Method for improving catalytic dehydration reaction activity of hydroxyl compounds and adjusting product selectivity

Abstract

The invention discloses a method for improving catalytic dehydration reaction activity of hydroxyl compounds and adjusting product selectivity. According to the method, on the premise of not increasing process condition harshness including reaction temperature, a small amount of co-feed substances are added into a reaction system, and under the conditions of not participating in reaction and not generating additional byproducts, the dehydration reaction activity of the hydroxyl compound is controllably improved, the selectivity is adjusted, olefin and ether products are prepared with high selectivity, and the method is suitable for industrial production. And the co-feeding substance in the system after the reaction is greatly different from the boiling point of the main reactant and the boiling point of the product, so that the separation process is simple, and the co-feeding substance can be cyclically fed after separation to realize reutilization.

Description

Technical Field

[0001] The invention belongs to the field of organic chemical synthesis and relates to a method for improving the catalytic dehydration reaction activity of hydroxyl compounds and adjusting the product selectivity. Background Art

[0002] Biomass is a type of abundant renewable organic carbon resource with diverse chemical structures. It can be used to prepare fuels and important chemicals through catalytic conversion, which can partially replace and supplement traditional synthetic routes based on fossil resources and reduce carbon dioxide emissions. However, due to the high oxygen content of biomass raw materials, the current main value-added strategy requires the use of pyrolysis and catalytic reactions to partially or completely deoxygenate them to achieve the lowest possible oxygen-to-carbon ratio. Therefore, efficient and controllable catalytic deoxygenation of biomass is an important topic that catalytic workers at home and abroad are committed to studying.

[0003] Dehydration reaction is a direct, efficient and controllable reaction to remove oxygen. It is one of the key steps in converting biomass into biofuels or platform compounds. The demand for dehydration reactions in the field of fuel production is growing to meet the continuous demand for fuels in the energy market. In the petroleum industry, dehydration reactions are widely used in the dehydration of ethanol to produce ethylene, which is one of the key raw materials for the synthesis of petrochemical products and fuels. Ether compounds generated by dehydration reactions are also important organic solvents and chemical intermediates.

[0004] Compared with the homogeneous catalytic system used in traditional industry, the heterogeneous catalytic system is easier to separate and recover the catalyst, has lower production costs, and the equipment will not be corroded. In addition, the interface between the multiphases can provide more reaction sites and special environments, which is conducive to the selective generation of target products in certain reaction routes and improves the catalytic activity. Because the catalyst fixed on the carrier can better resist the influence of external conditions such as toxic substances or high temperature, the catalyst in the heterogeneous catalytic system is generally more stable. The most important thing is that heterogeneous catalysis allows different reaction conditions to be used in different phases. This feature helps to optimize the temperature, pressure and other conditions in the catalytic reaction to obtain higher yield and selectivity.

[0005] In order to improve the efficiency and selectivity of dehydration reactions, scientists are committed to developing new and efficient catalysts. Optimizing catalysts can accelerate reaction rates, improve product purity, and reduce reaction temperatures and energy consumption, which is crucial for environmentally friendly production. In addition, a more convenient way to increase the rate of thermal catalytic reactions is to increase the temperature of the reaction system, but the corresponding energy consumption will increase, and the risk factor will also increase, which does not meet the economic, safe, and efficient production requirements. Summary of the invention

[0006] The present invention provides a method for improving the catalytic dehydration reaction activity of hydroxyl compounds and adjusting the product selectivity. The method, without increasing the harshness of process conditions including reaction temperature, can controllably improve the dehydration reaction activity of hydroxyl compounds and adjust the selectivity (for example, ether-olefin ratio) by adding a small amount of co-feed material to the reaction system without participating in the reaction and without generating additional by-products, and produce olefins and ether products with high selectivity. Moreover, the co-feed material in the system after the reaction has a large difference in boiling point from the main reactant and the product, and the separation process is simple. The co-feed material can be recycled after separation to achieve repeated use, thereby achieving the production purpose of low energy consumption, high efficiency, safety and economy.

[0007] The method of improving the catalytic dehydration reaction activity of hydroxyl compounds and adjusting the product selectivity of the present invention is as follows:

[0008] A mixture of a hydroxy compound and a co-feed material is subjected to a dehydration reaction in the presence of a solid acid catalyst to generate a corresponding olefin or ether compound or a mixed product of the two. The co-feed material is selected from ketones, aldehydes, cyclic ether polar non-protonic solvents, and alkane non-polar solvents.

[0009] The hydroxyl compounds described in the present invention are hydroxyl compounds commonly used in existing dehydration reaction processes to produce olefins or ethers, including but not limited to alcohols, phenols, etc., such as methanol, ethanol, n-propanol, butanol, cyclohexanol, phenol, glycerol, etc.

[0010] The solid acid catalyst described in the present invention is a solid catalyst commonly used in the existing hydroxy compound dehydration reaction to produce olefins or ethers process, including but not limited to hydrogen-type molecular sieves, supported heteropoly acids, ion exchange resins, Lewis acids and other catalysts. Among them, the hydrogen-type molecular sieve catalyst includes a carrier and an acidic component, the carrier is silica, alumina or a combination thereof, and the acidic component is amorphous silica-alumina, zeolite or a combination thereof; the supported heteropoly acid catalyst contains an element of IUPAC Group 13 and a metal of IUPAC Groups 4-6, the element of IUPAC Group 13 is at least one of boron, aluminum and gallium, and the metal of IUPAC Groups 4-6 is at least one of titanium, zirconium, niobium, hafnium and tantalum.

[0011] The ketone polar aprotic solvents described in the present invention include but are not limited to acetone, butanone, pentanone, etc., the aldehyde polar aprotic solvents include but are not limited to formaldehyde, acetaldehyde, etc., the cyclic ether polar aprotic solvents include but are not limited to 1,4-dioxane, etc., and the alkane non-polar solvents include but are not limited to cyclohexane, n-hexane, etc.

[0012] In a specific embodiment of the present invention, the co-feed material is represented by 1,4-dioxane, n-butyraldehyde, 2-methyl-butyraldehyde, isovaleraldehyde, n-valeraldehyde, acetone and n-hexane.

[0013] In the present invention, various types of co-feed materials can improve the activity of the dehydration reaction of hydroxyl compounds and adjust its selectivity, and different materials have different degrees of influence. For example, ketone and aldehyde polar non-protonic solvents have the greatest effect on improving the activity, while alkane non-polar solvents have the highest effect on regulating the ether-olefin ratio of the product.

[0014] The dehydration reaction conditions described in the present invention are the process conditions commonly used in the existing hydroxyl compound dehydration reaction to produce olefins or ethers. Specifically, the hydroxyl compound and the co-feed material mixture can be subjected to a liquid-solid phase dehydration reaction in the presence of a solid acid catalyst in liquid form. For the hydroxyl compound and the co-feed material mixture with a lower boiling point, it can be first gasified and then subjected to a gas-solid phase dehydration reaction in the presence of a solid acid catalyst in gas form. The liquid-solid phase dehydration reaction temperature is 100-150°C, and the reaction solvent is a solvent such as water, n-hexane, tetrahydrofuran, etc.; the gas-solid phase reaction temperature is 50-120°C, and the reaction carrier gas is an inert gas such as nitrogen, argon, or air. The pressure of the reactants is 0kPa-10kPa.

[0015] The amount of the co-feed material added to the mixture of the hydroxy compound and the co-feed material of the present invention is not particularly limited, and is preferably 1 wt % or more.

[0016] Preferably, after the dehydration reaction is completed, the unreacted hydroxyl compound and the co-feed material that does not participate in the reaction are separated and recycled.

[0017] The solid acid-catalyzed dehydration reaction of hydroxy compounds usually requires one or more hydroxy compound molecules to associate with protons to form monomers (single hydroxy compound molecules and protons), dimers (two hydroxy compound molecules and protons), and even trimers and larger clusters (three or more hydroxy compound molecules and protons). Among them, both monomers and dimers can undergo intramolecular dehydration to form corresponding dehydration products, but the activity of the latter is much lower than that of the former, and the activity of trimers and larger clusters is lower than that of dimers, or even almost inactive; dimers or larger clusters can also undergo intermolecular dehydration to form corresponding dehydration products. The present invention adds ketone polar aprotic solvents, aldehyde polar aprotic solvents, cyclic ether polar aprotic solvents or alkane non-polar solvents as co-feed materials on the basis of the original solid acid catalyst catalyzed dehydration reaction process of hydroxy compounds to enhance the activity of the dehydration reaction of hydroxy compounds, and the type of co-feed compound, functional group and specific molecular structure of the mechanism of action are also different. Generally, when alkanes and cyclic ether compounds are used as co-feed materials, their main function is to occupy the pore space of the solid acid catalyst carrier, which inhibits the formation of low-activity dimers and larger clusters to a certain extent, thereby increasing the surface active site ratio of the hydroxyl compound monomer, bringing about an increase in the reaction rate (especially the olefin formation rate); and when aldehydes and ketone compounds are used as co-feed materials, new clusters containing one or more hydroxyl compound molecules and one or more aldehyde and ketone molecules will be formed on the basis of monomers or dimers, and their activity is higher than that of monomers or dimers, so the reaction rate is increased. In addition, although the co-feed material will participate in the formation of clusters or occupy the internal space of the catalyst, it itself will not be transformed within the original hydroxyl compound dehydration reaction process conditions, that is, no side reactions will occur.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The present invention adds a co-feed material into the dehydration reaction system of the hydroxyl compound. The co-feed material can induce a significant increase in acid catalytic activity by interacting with active species on the catalyst surface without reacting itself, thereby improving the reaction conversion rate of the hydroxyl compound. The product selectivity can be adjusted by controlling the type of the co-feed material and reaction conditions such as the partial pressure of the co-feed material. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The diagram is a reaction mechanism diagram of the dehydration reaction of hydroxyl compounds in the present invention when a co-feed material system is introduced.

[0021] Figure 2 This is a graph showing the change in isopropanol conversion after the co-feed material acetone is introduced into the isopropanol dehydration reaction system in Example 1.

[0022] Figure 3This is a graph showing the change in isopropanol conversion after the co-feed material 3-methyl-2-butanone is introduced into the isopropanol dehydration reaction system in Example 2.

[0023] Figure 4 This is a graph showing the change in isopropanol conversion after the co-feed material 3-methyl-2-butanone is introduced into the isopropanol dehydration reaction system in Example 3.

[0024] Figure 5 This is a graph showing the improvement in reaction performance of ether products and olefin products after the introduction of different co-feed materials. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with specific embodiments and drawings.

[0026] Figure 1 This is a reaction mechanism diagram of the dehydration reaction of hydroxyl compounds in the system of co-feeding substances introduced into the present invention. It can be seen from the schematic diagram of the potential energy curve that the energy barrier of the direct (no co-feeding) dehydration reaction path is greater than the dehydration reaction energy barrier when the co-feeding substances are introduced. It can be seen from the chemical mechanism that the energy barrier size corresponds to the activation energy requirement that when the co-feeding substances are introduced into the dehydration reaction system, the activation energy required for the reaction is smaller, so the reaction activity is increased and the temperature required for the reaction is lower.

[0027] Example 1

[0028] In the dehydration reaction zone with H-ZSM-5 molecular sieve catalyst, a feed consisting of isopropanol and 0.30 kPa acetone was reacted to produce propylene and isopropyl ether at a temperature of 80°C, atmospheric pressure, and a partial pressure of 0.16 kPa isopropanol. The change in reaction conversion before and after the addition of acetone is shown in Figure 2 As can be seen from the figure, before the addition of acetone, the reaction conversion rate was about 15%. After the addition of acetone, the reaction conversion rate increased to 75%. At the same time, no acetone conversion and any by-products were detected.

[0029] Example 2

[0030] In the dehydration reaction zone with H-ZSM-5 molecular sieve catalyst, 0.53 kPa of isopropanol was reacted with 3-methyl-2-butanone as co-feed to produce propylene and isopropyl ether at 80°C and atmospheric pressure. The total conversion rate changes with the 3-methyl-2-butanone inlet pressure as shown in Figure 2. Figure 3 The results show that a very small amount of 3-methyl-2-butanone can increase the conversion rate by an order of magnitude (from 0.5% before co-feeding to 13%), and the conversion rate can be increased to 25% (about 50 times higher than before the increase). The selectivity of the reaction to produce propylene and isopropyl ether (ether-olefin ratio) changes with the change of 3-methyl-2-butanone injection pressure. Figure 4The results showed that the selectivity of ether in the product decreased from 17% before co-feed to 0.47%.

[0031] Example 3

[0032] Under the conditions of 80°C and normal pressure, in the dehydration reaction zone with H-ZSM-5 molecular sieve catalyst, 0.16kPa of isopropanol was reacted with different co-feed materials to produce propylene and isopropyl ether. The increase in the activity of olefin and isopropyl ether with different co-feed materials is shown in Figure 5 , it can be seen that different co-feed materials have different effects on improving the activity of isopropanol dehydration and on increasing the rates of the two products.

Claims

1. A method for improving the catalytic dehydration reaction activity of hydroxyl compounds and adjusting the product selectivity, characterized in that: The details are as follows: A mixture of a hydroxy compound and a co-feed material is subjected to a dehydration reaction in the presence of a solid acid catalyst to generate a corresponding olefin or ether compound or a mixed product of the two. The co-feed material is selected from ketones, aldehydes, cyclic ether polar non-protonic solvents, and alkane non-polar solvents.

2. The method according to claim 1, characterized in that The hydroxy compound is alcohol or phenol; the solid acid catalyst is hydrogen molecular sieve, supported heteropoly acid, ion exchange resin or Lewis acid catalyst.

3. The method according to claim 2, characterized in that The hydroxy compound is methanol, ethanol, n-propanol, butanol, cyclohexanol, phenol or glycerol; the hydrogen-type molecular sieve catalyst comprises a carrier and an acidic component, the carrier is silica, alumina or a combination thereof, the acidic component is amorphous silica-alumina, zeolite or a combination thereof; the supported heteropolyacid catalyst comprises an element of IUPAC Group 13 and a metal of IUPAC Groups 4-6, the element of IUPAC Group 13 is at least one of boron, aluminum and gallium, and the metal of IUPAC Groups 4-6 is at least one of titanium, zirconium, niobium, hafnium and tantalum.

4. The method according to claim 1, characterized in that: The ketone polar aprotic solvent is acetone, butanone or pentanone, the aldehyde polar aprotic solvent is formaldehyde or acetaldehyde, the cyclic ether polar aprotic solvent is 1,4-dioxane, and the alkane non-polar solvent is cyclohexane or n-hexane.

5. The method according to claim 1, characterized in that The co-feed material is 1,4-dioxane, n-butyraldehyde, 2-methyl-butyraldehyde, isovaleraldehyde, n-valeraldehyde, acetone or n-hexane.

6. The method according to claim 1, characterized in that The hydroxyl compound and the co-feed material mixture are subjected to a liquid-solid phase dehydration reaction in the presence of a solid acid catalyst in liquid form, or the hydroxyl compound and the co-feed material mixture are first gasified and then subjected to a gas-solid phase dehydration reaction in the presence of a solid acid catalyst in gas form.

7. The method according to claim 6, characterized in that The liquid-solid phase dehydration reaction temperature is 100-150°C, and the reaction solvent is water, n-hexane or tetrahydrofuran; the gas-solid phase reaction temperature is 50-120°C, and the reaction carrier gas is nitrogen, argon or air; the pressure of the reactants is 0 kPa-10 kPa.

8. The method according to claim 1, characterized in that The amount of the co-feed material added in the mixture of the hydroxyl compound and the co-feed material is more than 1 wt%.

9. The method according to claim 1, characterized in that: After the dehydration reaction is completed, the unreacted hydroxyl compound and the co-feed material that does not participate in the reaction are separated and recycled.

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