Fixed bed continuous production method for preparing levulinate from furfural

Abstract

The invention relates to a fixed bed continuous production method for preparing levulinate from furfural, and mainly solves the problems of low selectivity and incapability of continuous production of levulinate prepared from a bifunctional catalyst in the prior art. The method mainly comprises the following steps: in a fixed bed, carrying out furfural catalytic hydrogenation on a mixture of furfural, alcohol and water on an upper-layer metal catalyst to prepare furfuryl alcohol, and then catalyzing furfuryl alcohol etherification and ring opening by a lower-layer oxide catalyst to prepare levulinate. According to the method, hydrogenation of furfural and ring opening of furfuryl alcohol are separated in time and space, a fixed bed continuous production process is further utilized, levulinate can be efficiently, continuously and stably prepared, and the method can be applied to industrial production of preparing high additional products from furfural. The conversion rate of furfural in the whole reaction can reach 100%, and the total yield of levulinate is greater than 95%.

Description

Technical Field

[0001] The invention relates to the field of catalyst preparation and catalysis, and in particular to a fixed-bed continuous production method for preparing levulinate from furfural. Background Art

[0002] Biomass energy is an important renewable energy source. As the only clean energy source with carbon carrier, it can partially replace fossil energy. Scientists proposed the concept of biorefining in the 20th century, aiming to convert biomass into high-value-added chemicals, materials, energy and fuels. Furfural is a high-value-added platform compound derived from biomass. In industry, it can be converted into furfural through acid hydrolysis and dehydration of pentosan-rich biomass. Furfural has a wide range of uses. It can be used to synthesize a variety of chemicals such as furfuryl alcohol, furan, tetrahydrofuran, furoic acid, and synthesis.

[0003] Levulinic acid ester is a colorless transparent liquid with an aromatic odor. It is easily soluble in most organic solvents such as ethanol, ether, and chloroform. From the perspective of molecular structure, levulinic acid ester contains unsaturated carbonyl and ester groups, which can isomerize into enol structures and have high reactivity. It can be used as a reaction substrate to participate in various reactions such as hydrolysis, addition, substitution, transesterification, and redox, thereby deriving many chemicals with industrial significance.

[0004] The process of preparing levulinic ester from furfural is divided into two processes: hydrogenation and ring opening. First, the side chain aldehyde group on the furan ring of furfural is hydrogenated to produce furfuryl alcohol. This step requires the participation of a hydrogenation catalyst; the generated furfuryl alcohol needs to be further etherified and ring-opened to produce the corresponding levulinic ester. This process generally requires the catalyst to have a certain acidity. Therefore, the research on the preparation of levulinic ester from furfural mainly revolves around hydrogenation and ring-opening bifunctional catalysts. However, furfural and furfuryl alcohol are very easy to undergo polymerization reactions at the acidic sites on the catalyst surface to produce humus by-products, which leads to a decrease in the selectivity of levulinic ester. Chinese patent CN105728042A discloses an active component using precious metals as catalysts for the hydrogenation of furfural to produce furfuryl alcohol, H3PW 12O4 is an active component that catalyzes the etherification and ring opening of furfuryl alcohol. When the reaction temperature is 100-200°C and the reaction time is 10-30 h, the total yield of levulinic acid ester reaches 80-90%. The above method uses precious metals as catalysts and has a long reaction time. Chinese patent CN108675928A discloses an active component that replaces precious metals with Zr / MCM catalysts to catalyze the hydrogenation of furfural to produce furfuryl alcohol. Amberlyst 15 is an active component that catalyzes the etherification and ring opening of furfuryl alcohol. The catalytic process also has a long reaction time, and the total yield of levulinic acid ester reaches 80%. Chinese patent CN110981839A uses a one-pot method to prepare furfuryl alcohol or levulinic acid ester from furfural, and the maximum yield of levulinic acid ester can only reach 75.1%. The process also has the problem of too long reaction time. The above three patents are all batch reactor reactions, which are difficult to be continuously produced in industry. Moreover, the yield of the above three processes cannot be further increased to more than 95% because furfural and furfuryl alcohol are very easy to undergo polymerization reaction at the acid sites on the catalyst surface to generate humic byproducts. Therefore, it is of great significance to develop a process for preparing levulinic esters from furfural with high activity, high selectivity and continuous one-step method.

[0005] To solve the above problems, this invention proposes a fixed-bed continuous production method for preparing levulinic ester from furfural. This method separates the hydrogenation of furfural and the ring opening of furfuryl alcohol in time and space, avoiding the formation of humic by-products. By further utilizing the fixed-bed continuous production process, levulinic ester can be prepared efficiently, continuously and stably, and can be used in the industrial production of furfural to produce high value-added products. Summary of the invention

[0006] The purpose of the present invention is to provide a fixed-bed continuous production method for preparing levulinic acid ester from furfural, which separates the hydrogenation of furfural and the ring opening of furfuryl alcohol in time and space, avoids the generation of humic by-products, and further utilizes the fixed-bed continuous production process to efficiently, continuously and stably prepare levulinic acid ester, which can be used in the industrial production of furfural to produce high value-added products.

[0007] The invention provides a fixed-bed continuous production method for preparing levulinic acid ester from furfural, comprising the following steps: loading an oxide catalyst into a lower layer of a fixed bed, loading a supported metal catalyst into an upper layer of the fixed bed, adding a furfural reaction liquid from a feed port at the upper end of the fixed bed, firstly hydrogenating the furfural under the action of the supported metal catalyst to prepare furfuryl alcohol; and then etherifying and ring-opening the furfuryl alcohol under the catalysis of the oxide catalyst to prepare levulinic acid ester.

[0008] Wherein, the oxide catalyst is selected from one or more of Al2O3, ZrO2, Nb2O5, CeO2, ZSM-5 or TiO2; preferably TiO2.

[0009] Among them, the carrier of the supported metal catalyst is selected from one or more of Al2O3, ZrO2, Nb2O5, CeO2, ZSM-5 or TiO2, preferably TiO2; the metal is selected from one or more of Fe, Co, Ni, Cu or Zn, preferably Zn and Cu.

[0010] Furthermore, the metal loading in the supported metal catalyst is 0.01wt.%-50wt.%; preferably 1wt.%-50wt.%.

[0011] Furthermore, the preparation method of the supported metal catalyst comprises the following steps: (1) uniformly dispersing the carrier in a metal chloride aqueous solution, heating under reflux at 40-120°C for reaction, filtering, washing and drying after the reaction to obtain a pretreated carrier; (2) The pretreated support obtained in step (1) is impregnated in a metal nitrate aqueous solution by an equal volume impregnation method, dried, and calcined to obtain a supported metal catalyst.

[0012] In the preparation method of the above-mentioned supported metal catalyst, the metal chloride salt in step (1) is one or more of FeCl3, CoCl2, NiCl2, CuCl2 or ZnCl2, preferably ZnCl2; the mass concentration of the metal chloride salt aqueous solution is 1wt%-10wt%. The heating reflux time is 6-8h. The pre-treatment metal residue is 0.15-1wt%.

[0013] In the preparation method of the above-mentioned supported metal catalyst, the metal nitrate in step (2) is one or more of copper nitrate, nickel nitrate, and iron nitrate. The loading amount of the supported metal is 1-50 wt%.

[0014] In the above-mentioned method for preparing the supported metal catalyst, the calcination in step (2) is performed by heating the temperature in a muffle furnace at 10°C / min to 400°C for 4-5 hours under air atmosphere.

[0015] Furthermore, the oxide catalyst or supported metal catalyst is pressed into tablets and passed through a 30-40 mesh sieve before being loaded into a fixed bed.

[0016] Furthermore, the furfural reaction liquid is a mixed solution of furfural, alcohol and water; the alcohol is selected from one or more of methanol, ethanol, isopropanol, n-butanol or cyclohexanol.

[0017] Furthermore, the mass ratio of furfural, alcohol and water in the furfural reaction solution is 1:20:1.

[0018] Specifically, the fixed-bed continuous production method for preparing levulinic ester from furfural comprises reducing the catalyst in the fixed bed with hydrogen at 250°C for 1 h under normal pressure conditions, cooling to the reaction temperature after the reduction is completed, and charging 1 MPa of H2 into the fixed bed. The flow rate of the furfural reaction liquid is 0.1 mL / min.

[0019] Furthermore, the reaction temperature is 120°C-240°C.

[0020] The present invention provides a method for preparing levulinic ester from furfural in a continuous one-step process, which can efficiently, continuously and stably prepare levulinic ester and can be used in the industrial production of high value-added products from furfural. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of catalyst distribution and reaction in fixed bed. DETAILED DESCRIPTION

[0022] The present invention is further described below by means of specific embodiments. The embodiments described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention. Example 1

[0023] The metal catalyst supported on the upper layer was prepared as follows: (1) 1 g of TiO2 carrier was heated to reflux with 100 mL of 5 wt.% ZnCl2 aqueous solution at 60 °C for 6 h, and then filtered, washed, and vacuum dried to obtain pretreated TiO2. The Zn loading on the pretreated TiO2 was 1 wt.%.

[0024] (2) The pretreated TiO2 obtained in step (1) was treated with an equal volume impregnation method. First, Cu(NO3)2 was prepared into an aqueous solution. Then, the desired carrier was added. The solution was then vacuum dried and calcined in a muffle furnace at a temperature of 10°C / min to 400°C for 4 h in an air atmosphere to obtain a supported Cu catalyst. The supported Cu catalyst had a Cu loading of 5.1 wt.%.

[0025] (3) Weigh 3 g of the loaded Cu catalyst obtained in step (2), press it into tablets, and sieve it to obtain a 30-40 mesh catalyst. After loading it into a fixed bed, a metal catalyst loaded on the upper layer is obtained.

[0026] The lower oxide catalyst was prepared as follows: Weigh 3 g of TiO2 catalyst, press it into tablets and sieve it to obtain a 30-40 mesh catalyst, and load it into a fixed bed to obtain a lower layer oxide catalyst.

[0027] Furfural continuous one-step process to prepare levulinate ester reaction: First, the catalyst in the fixed bed was reduced with hydrogen at 250 °C for 1 h under normal pressure. After the reduction was completed, the temperature was lowered to 160 °C and 1 MPa of H2 was charged into the fixed bed. A mixed solution of furfural: methanol: water with a mass ratio of 1:20:1 was prepared and injected into the fixed bed at a flow rate of 0.1 mL / min. Samples were taken every two hours. The conversion rate of furfural was 100% and the selectivity of methyl levulinate was 98.3% according to gas phase analysis. Example 2

[0028] The metal catalyst supported on the upper layer was prepared as follows: (1) 1 g of TiO2 carrier was heated to reflux with 100 mL of 1 wt.% ZnCl2 aqueous solution at 60 °C for 6 h, and then filtered, washed, and vacuum dried to obtain pretreated TiO2. The Zn loading on the pretreated TiO2 was 0.15 wt.%.

[0029] (2) The pretreated TiO2 obtained in step (1) was firstly treated with Cu(NO3)2 in aqueous solution by an equal volume impregnation method, and then the desired carrier was added, followed by vacuum drying, and calcination in a muffle furnace at 10°C / min to 400°C for 4 h in an air atmosphere to obtain a supported Cu catalyst; the supported Cu catalyst loading was 5.1 wt.% (3) Weigh 3 g of the loaded Cu catalyst obtained in step (2), press it into tablets, and sieve it to obtain a 30-40 mesh catalyst. After loading it into a fixed bed, a metal catalyst loaded on the upper layer is obtained.

[0030] The lower oxide catalyst was prepared according to the method of Example 1.

[0031] Continuous one-step method for preparing methyl levulinate from furfural: The experimental operation was the same as in Example 1. The conversion rate of furfural according to gas phase analysis was 26.3%, and the selectivity of methyl levulinate was 45.6%. Example 3

[0032] The metal catalyst supported on the upper layer was prepared as follows: (1) 1 g of TiO2 carrier was heated to reflux with 100 mL of 5 wt.% ZnCl2 aqueous solution at 120 °C for 6 h, and then filtered, washed, and vacuum dried to obtain pretreated TiO2. The Zn loading on the pretreated TiO2 was 0.08 wt.%.

[0033] (2) The pretreated TiO2 obtained in step (1) was firstly treated with Cu(NO3)2 in aqueous solution by an equal volume impregnation method, and then the desired carrier was added, followed by vacuum drying, and calcination in a muffle furnace at 10°C / min to 400°C for 4 h in an air atmosphere to obtain a supported Cu catalyst; the supported Cu catalyst loading was 5.1 wt.% (3) Weigh 3 g of the loaded Cu catalyst obtained in step (2), press it into tablets, and sieve it to obtain a 30-40 mesh catalyst. After loading it into a fixed bed, a metal catalyst loaded on the upper layer is obtained.

[0034] The lower oxide catalyst was prepared according to the method of Example 1.

[0035] Continuous one-step method for preparing methyl levulinate from furfural: The experimental operation was the same as in Example 1. The conversion rate of furfural was 12.5% ​​and the selectivity of methyl levulinate was 32.6% according to gas phase analysis. Example 4

[0036] The metal catalyst supported on the upper layer was prepared as follows: (1) 1 g of TiO2 carrier was heated to reflux with 100 mL of 5% wt.% ZnCl2 aqueous solution at 60 °C for 6 h, and then filtered, washed, and vacuum dried to obtain pretreated TiO2. The Zn loading on the pretreated TiO2 was 1 wt.%.

[0037] (2) The pretreated TiO2 obtained in step (1) was treated with Ni(NO3)2 in an equal volume impregnation method to prepare an aqueous solution, and then the desired carrier was added. The solution was then vacuum dried and calcined in an air atmosphere at a temperature of 10°C / min to 400°C in a muffle furnace for 4 h to obtain a loaded Ni catalyst. The loaded Ni catalyst had a loading of 4.9 wt.%.

[0038] (3) Weigh 3 g of the loaded Ni catalyst obtained in step (2), press it into tablets, and sieve it to obtain a 30-40 mesh catalyst. After loading it into a fixed bed, a metal catalyst loaded on the upper layer is obtained.

[0039] The lower oxide catalyst was prepared according to the method of Example 1.

[0040] Continuous one-step method for preparing methyl levulinate from furfural: The experimental operation was the same as in Example 1. The conversion rate of furfural according to gas phase analysis was 100%, and the selectivity of methyl levulinate was 5.6%. Example 5

[0041] The metal catalyst supported on the upper layer was prepared as follows: (1) 1 g of TiO2 carrier was heated to reflux with 100 mL of 5 wt.% ZnCl2 aqueous solution at 60 °C for 6 h, and then filtered, washed, and vacuum dried to obtain pretreated TiO2. The Zn loading on the pretreated TiO2 was 1 wt.%.

[0042] (2) The pretreated TiO2 obtained in step (1) was treated with an equal volume impregnation method. First, Cu(NO3)2 was prepared into an aqueous solution. Then, the desired carrier was added. The solution was then vacuum dried and calcined in an air atmosphere at a temperature of 10°C / min to 400°C in a muffle furnace for 4 h to obtain a loaded Cu catalyst. The loaded Cu catalyst had a loading of 48.3 wt.%.

[0043] (3) Weigh 3 g of the loaded Cu catalyst obtained in step (2), press it into tablets, and sieve it to obtain a 30-40 mesh catalyst. After loading it into a fixed bed, a metal catalyst loaded on the upper layer is obtained.

[0044] The lower oxide catalyst was prepared according to the method of Example 1.

[0045] Continuous one-step method for preparing methyl levulinate from furfural: The experimental operation was the same as in Example 1. The conversion rate of furfural according to gas phase analysis was 100%, and the selectivity of methyl levulinate was 97.3%. Example 6

[0046] The metal catalyst supported on the upper layer was prepared according to the method of Example 1.

[0047] The lower oxide catalyst was prepared according to the following method: 3 g of Al2O3 catalyst was weighed, tableted and sieved to obtain a 30-40 mesh catalyst, and loaded into a fixed bed to obtain a lower oxide catalyst.

[0048] Continuous one-step method for preparing methyl levulinate from furfural: The experimental operation was the same as in Example 1. The conversion rate of furfural according to gas phase analysis was 100%, and the selectivity of methyl levulinate was 5.3%. Example 7

[0049] Referring to the preparation method of the upper and lower catalysts in Example 1, the difference is that the reaction temperature of the fixed bed is 200°C, and other operations and conditions remain unchanged. The conversion rate of furfural in gas phase analysis is 100%, and the selectivity of methyl levulinate is 96.3%. Comparative Example 1

[0050] Referring to the preparation method of the upper and lower catalysts in Example 1, the difference is that TiO2 is not pretreated with an aqueous solution of ZnCl2, and other operations and conditions remain unchanged. The conversion rate of furfural in gas phase analysis is 42.3%, and the selectivity of methyl levulinate is 33.6%. Comparative Example 2

[0051] Referring to the preparation method of the upper and lower catalysts in Example 1, the difference was that the copper loading was 1 wt.%, and other operations and conditions remained unchanged. The conversion rate of furfural in gas phase analysis was 52.3%, and the selectivity of methyl levulinate was 98.2%. Comparative Example 3

[0052] Referring to the preparation method of the upper and lower catalysts in Example 1, the difference is that TiO2 is pretreated with a 5 wt.% FeCl3 aqueous solution, and other operations and conditions remain unchanged. The conversion rate of furfural in gas phase analysis is 29.8%, and the selectivity of methyl levulinate is 10.6%. Comparative Example 4

[0053] Referring to the preparation method of the upper and lower catalysts in Example 1, the difference is that the TiO2 in the upper and lower layers are replaced with Al2O3, and other operations and conditions remain unchanged. The conversion rate of furfural in gas phase analysis is 62.8%, and the selectivity of methyl levulinate is 1.2%.

[0054] Table 1 Furfural conversion and selectivity and yield of methyl levulinate Conversion rate Selectivity Yield Example 1 100% 98.3% 98.3% Example 2 26.3% 45.6% 12.0% Example 3 12.5% 32.6% 4.1% Example 4 100% 5.6% 5.6% Example 5 100% 97.3% 97.3% Example 6 100% 5.3% 5.3% Example 7 100% 96.3% 96.3% Comparative Example 1 42.3% 33.6% 14.2% Comparative Example 2 52.3% 98.2% 51.4% Comparative Example 3 29.8% 10.6% 3.2% Comparative Example 4 62.8% 1.2% 0.8% It should be noted that the above is a preferred embodiment of the present invention. It should be pointed out that for the technology in the field, several improvements and supplements can be made without departing from the method of the present invention, and these improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A fixed-bed continuous production method for preparing levulinate from furfural, characterized in that: The method comprises the following steps: adding furfural reaction liquid from the upper feed port of a fixed bed, firstly hydrogenating furfural to produce furfuryl alcohol under the action of a supported metal catalyst; then etherifying and ring-opening furfuryl alcohol to produce levulinic ester by catalyzing furfuryl alcohol with an oxide catalyst; wherein the supported metal catalyst is located in the upper layer of the fixed bed, and the oxide catalyst is located in the lower layer of the fixed bed; the oxide catalyst is selected from one or more of Al2O3, ZrO2, Nb2O5, CeO2, ZSM-5 or TiO2; the carrier of the supported metal catalyst is selected from one or more of Al2O3, ZrO2, Nb2O5, CeO2, ZSM-5 or TiO2; the metal is selected from one or more of Fe, Co, Ni, Cu or Zn; the metal loading in the supported metal catalyst is 1-50 wt.%.

2. The fixed-bed continuous production method for preparing levulinate from furfural according to claim 1, characterized in that: The oxide catalyst is TiO2; the carrier of the supported metal catalyst is TiO2, and the metals are Zn and Cu.

3. The fixed-bed continuous production method for preparing levulinate from furfural according to claim 2, characterized in that: The supported metal catalyst has a Zn loading of 0.15-1 wt %, and a Cu loading of 1-50 wt %.

4. The fixed-bed continuous production method for preparing levulinate from furfural according to any one of claims 1 to 3, characterized in that: The method for preparing the supported metal catalyst comprises the following steps: (1) uniformly dispersing the carrier in a metal chloride aqueous solution, heating at 40-120°C for reflux reaction, filtering, washing and drying after the reaction to obtain a pretreated carrier; the residual amount of metal ions in the metal chloride in the pretreated carrier is 0.15-1 wt%; (2) The pretreated support obtained in step (1) is impregnated in a metal nitrate aqueous solution by an equal volume impregnation method, dried, and calcined to obtain a supported metal catalyst; the loading amount of the metal in the metal nitrate in the supported metal catalyst is 1-50 wt%.

5. The fixed-bed continuous production method for preparing levulinate from furfural according to claim 4, characterized in that: The mass concentration of the metal chloride aqueous solution in step (1) is 1wt%-10wt%; and / or the heating reflux time is 6-8h.

6. The fixed-bed continuous production method for preparing levulinate from furfural according to claim 4, characterized in that: The calcination in step (2) is carried out at 400° C. for 4-5 h in an air atmosphere.

7. The fixed-bed continuous production method for preparing levulinate from furfural according to claim 1, characterized in that: The furfural reaction solution is a mixed solution of furfural, alcohol and water; the alcohol is selected from one or more of methanol, ethanol, isopropanol, n-butanol or cyclohexanol.

8. The fixed-bed continuous production method for preparing levulinate from furfural according to claim 7, characterized in that: The mass ratio of furfural, alcohol and water in the furfural reaction solution is 1:20:

1.

9. The fixed-bed continuous production method for preparing levulinate from furfural according to claim 1, characterized in that: The temperature of the fixed bed continuous reaction is 120°C-240°C, the H2 pressure is 1MPa, and the flow rate of the furfural reaction liquid is 0.1mL / min.

10. The fixed-bed continuous production method for preparing levulinate from furfural according to claim 1, characterized in that: The oxide catalyst or supported metal catalyst is pressed into tablets and passed through a 30-40 mesh sieve before being loaded into a fixed bed.

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