TWI567050B - Method for producing isopropanol by catalytic conversion of cellulose - Google Patents

Description

Method for catalytically converting cellulose to isopropanol

The present invention relates to a process for producing isopropanol, and more particularly to a process for producing isopropanol from cellulose.

Isopropanol is an important chemical product and raw material. It is an excellent solvent and can be miscible with ethanol, ether, chloroform and water. Isopropanol is also an intermediate in the synthesis of various organic compounds. It can be widely used in the fields of pharmaceuticals, cosmetics, plastics, perfumes, coatings, etc. Among them, paints and inks are the main application areas, accounting for about the total consumption of isopropanol. 50%. In addition, isopropanol can be dehydrated to obtain another important industrial product, propylene, which is in high demand for propylene.

At present, the main method for producing isopropanol is propylene hydration. According to whether or not an intermediate product is formed, it can be further divided into propylene indirect hydration and direct propylene hydration. However, since propylene can be used to produce products such as polypropylene, phenol, acetone, butanol, octanol, acrylonitrile, propylene oxide, acrylic acid, and isopropanol, the demand for propylene is extremely high, which inevitably leads to a shortage of propylene resources. . Therefore, there is still a need to develop other processes for producing isopropanol, particularly raw materials other than propylene.

Cellulose is the most abundant renewable resource on the planet, with abundant sources, such as straw remaining in agricultural production, waste from forestry production, and so on. Therefore, it is very important to make full use of cheap cellulose to convert into high-value chemicals. Compared with other renewable resources, cellulose can not be eaten, thus minimizing the adverse effects of biomass energy conversion process on human food security.

Since cellulose has a molecular bond and an intramolecular hydrogen bond, it has a very stable structure. Conventional techniques usually first hydrolyze cellulose to glucose using an acid as a catalyst, and then hydrogenolyze into other chemicals.

In the process for preparing a polyol from the catalytic conversion of cellulose, a molecular sieve-supported noble metal catalyst is mostly used, the cost of such a catalyst is high, and the product selection rate is not easily controlled. The nickel-tungsten (Ni-W) catalyst has been used to catalyze cellulose, but the main product is ethylene glycol. For example, reference can be made to Chinese patents CN101723802, CN101735014A and the like. At present, the prior art does not have a technique for preparing isopropyl alcohol as a main product from cellulose catalysis.

In other conventional techniques for the catalytic conversion of cellulose, in order to increase the conversion rate and the yield of the target product, some mineral acid is also added to the reaction system, thereby generating a large amount of waste water. Also, since the acid is added, the requirements for the reaction equipment are also increased.

In addition, prior art shows that prior to the step of catalytic conversion, cellulose must undergo several pretreatments to achieve better catalytic effects, such as mechanical ball milling, chopping, beating, sodium hydroxide solution or liquid ammonia, and other chemical treatments. Ion-electron radiation, microwave sonication, steam explosion, etc., to reduce the crystallinity of cellulose and improve the reactivity of cellulose. These cumbersome pre-treatments increase manufacturing costs and are not conducive to industrial applications.

In addition to the shortcomings of the aforementioned acid addition and pretreatment, there are many technical literatures showing that the mass ratio of cellulose to water cannot be increased in the catalytic process, the reaction concentration is very low, and the requirements for product separation and purification are high. . Especially in the condition that the quality of cellulose and water is relatively high, coking phenomenon is easy to occur, which greatly affects the progress of catalytic conversion, and is not conducive to the operation and management of equipment.

The present invention provides a process for preparing isopropanol from cellulose, characterized in that a relatively pure cellulose raw material is subjected to a one-step catalytic reaction in the presence of a copper chromium catalyst to be converted into isopropanol. The relatively pure cellulose raw material means a raw material having a cellulose content of more than 85% by weight (wt%). The main sources of cellulose are hemp, wheat straw, straw, bagasse and the like. The main impurities are hemicellulose, lignin and some minerals. Salts, because too much impurities affect the catalytic activity and the yield of the target product, usually require a purified pretreatment step, but in the present invention, only the cellulose purity needs to be above 85%. The pre-processing steps can be referred to "dyeing and finishing technology, 2011, 33, 12-16".

By the copper-chromium catalyst provided by the present invention, cellulose can be directly catalytically converted into isopropanol in one step, and the copper-chromium catalyst has excellent isopropanol selectivity. The reaction pathway for catalyzing the conversion of cellulose using a copper chromium catalyst is as follows. First, the cellulose is hydrolyzed to glucose, followed by hydrogenation of the glucose to form sorbitol, followed by hydrogenolysis to form a product including isopropanol. The conversion of the present invention can be accomplished in one step, that is, the above-mentioned "hydrolysis-hydrogenation-hydrogenation" reaction can be carried out in a single reaction step in an actual industrial system.

In one embodiment, the copper-chromium catalyst comprises a CuCr ₂ O ₄ active phase or an active phase comprising a CuCr ₂ O ₄ active phase and a group of CuO and Cr ₂ O ₃ , for example, CuCr ₂ O The structure of ₄ , the structure of CuCr ₂ O ₄ /CuO, the structure of CuCr ₂ O ₄ /Cr ₂ O ₃ , etc., wherein the molar ratio of copper to chromium is 0.25 or more, for example, Mo/Cu of Mo/Cr The ratio is 0.3, 0.5, 1, 1.5, 2, 2.5, 4, 5, 6, 8, and the like. In a preferred embodiment, the Mo/r ratio of Cu/Cr is 0.5 or more.

The process of the present invention can be catalyzed at a higher cellulose to water mass ratio (water as medium, cellulose mass/water mass ratio) as compared to conventional techniques. In some embodiments, the mass ratio of cellulose to water is from 0.1 to 10 wt% and can be up to 15 wt%.

In one embodiment, the temperature of the catalytic reaction is from 200 ° C to 270 ° C, preferably from 220 ° C to 260 ° C.

The medium for the catalytic reaction according to the invention may be water. In one embodiment, a raw material comprising cellulose having a mass ratio of cellulose to water of 15 wt% or less is used in a water-based environment at a reaction temperature of 200 ° C to 270 ° C, including CuCr ₂ O _A one-step catalytic conversion to isopropanol in the presence of a copper-chromium catalyst having an active phase and a copper/chromium molar ratio of 0.25 or more.

In a preferred embodiment, a raw material comprising cellulose having a cellulose to water mass ratio of 0.1 to 10% by weight, in a water-based environment, a reaction temperature of 220 ° C to 260 ° C and 5-8 Under one reaction pressure of MPa, one-step catalytic conversion to isopropanol is carried out by a copper-chromium catalyst; wherein the copper-chromium catalyst comprises a structure of CuCr ₂ O ₄ /CuO, and the molar ratio of copper/chromium is 0.5 or more. In a preferred embodiment, the yield of isopropanol obtained according to the process of the present invention is calculated based on the total weight of cellulose used for the catalytic reaction, up to 25% or more, usually up to 45% or more. In a more preferred embodiment, the yield of isopropanol is 50% or more, for example, 55% or more, 60% or more, 65% or more, 70% or more, 80% or more, and the like.

The invention provides a technology for preparing isopropanol by one-step direct catalytic conversion of cellulose. The water is used as a medium, and no additional additives such as an acid are needed, and a copper-chromium catalyst is used for catalytic conversion, thereby achieving excellent activity and selectivity. According to the technique of the present invention, catalysis can be carried out at a high cellulose to water mass ratio, and coking phenomenon can be effectively prevented, and even if the cellulose is not subjected to pretreatment, a satisfactory result can be obtained. The technology of the invention is environmentally friendly, simple, and can achieve high isopropanol yield, and is very suitable for industrial mass production. The process according to the invention allows the conversion of cellulose to be above 30%, usually up to 50%. Yubu In some embodiments, the conversion rate of cellulose is 60% or more, preferably 80% or more, more preferably 90% or even 100%, depending on the set reaction parameters.

1. Preparation of copper chromium catalyst

For the preparation of the catalyst in this embodiment, see C. Liang, Z. et al., Catal. Lett. (2009), 130, 169-176; Z. Ma et al., J. Mater. Chem. (2010), 20, 755. -760; and Z. Xiao et al., Ind. Eng. Chem. Res. (2011), 50, 2031-2039, the entire contents of which are incorporated herein by reference. Specifically, the following methods can be used:

(1) Sol-gel method

Formulated Cr(NO ₃ ) ₃ . 9H ₂ O and Cu(NO ₃ ) ₂ . A 3H ₂ O ethanol solution (metal concentration of 0.3 g/ml (g/mL)) and a controlled metal Cu/Cr molar ratio of 0.25, 0.5, 1, 2 and 4, respectively. At 60 ° C, 18 mL of propylene oxide was added with stirring to obtain a gel. After drying overnight at 85 ° C, it was calcined in an air atmosphere at 500 ° C for 2 hours (h) to obtain a copper chromium catalyst.

(2) Carbon template method

Formulated Cr(NO ₃ ) ₃ . 9H ₂ O and Cu(NO ₃ ) ₂ . 3H ₂ O a mixed solution of ethanol and water, controlling the metal Cu/Cr molar ratio to 0.5, and immersing it in a high volume of activated carbon at an equal volume at room temperature. After drying overnight at 85 ° C, it was calcined in an air atmosphere at 500 ° C for 2 hours to obtain a copper chromium catalyst.

(3) Commercial catalyst

Commercial copper chromium catalysts were purchased from Southern Chemicals. The catalysts were columnar and needed to be ground into powder before use.

For the copper chromium catalysts employed in the present invention, preparation at different Cu/Cr molar ratios will affect the crystalline phase of the catalyst. Furthermore, the formation of the active phase CuCr ₂ O ₄ is also quite important for the copper-chromium catalyst, since the active phase CuCr ₂ O ₄ relatively achieves a higher cellulose conversion and isopropanol yield. Figure 1 shows the X-ray diffraction (XRD) pattern of the copper-chromium catalyst prepared by the sol-gel method. The results show that the Cu-Cr catalysts listed in Table 1 can form the active phase CuCr ₂ O except for the catalyst obtained by calcination at 300 °C. ₄ .

Second, the catalytic reaction of cellulose

The copper chromium catalyst was first reduced under hydrogen at 300 ° C for 2 hours before the catalytic reaction.

In one embodiment, cellulose (for example, cellulose purchased from Belleville Chemical, model Avicel pH-101) and a certain amount of water are added to a 50 mL autoclave for reaction, the reaction atmosphere is hydrogen, and the reaction pressure is controlled. Between 4-8 MPa, the temperature range is 200-270 ° C, and the mass ratio of cellulose to water is selected to be 15 wt% or less. The product obtained by the catalytic reaction is mainly a liquid phase product, and the gas phase products (such as CH ₄ , C ₂ H ₄ , CO _{2 ,} etc.) are few. The obtained liquid phase product was analyzed, and the conversion rate and the yield were calculated, and the calculation formula was: Conversion rate (%) = mass of converted cellulose / total mass of initial cellulose × 100%

Yield (%) = mass of product / total mass of initial cellulose x 100%.

The effects of various parameter conditions on the catalytic reaction were tested separately below.

(1) Effect of Cu/Cr molar ratio on catalytic reaction

The test was carried out with the aforementioned different preparation methods, sources, Cu/Cr molar ratio copper chromium catalyst. The reaction conditions were as follows: mass ratio of cellulose to water was 1 wt%, catalyst was 0.3 g, reaction pressure was 6 MPa, reaction temperature was 220 ° C, stirring speed was 900 rpm, and reaction time was 0.5 h. The results are shown in Table 2.

Comparing the above three copper-chromium catalysts, in the case of the same Cu/Cr molar ratio, the catalyst prepared by the sol-gel method and the catalyst prepared by the carbon template method have comparable conversion rates to cellulose (64.2% and 65.1%). However, the isopropanol yield of the catalyst prepared by the sol-gel method is significantly higher. Catalysts prepared by the carbon template method have a wide distribution of selectivity to products. The commercial copper-chromium catalyst has a slightly poorer activity on cellulose conversion, about 60.2%, and the obtained products are mainly glycerin, 1,2-propanediol and ethylene glycol. The yields of the three are similar, but the selectivity to isopropanol Very poor, only 1.1%. For copper chromium catalysts of the same Cu/Cr molar ratio, the difference in these catalytic reactions may be due to changes in some of the physicochemical properties of the catalyst, such as specific surface area, surface species, and the like.

Further, as shown in Table 2, for the copper-chromium catalyst prepared by the sol-gel method, as the Cu/Cr molar ratio increases, the conversion of cellulose increases, and the yield of isopropanol increases, and this result is related to Cu. The structure of the -Cr catalyst is related. Referring to Table 1 and the predominant crystalline phase catalytic reaction results in Table 2, when the Cu / Cr molar ratio less than the stoichiometric formed CuCr ₂ O ₄ ratio of 0.5 to form a structure of a _{CuCr 2 O 4 / Cr 2 O} 3 , it has been The conversion rate of cellulose can be more than 50%, and isopropanol and sorbitol are the main products; and when the ratio is more than 0.5, the structure of CuCr ₂ O ₄ /CuO is formed, wherein the formation of CuCr ₂ O ₄ It can increase the dispersion of copper-chromium catalyst, so that copper derived from CuCr ₂ O ₄ has higher catalytic activity, and when the total amount of catalyst is the same, the Cu/Cr molar ratio increases, so that the content of active copper also increases. The reaction time of 0.5 hours has made the cellulose conversion rate more than 60%, even more than 90%, and the selectivity of isopropyl alcohol is also significantly increased, up to 25%-62%. In the absence of a catalyst which forms the active phase CuCr ₂ O ₄ , it shows a lower cellulose conversion and a yield of isopropanol. Table 2 demonstrates that the structure of CuCr ₂ O ₄ /CuO is more favorable for the progress of the catalytic reaction and the selectivity of the target product isopropanol. At the same time, the formation of the active phase CuCr ₂ O ₄ can significantly increase the activity of the catalyst.

(2) Effect of reaction temperature on catalytic reaction

The copper chromium catalyst (Cu/Cr=4) prepared by the sol-gel method was subjected to a catalytic reaction. The reaction conditions were as follows: mass ratio of cellulose to water was 1 wt%, catalyst was 0.3 g, reaction pressure was 6 MPa, stirring speed was 900 rpm, and reaction time was 0.5 h. The results are shown in Table 3.

As shown in Table 3, as the reaction temperature increases, the cellulose conversion rate also rapidly increases. When the reaction temperature is increased from 200 ° C to 220 ° C, the cellulose conversion rate immediately jumps to over 90%, and when the reaction temperature reaches 240 ° C or higher, the conversion rate reaches 100%. Overall, the yield of isopropanol also increased with increasing temperature, but the reaction temperature exceeded 260 ° C, and the yield of isopropanol began to decrease.

Since high temperature favors cellulose hydrolysis and subsequent hydrogenolysis, the conversion of cellulose, the yield of isopropanol and sorbitol are significantly increased with increasing temperature over a suitable temperature range. However, when the temperature rises to a certain level (245 ° C), the hydrolysis of cellulose tends to be complete; if the temperature is raised (260 ° C), the hydrogenolysis of sorbitol becomes especially obvious, that is, sorbitol continues to hydrogen. Decomposition into other small molecule products results in a decrease in yield, but at this point the effect on isopropanol is low, which still maintains a fairly good yield. If the temperature is further increased (270 ° C), isopropanol will further hydrolyze into other gas phase products at high temperature, so the isopropanol yield decreases at the reaction temperature of 270 ° C, and the yield of other unknown products is obvious. Upgrade.

(3) Effect of reaction pressure on catalytic reaction

The copper chromium catalyst (Cu/Cr=4) prepared by the sol-gel method was subjected to a catalytic reaction. The reaction conditions were as follows: mass ratio of cellulose to water was 1 wt%, catalyst was 0.3 g, reaction temperature was 220 ° C, stirring speed was 900 rpm, and reaction time was 0.5 h. The results are shown in Table 4.

As shown in Table 4, when the hydrogen pressure is increased, the cellulose conversion rate is increased, and the yield of the target product isopropanol is rapidly increased first, and then tends to be stable. In addition, observing the yield of sorbitol is a parabolic trend. Obviously, increasing the reaction pressure is beneficial to cellulose conversion, but further increasing the reaction pressure enhances the hydrogenolysis of sorbitol and lowers the yield of sorbitol. The yield of ethylene glycol and 1,2-propanediol is increased. When the reaction pressure reaches 8 MPa, the subsequent hydrogenolysis may occur in the isopropanol, so that the yield is slightly lowered, but overall, the influence of the reaction pressure on the subsequent hydrogenolysis of the isopropanol has no influence on the reaction temperature.

(4) Effect of reaction time on catalytic reaction

The copper chromium catalyst (Cu/Cr=4) prepared by the sol-gel method was subjected to a catalytic reaction. The reaction conditions were a mass ratio of cellulose to water of 1 wt%, a catalyst of 0.3 g, a reaction temperature of 220 ° C, a reaction pressure of 6 MPa, and a stirring speed of 900 rpm. The results are shown in Table 5.

When the reaction time is 1 hour, 100% cellulose conversion can be achieved, and the yield of isopropanol can be stabilized at 0.5 hours in reaction time, and slightly lower at 4 hours, which should be a long-term reaction condition for subsequent hydrogen. The probability of occurrence of the solution was higher, and the same trend was observed in the observation of the yield of sorbitol.

(5) Effect of mass ratio of cellulose to water on catalytic reaction

The copper chromium catalyst (Cu/Cr=4) prepared by the sol-gel method was subjected to a catalytic reaction. The reaction conditions were as follows: catalyst 0.3 g, reaction temperature 220 ° C, reaction pressure 6 MPa, stirring speed 900 rpm, and reaction time of 0.5 h and 5 h, respectively. The results are shown in Table 6.

As shown in Table 6, the mass ratio of cellulose to water has a significant effect on the catalytic reaction. When the mass ratio of cellulose to water increases, the conversion of cellulose decreases, and the yield of isopropanol decreases slowly, which may be related to the adsorption equilibrium and mass transfer of reactants and products on the catalyst. Relatedly, a large amount of cellulose covers the active site, and the produced product cannot be effectively desorbed from the active site, resulting in a decrease in conversion rate.

Prolonging the reaction time, it was found that only the conversion of cellulose was increased, but the yield of isopropanol was not improved. As mentioned above, the prolonged time caused subsequent hydrogenolysis of isopropanol. Under the condition of high cellulose to water mass ratio, high carbon polyols such as isosorbide, hexanediol and hexanetriol are produced, which further explains the problem of competitive adsorption of the product. The catalyst does not have enough active sites to hydrogenate sorbitol to Low carbon polyol.

In addition, under this experimental condition, even if the mass ratio of cellulose to water is increased to 15 wt%, no coking phenomenon occurs, indicating that the copper-chromium catalyst effectively prevents the high cellulose to water mass ratio during the hydrogenolysis process. The phenomenon of coking.

(6) Effect of mass ratio of high cellulose to water on catalytic reaction

The copper chromium catalyst (Cu/Cr=4) prepared by the sol-gel method was subjected to a catalytic reaction. The reaction conditions were as follows: mass ratio of cellulose to water was 10 wt%, catalyst was 0.3 g, reaction temperature was 220 ° C, reaction pressure was 6 MPa, and stirring speed was 900 rpm. The results are shown in Table 7.

At a mass ratio of 10 wt% high cellulose to water, the effect of reaction time on the catalytic reaction is similar to the use of low cellulose to water mass ratio. On the whole, the cellulose conversion rate increases with time, but the isopropanol yield decreases. Obviously, under the condition of high cellulose to water mass ratio, prolonging the reaction time is more favorable for isopropanol and sorbitol. Subsequent hydrogenolysis causes an increase in the yield of other products.

The invention develops a new process for preparing isopropanol from raw material for the first time, and can prepare isopropanol from one-step direct catalytic conversion of cellulose without adding additional additives such as acid, so the equipment requirements are not high and will not be A large amount of wastewater is produced in the process. Moreover, the copper-chromium catalyst of the invention can achieve good activity and selectivity, and the preparation process is simple and inexpensive. By adopting the technology of the invention, the production conditions are relatively mild, the energy consumption is low, and the catalyst can be catalyzed at a high cellulose to water mass ratio, and the coking phenomenon is effectively prevented.

The preparation of isopropanol by one-step direct catalytic conversion of cellulose can solve the problem of the shortage of raw materials for preparing isopropyl alcohol from propylene hydration. At the same time, the isopropanol obtained by the method of the invention can be dehydrated to form propylene, but can be used as propylene. The source effectively compensates for the current situation of the propylene market being in short supply.

In summary, the technical solution of the present invention is environmentally friendly, simple, and can achieve a high yield of isopropanol, and is extremely suitable for industrial mass production.

The above description of the specific embodiments is intended to be illustrative of the invention, and is not intended to limit the invention. It will be understood by those skilled in the art that various changes or modifications may be made to the present invention without departing from the scope of the appended claims.

Figure 1 shows the X-ray diffraction (XRD) pattern of a copper chromium catalyst.

Claims (13)

A method for preparing isopropanol from cellulose, characterized in that: in the presence of a copper-chromium catalyst, the cellulose is catalytically reacted to convert to isopropanol in water; wherein the copper-chromium catalyst comprises CuCr ₂ O ₄ active phase, or an active phase comprising CuO and Cr ₂ O ₃ . The method of claim 1, wherein the transformation is carried out in a single industrial reaction. The method of claim 1 or 2, wherein the copper chromium catalyst is prepared by a sol-gel method. The method of claim 1 or 2, wherein the catalytic reaction is free of an acid additive. The method of claim 1 or 2, wherein the copper/chromium has a molar ratio of 0.25 or more in the copper-chromium catalyst. The method of claim 5, wherein the copper-chromium catalyst has a molar ratio of copper/chromium of 0.5 or more. The method of claim 1, wherein the cellulose to water mass ratio is 15% by weight or less. The method of claim 1, wherein the cellulose to water mass ratio is from 0.1 to 10% by weight. The method of claim 1 or 2, wherein the temperature of the catalytic reaction is from 200 ° C to 270 ° C. The method of claim 1 or 2, wherein the temperature of the catalytic reaction is from 220 ° C to 260 ° C. The method of claim 1 or 2, wherein the catalytic reaction has a pressure of 5 to 8 MPa. A method for preparing isopropanol from cellulose, characterized in that: in water as a medium, the mass ratio of cellulose to water is 0.1-10 wt%, the reaction temperature is 220 ° C to 260 ° C, and the pressure is 5-8 MPa. Under the condition, the copper-chromium catalyst is catalytically converted into isopropanol by one-step catalysis; wherein the copper-chromium catalyst comprises a structure of CuCr ₂ O ₄ /CuO, and the molar ratio of copper/chromium is 0.5 or more. The method of claim 12, wherein the copper chromium catalyst is prepared by a sol-gel method.