CN108325535B

CN108325535B - Catalyst for preparing n-propanol by hydrogenolysis of glycerol and preparation and use methods thereof

Info

Publication number: CN108325535B
Application number: CN201810194278.5A
Authority: CN
Inventors: 刘勇军; 楚素娅; 张陈洋; 周伟霞
Original assignee: Huaqiao University
Current assignee: Huaqiao University
Priority date: 2018-03-09
Filing date: 2018-03-09
Publication date: 2020-12-01
Anticipated expiration: 2038-03-09
Also published as: CN108325535A

Abstract

The invention discloses a catalyst for preparing n-propanol by hydrogenolysis of glycerol and a preparation and use method thereof, the prepared metal-heteropoly acid bifunctional catalyst is suitable for the hydrogenolysis reaction for preparing propanol by using water as a solvent, thereby avoiding the use of volatile, polluted or toxic solvents, being green and environment-friendly and saving the production cost; meanwhile, the method is suitable for the characteristic that the byproduct glycerol from the biodiesel device often contains a large amount of water, and also overcomes the defect that the existing catalyst is easy to inactivate in a water-containing environment.

Description

Catalyst for preparing n-propanol by hydrogenolysis of glycerol and preparation and use methods thereof

Technical Field

The invention relates to a catalyst for preparing n-propanol from glycerol by-product in the preparation process of biodiesel through hydrogenolysis and a preparation method thereof.

Background

N-propanol is an important organic raw material and a platform compound, has wide downstream application fields, is mainly used for directly being used as a solvent or synthesizing n-propyl acetate, and can also be used in the industries of paint solvents, printing ink, cosmetics and the like, and synthetic medicines, pesticides, feed additives, synthetic perfumes, plasticizers, cleaning agents and the like. In recent years, the market demand for n-propanol has also been on the rise with the annual increase in the consumption of environmentally friendly solvents. However, because the supply of the domestic n-propanol is insufficient, the import quantity of the n-propanol in China is increased from about 1.7 ten thousand tons in 2008 to 4.56 ten thousand tons in 2015, and the import speed is increased rapidly.

The glycerol is a highly functionalized three-carbon alcohol, contains three hydroxyl groups, has higher reaction activity, and can be used for preparing various organic matters such as n-propanol, isopropanol, propylene glycol, acetone, propionaldehyde, ethanol, methanol and the like. In recent years, with the increase of the demand of people for clean diesel oil products, the biodiesel industry is rapidly developed, and a large amount of glycerin is produced as a byproduct when biodiesel is prepared by an ester exchange method. In the global glycerol market, 90% of glycerol comes from the by-product of biodiesel plants, only around 10% is obtained by synthesis. It is expected that by 2022 the global production of glycerol will exceed 350 million tons and glycerol will enter a serious surplus, and the average price of glycerol is currently less than $ 250/ton (whereas the average price of propanol is $ 1257/ton). The high value-added utilization of glycerol has become an important issue at present.

At present, the method for industrially producing the n-propanol in the global range mainly comprises the steps of synthesizing ethylene, carbon monoxide and hydrogen through carbonyl to obtain propionaldehyde, and then hydrogenating to obtain the n-propanol. The method is heavily dependent on the petrochemical industry, and has the disadvantages of high pollution, high energy consumption, complex process and high production cost. At present, the glycerol conversion is researched more, and mainly the reactions such as hydrogenolysis, esterification, etherification, oxidation, dehydration, reforming and the like are used for preparing glycol, ester, ether, polymer, synthesis gas and the like. The target product prepared by hydrogenolysis of glycerol has higher added value and industrial application prospect, and the research of the trend of heat in recent years is trending. However, the method mainly focuses on the preparation of 1, 2-propylene glycol and 1, 3-propylene glycol, and there is little research on the application of glycerol to propanol. Generally, the existing glycerol hydrogenolysis catalysts have the problems of harsh reaction conditions, low glycerol conversion rate, low selectivity to a single target product, poor stability and the like. Meanwhile, the byproduct glycerin obtained by the biodiesel preparation device often contains a large amount of water, water molecules and glycerin molecules both contain polar hydroxyl groups, competitive adsorption exists on the surface of the catalyst, and meanwhile, the aqueous solution easily causes the structural change and activity loss of the catalyst to influence the catalytic performance, so that the existing documents all require that pure glycerin is used for reaction in a solvent environment to improve the reaction efficiency.

Disclosure of Invention

The invention provides a supported heteropolyacid bifunctional catalyst which can be suitable for preparing n-propanol by hydrogenolysis of glycerol using water as a solvent, and a preparation method and a use method thereof. The invention aims to overcome the defects that the conversion rate is low, the selectivity is low and the glycerol needs to be purified and dewatered firstly in the conventional preparation of the propanol by the hydrogenolysis of the glycerol, and provides a green and efficient new way for preparing the n-propanol by the hydrogenolysis of the glycerol.

The heteropoly acid selected by the invention is a heteropoly acid compound modified by transition metal. The heteropoly acid preferably adopts silicotungstic acid or phosphotungstic acid with a Keggin structure with good thermal stability and super strong acidity. The transition metal is preferably one or more of Co, Ni, Zn and Cu.

The carrier used in the present invention is preferably Al₂O₃、SiO₂、TiO₂Or a complex thereof.

The invention adopts transition metal salt and heteropoly acid to react in acid solution, the molar ratio of transition metal ion to heteropoly acid is 0.1: 1-1:1, PH value of 3-7, reacting in constant temperature water bath (40-100 ℃) for 0.5-3 hours, standing for 5-20 hours at room temperature, evaporating to dryness in oil bath, and drying in a vacuum drying oven at 30-110 ℃ overnight to form H₄MSiW₁₂Or H₃MPW₁₂The heteropoly acid with (M ═ Co, Ni, Zn, etc.) structure can modify the heteropoly acid structure partially, improve the performance and introduce transition metal into the heteropoly acid structure system.

Before the dipping treatment of the heteropoly acid and the metal, the catalyst carrier is pretreated by ethanol, propanol, oxalic acid or a mixture thereof, so that the subsequent co-dipping solution of the heteropoly acid and the metal can be uniformly dipped on the surface of the carrier. The specific method comprises the following steps: soaking the carrier in the solution for 0.5-2 hr, filtering until the soaking is balanced, and drying in an oven at 100-150 deg.C for 2-5 hr.

The invention adopts H prepared by the steps of₄MSiW₁₂Or H₃MPW₁₂The heteropoly acid and the same or different transition metal salt thereof are dissolved inPreparing co-impregnation liquid with different concentrations in distilled water, and uniformly loading the co-impregnation liquid on the surface of the carrier. So as to form hydrogenation active sites near the acid center of the orthosilicotungstic acid or phosphotungstic acid. The reaction for preparing the propanol by hydrogenolysis of the glycerol simultaneously needs a strong acid center and a good hydrogenation active center, and the two are in coordination, so that the reaction conversion efficiency can be improved. The invention organically combines two active centers, so that the two active centers can be effectively coordinated, and the reaction for preparing the propanol by the hydrogenolysis of the glycerol is promoted.

The invention adopts a 'multiple dispersion dripping and dipping method' to uniformly load the prepared co-dipping solution on the surface of a carrier, and the specific method comprises the following steps: firstly measuring the water absorption of the used carrier, determining the volume of the used co-immersion liquid, selecting the co-immersion liquid with different concentrations according to the finally required loading amounts of the heteropoly acid salt and the transition metal, dividing the co-immersion liquid into n equal parts (n is more than 5), drying the carrier in a vacuum drying oven for 30 minutes at 110 ℃, taking out, spraying the 1 st part of the co-immersion liquid on the carrier, and fully and uniformly stirring; the support was then dried again in a vacuum oven at 110 ℃ for 30 minutes, removed and sprayed with the 2 nd portion of the impregnation solution. And repeating the steps until the impregnation liquid is completely loaded.

The prepared catalyst is roasted in a muffle furnace for 2-8 hours at the temperature of 300-500 ℃ to form an oxidation state catalyst; before use, the catalyst is subjected to reduction activation for 2 to 8 hours in a hydrogen atmosphere (the hydrogen flow is 30 to 100ml/min) at the temperature of 300 ℃ and 500 ℃ to finally form M1/H₄M2SiW₁₂Support or M1/H₃M2PW₁₂A supported bifunctional catalyst (M1 or M2 ═ Co, Ni, Zn, Cu, etc.).

The application method of the catalyst in preparing the n-propanol by the hydrogenolysis of the glycerol comprises the following steps: the prepared catalyst is used for converting glycerol into n-propanol in a high-pressure reaction kettle by hydrogenolysis, and the reaction solvent is water; the pressure of the reaction hydrogen is 0.1-8 MPa, preferably 3-6 MPa; the reaction temperature is 200-500 ℃; the mass concentration of the glycerol aqueous solution is 20-50%; the mass ratio of the glycerol to the catalyst is 5:1-10: 1; the reaction time is 3-10 hours.

Compared with the prior art, the invention has the following obvious advantages:

(1) the catalyst is suitable for the reaction of preparing the propanol by hydrogenolysis with water as a solvent, avoids the use of volatile, polluted or toxic solvents, is green and environment-friendly, and saves the production cost; meanwhile, the method is suitable for the characteristic that the byproduct glycerol from the biodiesel device often contains a large amount of water, and also overcomes the defect that the existing catalyst is easy to inactivate in a water-containing environment.

(2) The modified heteropoly acid and the transition metal salt are uniformly co-impregnated by a plurality of methods to prepare the catalyst, so that the catalyst has very high B acidity and simultaneously generates good coordination action of a strong acid center and a hydrogenation active center, thereby showing excellent glycerol hydrogenolysis conversion rate and n-propanol selectivity. Under the reaction condition of the invention, the hydrogenolysis conversion rate of the glycerol is more than 70 percent, and the selectivity of the n-propanol is more than 90 percent.

(3) The main components of the catalyst are transition metals such as Co, Ni, Zn, Cu and the like, so that the use of rare noble metals such as Pb, Pt and the like is avoided, and the production cost of the catalyst is obviously lower than that of the noble metal catalysts reported in most documents.

Drawings

FIG. 1 is a flow chart of the process for preparing the catalyst of the present invention. Firstly, heteropoly acid and transition metal cation are selected to react in acetic acid solution to carry out heteropoly acid structure modification, and transition metal ions are introduced to be doped into a heteropoly acid system. Then, preparing co-impregnation liquid by the modified heteropoly acid and the transition metal salt, uniformly impregnating the impregnation liquid on the pretreated carrier by adopting a multi-time dispersion dripping and dipping method, and then roasting, and carrying out hydrogen reduction activation to prepare the final bifunctional catalyst for preparing the propyl alcohol by the hydrogenolysis of the glycerol.

Detailed Description

Example 1: dissolving 0.1mol of silicotungstic acid and 0.03mol of nickel nitrate in 200ml of acetic acid solution, adjusting the pH value of the solution to 3.5, reacting in a constant-temperature water bath at 80 ℃ for 0.5 hour, standing at room temperature for 8 hours, evaporating in an oil bath to dryness, and drying in a vacuum drying oven at 50 ℃ overnight to obtain H₄NiSiW₁₂And (3) powder. Al to be used as a carrier₂O₃Soaking in propanol for 2 hr, filtering, and oven drying at 110 deg.C for 2 hr to obtain pretreated Al₂O₃Carrier. Then 3g of heteropoly acid H prepared above was added₄NiSiW₁₂Dissolving 4.95g nickel nitrate in 20ml distilled water to prepare a co-immersion liquid, dividing the co-immersion liquid into 5 equal parts, and spraying the co-immersion liquid on 20g pretreated Al for 5 times₂O₃And (3) fully and uniformly stirring the carrier after each spraying, and drying the carrier in a vacuum drying oven for 30 minutes at 110 ℃ until the impregnation liquid is completely loaded. Roasting the impregnated catalyst in a muffle furnace at 350 ℃ for 5 hours, and then reducing and activating the catalyst in a 60ml/min hydrogen atmosphere at 350 ℃ for 5 hours to form Ni/H₄NiSiW₁₂/Al₂O₃A catalyst.

Ni/H to be prepared₄NiSiW₁₂/Al₂O₃4g of catalyst, 70g of distilled water and 30g of glycerol are put into a high-pressure reaction kettle, initial pressure (hydrogen) is added to 6MPa, the mixture is stirred for 700 r/min, the temperature is raised to 240 ℃, the reaction is carried out for 8 hours, the conversion rate of the glycerol is 72.3 percent, and the selectivity of the n-propanol in the product is 91.7 percent.

Example 2: dissolving 0.1mol of phosphotungstic acid and 0.03mol of zinc nitrate in 200ml of acetic acid solution, adjusting the pH value of the solution to 5.5, reacting in a constant-temperature water bath at 80 ℃ for 1 hour, standing at room temperature for 10 hours, evaporating in an oil bath to dryness, and drying in a vacuum drying oven at 50 ℃ overnight to obtain H₃ZnPW₁₂And (3) powder. TiO to be used as a carrier₂Soaking in propanol for 2 hr, filtering, and oven drying at 110 deg.C for 3 hr to obtain pretreated Al₂O₃And (3) a carrier. Then 5.67g of heteropoly acid H prepared previously was added₃NiPW₁₂Dissolving 4.55g zinc nitrate in 20ml distilled water to obtain a co-soaking solution, dividing into 5 equal parts, and spraying onto 20g pretreated Al in 5 times₂O₃And (3) fully and uniformly stirring the carrier after each spraying, and drying the carrier in a vacuum drying oven for 30 minutes at 110 ℃ until the impregnation liquid is completely loaded. Roasting the impregnated catalyst in a muffle furnace at 350 ℃ for 5 hours, and then reducing and activating the catalyst in a hydrogen atmosphere of 70ml/min at 350 ℃ for 3 hours to form Zn/H₃ZnPW₁₂/TiO₂A catalyst.

Prepared Zn/H₃ZnPW₁₂/TiO₂6.5g of catalyst, 70g of distilled water and glycerol30g, putting the mixture into a high-pressure reaction kettle, adding initial pressure (hydrogen) to 4MPa, stirring for 700 r/min, heating to 350 ℃, reacting for 8 hours, wherein the conversion rate of the glycerol is 85 percent, and the selectivity of the n-propanol in the product is 90.6 percent.

Example 3: 0.1mol of silicotungstic acid and 0.03mol of zinc nitrate were dissolved in 200ml of acetic acid solution in a similar manner to example 1 using SiO₂As a carrier, preparing Zn/H₄ZnSiW₁₂/SiO₂A catalyst. Prepared Zn/H₄ZnSiW₁₂/SiO₂2g of catalyst, 70g of distilled water and 30g of glycerol are put into a high-pressure reaction kettle, initial pressure (hydrogen) is added to 6MPa, the mixture is stirred for 700 r/min, the temperature is raised to 450 ℃, the reaction is carried out for 8 hours, the conversion rate of the glycerol is 87.8 percent, and the selectivity of the n-propanol in the product is 90.9 percent.

Example 4: in a similar manner to example 1, a copper nitrate solution was used together with a heteropoly acid H₄NiSiW₁₂Preparing co-immersion liquid to prepare Cu/H₄NiSiW₁₂/Al₂O₃A catalyst. Prepared Cu/H₄NiSiW₁₂/Al₂O₃4g of catalyst, 70g of distilled water and 30g of glycerol are put into a high-pressure reaction kettle, initial pressure (hydrogen) is added to 6MPa, the mixture is stirred for 700 r/min, the temperature is raised to 240 ℃, the reaction is carried out for 8 hours, the conversion rate of the glycerol is 28 percent, and the selectivity of the n-propanol in the product is 31 percent.

Example 5: 0.1mol of phosphotungstic acid and 0.03mol of nickel nitrate were dissolved in 200ml of acetic acid solution in a similar manner to that of example 2, using Al₂O₃As a carrier, preparing Ni/H₃NiPW₁₂/Al₂O₃A catalyst. Ni/H to be prepared₃NiPW₁₂/Al₂O₃2g of catalyst, 70g of distilled water and 30g of glycerol are put into a high-pressure reaction kettle, initial pressure (hydrogen) is added to 6MPa, the mixture is stirred for 700 r/min, the temperature is raised to 250 ℃, the reaction is carried out for 8 hours, the conversion rate of the glycerol is 100 percent, and the selectivity of the n-propanol in the product is 92 percent.

Claims

1. A catalyst for preparing n-propanol by hydrogenolysis of glycerol is characterized in that: the catalyst comprises a carrier, and a heteropoly acid component and a transition compound attached to the carrierA metal component, said heteropoly acid component having H₄MSiW₁₂Or H₃MPW₁₂A heteropolyacid of structure wherein M is a transition metal;

the preparation method of the catalyst comprises the following steps:

a) reacting heteropoly acid with transition metal salt in acidic solution environment to form H₄MSiW₁₂Or H₃MPW₁₂A heteropolyacid of structure; wherein M is a transition metal;

b) soaking the catalyst carrier by adopting ethanol, propanol, oxalic acid or a mixture thereof for pretreatment so as to ensure that the subsequent co-impregnation liquid can be uniformly impregnated on the surface of the carrier;

c) will be prepared to have H₄MSiW₁₂Or H₃MPW₁₂Dissolving heteropolyacid with a structure and the same or different transition metal salt in the step a) in distilled water to prepare co-impregnation liquid with different concentrations, and then uniformly loading the prepared co-impregnation liquid on the surface of a carrier;

d) roasting the product of step c) in a muffle furnace at 300-500 ℃ for 2-8 hours; before use, the catalyst is subjected to reduction activation for 2 to 8 hours under a hydrogen atmosphere at the temperature of 300-500 ℃ to finally form M1/H₄M2SiW₁₂Support or M1/H₃M2PW₁₂A supported bifunctional catalyst;

m, M1 and M2 are one or the combination of Ni and Zn.

2. The catalyst of claim 1, wherein the support is Al₂O₃、SiO₂、TiO₂Or a complex thereof.

3. The catalyst of claim 1, wherein the transition metal salt is one of a carbonate, oxalate, acetate or chloride salt or a combination thereof.

4. A method for preparing the catalyst for the hydrogenolysis of glycerol to n-propanol as claimed in claim 1, comprising the steps of:

d) roasting the product of step c) in a muffle furnace at 300-500 ℃ for 2-8 hours; before use, the catalyst is subjected to reduction activation for 2 to 8 hours under a hydrogen atmosphere at the temperature of 300-500 ℃ to finally form M1/H₄M2SiW₁₂Support or M1/H₃M2PW₁₂A/carrier bifunctional catalyst.

5. The method of claim 4, wherein the co-impregnation liquid prepared in step c) is uniformly loaded on the surface of the support by using a plurality of times of dripping.

6. A process for producing n-propanol by the catalytic hydrogenolysis of glycerin, characterized by using the catalyst of claim 1.

7. The method of claim 6, wherein the hydrogenolysis solvent is water.

8. The method for producing n-propanol by the catalytic hydrogenolysis of glycerol as claimed in claim 7, wherein the reaction hydrogen pressure is 0.1 to 8 Mpa; the reaction temperature is 300-500 ℃; in the reaction, the mass ratio of the glycerol to the catalyst is 5:1-10: 1; the reaction time is 3-10 hours.