CN104387249A - Preparation method of acraldehyde - Google Patents

Abstract

The invention provides a method for preparing acraldehyde by carrying out catalytic dehydration on desalted crude glycerine. The method for preparing acraldehyde is characterized in that biodiesel byproduct crude glycerine is taken as a raw material, almost only desalination treatment is carried out, and a catalytic dehydration reaction is directly carried out for preparing acraldehyde without carrying out essential water evaporation concentration and removal of methanol, fatty acid, fatty acid ester and other impurity compounds. Experiments find that a catalytic effect is equivalent to that if refined glycerine is taken as a raw material when salt content of desalted crude glycerine is lower than 1wt%, and desalination operation cost is reduced; the biodiesel byproduct desalted crude glycerine is adopted as the raw material, and refining processes such as water evaporation concentration and removal of organic matter impurities with high energy consumption, complex steps and high cost are eliminated, thus the yield, the same as that if the refined glycerine is taken as the raw material, of the target product acraldehyde can be obtained; meanwhile, operation is simple, raw material cost is low, loss of glycerine in the refining process is reduced, the utilization rate of crude glycerine is high, the reaction rate is high, the yield of acraldehyde is high, catalyst life is long, and green chemistry industrial requirements are met.

Description

Acrolein preparation method

technical field

The present invention generally relates to a method for preparing acrolein, and in particular to a method for preparing acrolein using glycerin.

Background technique

Acrolein is an important intermediate in organic synthesis, which plays a bridge role in the conversion and utilization of crude glycerol - acrolein can be further oxidized to produce acrylic acid and its esters, which are widely used, and can also be used as a raw material for polymerization reactions to synthesize polymer materials (such as: sodium polyacrylate), the reaction formula is as shown in formula (1):

Acrolein can also be used to synthesize methionine, and the reaction formula is as shown in formula (2): methionine is an amino acid that cannot be synthesized by a living body, and it can be used to promote animal growth. The natural methionine source (plant, microorganism) provides Methionine concentration and production are relatively low, unable to meet human needs. At present, the global production capacity of methionine has reached 500,000 tons, while the human demand for methionine is still growing at a rate of 3-7%.

In addition, acrolein can also be used as a fungicide for oilfield injection water (inhibiting the growth of bacteria in the injection water, preventing bacteria from causing corrosion and blockage in the formation); its dimer can be used to make dialdehyde compounds, which are widely used in papermaking , tanning and textile auxiliaries; acrolein is also a raw material for glutaraldehyde, 1,2,6-hexanetriol and cross-linking agents, and is also used in the manufacture of colloidal osmium, ruthenium, and rhodium. The action of acrolein and bromine can give 2,3-dibromopropanal. 2.3-Dibromopropionaldehyde is a pharmaceutical intermediate used to produce antineoplastic drugs such as methotrexate.

The industrial production methods of acrolein mainly include formaldehyde-acetaldehyde condensation method, propylene oxidation method, propane oxidation method and glycerin catalytic dehydration method, etc. As early as 1938, German Degussa company used silica gel impregnated with sodium silicate to produce acrolein through gas-phase condensation of formaldehyde and acetaldehyde, and industrialized it in 1941. Formaldehyde aqueous solution and a slight excess of acetaldehyde passed through the catalyst in the tubular reactor The bed layer, the reaction temperature is 300-320°C, and the yield is 75% in terms of acetaldehyde. With the development of the petroleum industry, a large amount of propylene raw materials are provided, and the propylene oxidation method has become the most widely used route in the world. The process flow is: propylene, air and water vapor are mixed in a certain proportion, and then oxidized at 290-380°C and 200-300kPa under the action of a catalyst to generate acrolein and other by-products, and release a lot of heat at the same time. , The process should control the reaction temperature to be stable, the gas from the reactor is cooled and quenched with a large amount of water to remove the acidic by-products. The aqueous solution containing acrolein is stripped and refined to obtain the product acrolein. In recent years, with the depletion of petroleum resources and the deterioration of the ecological environment, the cost of producing acrolein using propylene propane as raw material has increased year by year.

With the vigorous development of biodiesel with superior environmental performance, the production of glycerol by-product of biodiesel is also increasing year by year, as shown in formula (3), it can be seen that crude glycerol by-product will be produced simultaneously in the production process of biodiesel .

According to statistics, for every 10 tons of biodiesel produced, 1 ton of crude glycerol will be produced as a by-product. With the development of biodiesel industry, the output of crude glycerin has increased year by year. A series of processes for the removal of methanol, fatty acids, fatty acid esters and other impurity compounds require high energy consumption and high cost. Therefore, the output and demand of refined glycerol have not increased significantly, so the accumulation of surplus crude glycerol has gradually formed. The accumulation of crude glycerol has led to a sharp drop in its price and has become a bottleneck for the development of biodiesel. Therefore, finding a reasonable downstream utilization route for crude glycerol has become an urgent problem to be solved. Statistics show that during the 20 years from 1995 to 2015, the price of crude glycerin dropped from US$900/t to US$150/t, and the main components of crude glycerin are glycerol (40%-50%), methanol (20%-30%) , Alkaline salt catalyst (3% to 5%) and soap (20% to 25%). Separation and refinement of biodiesel by-product glycerin, decolorization and distillation treatment can obtain high-purity glycerin. Due to the high cost of refined glycerin due to the separation process, the price of refined glycerin is around US$900-1000/t. Through research, it is found that the overall trend of the price of acrolein is rising steadily. For example, from January 2007 to December 2013, the price of acrolein rose from US$1,200/t to US$1,300/t. Therefore, after a comprehensive analysis of various factors such as raw materials, products and production costs, we can draw the conclusion that the selective dehydration of crude glycerol to prepare acrolein has great market prospects, and its research is also very necessary.

There are two methods for preparing acrolein from glycerol: homogeneous catalysis and heterogeneous catalysis. Patent CN200810243155.2 describes the influence of reaction temperature, H ₂ SO ₄ concentration, glycerin concentration and pressure on the performance of glycerin selective dehydration reaction under the condition of hot pressurized water, using refined glycerin aqueous solution as raw material. The results show that high concentration More glycerol and H ₂ SO ₄ as well as higher temperature and pressure are conducive to the formation of acrolein. Under the conditions of 400°C and 34.5MPa, the conversion rate of glycerol reaches 90%, and the selectivity of acrolein reaches 90%. Since the homogeneous reaction is carried out under the critical state of high temperature and high pressure, the aqueous solution will corrode the equipment, and the corrosion will be intensified after adding acid or inorganic acid salt; secondly, under high temperature conditions, coking is serious when crude glycerin interacts with acid; thirdly, high pressure operation does not Economical, low reactivity; finally, because it is a homogeneous reaction, the catalyst and the product need to be separated. Therefore, the preparation of acrolein by glycerol heterogeneous catalysis has significant advantages such as mild reaction conditions, high reactivity, low equipment requirements, and easy recovery and separation of catalysts. In summary, the use of heterogeneous solid acid catalyst system for gas-solid reaction dehydration to prepare acrolein has obvious advantages.

Most of the existing research results use refined glycerin as raw material. In order to obtain glycerin raw material with high purity and low impurity content, it is necessary to evaporate and concentrate crude glycerin, remove organic matter such as methanol, desaltize, decolorize, and adjust pH. Pretreatment, in which water evaporation needs to be carried out under vacuum conditions, these purification operations have high energy consumption, complicated process, and cause a large amount of glycerin loss at the same time, so the utilization rate of crude glycerol in the whole reaction process is poor, which does not meet the requirements of green chemistry and increases The cost of dehydration of biomass crude glycerol to produce acrolein has become a bottleneck limiting the production of acrolein from glycerin.

Patent FR 695931 proposes a method for preparing acrolein using solid acid as a catalyst and 20% refined glycerol aqueous solution as a raw material. The 20wt% refined glycerin aqueous solution is gasified and passed through a fixed-bed reactor under high temperature conditions. The catalyst uses a supported tribasic acid , the highest yield of acrolein can reach 80%, but the method is repeated according to the patent DE 423493, and the corresponding yield cannot be obtained.

Patents US 5426249 and CN 1034803C disclose the method of preparing acrolein with alumina, HZSM-5, HY and other supported phosphates as catalysts and refined glycerin as raw material, but when the highest yield of acrolein can reach 71%, glycerin Conversion rate is only 19%

Chinese patent CN 201010213226.1 proposes a method for preparing acrolein using refined glycerol as a raw material in a miniature fixed-bed reactor with heteropolyacid supported on alumina, diatomaceous earth, activated carbon, rutile titanium dioxide or kaolin as a catalyst. The conversion of glycerin is 13.5-80.6%, the highest yield of acrolein is 49.0-90.5%, but the catalyst is easy to deactivate, the life is short, and the conversion selectivity is significantly reduced in the later stage.

Patent CN200880105819.7 adopts the method of reaction evaporation to directly prepare acrolein from crude glycerol, and uses crude glycerol as raw material, and simultaneously evaporates and purifies in the reactor to remove moisture and other impurities in glycerin, and then reacts on the catalyst, but Because the evaporation purification and dehydration reactions are not easy to control, and the glycerin purification operation is not complete enough, there are still a large number of salts in the crude glycerin that have not been removed before the reaction, causing a large amount of salts to deposit on the catalyst, resulting in significant catalyst activity and selectivity in the later stage of the reaction. After 26 hours of reaction, the yield of acrolein is only 20-30%.

Contents of the invention

The present invention has been made in view of the above circumstances.

According to one aspect of the present invention, there is provided a method for preparing acrolein, which is characterized in that crude glycerin is used as a raw material, and basically only the crude glycerin is desalted, and the desalted crude glycerin is combined with The catalyst carries out dehydration reaction in the reactor to prepare acrolein.

The desalting treatment of the crude glycerin basically includes not performing any of the following treatments on the crude glycerin: water evaporation concentration, methanol removal, fatty acid removal, fatty acid ester removal, and other impurity compound removal.

The desalting treatment of the crude glycerol can desalt the crude glycerol to a salt content of 1 wt% or less.

The crude glycerol desalting method can be one of electrodialysis, reverse osmosis and ion exchange resin.

Crude glycerin desalting method can adopt ion exchange resin method.

In one example, in the ion exchange resin desalination process, macroporous strong acid cation exchange resin is used for desalination, the operating flow rate of crude glycerin is 2.0-3.0 mL/min, and the volume ratio of water/crude glycerin is 0.5-2. In one example, crude glycerin operates at a flow rate of 2.5 mL/min with a water/crude glycerol volume ratio of 1

In one example, regarding the preparation method of acrolein, the concentration of the desalted crude glycerol aqueous solution as the raw material is 10%-60%, the reactor adopts a fixed bed, the reaction temperature is 250-350° C., and the reaction pressure is normal pressure.

In one example, the method for preparing acrolein uses a supported heteropoly compound as a catalyst.

In one example, the supported heteropoly compound used in the preparation method of acrolein is heteropoly acid such as phosphotungstic acid, phosphomolybdic acid, silicotungstic acid or its phosphotungstate, phosphomolybdate, silicotungstate One of them, the carrier is one of various metals, non-metal oxides and molecular sieves.

The method for producing acrolein by catalytic dehydration reaction of desalted crude glycerol according to the embodiment of the present invention directly uses biomass crude glycerol as raw material, and basically only desalts the crude glycerol to a salt content of 1 wt% or below, and does not affect the crude glycerol. Glycerin is subjected to water evaporation and concentration, methanol, fatty acid, fatty acid ester and other colored compounds are removed, and the same target product yield and catalyst stability as refined glycerin can be obtained, eliminating the need for crude glycerin evaporation and concentration, organic matter removal, decolorization, etc. Refining steps reduce costs and energy consumption.

For example, the desalting process of crude glycerin can use electrodialysis, reverse osmosis and ion exchange resin method, preferably ion exchange resin method, to desalt to a salt content of 1 wt% or less. The desalination ion exchange resin adopts macroporous strong acid cation exchange resin to remove alkali metal ions; the operating flow rate of crude glycerol in the desalination process is 2.0-3.0mL/min, preferably 2.5mL/min; the water/crude glycerol volume ratio is 0.5-2, preferably The volume ratio is 1. The desalination by ion exchange resin method is carried out as follows: the ion exchange column adopts Φ30×800mm glass column, respectively filled with macroporous acidic cation exchange resin, pumps the ion exchange column filled with resin from the top of the column with a peristaltic pump, and the liquid flows out from the bottom of the column. Collect and measure the outflow volume with a graduated cylinder.

Crude glycerol dehydration catalyst preparation can be carried out, for example, using the following procedure:

1) Cs2CO3 is formulated into an aqueous solution with a molar concentration of 0.1 to 0.25 mol·L-1, and the SBA-15 carrier is added to the aqueous solution, stirred and impregnated at room temperature so that the loading capacity is 5% to 70%, preferably The load is 50%, dry for standby;

2) The molar ratio of Cs2CO3:heteropolyacid=0.5:1～1.5:1, preferably the molar ratio of Cs2CO3:heteropolyacid=1.25:1. Weigh the heteropoly acid and make it into an aqueous solution with a molar concentration of 0.05-0.1mol L-1, after stirring, impregnate, filter, wash and dry at room temperature, and calcinate at a temperature of 400-700°C for 3-5 hours, preferably calcining The temperature is 500°C, and the supported catalyst whose active component is cesium phosphotungstate salt is prepared, and the catalyst is pressed into tablets, pulverized and then sieved for later use.

An exemplary process for preparing acrolein can be carried out using the following procedure: the reaction is carried out in a miniature fixed-bed reactor, the catalyst is placed in the isothermal section in the middle of the reactor, and the concentration of the aqueous glycerin solution is 10%-60%, preferably 10-30%. , the desalted crude glycerin aqueous solution is pumped into the reactor, vaporized in the reactor vaporization section and then passed over the catalyst, the liquid space velocity is 1.3h ^-1 , the raw material and the catalyst are contacted at 300°C, and a gas phase dehydration reaction occurs to obtain acrolein. The product was condensed and collected in an ethanol-cooled gas-liquid separator, and the product was analyzed quantitatively and qualitatively by gas chromatography.

The process of preparing acrolein by dehydration of crude glycerin using the catalyst of the present invention has the outstanding advantages of:

(1) Crude glycerol obtained through biological pathways can be used as raw material, and the same target product acrolein can be obtained as raw material with refined glycerin only through simple desalination treatment without water evaporation and concentration and other unnecessary impurity removal processes. It is an environment-friendly green biochemical process that avoids the waste of raw materials caused by the purification of crude glycerin, and at the same time simplifies the process of preparing acrolein from crude glycerin to reduce production costs.

(2) The operation of the desalting treatment is simple, and the requirement for the purity of the glycerin is low, and the salt content in the desalted crude glycerin is 1 wt% to meet the requirement.

(3) Glycerol desalination is carried out by ion exchange resin method, which is simple in operation and high in desalination rate.

(4) Reaction under normal pressure at 300°C, with mild conditions, and the use of solid catalyst gas phase should require less equipment.

(5) The catalyst has a short induction period, quickly reaches the optimum conversion rate and selectivity, and has high selectivity, few by-products (mainly hydroxyacetone), and long life.

(6) The conversion rate of desalted crude glycerol and the selectivity of acrolein are high, and the optimal ratio of 50HPW/Cs-SBA catalyst can reach 100% and 88%, respectively, and the catalyst has a long life, and the initial reaction activity is still maintained after 120h of reaction.

(7) The catalyst has good thermal stability, and its activity can be maintained by burning charcoal at 500°C.

(8) The acrolein solution obtained as a product containing some impurities can be refined and purified directly by the impurity removal process for preparing acrolein by the oxidation of propane and propylene.

Detailed ways

In order to enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below in conjunction with specific embodiments.

The terms "crude glycerin" and "refined glycerin" in this specification are commonly used terms by those skilled in the art. They adopt the common meaning in this field. Generally, the concentration of glycerin in crude glycerin is about 30-85%, and the concentration of glycerin in refined glycerin is between 30% and 85%. above 95.

The "substantially" in the expression "substantially only desalted crude glycerol" or "substantially only desalted crude glycerin" or "crude glycerin that has only undergone desalted crude glycerin" means Desalination of crude glycerol without the substantive processing required industrially to make refined glycerol from crude glycerol, but does not preclude some basic simple processing of crude glycerol including, for example, filtration , desalination, etc., but not limited to these.

The present inventor thought that if the crude glycerol produced by biomass can be used as a raw material, the impurities that have an impact on the dehydration reaction used to prepare acrolein can be determined and the impurities can be specifically removed without the need for crude glycerol to undergo complicated procedures. The refining process can simplify the process of preparing acrolein from crude glycerin and reduce production costs.

The inventor found through experiments that the salt in crude glycerol has a great influence on the dehydration reaction for preparing acrolein. By carrying out catalytic dehydration experiments on crude glycerin containing different impurity components, it was found that basically only the crude glycerin needs to be desalted. Instead of evaporating and concentrating crude glycerol, removing organic matter such as methanol, fatty acids and their esters, dehydration reaction can be carried out to obtain a higher yield of acrolein, and the catalyst reaction effect is equivalent to that of refined glycerin as raw material. The reaction effect and life of the catalyst will not be affected by organic substances such as moisture, methanol, fatty acids and their esters.

The experiment found that the catalyst selectivity and conversion rate decreased significantly after 40 hours when undesalted glycerol was used as the raw material for the dehydration reaction. Therefore, the desalination operation is necessary for the glycerol dehydration reaction.

For this reason, the highest salt content to ensure acrolein yield and catalyst stability is determined through experiments to reduce the cost of the desalination process. As long as the salt content of desalted glycerin is below 1 wt%, the obtained acrolein yield can be guaranteed to be comparable to that of refined glycerin. Because the raw materials are the same, other impurities contained in the desalted crude glycerin have no influence on the reaction result.

Based on experiments, by adding methanol, fatty acids and their esters and other organic substances to refined glycerin as raw materials for reaction evaluation, it can be known that moisture, methanol, fatty acids and their esters and other organic substances contained in desalted crude glycerin will not affect the catalytic reaction. Evaporation and concentration of crude glycerol, removal of organic matter such as methanol, fatty acids and their esters are not necessary for the reaction of glycerol to acrolein. Compared with the evaporation and concentration of water, the removal of methanol, fatty acids and their esters and other organic substances, the desalination operation cost is low and the operation is simple. At the same time, it only needs to ensure that the salt content of the desalted crude glycerol is less than 1wt% to meet the catalytic reaction dehydration to prepare acrolein. Therefore, the embodiment of the present invention basically only desalts the crude glycerin, that is, uses the desalted crude glycerin and the catalyst to perform dehydration reaction in the reactor to prepare acrolein, which can greatly reduce the simplification of crude glycerin to prepare propylene. Aldehyde process and reduce production costs.

The crude glycerin desalination method can be electrodialysis, reverse osmosis or ion exchange resin method, preferably ion exchange resin method. The ion exchange resin uses macroporous strong acid cation exchange resin to remove alkali metal salts. The operating flow rate of crude glycerol in the desalination process is 2.0-3.0mL/min, preferably 2.5mL/min; the volume ratio of water/crude glycerol is 0.5-2, preferably the volume ratio of water/crude glycerol is 1

The catalytic reaction process can use a fixed bed for gas-solid catalytic reaction, the reaction temperature is 280-350°C, preferably 300°C, the reaction pressure is normal pressure, and the concentration of glycerin aqueous solution is 10%-60%, preferably 10-30%. A supported heteropoly compound is used as a catalyst, and the heteropoly acid is phosphotungstic acid, silicotungstic acid, cesium phosphomolybdate salt or silicomolybdenum acid. Preferably Cs/H in phosphotungstate Cs _x H _3-x PW ₁₂ O ₄₀ , x=2-3 and preferably x=2.5. The carrier is various metals, non-metal oxides or molecular sieves, preferably molecular sieve SBA-15. The active ingredient loading is 5%-70%, and preferably 50%.

A specific method of the present invention provides a method for preparing acrolein by catalytic dehydration of desalted crude glycerol. The crude glycerol by-product of biodiesel is used as raw material, and only undergoes desalination treatment without evaporation and concentration of water. Methanol, fatty acid, fat The removal of acid esters and other impurity compounds directly carries out the method of catalytic dehydration reaction to prepare acrolein. The desalted crude glycerol obtained by simple desalination treatment without water evaporation and concentration, removal of methanol, fatty acid, fatty acid ester and other impurity compounds is used as raw material to directly carry out catalytic dehydration reaction. After more than 100 hours of reaction, the conversion rate of glycerin reaches 100%, and the selectivity of acrolein reaches 87-90%. The yield of acrolein is equivalent to that of the refined glycerol obtained after water evaporation and concentration, desalination, and removal of methanol, fatty acid, fatty acid ester and other impurity compounds as raw material for catalytic dehydration. After comparing the reaction effects of glycerin with different impurity components as raw materials, it was found that the salt in crude glycerin is the key factor affecting the catalyst effect, and water and other impurity compounds have no obvious influence on the catalytic reaction. In addition, it was also found that when the desalted crude glycerin contains salt When the amount is less than 1 wt%, the catalytic effect can be guaranteed to be equivalent to that of using refined glycerin as a raw material, and the desalination operation cost can be reduced. Therefore, using the desalted crude glycerol produced by biodiesel as a raw material saves the energy-intensive, complicated steps, and high-cost refining processes such as water evaporation and concentration and removal of organic impurities, and can obtain the same crude glycerol as the raw material. The target product acrolein yield. The operation is simple, the cost of raw materials is low, the loss of glycerin in the refining process is reduced, the utilization rate of crude glycerin is high, the reaction rate is fast, the yield of acrolein is high, and the service life of the catalyst is long, which meets the requirements of the green chemical industry.

Example 1 (reaction effect comparison between desalted crude glycerin and crude glycerin)

This example compares the reaction effect of dehydration reaction to prepare acrolein with crude glycerol that has been desalted substantially as raw material and the reaction effect of dehydration reaction with crude glycerol as raw material.

Catalyst production: Weigh 0.25g of Cs ₂ CO ₃ according to the loading capacity of 20%, and make it into an aqueous solution with a concentration of 0.2mol L ^-1 , add 8g of SBA-15 carrier to the above aqueous solution, so that the loading capacity is 50% , vigorously stirred for 2-5 hours, soaked overnight at room temperature, dried at 80°C for later use, weighed an appropriate amount of heteropolyacid H ₃ PW ₁₂ O ₄₀ ·12H ₂ O and made it into an aqueous solution with a concentration of 0.08mol·L ^-1 Cs _x H _3-x PW ₁₂ O ₄₀ where x=2.5 and mixed with the above-mentioned carrier, vigorously stirred for 2-5 hours by equal volume impregnation, impregnated overnight at room temperature, filtered, washed and dried. The dried catalyst was calcined at 500° C. for 4 hours to obtain a supported heteropolyacid cesium salt 50HPW/Cs-SBA catalyst. The catalyst was pressed into tablets, crushed and sieved into 30-50 mesh for later use.

Preparation of crude glycerol that has only undergone desalination treatment (hereinafter referred to as "desalted crude glycerin"): crude glycerin is ion-exchanged and desalted with a glass column of Φ30×2×800mm, filled with macroporous acidic cation exchange resin, crude glycerin solution Use a peristaltic pump to pump from the top of the column into the ion exchange column equipped with resin. The crude glycerol operating flow in the desalination process is 2.5mL/min, the water/crude glycerin volume ratio is 1, and the salt content is lower than 1wt% after desalting. The effluent was collected with a graduated cylinder.

Using 20% crude glycerol without any treatment and desalted crude glycerin aqueous solution after ion exchange desalination as raw materials, carry out selective dehydration reaction of crude glycerol in a micro fixed bed reactor, using a metering pump (Series 2,.001 -5ml/min, SS, S.G.Seal Self Flush, Pulse Damper) continuous feeding, using stainless steel tube as the reactor (Φ10mm×40mm). The first section (20mm) is a preheating gasification section, where 0.5g of catalyst is loaded and diluted with quartz sand, and the selective dehydration temperature is 300°C. Sampling was carried out after continuous reaction for 1, 10, 20, and 40 hours to evaluate the activity, selectivity and stability of the catalyst, and the results were compared in Table 1 below.

It can be seen from Table 1 that when crude glycerol is directly used as raw material, the activity selectivity of the catalyst decreases significantly after 20 hours of reaction, and the reaction is carried out by using desalted crude glycerol as raw material, the catalyst has good stability, and the conversion rate of glycerin remains basically unchanged after 40 hours. The selectivity was 88%. It can be seen that the desalting treatment of crude glycerol is beneficial to improve the reaction activity of the catalyst and the yield of the target product acrolein, and at the same time improve the stability of the catalyst and prolong the life of the catalyst.

Table 1

Example 2 (desalted crude glycerin and refined glycerol are raw materials for reaction effect comparison)

This embodiment compares the reaction effect of desalted crude glycerin as raw material to prepare acrolein by dehydration reaction and that of refined glycerin as raw material.

Respectively adopt refined glycerol after water evaporation and concentration, desalination, removal of organic matter such as methanol, fatty acid and its esters, and basically only desalination treatment (for example, desalination treatment to a salt content lower than 1wt%), without other The desalted crude glycerol in the refining operation is used as raw material, and the catalytic dehydration reaction is carried out under the same conditions as other conditions; the preparation of the catalyst and the reaction conditions are the same as in Example 1. The results are compared in Table 2 below.

It can be seen from Table 2 that the conversion rate of glycerin remained basically unchanged after 40 hours using desalted crude glycerol, and the selectivity of acrolein was 88%, which was the same as that of refined glycerin. It shows that the crude glycerol only needs to be desalted until the salt content is lower than 1wt%, and there is no need to evaporate and concentrate the crude glycerol, remove methanol, fatty acids and their esters and other organic substances, and then carry out dehydration reaction to obtain higher acrolein The yield and the catalyst reaction effect are comparable to that of refined glycerin as raw material.

Table 2

Embodiment 3 (glycerol containing different impurities is a raw material for reaction effect comparison)

Using the refined glycerol after water evaporation and concentration, desalting, methanol, fatty acid and its esters and other organic matter removal as raw material, add 2wt% methanol, 2wt% fatty acid, 2wt% fatty acid ester and 2wt% salt for reaction. Carry out sampling evaluation catalyst activity after continuous reaction 40h, selectivity and stability, catalyst composition and other reaction conditions are with embodiment example 1, and the result is compared in following table 3.

By comparing the reaction yields in Table 3, it can be seen that organic impurities such as methyl alcohol in crude glycerin, fatty acid, and fatty acid ester will not affect the catalyst reaction effect. The yield of acrolein is 88%, comparable to that of refined glycerin and desalted crude glycerin. However, the catalytic activity of refined glycerol containing salt impurities is significantly reduced. After 40 hours, the conversion rate is 84%, and the selectivity of acrolein is reduced to 76%. It can be seen that the salt impurities in the crude glycerol lead to the reduction of the reaction yield of acrolein from crude glycerin dehydration. major factor. It further illustrates that crude glycerin only needs simple desalination treatment instead of water evaporation and concentration of crude glycerin, removal of methanol, fatty acids and their esters and other organic substances, and dehydration reaction can be carried out to obtain a higher yield of acrolein, desalination Other impurities in crude glycerol will not affect the reaction yield of desalted crude glycerol to prepare acrolein, and the catalyst reaction effect is equivalent to that of refined glycerol as raw material.

table 3

Example 4 (Desalted glycerin with different salt contents is used as a raw material for reaction effect comparison)

With the salt content 0.5wt～1.5wt% being the desalted crude glycerin as the raw material, carry out the reaction after continuous reaction 40h, carry out sampling and evaluate the activity of catalyst, selectivity and stability, catalyst composition and other reaction conditions are the same as embodiment example 1, the result is as follows Table 4 for comparison.

From the comparison of the reaction yield in Table 4, it can be seen that when the salt content is greater than 1 wt%, the activity of the glycerin catalyst will be affected, and the conversion rate will be significantly reduced to 86% after 40 hours, and the selectivity of acrolein will be reduced to 79%. When the salt content of the desalted crude glycerol is 1 wt%, the yield of acrolein is still 88% after 40 hours of reaction, which is equivalent to that of refined glycerin, and further reduction of the salt content will not increase the yield of acrolein. It can be seen that the salt content in the desalted crude glycerin is less than 1 wt%, which can ensure that the catalyst activity will not be affected by salt impurities. It is further explained that the desalination treatment does not need to completely remove the salts, and the dehydration reaction can be carried out to obtain a higher yield of acrolein, and the remaining salts in the desalted crude glycerin will not affect the reaction yield of the acrolein prepared from the desalted crude glycerin , the catalyst reaction effect is equivalent to that of refined glycerin as raw material.

Table 4

Example 5

The preferred load is 50%, Cs ₂ CO ₃ : heteropolyacid = 1.25:1, the calcination temperature is 500°C, and the calcination time is 4 hours. The desalted crude glycerol after desalination is Raw materials were subjected to life tests.

Other reaction conditions are with embodiment 1.

Sampling was carried out after 120 hours of reaction, and the conversion rate of desalted crude glycerin was 100%, and the selectivity of acrolein was 88%. In order to evaluate the stability of the catalyst, air was introduced and charcoal was burned at 500°C for 3 hours. After regeneration, the conversion rate of glycerin was 100%, and the selectivity of acrolein was 87%. The experimental results show that crude glycerol only needs to be desalted, and does not need to undergo refining steps such as evaporation and concentration of water, removal of organic substances such as methanol, fatty acids and their esters, etc., so that a higher yield of acrolein can be obtained. Other impurities will not affect the thermal stability of the catalyst, and the catalyst can perform charcoal regeneration at a high temperature of 500°C.

Embodiment 6 (glycerol desalination condition selection)

Crude glycerol uses a Φ30×800mm glass column for ion exchange desalination, filled with macroporous acidic cation exchange resin, and the crude glycerin solution is pumped from the top of the column into the ion exchange column filled with resin by a peristaltic pump. The operating flow rate of crude glycerol in the desalination process is 1.5-3.5mL/min, water/crude glycerin volume ratio 1, the effluent at the bottom of the column was collected with a graduated cylinder, and the desalination rate was determined by atomic absorption spectrometry.

The results are compared in Table 5 below. When the operating flow rate of crude glycerol is less than 2, reducing the flow rate has little effect on the desalination rate. Considering that the flow rate reduction will reduce the crude glycerin processing capacity, the operating flow rate of crude glycerin is 2, which is optimal.

When the volume ratio of water/crude glycerin is increased to 1, the increase of water consumption has little effect on the desalination rate. Considering that the increase of water consumption will increase the energy consumption of glycerin concentration, the water/crude glycerin volume ratio is taken as 1, which is the best.

Experiments show that the cost of the desalination process is low and the operation is simple, and the allowable salt content that meets the requirements for the preparation of acrolein from desalted crude glycerin can be obtained through the ion exchange desalination operation.

table 5

Embodiment 7, 7a and 7b (compared with existing catalyst)

React with 20% desalted crude glycerin aqueous solution as raw material, and other reaction conditions are with implementation example 1

For Example 7b, weigh the heteropolyacid at a molar ratio of Cs ₂ CO ₃ : heteropolyacid = 1.25:1 and prepare an aqueous solution with a molar concentration of 0.05 mol·L ^-1 , after stirring, filter and wash at room temperature and dried, calcined at 500°C for 4 hours to obtain a Cs _2.5 H _0.5 PW ₁₂ O ₄₀ cesium phosphotungstate catalyst, which was pressed into tablets, crushed and sieved into 30-50 meshes for later use.

Reaction condition is the same as implementation example 1

The results are compared in Table 6 below. By comparing the reaction effects of three different catalysts for the preparation of acrolein by dehydration of crude glycerol, it can be seen that the effect of the supported catalyst is the best, and the sample analysis is carried out after 40 hours of reaction, and the yield of acrolein can be 86%. For the existing SBA-15 molecular sieve catalyst, only 16% acrolein selectivity can be obtained. For the unloaded cesium phosphotungstate catalyst, the activity of the catalyst was high at the beginning of the reaction, and the yield of acrolein was 94%. After 40 hours of reaction, the catalyst was severely deactivated and the stability of the catalyst was poor. Therefore, considering the activity, selectivity and stability of the catalyst comprehensively, the supported catalyst is the best.

Table 6

Example 8

Weigh 0.7g of Cs ₂ CO ₃ according to the loading capacity of 5%, and make it into an aqueous solution with a concentration of 0.2mol·L ^-1 , add 8g of SBA-15 carrier into the above aqueous solution, stir and impregnate at room temperature to make the loading capacity 10%, 30%, 50%, 70% respectively, dried for later use. According to the molar ratio of Cs ₂ CO ₃ : phosphotungstic acid = 1.25: 1, weigh the heteropoly acid and prepare an aqueous solution with a molar concentration of 0.1 mol·L ^-1 , after stirring, soak, filter, wash and dry at room temperature, and then Calcined at 500°C for 5 hours to prepare a supported catalyst whose active component is cesium phosphotungstate salt Cs _2.5 H _0.5 PW ₁₂ O ₄₀ . The catalyst is pressed into tablets, pulverized and sieved for later use.

Reaction condition is with implementation example 1.

The results are compared in Table 7 below.

It can be seen that the preferred catalyst loading is 50%, at this time the conversion rate of glycerin is 100%, and the selectivity of acrolein is 88%. After 40 hours, the conversion rate of glycerin remained basically unchanged, and the selectivity of acrolein was 85%.

Table 7

Example 9

The Cs ₂ CO ₃ was made into an aqueous solution with a molar concentration of 0.1 mol·L ^-1 , the SBA-15 carrier was added into the aqueous solution, stirred and impregnated at room temperature to make the loading capacity 50%, dried for later use. According to the molar ratio of Cs ₂ CO ₃ : phosphotungstic acid = 0.5:1, 1:1, 1.25:1, 1.5:1, weigh the heteropoly acid and prepare an aqueous solution with a molar concentration of 0.1mol·L ^-1 , after stirring Impregnated at room temperature, filtered, washed and dried, and calcined at 500°C for 3h. A supported catalyst whose active component is cesium phosphotungstate Cs _2.5 H _0.5 PW ₁₂ O ₄₀ was prepared, and the catalyst was pressed into tablets, crushed and sieved for later use.

Reaction condition is with implementation example 1.

The results are compared in Table 8 below.

It can be seen that the preferred ratio of Cs ₂ CO ₃ : phosphotungstic acid = 1.25:1, at this time, the conversion rate of glycerin is 100%, and the selectivity of acrolein is 88%. After 40 hours, the conversion rate of glycerin remained basically unchanged, and the selectivity of acrolein was 88%.

Table 8

Example 10

The Cs ₂ CO ₃ was made into an aqueous solution with a molar concentration of 0.1 mol·L ^-1 , the SBA-15 carrier was added into the aqueous solution, stirred and impregnated at room temperature to make the loading capacity 50%, dried for later use. According to the molar ratio of Cs ₂ CO ₃ :heteropolyacid=1.25:1, the cesium salt of heteropolyacid is phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, silicomolybdic acid. Weigh the heteropoly acid and make it into an aqueous solution with a molar concentration of 0.05 mol·L ^-1 , after stirring, impregnate, filter, wash and dry at room temperature, and calcinate at 500°C for 3 hours to obtain the active components as follows: The supported catalyst of cesium phosphotungstate, cesium silicotungstate, cesium phosphomolybdate and cesium silicomolybdate. The catalyst is pressed into tablets, pulverized and sieved for later use.

Reaction condition is with implementation example 1.

The results are compared in Table 9 below.

It can be seen that the supported catalyst of cesium phosphotungstate is preferred, at this time, the conversion rate of glycerol is 100%, and the selectivity of acrolein is 88%. After 40 hours, the conversion rate of glycerin remained basically unchanged, and the selectivity of acrolein was 88%.

Table 9

The specific implementations of the present invention have been described in detail above in conjunction with the examples, but it should be pointed out that the protection scope of the present invention is not limited by these specific implementations, but is determined by the claims. Those skilled in the art can make appropriate changes, substitutions, combinations and sub-combinations to these embodiments without departing from the technical idea and gist of the present invention, all of which are included in the protection scope of the present invention.

Claims (10)

1. prepare a propenal preparation method for propenal, it is characterized in that taking raw glycerine as raw material, substantially only desalting treatment is carried out to this raw glycerine, utilize the raw glycerine after such desalting treatment and catalyzer in reactor, carry out dehydration reaction and prepare propenal.

2. propenal preparation method as claimed in claim 1, describedly substantially only carries out desalting treatment to this raw glycerine and comprises any one process do not carried out raw glycerine in lower column processing: moisture evaporation concentration, methanol stripper, lipid acid remove, fatty acid ester removes, other impurity compounds remove.

3. propenal preparation method as claimed in claim 1, is characterized in that raw glycerine desalination to saltiness is 1wt% or following.

4. propenal preparation method as claimed in claim 1, is characterized in that raw glycerine desalting method adopts electrodialysis, the one in reverse osmosis method and ion-exchange-resin process.

5. propenal preparation method as claimed in claim 1, is characterized in that raw glycerine desalting method adopts ion-exchange-resin process.

6. propenal preparation method as claimed in claim 5, is characterized in that in ion-exchange-resin process demineralising process, adopts large porous strong acid cation exchange resin desalination, and raw glycerine operation flow is 2.0-3.0mL/min, and water/raw glycerine volume ratio is 0.5-2.

7. propenal preparation method as claimed in claim 6, it is characterized in that raw glycerine operation flow is 2.5mL/min, water/raw glycerine volume ratio is 1.

8. propenal preparation method as claimed in claim 1, is characterized in that the concentration of the raw material desalination raw glycerine aqueous solution is 10%-60%, and reactor adopts fixed bed, and temperature of reaction is 250-350 DEG C, and reaction pressure is normal pressure.

9. propenal preparation method as claimed in claim 1, is characterized in that adopting supported heteropoly compound to be catalyzer.

10. propenal preparation method as claimed in claim 1, described supported heteropoly compound is phospho-wolframic acid, phospho-molybdic acid, the heteropolyacids such as silicotungstic acid or its Suanphosphotungstate, phosphomolybdate, the one in silicotungstate, carrier is each metalloid, the one in nonmetal oxide and molecular sieve.