Method for preparing lactic acid through catalysis of ethylene glycol

Abstract

The invention relates to the field of fine chemical engineering, in particular to a method for preparing lactic acid through ethylene glycol catalysis and a used catalyst. According to the method, ethylene glycol and methanol are used as raw materials, a supported composite noble metal is used as a catalyst, and lactic acid is obtained through reaction. The catalyst takes noble metal Au and other noble metal additives as active components, and takes a ZSM-5 molecular sieve as a carrier; the noble metal additive is selected from at least one of Ag, Pd, Pt and Ru; on the basis of the total weight of the catalyst, the content of Au is 0.1-3 wt.%, the content of the noble metal additive is 0.2-20 wt.%, and the balance is the ZSM-5 molecular sieve; the silica-alumina ratio of the ZSM-5 molecular sieve is (80-150): 1. Compared with the prior art, the method has the advantages that the reaction conditions for preparing lactic acid through ethylene glycol catalysis are mild, the conversion rate of ethylene glycol is not lower than 99%, and the selectivity of lactic acid is not lower than 95%.

Description

Technical Field

[0001] The present invention relates to the field of fine chemicals, and in particular to a method for preparing lactic acid by catalysis of ethylene glycol. Background Art

[0002] Lactic acid is a common metabolic product of organisms and an important organic acid widely used in food, medicine, and chemical industries. However, the traditional production of lactic acid through fermentation is characterized by long cycles, low efficiency, and high costs, making it difficult to meet large-scale industrial applications.

[0003] CN110357770B discloses a method for producing lactic acid by selective catalytic conversion of ethylene glycol. The method uses ethylene glycol and methanol as raw materials, an alkali metal or alkaline earth metal hydroxide as a base, and a nitrogen heterocyclic carbene metal coordination compound as a catalyst. The reaction is carried out in a closed chamber at 100-200°C for 0.5-12 hours to produce lactic acid. However, the nitrogen heterocyclic carbene catalyst employed in this method requires stringent preparation conditions, poor reproducibility, and high costs, and has not yet been used in industrial catalysis.

[0004] In addition, in the prior art, it is difficult for the conversion rate and lactic acid yield of ethylene glycol to directly produce lactic acid to exceed 95% at the same time. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems raised in the background technology, thereby providing a method for preparing lactic acid by catalysis of ethylene glycol.

[0006] The first aspect of the present invention provides a method for preparing lactic acid from ethylene glycol, wherein the method uses ethylene glycol and methanol as raw materials and a supported composite noble metal as a catalyst; wherein:

[0007] The catalyst uses precious metal Au and other precious metal additives as active components and ZSM-5 molecular sieve as a carrier;

[0008] The precious metal additive is selected from at least one of Ag, Pd, Pt, and Ru;

[0009] Based on the total weight of the catalyst, the content of Au is 0.1-3 wt.%, the content of the noble metal additive is 0.2-20 wt.%, and the rest is ZSM-5 molecular sieve;

[0010] The silicon-aluminum ratio of the ZSM-5 molecular sieve is (80-150):1.

[0011] A second aspect of the present invention provides a method for preparing the above-mentioned catalyst, the method comprising the following steps:

[0012] (1) pre-treating the ZSM-5 molecular sieve with an acid solution or an alkali solution, and obtaining the pre-treated ZSM-5 molecular sieve after washing and drying;

[0013] (2) adding the pretreated ZSM-5 molecular sieve to the salt solution of the precious metal and uniformly mixing them to form a first mixed solution;

[0014] (3) adding a reducing agent to the first mixed solution and uniformly mixing the mixture to form a second mixed solution;

[0015] (4) separating the second mixed liquid into solid and liquid, and washing and drying the obtained solid phase to obtain the catalyst; wherein,

[0016] The silicon-aluminum ratio of the ZSM-5 molecular sieve is (80-150):1;

[0017] The noble metal is Au and other noble metal additives;

[0018] The noble metal additive is selected from at least one of Ag, Pd, Pt, and Ru.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The catalyst of the present invention uses precious metal Au and other precious metal additives as active components and ZSM-5 molecular sieve as a carrier to convert ethylene glycol and methanol into lactic acid. The ethylene glycol conversion rate is not less than 99%, and the lactic acid selectivity is not less than 95%, which is easy to industrialize.

[0021] Second, the catalyst of the present invention has relatively mild reaction conditions when catalyzing the conversion of ethylene glycol and methanol to produce lactic acid, especially the low liquid phase reaction temperature, which can avoid the reaction of alcohol conversion to olefins and ensure that the reaction has high lactic acid selectivity.

[0022] 3. In the method for preparing the catalyst of the present invention, ZSM-5 molecular sieve with a silicon-aluminum ratio of (80-150):1 is selected as the carrier, thereby improving the ethylene glycol conversion rate and lactic acid selectivity.

[0023] 4. In the method for preparing the catalyst of the present invention, pretreatment of the ZSM-5 molecular sieve is beneficial to the contact of ethylene glycol and methanol raw materials at the active center of the ZSM-5 molecular sieve catalyst, thereby improving the ethylene glycol conversion rate and lactic acid selectivity.

[0024] 5. The catalyst preparation method of the present invention is simple, the raw materials are easy to obtain, and the reproducibility is high. DETAILED DESCRIPTION

[0025] The present invention will be further described below through specific embodiments, which does not mean that the scope of the present invention is limited thereto.

[0026] A first aspect of the present invention provides a method for preparing lactic acid by catalyzing ethylene glycol, wherein the method uses ethylene glycol and methanol as raw materials and a supported composite noble metal as a catalyst.

[0027] The reaction conditions for preparing lactic acid from ethylene glycol include: a molar ratio of ethylene glycol to methanol in the raw materials of 1:(1-10); an amount of catalyst added of 10-100 g / L; a reaction temperature of 100-250° C.; a reaction pressure of 0.1-10 MPa; a reaction time of 1-50 h; and a reaction medium of at least one of nitrogen, air, or hydrogen.

[0028] Furthermore, the reaction conditions are relatively mild, especially the low liquid phase reaction temperature, which can avoid the conversion of alcohols into olefins and ensure that the reaction has high lactic acid selectivity.

[0029] The catalyst uses precious metal Au and other precious metal additives as active components and ZSM-5 molecular sieve as a carrier;

[0030] The noble metal additive is selected from at least one of Ag, Pd, Pt, and Ru.

[0031] Based on the total weight of the catalyst, the content of Au is 0.1-3 wt.%, the content of the noble metal additive is 0.2-20 wt.%, and the rest is ZSM-5 molecular sieve.

[0032] In some embodiments, the silicon-aluminum ratio of the ZSM-5 molecular sieve is (80-150):1.

[0033] In some embodiments, the catalyst has an ethylene glycol conversion rate of not less than 99% and a lactic acid selectivity of not less than 95% when catalyzing ethylene glycol to lactic acid.

[0034] In some embodiments, the ZSM-5 molecular sieve can directly catalyze the conversion of ethylene glycol into lactic acid, but the ethylene glycol conversion rate and lactic acid selectivity are both low.

[0035] Those skilled in the art will appreciate that the silicon-to-aluminum ratio is the molar ratio of silicon to aluminum in the molecular sieve unit cell, which can be expressed as SiO2 / Al2O3.

[0036] A second aspect of the present invention provides a method for preparing a catalyst for the above method, the preparation method comprising the following steps:

[0037] (1) pre-treating the ZSM-5 molecular sieve with an acid solution or an alkali solution, and obtaining the pre-treated ZSM-5 molecular sieve after washing and drying;

[0038] (2) adding the pretreated ZSM-5 molecular sieve to the salt solution of the precious metal and uniformly mixing them to form a first mixed solution;

[0039] (3) adding a reducing agent to the first mixed solution and uniformly mixing the mixture to form a second mixed solution;

[0040] (4) separating the second mixed liquid into solid and liquid, and washing and drying the obtained solid phase to obtain the catalyst; wherein,

[0041] The silicon-aluminum ratio of the ZSM-5 molecular sieve is (80-150):1;

[0042] The noble metal is Au and other noble metal additives;

[0043] The noble metal additive is selected from at least one of Ag, Pd, Pt, and Ru.

[0044] In some embodiments, in step (1), the acid solution is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, citric acid, lactic acid, and tartaric acid;

[0045] The alkali solution is selected from at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium aluminate, potassium carbonate, potassium bicarbonate, ammonia water, tetrapropylammonium bromide, tetrapropylammonium hydroxide or tetramethylammonium hydroxide solution.

[0046] Furthermore, the concentration of the acid solution or alkali solution is 0.5-10 wt.%.

[0047] In some embodiments, in the pretreatment of step (1), the mass ratio of the alkaline solution or acid solution to the ZSM-5 molecular sieve is (5-20):1.

[0048] Furthermore, the pretreatment temperature is 30-90° C., and the pretreatment time is 3-25 hours.

[0049] In some embodiments, in step (1), the ZSM-5 molecular sieve is washed after pretreatment until the washing liquid is neutral, and the obtained filter cake is dried at 100-140° C. for 8-24 hours.

[0050] Furthermore, pre-treating the molecular sieve with acid or alkali can facilitate the contact of ethylene glycol and methanol raw materials at the active center of the ZSM-5 molecular sieve catalyst, thereby improving the conversion rate of ethylene glycol and the selectivity of lactic acid.

[0051] In some embodiments, in step (2), the salt of the noble metal is selected from at least one of a chloride of the noble metal, a nitrate of the noble metal, and a sulfate of the noble metal.

[0052] Wherein, the noble metal is Au and other optional noble metal additives.

[0053] Wherein, the precious metal additive is selected from at least one of Ag, Pd, Pt and Ru.

[0054] In some embodiments, in step (2), the concentration of the Au salt solution is 3-30 mmol / L, and the concentration of the noble metal additive salt solution is 5-550 mmol / L.

[0055] Furthermore, the weight ratio of the noble metal salt solution to the molecular sieve is (2-10):1.

[0056] In some embodiments, in step (3), the reducing agent is selected from at least one of potassium borohydride, sodium borohydride, formaldehyde, acetaldehyde, ascorbic acid, sodium citrate, propylene glycol, or ethylene glycol;

[0057] Furthermore, the reducing agent is added by slowly dropping the reducing agent into the salt solution of the precious metal in a water bath at 0°C under inert gas protection. This method avoids the need for a separate high-temperature hydrogen reduction step and simplifies the catalyst preparation process.

[0058] In some embodiments, the molar ratio of the reducing agent in step (3) to the noble metal salt in the noble metal salt solution in step (2) is (1-120):1.

[0059] In some embodiments, in step (4), after the second mixed solution is subjected to solid-liquid separation, the solid phase is washed until the washing liquid is neutral, and the obtained filter cake is dried at 100-140° C. for 8-24 hours.

[0060] The present invention will be described in detail below through examples. In the following examples and comparative examples, the ZSM-5 molecular sieve was purchased from Beijing Yinuokai Technology Co., Ltd.

[0061] Example 1

[0062] (1) At 50° C., 97.5 g of ZSM-5 molecular sieve (silicon-aluminum ratio of 80:1) was uniformly soaked in 587.5 g of sodium hydroxide solution (0.5 wt.%, i.e., 0.125 mol / L) for 3 h. After soaking, the molecular sieve was filtered and washed to neutrality, and finally dried at 120° C. for 12 h to obtain the pretreated ZSM-5 molecular sieve for later use;

[0063] (2) 2.538 mmol of chloroauric acid (containing 0.5 g of Au element) and 19.79 mmol of ruthenium nitrate (containing 2 g of Ru element) were uniformly dissolved in 300 ml of deionized water, and then the pretreated ZSM-5 molecular sieve was added and stirred to form a first mixed solution;

[0064] (3) In a 0°C water bath under nitrogen protection, 893.14 mL of sodium borohydride solution (0.5 mol / L) was added dropwise to the first mixed solution. After the addition was completed, stirring was continued for 8 h to obtain a second mixed solution.

[0065] That is, the molar ratio of the sodium borohydride reducing agent to the noble metal salt (composed of chloroauric acid and ruthenium nitrate) is 20:1 (446.57:(2.538+19.79));

[0066] (4) The second mixed solution was centrifuged, the obtained solid phase was washed to neutrality, and finally dried at 120°C for 12 h;

[0067] Finally, catalyst A1 with an Au loading of 0.5 wt.% and a Ru loading of 2 wt.%, ie, Au(0.5)-Ru(2)-ZSM-5(97.5), was obtained.

[0068] Example 2

[0069] The difference from Example 1 is that in step (1), the amount of ZSM-5 molecular sieve (silicon to aluminum ratio of 100:1) is 98 g;

[0070] In step (2), the amount of chloroauric acid used is 5.076 mmol (containing 1 g of Au element), and the amount of ruthenium nitrate used is 9.90 mmol (containing 1 g of Ru element);

[0071] In step (3), the molar ratio of the sodium borohydride reducing agent to the noble metal salt (composed of chloroauric acid and ruthenium nitrate) is 30:1 (446.57:(5.076+9.90));

[0072] Finally, catalyst A2 with an Au loading of 1 wt.% and a Ru loading of 1 wt.%, namely Au(1)-Ru(1)-ZSM-5(98), was obtained.

[0073] Example 3

[0074] The difference from Example 1 is that in step (1), the amount of ZSM-5 molecular sieve (silicon to aluminum ratio of 120:1) is 95 g;

[0075] In step (2), the amount of chloroauric acid used is 5.076 mmol (containing 1 g of Au element), and the amount of ruthenium nitrate used is 39.58 mmol (containing 4 g of Ru element);

[0076] In step (3), the molar ratio of the sodium borohydride reducing agent to the noble metal salt (composed of chloroauric acid and ruthenium nitrate) is 10:1 (446.57:(5.076+39.58));

[0077] Finally, catalyst A3 with an Au loading of 1 wt.% and a Ru loading of 4 wt.%, namely Au(1)-Ru(4)-ZSM-5(95), was obtained.

[0078] Example 4 (Replacing Ru with Ag)

[0079] The difference from Example 1 is that in step (1), the amount of ZSM-5 molecular sieve (silicon-aluminum ratio of 140:1) is 82.8 g;

[0080] In step (2), the amount of chloroauric acid used is 1.015 mmol chloroauric acid (containing 0.2 g Au element), and the amount of silver nitrate used is 157.6 mmol (containing 17 g Ag element);

[0081] In step (3), the molar ratio of the sodium borohydride reducing agent to the noble metal salt (composed of chloroauric acid and silver nitrate) is 2.8:1 (446.57:(1.015+157.6));

[0082] Finally, catalyst A4 with an Au loading of 0.2 wt.% and an Ag loading of 17 wt.%, namely Au(0.2)-Ag(17)-ZSM-5(82.8), was obtained.

[0083] Example 5 (Pt replaced Ru)

[0084] The difference from Example 1 is that in step (1), the amount of ZSM-5 molecular sieve (silicon to aluminum ratio of 120:1) is 99.2 g;

[0085] In step (2), the amount of chloroauric acid used is 1.015 mmol (containing 0.2 g of Au element), and the amount of platinum nitrate used is 3.076 mmol (containing 0.6 g of Pt element);

[0086] In step (3), the molar ratio of the reducing agent to the noble metal salt (composed of chloroauric acid and platinum nitrate) is 109:1 (446.57:(1.015+3.076));

[0087] Finally, catalyst A5 with an Au loading of 0.2 wt.% and a Pt loading of 0.6 wt.%, ie, Au(0.2)-Pt(0.6)-ZSM-5(99.2), was obtained.

[0088] Example 6 (Pd replaced by Ru)

[0089] The difference from Example 1 is that in step (1), the amount of ZSM-5 molecular sieve (silicon to aluminum ratio of 90:1) is 98.3 g;

[0090] In step (2), the amount of chloroauric acid used is 7.616 mmol (containing 1.5 g of Au element), and the amount of palladium nitrate used is 1.879 mmol (containing 0.2 g of Pd element);

[0091] In step (3), the molar ratio of the reducing agent to the noble metal salt (composed of chloroauric acid and palladium nitrate) is 47:1 (446.57:(7.616+1.879));

[0092] Finally, catalyst A6 with an Au loading of 1.5 wt.% and a Pd loading of 0.2 wt.%, ie, Au(1.5)-Pd(0.2)-ZSM-5(98.3), was obtained.

[0093] Comparative Example 1 (molecular sieve alone as catalyst)

[0094] The difference from Example 1 is that the pretreated molecular sieve ZSM-5 obtained in step (1) is directly used as the final catalyst D1, namely ZSM-5 (100).

[0095] Comparative Example 2 (molecular sieve is not pretreated)

[0096] The difference from Example 1 is that the ZSM-5 molecular sieve is not subjected to step (1) and is directly used as the "pretreated molecular sieve" in step (2);

[0097] Finally, the catalyst D2 with an Au loading of 0.5 wt.% and a Ru loading of 2 wt.%, ie, Au(0.5)-Ru(2)-ZSM-5(97.5), was obtained.

[0098] Comparative Example 3 (Silicon-to-aluminum ratio of molecular sieve is greater than the limited range)

[0099] The difference from Example 1 is that in step (1), the silicon-aluminum ratio of the selected ZSM-5 molecular sieve is 200:1;

[0100] Finally, the catalyst D3 with an Au loading of 0.5 wt.% and a Ru loading of 2 wt.%, ie, Au(0.5)-Ru(2)-ZSM-5(97.5), was obtained.

[0101] Comparative Example 4 (Silicon-to-aluminum ratio of molecular sieve is less than the specified range)

[0102] The difference from Example 1 is that in step (1), the silicon-aluminum ratio of the selected ZSM-5 molecular sieve is 25:1;

[0103] Finally, the catalyst D4 with an Au loading of 0.5 wt.% and a Ru loading of 2 wt.%, ie, Au(0.5)-Ru(2)-ZSM-5(97.5), was obtained.

[0104] Catalyst performance testing

[0105] Place 1.053 g (17 mmol) of ethylene glycol, 6 ml (4.7508 g, or 0.148 mol) of methanol, and 70 mg of catalyst in a 25 ml magnetically stirred reactor. Replace the air in the reactor with nitrogen, maintaining an initial nitrogen pressure of 0.5 MPa. Raise the temperature to 160°C and maintain for 24 hours. After cooling, remove the product.

[0106] The solid-phase catalyst was recovered by centrifugation, and the liquid product was analyzed by Shimadzu SIL-20A liquid chromatograph. The ethylene glycol conversion and lactic acid selectivity were calculated based on the chromatographic data. The results are shown in Table 1.

[0107] Table 1:

[0108]

[0109] The present invention has described in detail the preferred embodiments of the present invention, but the embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various other simple modifications and combinations within the scope of the present invention, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing lactic acid by catalysis of ethylene glycol, characterized in that: The method uses ethylene glycol and methanol as raw materials and a supported composite noble metal as a catalyst to carry out a reaction in a reaction medium; wherein, The catalyst uses precious metal Au and other precious metal additives as active components and ZSM-5 molecular sieve as a carrier; The precious metal additive is selected from at least one of Ag, Pd, Pt, and Ru; Based on the total weight of the catalyst, the element content of Au is 0.1-3 wt.%, the element content of the precious metal additive is 0.2-20 wt.%, and the rest is ZSM-5 molecular sieve; The silicon-aluminum ratio of the ZSM-5 molecular sieve is (80-150):

1.

2. The method according to claim 1, characterized in that The reaction conditions for preparing lactic acid by catalysis of ethylene glycol include: the molar ratio of ethylene glycol to methanol in the raw material is 1:(1-10); The amount of catalyst added is 10-100g / L; The reaction temperature is 100-250°C; The reaction pressure is 0.1-10MPa; Reaction time is 1-50h; The reaction medium is at least one of nitrogen, air and hydrogen.

3. A method for preparing a catalyst for the method according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: (1) pre-treating the ZSM-5 molecular sieve with an acid solution or an alkali solution, and obtaining the pre-treated ZSM-5 molecular sieve after washing and drying; (2) adding the pretreated ZSM-5 molecular sieve to the salt solution of the precious metal and uniformly mixing them to form a first mixed solution; (3) adding a reducing agent to the first mixed solution and uniformly mixing the mixture to form a second mixed solution; (4) separating the second mixed liquid into solid and liquid, and washing and drying the obtained solid phase to obtain the catalyst; wherein, The silicon-aluminum ratio of the ZSM-5 molecular sieve is (80-150):1; The noble metal is Au and other noble metal additives; The noble metal additive is selected from at least one of Ag, Pd, Pt, and Ru.

4. The preparation method according to claim 3, characterized in that In step (1), the acid solution is selected from at least one of hydrochloric acid, sulfuric acid, oxalic acid, citric acid, lactic acid, nitric acid, and tartaric acid; The alkali solution is selected from at least one of sodium hydroxide, sodium aluminate, sodium carbonate, sodium bicarbonate, ammonia water, potassium hydroxide, potassium carbonate, potassium bicarbonate, tetrapropylammonium bromide, tetrapropylammonium hydroxide or tetramethylammonium hydroxide solution; Furthermore, the concentration of the acid solution or alkali solution is 0.5-10 wt.%; Preferably, in the pretreatment, the mass ratio of the alkali solution or acid solution to the ZSM-5 molecular sieve is (5-20):

1.

5. The preparation method according to claim 3 or 4, characterized in that In step (1), the pretreatment temperature is 30-90° C., and the pretreatment time is 3-25 h.

6. The preparation method according to any one of claims 3 to 5, characterized in that In step (2), the noble metal salt is selected from at least one of noble metal chlorides, noble metal nitrates, and noble metal sulfates; In step (2), the concentration of the Au salt solution is 3-30 mmol / L, and the concentration of the noble metal additive salt solution is 5-550 mmol / L; Furthermore, the weight ratio of the noble metal salt solution to the molecular sieve is (2-10):

1.

7. The preparation method according to any one of claims 3 to 6, characterized in that In step (3), the reducing agent is selected from at least one of potassium borohydride, sodium borohydride, formaldehyde, acetaldehyde, ascorbic acid, sodium citrate, propylene glycol, and ethylene glycol; Preferably, the molar ratio of the reducing agent to the noble metal salt in the noble metal salt solution of step (2) is (1-120):

1.

8. The preparation method according to any one of claims 3 to 7, characterized in that In step (3), the reducing agent is added by slowly dropping the reducing agent into the salt solution of the precious metal in a water bath at 0° C. under the protection of an inert gas.

9. A catalyst prepared by the preparation method according to any one of claims 3 to 8; Preferably, the catalyst uses precious metal Au and other precious metal additives as active components and ZSM-5 molecular sieve as a carrier; The precious metal additive is selected from at least one of Ag, Pd, Pt, and Ru; Based on the total weight of the catalyst, the element content of Au is 0.1-3 wt.%, the element content of the precious metal additive is 0.2-20 wt.%, and the rest is ZSM-5 molecular sieve; The silicon-aluminum ratio of the ZSM-5 molecular sieve is (80-150):

1.

10. Use of the catalyst according to claim 9 in the preparation of lactic acid, wherein The raw materials for the preparation of lactic acid are ethylene glycol and methanol.

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