WO2017070874A1 - Polyacid catalyst for catalysing lignocellulose directional conversion - Google Patents

Abstract

A polyacid catalyst for catalysing lignocellulose directional conversion, having a Keggin structure, the formula thereof being [C₁₆H₃₃N(CH₃)₃]_3+2x[PW_12-xTi_xO₄₀](x=1, 2, 3). The catalyst can be used for catalysing lignocellulose to prepare glucose, xylose, and vanillin.

Description

Catalytic conversion of lignocellulose to polyacid catalyst Technical field

The invention relates to the technical field of catalyst preparation and application, in particular to a novel nano solid polyacid catalyst. At the same time, the invention also relates to the use of such nanocatalysts for the targeted conversion of lignocellulose.

Background technique

In the 21st century, the development of modern society faces serious problems such as resource shortage, energy crisis and environmental degradation. The shortage of fossil resources has become one of the bottlenecks of global economic development. Therefore, all countries have proposed corresponding development strategies. In order to protect the environment and save energy, people will focus on renewable resources, and biomass materials and energy will gradually surface, so the development of biomass industry has become an important development strategy of China. Biomass is widespread on the earth. It is an organic matter formed by photosynthesis of green plants, mainly including sugars (such as monosaccharides, starches, etc.), straw, lignocellulose, oils, etc. Therefore, biomass is taken An inexhaustible treasure trove of resources.

Among them, lignocellulose is a renewable resource widely distributed in nature. Non-edible lignocellulose includes various grasses, forestry processing residues, and agricultural waste straw. China is a large agricultural country with abundant lignocellulosic resources. Among them, about 200 million tons of crop straw are produced each year, and straw has become a useless burden. The burning of straw on the spot is becoming more and more serious, and the generated smoke has become a major public hazard. The main components of straw are fiber, semi-fibres and lignin. After hydrolysis and saccharification, cellulose materials can be converted into monosaccharides, which can be converted into fuel, gas and chemicals by chemical means on the one hand; In terms of biocatalysis, it can be converted into bulk fermentation products and liquid biofuels; the monosaccharide crystals obtained by the crystallization purification technology are more important industrial raw materials. The technology of lignocellulose raw sugar production (including glucose and xylose) is the key to the preparation of chemicals for crop straw utilization and is a key and limiting step for subsequent transformation.

The pretreatment methods currently used internationally mainly include physical methods (thermal degradation, radiation degradation, and mechanical degradation), biological methods (microorganisms), and chemical methods (oxidation and hydrolysis). The physical method is simple in process and easy to operate, but its degradation products are complicated, and the target product is difficult to control and has poor selectivity. The microbiological method has mild reaction conditions, environmental friendliness, high selectivity and simple equipment. With the development of modern biological research technology, it has become a hot spot of current research. However, the production cost is high, the preparation and purification are difficult, the catalytic activity and stability are low, the reaction time is long, and the pretreatment process is complicated, and it is still difficult to realize large-scale industrial application. Chemical methods include oxidative degradation and hydrolysis. Conventional inorganic acids such as H ₂ SO ₄ pretreatment are widely used pretreatment methods, which release most of the pentose sugars at high temperatures (170-240 ° C) and high pressure, and can improve the hydrolysis of cellulose. . However, hemicellulose is decomposed into xylose under these conditions. Xylose is not resistant to high temperature and high pressure and continues to degrade to form fermentation inhibitor furfural. At the same time, the removal rate of lignin is lower in a single treatment, within 20%; the product needs to be deacidified. A large amount of wastewater is produced. The problems of high energy consumption, equipment corrosion, complicated process, large amount of waste acid and environmental pollution have become technical bottlenecks restricting the large-scale production of cellulose. Alkaline pretreatment of NaOH and KOH is more conducive to breaking the ester bond between lignin, hemicellulose and cellulose than in the case of acid and other oxidants without degrading the hemicellulose polymer, but higher Cost and de-alkali treatment limit the large-scale use of the process. Oxidation pretreatment uses wet oxidation (Wet oxidation) technology to oxidize lignocellulosic feedstock in the presence of high temperature steam and high pressure oxygen to dissolve some lignin and most hemicellulose, but still has high consumption and high equipment cost. problem.

Polyoxometalates (POMs, also known as polyacids HPAs) with good

Acidity and redox properties are a class of acids and redox catalysts that have significant applications in the industry. Compared with the traditional catalyst sulfuric acid, it is non-toxic and non-polluting, and is a green environmentally friendly solid acid type and oxidation type catalyst. Among many POMs, Keggin-type titanium-containing polyacid H _3+2x [PW _12-x Ti _x O ₄₀ ] (x=1-3) is used in oxidation reaction with good catalytic oxidation ability and certain acid properties. Used in numerous organic reactions. The use of catalyzed directional conversion of lignocellulose has not been reported so far.

The use of Keggin-structured polyacids as catalysts can solve many technical problems in the lignocellulose orientation process:

1. The Keggin structure of polyacids contains Ti and W, which has high oxidizing ability. At the same time, due to the presence of Lewis acid center, the catalyst has certain acid properties, which can satisfy the acid/oxidation double pretreatment to separate lignin, cellulose and hemicellulose. Need to achieve the targeted conversion of lignocellulosic to glucose, xylose and vanillin;

2. The POMs system is a solid catalyst for acid/oxidation dual center. In the lignocellulose reaction system, it is a heterogeneous catalyst, which is easy to separate from the reaction system, and the regeneration method is simple, does not generate a large amount of sewage, and reduces the use cost of the catalyst.

3, POMs solid catalyst self-assembly in the water system to form a "nano system", improve the specific surface area of the catalyst to improve the catalytic activity of the catalyst. The catalyst conversion efficiency is high.

4, POMs one-step treatment of lignocellulose, simple operation, no separation process of intermediate products, low production costs, and secondary pollution of green, no oxidants.

By designing and synthesizing polyacid catalysts with different compositions, the requirements for the targeted conversion of lignocellulose to glucose, xylose and vanillin can be met, and the utility is strong.

Summary of the invention

It is an object of the present invention to provide a process for the preparation of POMs and for use in the targeted conversion of lignocellulose.

The present invention contemplates providing a polyacid catalyst having a nanostructure for use in lignocellulose conversion.

To achieve this, it is implemented through the following solutions.

A solid nanocatalyst is prepared by the following method:

The polyacid compound K _3+2x [PW _12-x Ti _x O ₄₀ ]·6H ₂ O and the surfactant [C ₁₆ H ₃₃ (CH ₃ ) ₃ N]Br are weighed according to a molar ratio of 1:0-5; Pour the polyacid compound K _3+2x [PW _12-x Ti _x O ₄₀ ]·6H ₂ O into the reactor, add distilled water with a mass ratio of 1:5-10 times, heat to 50-70 ° C, stir to dissolve Further adding a surfactant thereto, the reaction solution is aged for 5-10 hours, a white solid is precipitated, filtered, and the precipitate is washed 2-3 times with distilled water until the pH of the eluate reaches 5-8 to obtain a precipitate; The precipitate was placed in a muffle furnace and sintered at 150-300 ° C for 2-6 hours to obtain a lignocellulose-directed polyacid catalyst. Its yield is 50%.

A method for catalyzing the targeted conversion of lignocellulose to glucose, xylose and vanillin by using a polyacid catalyst for catalyzing the conversion of lignocellulose provided by the present invention is as follows:

The wood fiber, the catalyst and the water are added to the high-pressure reactor according to a certain ratio (1:4.5:70), and the reaction temperature is set to be 80-140 ° C. The reaction time is 5 to 10 hours, which converts lignocellulose into glucose, xylose and vanillin. The amount of the catalyst is 10 to 50 mg. After the end of the reaction, the catalyst and unreacted wood fibers were separated by centrifugation, and the conversion was repeated. The product was extracted twice with methyl isobutyl ketone, and the organic phase was distilled under reduced pressure at 40 ° C to distill off methyl isobutyl ketone to obtain the product vanillin; the aqueous phase was extracted with ethanol, and the ethanol phase was distilled under reduced pressure at 40 ° C to give ethanol. Glucose; the remaining aqueous phase was distilled under reduced pressure at 50 ° C to obtain xylose.

detailed description

Embodiment 1

The molar ratio of 1:4 polyacid compound K ₅ [PW ₁₁ TiO ₄₀ ]·6H ₂ O and the surfactant [C ₁₆ H ₃₃ (CH ₃ ) ₃ N]Br were respectively weighed; the polyacid compound K ₅ [PW ₁₁ TiO ₄₀ ··6H ₂ O was poured into the reactor, distilled water having a mass ratio of 6 times was added, heated to 60 ° C, stirred and dissolved; a surfactant was added thereto, and the reaction solution was aged for 7 hours to precipitate a white solid. After filtration, the precipitate was washed 3 times with distilled water until the pH of the eluate reached 7.1, and a precipitate was obtained; the precipitate was placed in a muffle furnace and sintered at 170 ° C for 2 hours to obtain a lignin-directed transformation. Acid catalyst. Its yield is 50%.

Embodiment 2

Put a catalyst of 1 g of lignocellulose, 30 mg [C ₁₆ H ₃₃ (CH ₃ ) ₃ N] ₅ [PW ₁₁ TiO ₄₀ ]·6H ₂ O into a high pressure reactor, add 6 mL of deionized water, and heat Stir. The reaction temperature was 100 ° C and the reaction time was 8 hours. After the end of the reaction, after cooling, the reaction mixture was placed in a centrifuge tube for centrifugation. The supernatant contained the product glucose, xylose and vanillin, and the precipitated unreacted lignocellulose and catalyst. The product was extracted twice with methyl isobutyl ketone, and the organic phase was distilled under reduced pressure at 40 ° C to distill off methyl isobutyl ketone to obtain the product vanillin; the aqueous phase was extracted with ethanol, and the ethanol phase was distilled under reduced pressure at 40 ° C to give ethanol. Glucose; the remaining aqueous phase was distilled under reduced pressure at 50 ° C to obtain xylose. The yields were 45%, 30% and 61%, respectively.

Claims (2)

1. A polyacid catalyst for catalyzing the acidification and oxidation of lignocellulose, comprising glucose, xylose, and vanillin, characterized by being a polyacid compound having a Keggin structure; said Keggin structure The general formula of polyacid compounds is:

   [C ₁₆ H ₃₃ N(CH ₃ ) ₃ ] _3+2x [PW _12-x Ti _x O ₄₀ ] (x=1, 2, 3).
2. A polyacid catalyst for catalyzing the directional conversion of lignin according to claim 1, wherein said polyacid compound is preferably:

   [C ₁₆ H ₃₃ (CH ₃ ) ₃ N] ₉ [PW ₉ Ti ₃ O ₄₀ ]·6H ₂ O

   [C ₁₆ H ₃₃ (CH ₃ ) ₃ N] ₇ [PW ₁₀ Ti ₂ O ₄₀ ]·6H ₂ O

   [C ₁₆ H ₃₃ (CH ₃ ) ₃ N] ₅ [PW ₁₁ TiO ₄₀ ]·6H ₂ O