h -1 、23000h -1 , 24000 h -1 , 25000 h -1 , 27000 h -1 , 29000 h -1 .

[0153] The conversion rate of dimethyl maleate in step (a) is ≥99.9%.

[0154] The selectivity of dimethyl succinate in step (a) is ≥99%, for example ≥99.1%, ≥99.2%, ≥99.3%, ≥99.4%, ≥99.5%, ≥99.6%, ≥99.7%, ≥99.8%.

[0155] In step (a), the content of γ-butyrolactone in the crude dimethyl succinate is ≤5 wt %, for example, ≤4 wt %, ≤3 wt %, ≤2 wt %, ≤1 wt %, ≤0.5 wt %, ≤0.1 wt %, ≤0.05 wt %, ≤0.01 wt %, ≤0.005 wt %, ≤0.003 wt %, ≤0.002 wt %, ≤0.001 wt %.

[0156] In step (a), dimethyl succinate is prepared using the molar ratio of dimethyl maleate to hydrogen, reaction pressure, reaction temperature, and reactor gas phase space velocity conditions defined herein, which can effectively improve the conversion rate of dimethyl maleate and the selectivity of dimethyl succinate, and control the content of γ-butyrolactone in dimethyl succinate.

[0157] In step (b), the distillation is a three-stage distillation. The three-stage distillation includes a first-stage distillation. The operating pressure of the first-stage distillation is 5-50 kPaA, preferably 10-30 kPaA, 10-20 kPaA, or 20-30 kPaA. The operating temperature of the first-stage distillation is 130-180°C, for example, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, or 175°C, preferably 145-175°C, 130-170°C, or 140-165°C. The three-stage distillation includes a second-stage distillation. The operating pressure of the second stage distillation is 0.1-10 kPaA, such as 0.2 kPaA, 0.5 kPaA, 1 kPaA, 2 kPaA, 3 kPaA, 4 kPaA, 5 kPaA, 8 kPaA, preferably 0.5-6.5 kPaA, 1-5 kPaA, 1-3 kPaA. The operating temperature of the second stage distillation is 130-200°C, such as 135°C, 140°C, 145°C, 150°C, 155°C, 165°C, 170°C, 172°C, 178°C, 190°C, preferably 135-185°C, 140-180°C, 150-175°C. The three-stage distillation includes a third stage distillation. The operating pressure of the third stage distillation is 1-30 kPaA, such as 2 kPaA, 5 kPaA, 8 kPaA, 10 kPaA, 15 kPaA, 20 kPaA, 25 kPaA, 30 kPaA, preferably 1-20 kPaA. The operating temperature of the third stage distillation is 110-170°C, such as 120°C, 130°C, 135°C, 140°C, 150°C, 160°C, 168°C, 170°C, preferably 125-165°C, 130-170°C, 150-168°C.

[0158] The purity of the dimethyl succinate prepared in step (b) is ≥95wt%, for example, ≥96wt%, ≥97wt%, ≥98wt%, ≥99wt%, ≥99.1wt%, ≥99.2wt%, ≥99.3wt%, ≥99.4wt%, ≥99.5wt%, ≥99.6wt%, ≥99.7wt%, ≥99.8wt%, ≥99.9wt%.

[0159] The color number of the dimethyl succinate prepared in step (b) is ≤10 APHA, for example, 10 APHA, 9 APHA, 8 APHA, 7 APHA, 6 APHA, 5 APHA, 4 APHA, 3 APHA, 2 APHA, 1 APHA, preferably 2-8 APHA, 3-5 APHA.

[0160] In step (b), the crude dimethyl succinate obtained in step (a) is further distilled using the three-stage distillation conditions defined in the present invention to obtain a high-purity, low-color dimethyl succinate product.

[0161] The present invention also provides a method for preparing polybutylene succinate, which comprises the steps of:

[0162] (A) providing the catalyst of the present invention, or providing a catalyst prepared by the method of the present invention;

[0163] (B) preparing dimethyl succinate by hydrogenating dimethyl maleate with hydrogen under the catalytic action of the catalyst;

[0164] (C) polymerizing the dimethyl succinate obtained in step (B) with 1,4-butanediol to obtain polybutylene succinate.

[0165] The catalyst of the present invention, the method for preparing the catalyst of the present invention, and the method for preparing dimethyl succinate by hydrogenating dimethyl maleate are as described in any embodiment herein.

[0166] In some embodiments, in step (C), the molar ratio of dimethyl succinate to 1, 4-butanediol is 1:(1-1.5), for example, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, preferably 1:(1-1.3), 1:(1-1.2).

[0167] Step (C) comprises the steps of:

[0168] (C1) esterifying dimethyl succinate with 1,4-butanediol;

[0169] (C2) subjecting the reaction solution obtained after the reaction in step (C1) to a preliminary polycondensation reaction;

[0170] (C3) subjecting the reaction liquid obtained after the reaction in step (C2) to a final polycondensation reaction.

[0171] In some embodiments, the reaction pressure of the esterification reaction is 5-20 kPaG, for example, 5 kPaG, 8 kPaG, 10 kPaG, 12 kPaG, 15 kPaG, 18 kPaG, 20 kPaG, preferably 5-10 kPaG, 10-20 kPaG, 5-15 kPaG.

[0172] In some embodiments, the reaction temperature of the esterification reaction is 140-200°C, for example, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, preferably 140-160°C, 160-200°C.

[0173] In some embodiments, the reaction time of the esterification reaction is 3-10 h, for example, 3 h, 4 h, 6 h, 8 h, 10 h, preferably 3-6 h, 6-10 h, 3-8 h.

[0174] In some embodiments, the esterification reaction is terminated when the content of dimethyl succinate in the test reaction system drops below 500 ppm.

[0175] In some embodiments, the pre-polycondensation reaction is carried out under the catalysis of a polymerization catalyst. Preferably, the polymerization catalyst is a Ti-containing catalyst, preferably tetraisopropyl titanate (TtiPO, CAS: 546-68-9).

[0176] In some embodiments, the molar ratio of the polymerization catalyst to dimethyl succinate is 1:(300-500), for example, 1:320, 1:340, 1:360, 1:380, 1:400, 1:420, 1:440, 1:480, preferably 1:(400-500) or 1:(300-400).

[0177] In some embodiments, the reaction temperature of the pre-polycondensation reaction is 180-250°C, such as 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, preferably 180-210°C, 210-250°C.

[0178] In some embodiments, the reaction pressure of the pre-polycondensation reaction is 0.5-2 kPaA, such as 0.8 kPaA, 1 kPaA, 1.2 kPaA, 1.4 kPaA, 1.6 kPaA, 1.8 kPaA, preferably 0.5-1 kPaA, 1-2 kPaA.

[0179] In some embodiments, the reaction time of the pre-polycondensation reaction is 2-5 h, for example, 3 h, 4 h.

[0180] In some embodiments, the reaction pressure of the final polycondensation reaction is 50-80 PaA, such as 55 PaA, 60 PaA, 65 PaA, 70 PaA, 75 PaA, preferably 60-80 PaA, 65-80 PaA.

[0181] In some embodiments, the reaction temperature of the final polycondensation reaction is 200-250°C, for example, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, 235°C, 240°C, preferably 225-250°C.

[0182] In some embodiments, the reaction time of the final polycondensation reaction is 1-5 h, for example, 2 h, 3 h, or 4 h.

[0183] In some embodiments, the viscosity of the reaction system of the final polycondensation reaction no longer increases (ie, the viscosity of the reaction system remains stable), and the final polycondensation reaction is completed.

[0184] In some embodiments, before the esterification reaction, dimethyl succinate and 1,4-butanediol are fully dissolved, for example, by heating. The heating can be performed at 100-150° C. for 0.5-5 h.

[0185] The polybutylene succinate prepared by the method of the present invention has a terminal carboxyl group content of 30-80 mol / t, for example, 35 mol / t, 40 mol / t, 45 mol / t, 50 mol / t, 55 mol / t, 60 mol / t, 65 mol / t, 70 mol / t, 75 mol / t, preferably 35-80 mol / t, 40-80 mol / t, 45-80 mol / t, 45-50 mol / t.

[0186] The melt index of the polybutylene succinate prepared by the method of the present invention is 5.0-8.0 g / min, for example, 5.5 g / min, 6.0 g / min, 6.2 g / min, 6.5 g / min, 7.0 g / min, 7.5 g / min, 8.0 g / min, preferably 6.0-8.0 g / min, 6.2-8.0 g / min, 6.2-7.0 g / min.

[0187] The oxidation induction time of the polybutylene succinate prepared by the method of the present invention is 60-150 min, for example, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min, 100 min, 105 min, 110 min, 115 min, 116 min, 120 min, 125 min, 130 min, 135 min, 140 min, 145 min, preferably 65-116 min, 116-150 min, 90-120 min.

[0188] The oxidation induction temperature of the polybutylene succinate prepared by the method of the present invention is 250-350°C, for example, 255°C, 260°C, 265°C, 270°C, 275°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, preferably 280-320°C, 250-300°C, 290-340°C.

[0189] Polybutylene succinate is prepared using the molar ratio of dimethyl succinate to 1, 4-butanediol, esterification reaction conditions, pre-polycondensation reaction conditions, and final polycondensation reaction conditions defined in this article. The physical properties of the prepared polybutylene succinate, such as terminal carboxyl groups, melt index, and antioxidant properties, are more in line with the requirements of downstream products.

[0190] Due to the advanced nature of the catalyst of the present invention and its preparation method and application, the catalyst of the present invention can be widely used in application fields such as petrochemical industry, catalyst research and development, environmental protection and energy conservation.

[0191] In the field of petrochemicals, the present invention provides a novel modified composite-supported Ni-based catalyst for the vapor-phase hydrogenation of dimethyl maleate (DMM) to produce dimethyl succinate (DMS), and also provides a production process for producing DMS using this catalyst. The process for producing DMS using the catalyst of the present invention for vapor-phase hydrogenation of DMM has the advantages of high DMS conversion, high DMS selectivity, and low production cost. It also significantly reduces side reactions and the formation of byproducts during the DMM hydrogenation reaction.

[0192] The present invention provides an optimized hydrogenation reaction process. This process utilizes a reactor with a special structure, which allows for maintaining a low pressure drop in the reactor even at high hydrogen circulation rates and eliminating hotspot temperatures in the catalyst bed. This process offers advantages such as high product purity, low energy consumption, and ease of control. It can significantly increase the yield and quality of DMS, reduce production costs, and promote the rapid development of the biodegradable plastic (PBS) industry.

[0193] In the field of environmental protection and energy conservation, the method of the present invention adopts cold hydrogen circulation to strictly control the temperature rise of the bed, avoids the occurrence of hot spots, improves the safety and stability of the reaction, reduces energy waste, reduces carbon emissions in the production process, and is beneficial to environmental protection and sustainable development.

[0194] In summary, the method for preparing DMS of the present invention has the characteristics of high selectivity and low energy consumption, which is conducive to reducing resource waste, improving resource utilization efficiency, and achieving the goals of environmental protection and energy saving.

[0195] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples, for which specific conditions are not specified, are generally based on conventional conditions or the conditions recommended by the manufacturer. Unless otherwise stated, percentages and parts are calculated by weight.

[0196] In this paper, the specific surface area test method of the composite support is as follows: it is measured by the BET method, using a Japanese Micoratrca BELSORP-mini x specific surface area meter, using the static volume method, and the degassing condition is 300°C for 8 hours. The specific surface area is calculated using the Brunauer–Emmett–Teller (BET) equation.

[0197] In this article, the total pore volume and average pore size of the composite support are calculated using the BJH (Barrett-Joiner-Halenda) model. The average pore size of the composite support is equal to the result of dividing the corresponding pore volume by the corresponding specific surface area. Calculation formula:

[0198] Average pore diameter P aver = k × total pore volume / specific surface area, where k is based on cylindrical pores, k=4.

[0199] Preparation Example 1: Preparation of Catalyst 1

[0200] (1) Preparation of zirconium-rare earth Zr1Ce 0.01 Modifier

[0201] Prepare a certain amount of 2.0 mol / L ZrO(NO3)2 aqueous solution, add Ce(NO3)3·6H2O according to the molar ratio of Zr to Ce in the aqueous solution of 1:0.01, mix well and add it into the high-pressure reactor, increase the pressure to 3.0 MPa, and react at 130℃ for 6 hours to obtain zirconium-rare earth Zr1Ce 0.01 Modifier, reduce to normal pressure and room temperature, and set aside.

[0202] (2) Diatomaceous earth (P) pretreatment

[0203] A certain amount of purchased natural diatomite (Chuanyi diatomite ore, Changbai diatomite vein, Jilin) was weighed and first heat-treated by calcining it at 600°C in air for 2 hours to eliminate the organic matter contained in the natural diatomite ore. The heat-treated diatomite was then ground into a uniform powder. The heat-treated diatomite powder was then chemically treated in sulfuric acid to remove the alkali ions. The ground powder was suspended in dilute sulfuric acid at a concentration of 0.2 mol / L and a solid content of 30 wt%. The suspension was stirred continuously at 50°C for 8 hours. The mixture was then separated by suction and washed with deionized water. The filter cake was dried at 120°C to constant weight and ground into a powder.

[0204] (3) Preparation of composite carrier Zr x R y P

[0205] Weigh 100 g of diatomaceous earth treated in step (2), add 300 mL of a mixed solution of ethanol and water (volume ratio of 5:1), stir until suspended, add the modifier prepared in step (1) according to the zirconium content of 5 wt% (based on the amount of natural diatomaceous earth), stir continuously at 80 ° C for 4 hours, stop stirring and let it stand at 80 ° C for 24 hours until a stable colloidal precipitate is formed, remove the solvent by filtration, and then dry the precipitate at 120 ° C in an air atmosphere for 8 hours. Finally, calcined the carrier sample at 450 ° C for 4 hours to obtain a composite carrier. The specific surface area (BET) of the prepared composite carrier is 180 m 2 / g, and the total pore volume is 0.5cm 3 / g, and the average pore diameter is 12nm.

[0206] (4) Preparation of catalyst precursor

[0207] Active metal Ni was loaded onto the composite support using an impregnation method. First, 54.2 g of Ni(NO₃)₂·6H₂O was weighed and prepared into 200 mL of nickel salt aqueous solution. Citric acid was added to the prepared nickel salt aqueous solution at a volume ratio of nickel salt aqueous solution to citric acid of 1:0.1. The composite support was impregnated with a mixed solution of nickel salt aqueous solution and citric acid. The amount of composite support was selected based on the amount of Ni loaded on the catalyst to be prepared in step (5). The mixture was allowed to stand for 120 minutes, and the excess solution was removed by filtration. After drying at 120°C for 4 hours, the mixture was calcined at 550°C in an air atmosphere for 8 hours to obtain a catalyst precursor.

[0208] (5) Preparation of 10 wt% Ni-loaded catalyst

[0209] The catalyst precursor prepared in step (4) was reduced under reducing gas to obtain a catalyst with metal Ni as the active center. The reducing gas was a mixture of nitrogen and hydrogen with a molar ratio of nitrogen to hydrogen of 1:0.05. The temperature was raised to 350°C by programmed heating at a rate of no more than 10°C / h. After reaching the set temperature, the temperature was maintained for 24 hours and then naturally cooled to room temperature to obtain a catalyst Ni with a Ni content of 10 wt%. 10 -Zr1R 0.01 P, the prepared catalyst is sealed by adding deionized water and stored in an air-tight manner.

[0210] Preparation Example 2: Preparation of Catalyst 2

[0211] The method of Preparation Example 1 was repeated, with the only difference being that purchased sepiolite powder (from Xiangtan Sepiolite Technology Co., Ltd.) was used instead of diatomaceous earth.

[0212] The specific surface area of the prepared composite carrier is 187m 2 / g, and the total pore volume is 0.42cm 3 / g, and the average pore size is 10nm.

[0213] Preparation Example 3: Preparation of Catalyst 3

[0214] The method of Preparation Example 1 was repeated, with the only difference being that Y(NO3)3·4H2O was used instead of Ce(NO3)3·6H2O.

[0215] The specific surface area of the prepared composite carrier is 188m 2 / g, and the total pore volume is 0.40m 3 / g, and the average pore diameter is 12nm.

[0216] Preparation Example 4: Preparation of Catalyst 4

[0217] The method of Preparation Example 1 was repeated, with the only difference being that La(NO3)3·6H2O was used instead of Ce(NO3)3·6H2O.

[0218] The specific surface area of the prepared composite carrier is 177m 2 / g, and the total pore volume is 0.38m 3 / g, and the average pore size is 10nm.

[0219] Preparation Example 5: Preparation of Catalyst D1

[0220] The method of Preparation Example 1 was repeated, except that a commercial activated alumina carrier (Jiulong Chemical, JL-C-02 activated alumina) was used instead of diatomaceous earth. The activated alumina carrier did not contain a modifier. The specific surface area of the activated alumina carrier was 170 m 2 / g, and the total pore volume is 0.6cm 3 / g, and the average pore diameter is 12nm.

[0221] Preparation Example 6: Preparation of Catalyst D2

[0222] The method of Preparation Example 1 was repeated, except that commercial silica (Q-15 series SiO2 carrier from Fuji, Japan) was used instead of diatomaceous earth. The silica carrier did not contain a modifier. The specific surface area of the silica carrier was 200 m 2 / g, and the total pore volume is 1.0 cm 3 / g, and the average pore size is 15nm.

[0223] Example 1

[0224] The method of the present invention is as follows Figure 1 100 kg of catalyst 1 prepared in Preparation Example 1 was weighed and loaded into the fixed bed reactor. The gas phase space velocity of the reactor was set at 20,000 h / min. -1For the calculation, dimethyl maleate (DMM) raw material was purchased from Hengli New Materials Co., Ltd. The feed composition and feed conditions are shown in Table 1. The DMM feed rate was 38 kg / h, with a molar ratio of DMM feed to recycled hydrogen of 1:300. The reaction pressure was 3.0 MPaG, and the reaction temperature was 190°C. The DMM feed was heated to 190°C by a heater and instantly vaporized upon entering the gas-liquid separator. A small amount of unvaporized heavy impurities were separated and discharged. The vaporized DMM and hydrogen mixture was then added to the reactor from the bottom. The reactor bed temperature difference was monitored at the reactor's temperature measuring points. The bed temperature difference, ∆t, of the fixed-bed reactor was maintained at ≤0.1°C, and the bed pressure drop, ∆P, was ≤0.1 MPa.

[0225] Table 1

[0226]

[0227] The reactants are taken out from the top of the reactor, and after heat recovery, the gaseous reactants are condensed into a liquid phase to obtain a crude DMS product, which is subjected to chromatographic analysis. The conversion rate is calculated based on the consumption of DMM, and the selectivity is calculated based on the DMS content in the reaction liquid.

[0228] The crude DMS reaction liquid is fed into the distillation unit for further purification and separation. The first distillation step is used to initially separate the crude DMS, removing light components such as methanol and dimethyl ether. The light components are distilled overhead. The operating pressure is 20 kPaA and the operating temperature is 165°C.

[0229] The second distillation tower is the product tower, which refines the final DMS product after removing light components. The operating pressure is 3 kPaA and the temperature is 172°C. Industrial-grade DMS is produced from the top of the tower, polymerization-grade DMS is produced in the middle, and heavy components are discharged from the bottom of the tower. The purity of polymerization-grade DMS is 99.93%.

[0230] The third distillation tower is a light component tower, which recovers DMS in the light component. The top of the tower is the light component and the bottom of the tower is crude DMS. The operating pressure is 10kPaA and the operating temperature is 168℃.

[0231] Example 2

[0232] The method of Example 1 was repeated, with the only difference being that Catalyst 2 prepared in Preparation Example 2 was used instead of Catalyst 1.

[0233] Example 3

[0234] The method of Example 1 was repeated, except that Catalyst 3 prepared in Preparation Example 3 was used instead of Catalyst 1.

[0235] Example 4

[0236] The method of Example 1 was repeated, with the only difference being that Catalyst 4 prepared in Preparation Example 4 was used instead of Catalyst 1.

[0237] Comparative Example 1

[0238] The method of Example 1 was repeated, except that Catalyst D1 obtained in Preparation Example 5 was used instead of Catalyst 1.

[0239] Comparative Example 2

[0240] The method of Example 1 was repeated, except that Catalyst D2 obtained in Preparation Example 6 was used instead of Catalyst 1.

[0241] Test Example 1

[0242] The crude DMS product produced in the fixed-bed reactor was directly analyzed for composition. The contents of the various components in the crude DMS and the performance of the catalyst are shown in Table 2.

[0243] 1. DMM conversion and DMS purity were measured using an Agilent 7890 chromatograph. The chromatographic analysis method was set as follows:

[0244] Chromatographic column: CP-SIL8CB 50*0.32*1.2;

[0245] Detector temperature: 300°C;

[0246] Inlet temperature: 250°C;

[0247] Split ratio: 25:1;

[0248] Column flow rate: 2.4 mL / min.

[0249] 2. The DMM conversion rate is calculated according to the following formula:

[0250] ,

[0251] X A : conversion calculated based on reactant A;

[0252] A1: starting mass of reactant A;

[0253] A2: the remaining mass of reactant A after reaction;

[0254] Reactant A was DMM.

[0255] 3. Using DMM, the catalyst selectivity is calculated according to the following formula:

[0256] ,

[0257] S: Selective;

[0258] B: the mass of the reaction target product B;

[0259] A1: starting mass of reactant A;

[0260] A2: the remaining mass of reactant A after reaction;

[0261] The target product B is DMS, and the reactant A is DMM.

[0262] Table 2

[0263]

[0264] Test Example 2

[0265] The refined DMS product obtained by three-stage distillation was analyzed for composition and color.

[0266] The content of each component in the product was detected using the same method as in Test Example 1.

[0267] The color number and content of each component of the DMS product obtained after three-stage distillation are shown in Table 3.

[0268] Color number testing is in accordance with GB3143-1982, measured by Lovibond Tintometer PFX190.

[0269] Table 3

[0270]

[0271] “Trace” means the amount is very small, the detection peak is almost invisible, and the content is generally less than 1ppm.

[0272] The above analysis of the hydrogenation reaction results (Table 1) demonstrates that the catalysts of the present invention achieve excellent hydrogenation performance, with superior conversion and selectivity compared to other catalysts. The side reaction of GBL formation is effectively suppressed, facilitating distillation to obtain high-purity DMS. Furthermore, the use of the fixed-bed reactor of the present invention significantly increases the cold hydrogen circulation rate without affecting the reactor pressure drop, thereby eliminating hot spots in the catalyst bed and effectively suppressing the formation of various byproducts. This results in a purity of ≥99.9% for the polymer-grade DMS produced after distillation.

[0273] Application Examples

[0274] The DMS product prepared in Example 1, commercially available succinic acid (Shandong Feiyang Chemical Co., Ltd., meeting the T / HNPCIA13-2019 quality standards), commercially available succinic anhydride (Henan Energy Group Hebi Coal Chemical Co., Ltd., meeting the GB34686-2017 quality standards), the DMS products prepared in Comparative Example 1, and the DMS products prepared in Comparative Example 2 were used as polymerization raw materials in a 200 L batch PBS polymerization test. The specifications of the commercially available succinic acid and succinic anhydride are shown in Tables 4-5.

[0275] Table 4: Commercially available succinic acid specifications

[0276]

[0277] Table 5: Commercially available succinic anhydride specifications

[0278]

[0279] Feeding: Add the above-mentioned polymer raw materials and BDO into the reactor at a molar ratio of 1:1.2 at the same time, stir and mix. If the dissolution is not good, heat at 140°C for 1 hour, and then add the mixed slurry into the reactor for esterification reaction.

[0280] Esterification reaction: The reaction pressure is 10 kPaG and the reaction temperature is 160 ± 2 ° C. The reaction liquid in the reactor is sampled once every 1 hour and the DMS content in the reaction liquid is analyzed. After about 6 hours, the DMS content drops below 500 ppm and remains stable, indicating that the esterification reaction is complete. The reaction liquid is transferred to a pre-polycondensation reactor for pre-polycondensation reaction.

[0281] Pre-polycondensation reaction: Using tetraisopropyl titanate (TtiPO, CAS: 546-68-9) as a catalyst, with a catalyst to polymerization raw material molar ratio of 1:400, the reaction system was heated to 210°C and maintained under a vacuum of 1 kPaA for 3 hours to obtain a pre-polycondensation product. The reaction liquid in the pre-polycondensation reactor was completely transferred to the final polycondensation reactor.

[0282] Final polycondensation reaction: The reaction pressure is 65±2 PaA, the reaction temperature is 225±5°C, and the stirring speed is 210 rpm. The stirring speed is maintained until the stirrer power stops increasing and slightly decreases, marking the end of the final polycondensation. The reaction time is about 3 hours. The stirrer speed is reduced at appropriate times during the reaction to prevent excessive shear heat.

[0283] Pelletizing: The polycondensation product obtained in the final polycondensation step is dried and then pelletized to obtain the finished PBS. When the end point is reached, nitrogen is added and the material is discharged for pelletizing. The granulation process requires that the material be kept clean throughout to avoid external contamination.

[0284] Application test case

[0285] The performance of the PBS prepared according to the corresponding use case was tested using the following method. The test results are shown in Table 4.

[0286] The terminal carboxyl content refers to the content of carboxyl functional groups near the two ends of the PBS molecule, and is mainly used to characterize information such as the average molecular weight. The level of terminal carboxyl content directly affects the thermal stability, degradation rate and color of the product. The terminal carboxyl content is determined by titration analysis-photometry. The sample is refluxed and dissolved in a mixed solvent of o-cresol-CHCl3. After cooling, bromophenol blue is used as an indicator and titrated with a sodium hydroxide-ethanol standard titrant. The terminal carboxyl content of PBS is calculated based on the consumption of the standard titrant. The formula is as follows:

[0287] ,

[0288] Where:

[0289] Indicates the volume of sodium hydroxide-ethanol standard titrant consumed by the sample, mL;

[0290] Indicates the volume of sodium hydroxide-ethanol standard titrant consumed in the blank, mL;

[0291] Indicates the concentration of sodium hydroxide-ethanol standard titrant, mol / L;

[0292] Indicates the sample weight, g.

[0293] The melt index test was performed according to ASTM-D1238 using Ray-Ran MFR300.

[0294] The oxidation resistance was characterized by oxidation induction time and oxidation induction temperature according to ASTM D3895-14 method using TGA / DSC 3 + Differential Scanning Calorimeter. During the test, in order to eliminate the thermal history of the sample, the sample was first heated to 150°C at a rate of 20°C / min, kept at that temperature for 5 minutes, and then cooled to 25°C at a rate of 20°C / min before the test conditions were met. A sample with a mass of 5.5±0.5 mg that met the test conditions was taken and heated to 220°C in a nitrogen atmosphere. After isothermal maintenance at 220°C for 5 minutes, the nitrogen atmosphere was switched to an oxygen atmosphere (both gas flow rates were 50 ml / min), and then the temperature was maintained for 120 minutes, or until a peak appeared in the differential scanning calorimetry (DSC) curve. An uncovered aluminum crucible was used. All samples were measured twice.

[0295] It can be seen from Table 6 that the performance of the PBS plastic prepared using the DMS prepared in Example 1 as a raw material is better than that of the PBS prepared using Comparative Examples 1-2, commercially available succinic acid, and commercially available succinic anhydride as raw materials.

[0296] Table 6

[0297]

[0298] In summary, the use of the catalyst of the present invention and the method for producing dimethyl succinate by hydrogenating dimethyl maleate of the present invention can effectively improve the selectivity of DMS and increase the purity of the DMS product. Further, the use of the fixed-bed reactor of the present invention to control the bed temperature difference can reduce energy consumption and production costs, thereby improving the economic benefits of the production of biodegradable plastic PBS.

Claims

1. A catalyst for catalyzing the gas-phase hydrogenation of dimethyl maleate to produce dimethyl succinate, characterized in that: The catalyst includes a composite carrier and active metal Ni loaded on the composite carrier, the composite carrier is composed of a modifier and natural minerals, the modifier includes zirconium and rare earth metals; the natural minerals are selected from one or more of diatomaceous earth, sepiolite, halloysite, attapulgite, vermiculite and molybdenite; the rare earth metals are selected from one or more of yttrium, lanthanum, cerium, neodymium, samarium, europium, gadolinium and ytterbium; in the modifier, the molar ratio of zirconium to rare earth metal is 1:(0.01-0.1); the content of zirconium element is 0.01-30wt% of the content of the natural minerals; in the catalyst, the content of active metal Ni is 1-40wt%; the modifier is prepared by a high-pressure hydrothermal method from an aqueous solution containing a zirconium salt and a rare earth metal salt.

2. The catalyst according to claim 1, wherein The catalyst has one or more of the following characteristics: The modifier consists of zirconium and rare earth metals; The specific surface area of the composite carrier is 150-450m 2 / g; The total pore volume of the composite carrier is 0.15-1.5m 3 / g; The average pore size of the composite carrier is 5-30 nm.

3. A method for preparing the catalyst according to claim 1 or 2, characterized in that: The method comprises the steps of: (1) preparing a modifier by subjecting an aqueous solution containing a zirconium salt and a rare earth metal salt to a high-pressure hydrothermal method; (2) allowing the modifier and the natural mineral to form a precipitate in a dispersant, collecting the precipitate by filtration, drying, and calcining to obtain a composite carrier; (3) impregnating the composite support in an aqueous solution containing nickel salt, filtering out the solution, drying, and calcining to obtain a catalyst precursor; (4) subjecting the catalyst precursor to a reduction reaction in a reducing gas to obtain the catalyst.

4. The method according to claim 3, wherein Step (1) has one or more of the following characteristics: The zirconium salt is selected from one or more of zirconium nitrate, zirconium chloride and zirconium alkoxide; The rare earth metal salt is selected from one or more of Gd(NO3)3·6H2O, Yb(NO3)3·5H2O, Y(NO3)3·4H2O, La(NO3)3·xH2O, Ce(NO3)3·6H2O, Nd(NO3)3·6H2O, Sm(NO3)3·6H2O, Eu(NO3)3·5H2O and chloride salts of the rare earth metal; In the aqueous solution, the concentration of the zirconium salt is 2-2.5 mol / L; In the aqueous solution, the molar ratio of zirconium to rare earth metal is 1:(0.001-0.5); The reaction pressure of the high-pressure hydrothermal method is 1.0-3.0 MPa; The reaction temperature of the high-pressure hydrothermal method is 110-150°C; The reaction time of the high-pressure hydrothermal method is 3-24 hours.

5. The method according to claim 3, wherein Step (2) has one or more of the following characteristics: The amount of the modifier added is such that the content of zirconium in the modifier is 0.01-30 wt % of the content of the natural mineral; The conditions for forming the precipitate are: stirring and dispersing the modifier and the natural mineral under heating conditions, and then allowing them to stand under heating conditions until a precipitate is formed; The drying temperature is 100-150°C; The drying time is 2-48h; The calcination temperature is 150-800°C; The calcination time is 0.5-12h; Before performing step (2), the natural mineral is subjected to heat treatment and / or chemical treatment.

6. The method according to claim 3, wherein Step (3) has one or more of the following characteristics: The nickel salt is selected from one or more of nickel nitrate, nickel chloride and nickel sulfate; The aqueous solution containing nickel salt also includes an organic acid; In the aqueous solution containing nickel salt, the concentration of nickel salt is 0.01-2.0 g / mL; The dipping time is 20-240 min; The drying temperature is 80-120°C; The drying time is 2-12 hours; The calcination temperature is 150-550°C; The calcination time is 0.5-50h.

7. The method according to claim 3, wherein Step (4) has one or more of the following characteristics: The reducing gas includes hydrogen and a protective gas, wherein the protective gas is selected from one or more of nitrogen, helium and argon; The temperature of the reduction reaction is 130-650°C; Heating the reduction reaction system to a set temperature at a heating rate not exceeding 10°C / h; After the temperature of the reduction reaction system reaches the set value, it is maintained for 4-48 hours.

8. A method for preparing dimethyl succinate, characterized in that: The method comprises step (a): under the catalytic action of a catalyst, hydrogenating dimethyl maleate with hydrogen to obtain crude dimethyl succinate, wherein the catalyst is the catalyst according to claim 1 or 2 or a catalyst obtained by the method according to any one of claims 3 to 7.

9. The method according to claim 8, wherein: The method further comprises step (b): distilling the crude dimethyl succinate to obtain dimethyl succinate; and / or, Step (a) has one or more of the following characteristics: The molar ratio of dimethyl maleate to hydrogen is 1:(100-500); The reaction pressure is 1.0-10.0 MPaG; The reaction temperature is 110-230°C; The gas phase space velocity of the reactor is 20000-30000 h -1 ; The conversion rate of dimethyl maleate in step (a) is ≥99.9%; The selectivity of dimethyl succinate in step (a) is ≥99%; In step (a), the content of γ-butyrolactone in the crude dimethyl succinate is ≤5 wt %.

10. A method for preparing polybutylene succinate, characterized in that: The method comprises the steps of: (A) providing the catalyst according to claim 1 or 2, or providing a catalyst prepared by the method according to any one of claims 3 to 7; (B) preparing dimethyl succinate by hydrogenating dimethyl maleate with hydrogen under the catalytic action of the catalyst; (C) polymerizing the dimethyl succinate obtained in step (B) with 1,4-butanediol to obtain polybutylene succinate.

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