A method for the synthesis of alkyl glyceryl ethers from glycerol ethers

Abstract

A method for synthesizing alkyl glycerol ethers by glycerol etherification involves adding a eutectic solvent to glycerol, purging with nitrogen to remove oxygen, and then introducing the solution into a microchannel reactor. Gaseous olefins are then introduced into the microchannel reactor, where they react. The reaction products undergo gas-liquid separation, and the liquid is purified to obtain the alkyl glycerol ether. The eutectic solvent is a mixture of methylimidazolium sulfonate and oxalic acid. This invention utilizes a specific eutectic solvent and a microchannel reactor to jointly promote the dissolution of olefins in the eutectic solvent, transforming the heterogeneous reaction between gaseous olefins and liquid glycerol into a homogeneous reaction. This reduces side reactions in olefin polymerization without the need for additional polymerization inhibitors, thereby increasing product yield. The technical solution of this invention enables continuous production and improves production efficiency.

Description

Technical Field

[0001] This invention relates to the field of fuel additive technology, and more specifically to a method for preparing alkyl glycerol ethers by glycerol etherification. Background Technology

[0002] Glycerin is a byproduct of the transesterification process of vegetable oils to produce biodiesel. With the development of the biodiesel industry, there is a global surplus of glycerin. How to fully and rationally utilize this inexpensive glycerin has become an important issue. In recent years, research has focused on the preparation of glycerol ethers from glycerin as fuel additives.

[0003] Etherification reactions using inexpensive glycerol and alkylating agents can utilize glycerol, a byproduct of biodiesel production, addressing the issue of glycerol surplus and reducing production costs. Simultaneously, the resulting alkyl glycerol ethers can be used as fuel additives in diesel fuel to improve its cetane number and other properties. Therefore, research on alkyl glycerol ethers has significant practical implications.

[0004] Existing technologies typically employ etherification reactions of glycerol with alcohols and olefins. The resulting glycerol ethers are mixtures of tert-butylglycerol monoether, tert-butylglycerol diether, and tert-butylglycerol triether. Among these, the diether and triether are highly compatible with diesel fuel and can be used as diesel additives. When added to standard diesel fuel containing 30%–40% aromatics, they can significantly reduce the content of particulate matter, hydrocarbons, and carbon monoxide in the exhaust gas. It is well known that the etherification reaction of glycerol with alcohols is more difficult than that with glycerol with olefins, and the atom utilization rate is lower. Furthermore, when using alcohols as etherifying agents, the reaction equilibrium is limited by the byproduct water, requiring continuous water removal during the reaction. In the etherification reaction of glycerol with olefins, because it is a heterogeneous catalytic reaction, the reaction is relatively difficult, and the product contains 20%–50% monosubstituted glycerol alkyl ethers (of poor quality). Simultaneously, because olefins readily self-polymerize, the reaction produces a large amount of olefin dimer byproducts, reducing the conversion rate of olefins to alkyl glycerol ethers.

[0005] CN102531852A discloses a process for preparing tert-butyl glycerol ether using rare earth modified molecular sieves. The process involves preparing a rare earth salt solution using soluble salts of lanthanum, cerium, neodymium, europium, samarium, and praseodymium. Hβ molecular sieves undergo ion exchange in the rare earth salt solution through microwave heating and stirring or conventional heating and stirring. After filtration, drying, and calcination, a rare earth modified β molecular sieve catalyst is prepared and added to a reaction vessel. Under a reaction pressure of 1-2 MPa and a reaction temperature of 50-100 °C, a mixture of tert-butyl glycerol ethers containing mono-tert-butyl glycerol ether (MTBGs), di-tert-butyl glycerol ether (DTBG), and tri-tert-butyl glycerol ether (TTBG) is synthesized. This method uses a precious metal catalyst, which is expensive and difficult to recycle.

[0006] CN103910612B discloses a process for preparing glycerol ethers by catalytic etherification of glycerol. The process uses pure glycerol and isobutylene as raw materials, and generates glycerol monoether, glycerol diether, and glycerol triether under the catalysis of sulfonated graphene catalyst. The resulting mixture is then extracted and separated using glycerol. Glycerol is added to the mixture, and through mixing, mass transfer, and sedimentation, the system separates into two phases. The upper phase mainly contains glycerol triether and glycerol diether products, which are recovered as the final product. The lower phase contains glycerol, a small amount of glycerol ether, and catalyst. After isobutylene is introduced, the reaction continues. This "reaction-extraction" cycle achieves the synthesis, product collection, and catalyst recycling of glycerol ethers by catalytic etherification of glycerol. However, this method employs a multiphase reaction between isobutylene gas and liquid glycerol, resulting in low glycerol conversion and low yield of the target product. Furthermore, isobutylene is prone to self-polymerization, producing a large amount of olefin dimer byproducts, which reduces the conversion rate of olefins to alkyl glycerol ethers.

[0007] CN105732332B discloses a method for producing glycerol alkyl ethers based on heterogeneous catalysis. Liquid glycerol enters the upper part of a bubble column reactor and comes into countercurrent contact with low-carbon alcohols dispersed by a gas distributor entering from the bottom of a gasification column. Under the action of a catalyst, a heterogeneous reaction is carried out to produce glycerol alkyl ethers. The ethers are then removed from the reactor through a reflux demister zone and flash-evaporated to obtain the final glycerol alkyl ether product. This method uses the reaction of low-carbon alcohols with glycerol, which produces water byproducts. The water from the reaction needs to be continuously removed, and the catalyst also needs to be water-resistant. Furthermore, the selectivity for diethers and triethers in the product is low. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a method for synthesizing alkyl glycerol ethers by glycerol etherification. This method uses a specific eutectic solvent in conjunction with a microchannel reactor to promote the mixing of gaseous olefins and liquid glycerol, and to catalyze the reaction, resulting in a reaction with high conversion rate and selectivity.

[0009] To achieve the above-mentioned technical objectives, the technical solution of the present invention is as follows:

[0010] A method for synthesizing alkyl glycerol ethers by glycerol etherification involves adding a eutectic solvent to glycerol, purging with nitrogen to remove oxygen, and then introducing the solution into a microchannel reactor. A gaseous olefin is then introduced into the microchannel reactor, and the two react. The reaction product is subjected to gas-liquid separation, and the liquid is purified to obtain the alkyl glycerol ether. The eutectic solvent is a mixture of methylimidazolium sulfonate and oxalic acid.

[0011] Furthermore, the eutectic solvent is a mixture of methylimidazolium sulfonate and oxalic acid in a molar ratio of 1:1 to 1:5, preferably 1:1 to 1:3, and most preferably 1:1 to 1:2.

[0012] Furthermore, as a more specific embodiment, the eutectic solvent is obtained by the following method: methyl imidazole sulfonate is mixed with oxalic acid and stirred continuously at 60-150°C for 30-90 minutes until a uniform transparent liquid is formed, and then cooled for later use.

[0013] Furthermore, the amount of eutectic solvent used is 5%-30% of the mass of glycerol, preferably 10%-20%.

[0014] Furthermore, the space velocity relative to the volume of the microchannel reactor is 1-10 h⁻¹, based on the volume of the glycerol and eutectic solvent mixture. -1 Preferred 2-5 hours -1 .

[0015] Furthermore, the olefin is isobutylene and / or isopentene. The olefin and glycerol are introduced into the microchannel reactor at a gas-liquid molar ratio of 10-20:1, preferably 15-20:1.

[0016] Furthermore, the reaction conditions in the microchannel reactor are as follows: the reaction temperature is 20-100℃, preferably 50-100℃, and the reaction pressure is 0.2-2MPa, preferably 0.5-1.5MPa.

[0017] Furthermore, the microchannel reactor is commercially available or homemade. The reactor is made of special glass, ceramic, polytetrafluoroethylene, stainless steel, or alloys, and its structure is heart-shaped, rhomboid, rectangular, or other shapes that enhance reactant mixing. The reactor's inner diameter is 0.2-1.2 mm. The microchannel reactor includes at least two inlets and one outlet, and the number and position of the inlets can be changed according to reaction requirements.

[0018] Furthermore, the mixture of glycerol and eutectic solvent, as well as the olefin, are all fed into the microchannel reactor via a metering pump.

[0019] Furthermore, after gas-liquid separation of the product flowing out of the microchannel reactor, the gaseous portion consists of unreacted olefins, which can be recycled as olefin feedstock. The liquid portion is separated in a separation tower by at least one method selected from water washing, extraction, and distillation. The bottom product of the tower is trace amounts of unreacted glycerol, eutectic solvent, and glycerol monoether, which can be recycled. The top product is a small amount of glycerol monoether and the main products of glycerol diether and glycerol triether.

[0020] The alkyl glycerol ether synthesized in this invention can be used as a diesel cetane number additive, significantly reducing the content of particulate matter, hydrocarbons and carbon monoxide in diesel vehicle exhaust.

[0021] The technical solution of this invention has the following advantages:

[0022] (1) The present invention uses a specific eutectic solvent and a microchannel reactor to promote the dissolution of olefins in the eutectic solvent, so that the heterogeneous reaction of gaseous olefins and liquid glycerol is transformed into a homogeneous reaction. Under the condition that no additional polymerization inhibitor is required, the side reactions of olefin polymerization are reduced and the product yield is improved. The technical solution of the present invention can realize continuous production and improve the production efficiency of the product.

[0023] (2) The eutectic solvent methylimidazolium sulfonate / oxic acid used in this invention has a synergistic effect with the microchannel reactor. The eutectic solvent has super acidity in the microchannel reactor, which can improve the reaction activity and the selectivity of glycerol diether and glycerol triether. At the same time, the eutectic solvent can achieve a dual effect in the microchannel reactor, acting as both a solvent and a catalyst, promoting the mixing and reaction of glycerol and olefin phases, and improving the product conversion rate.

[0024] (3) The reaction conditions of this invention are mild, the glycerol conversion rate is high, the process is simple and easy to industrialize. The synthesized alkyl glycerol ether can be used as a diesel cetane number additive, which can significantly reduce the content of particulate matter, hydrocarbons and carbon monoxide in diesel vehicle exhaust.

[0025] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the reaction process used in the method of the present invention;

[0027] Among them: 1. Olefin storage tank, 2. Glycerin storage tank, 3. Metering pump I, 4. Metering pump II, 5. Microchannel reactor, 6. Insulated oil bath device, 7. Gas-liquid separation device, 8. Separation tower. Detailed Implementation

[0028] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0029] The composition of the product of this invention, the content of the prepared alkyl glycerol ethers, and the analysis performed using gas chromatography were described. Gas chromatography conditions: Agilent GC-2010 gas chromatograph with an FID detector; SP-2560 capillary column, 100m × 0.25mm × 0.20μm; injection port temperature 280℃; injection volume 1μL; split injection, split ratio 200:1; column initiation temperature 180℃, increased to 290℃ at a rate of 8℃ / min, held for 5min; detector temperature 280℃.

[0030] Glycerol conversion rate A = (m1 - m2) / m1 * 100%. Where m1 is the mass of glycerol fed into the reactor; m2 is the mass of glycerol separated after the reaction.

[0031] In the following embodiments, the following methods are adopted. Figure 1 The process flow shown completes the reaction: the reaction apparatus includes an olefin storage tank 1, a glycerol storage tank 2, metering pump I 3, metering pump II 4, a microchannel reactor 5, an insulated oil bath device 6, a gas-liquid separation device 7, and a separation tower 8; the microchannel reactor 5 is immersed in the insulated oil bath device 6. First, the eutectic solvent and glycerol are mixed in the glycerol storage tank 2. Through metering pump II 4, the mixture is fed into the microchannel reactor 5 at a certain space velocity. At the same time, olefin gas stored in the olefin storage tank 1 is fed into the microchannel reactor 5 through metering pump I 3 at a certain molar ratio with the mixture. The reaction is carried out under certain temperature and pressure. After the reaction is completed, the mixture is separated by the gas-liquid separation device 7. The gaseous part is unreacted olefins, which can be recycled as olefin feedstock. The liquid part is separated by the separation tower 8 by at least one method selected from water washing, extraction, and distillation. The bottom of the tower is unreacted trace amounts of glycerol, eutectic solvent, and glycerol monoether, which can be recycled as circulating material; the top of the tower is the product with a high content of glycerol diether and glycerol triether.

[0032] Example 1

[0033] Eutectic solvent A: Mix methylimidazolium sulfonate and oxalic acid at a molar ratio of 1:1.5, stir continuously at 100°C for 60 min until a uniform transparent liquid is formed, and then cool to room temperature for later use.

[0034] Add 15% (by weight) of eutectic solvent A to glycerol, purge with nitrogen for 30 min to remove oxygen, and then proceed with the reaction at a space velocity of 3 h⁻¹. -1 The product is fed into microchannel reactor 5, along with isobutylene gas at a gas-liquid molar ratio of 17:1 to glycerol. Microchannel reactor 5 is made of stainless steel, has a heart-shaped structure, and an inner diameter of 0.5 mm. The reaction temperature is controlled at 70℃ and the pressure at 1 MPa. The material exiting the microchannel reactor undergoes gas-liquid separation. The gaseous portion, consisting of unreacted isobutylene, can be directly returned to olefin storage tank 1. The liquid portion enters separation tower 8, where it is separated by water washing. The bottom output contains trace amounts of unreacted glycerol, eutectic solvent, and glycerol monoether, while the upper portion contains the product, including a small amount of glycerol monoether and the main components of glycerol diether and triether.

[0035] Calculations showed that the glycerol conversion rate was 95.4%, and the total selectivity of the diether and triether products was 78.6%.

[0036] Example 2

[0037] The preparation and reaction conditions of the eutectic solvent were the same as in Example 1, except that methyl imidazole sulfonate and oxalic acid were mixed in a 1:1 molar ratio to prepare eutectic solvent B.

[0038] Other operations are the same as in Example 1.

[0039] In the reaction, the glycerol conversion rate was 87.3%, and the overall selectivity of the diether and triether products was 72.6%.

[0040] Example 3

[0041] The preparation and reaction conditions of the eutectic solvent were the same as in Example 1, except that methyl imidazole sulfonate and oxalic acid were mixed in a molar ratio of 1:2 to prepare eutectic solvent C.

[0042] Other operations are the same as in Example 1.

[0043] In the reaction, the glycerol conversion rate was 96.4%, and the overall selectivity of the diether and triether products was 79.3%.

[0044] Example 4

[0045] The eutectic solvent ratio is the same as in Example 1, except that the eutectic solvent D is obtained by stirring at 150°C.

[0046] Other operations are the same as in Example 1.

[0047] In the reaction, the glycerol conversion rate was 96.3%, and the overall selectivity of the diether and triether products was 78.5%.

[0048] Example 5

[0049] The eutectic solvent ratio is the same as in Example 1, except that the eutectic solvent E is obtained by stirring for 90 min.

[0050] Other operations are the same as in Example 1.

[0051] In the reaction, the glycerol conversion rate was 96.1%, and the overall selectivity of the diether and triether products was 78.7%.

[0052] Example 6

[0053] Except that the amount of eutectic solvent A added is 8% of the mass of glycerol, the other operations are the same as in Example 1.

[0054] In the reaction, the glycerol conversion rate was 80.8%, and the overall selectivity of the diether and triether products was 68.6%.

[0055] Example 7

[0056] Except for glycerol and eutectic solvent A, the space velocity is 8 h⁻¹. -1 Apart from that, other operations are the same as in Example 1.

[0057] In the reaction, the glycerol conversion rate was 78.8%, and the overall selectivity of the diether and triether products was 61.9%.

[0058] Example 8

[0059] Except that isobutylene gas was added to the reaction system at a molar ratio of 10:1 to glycerol gas-liquid, the other operations were the same as in Example 1.

[0060] In the reaction, the glycerol conversion rate was 79.7%, and the overall selectivity of the diether and triether products was 64.8%.

[0061] Example 9

[0062] Except for adjusting the reaction temperature in the microchannel reactor to 30°C, the other operations are the same as in Example 1.

[0063] In the reaction, the glycerol conversion rate was 73.1%, and the overall selectivity of the diether and triether products was 51.9%.

[0064] Example 10

[0065] Except for adjusting the reaction pressure inside the microchannel reactor to 0.3 MPa, the other operations are the same as in Example 1.

[0066] In the reaction, the glycerol conversion rate was 70.3%, and the overall selectivity of the diether and triether products was 50.5%.

[0067] Example 11

[0068] The microchannel reactor used in Example 1 is different from that used in Example 1. It is made of stainless steel, has a rhomboid structure, and has an inner diameter of 1 mm. Other operations are the same as in Example 1.

[0069] In the reaction, the glycerol conversion rate was 95.0%, and the overall selectivity of the diether and triether products was 78.2%.

[0070] Comparative Example 1

[0071] A conventional stainless steel pressurized stirred reactor was used. Glycerol, eutectic solvent, and olefin gas, similar to those in Example 1, were fed into the reactor and thoroughly backmixed to carry out the reaction. Because the reaction between olefins and glycerol is a multiphase reaction in a conventional reactor, the glycerol conversion rate is low, and the main product is glycerol monoether. The glycerol conversion rate is less than 50%, and the total selectivity for diethers and triethers is 24.4%.

[0072] Comparative Example 2

[0073] The difference from Comparative Example 1 is that the reaction temperature was increased to 150°C, while everything else remained the same as Comparative Example 1. Due to the excessively high reaction temperature, there were more side reactions in the olefin polymerization, the glycerol conversion rate was less than 60%, and the total selectivity of diethers and triethers was only 21.3%.

[0074] Comparative Example 3

[0075] The difference from Example 1 is that no eutectic solvent is added. Glycerol does not react substantially with the olefin, so the product cannot be obtained.

[0076] Comparative Example 4

[0077] The eutectic solvent was replaced with 98% sulfuric acid, a conventional acidic catalyst, and otherwise remained the same as in Example 1. The reaction between glycerol and olefins was essentially a heterogeneous reaction, with a low glycerol conversion rate and the main product being a glycerol monoether. The glycerol conversion rate was less than 50%, and the overall selectivity for diethers and triethers was 12.7%.

[0078] Performance testing experiment: The base diesel used in the test examples of this invention has a cetane number < 51, and its specific properties are shown in Table 1.

[0079] Table 1

[0080]

[0081] The cetane number improver products prepared in the embodiments and comparative examples of this invention were added to the above-mentioned base diesel oil, and product performance tests were conducted. The test results are shown in Table 2.

[0082] Table 2

[0083]

[0084] As shown in Table 2, when glycerol is directly used to blend base diesel, glycerol is incompatible with the base diesel. Glyceryl monoether has a certain effect on increasing the cetane number of the base diesel, but its compatibility with the base diesel is poor. Glyceryl diether and glyceryl triether alone can increase the cetane number of diesel within a certain range, enabling it to meet standard requirements. In the examples, when the addition amount of glyceryl ether was 1%~2%, the cetane number of the base diesel met the China VI standard requirements (cetane number ≥ 51), and it was well compatible with the base diesel.

Claims

1. A method for synthesizing alkyl glycerol ethers by glycerol etherification, characterized in that, The process involves adding a eutectic solvent to glycerol, purging with nitrogen to remove oxygen, and then introducing the solution into a microchannel reactor. A gaseous olefin is then introduced into the microchannel reactor, where the two react. The reaction products are then separated into gas and liquid components, and the liquid is purified to obtain alkyl glycerol ethers. The eutectic solvent is a mixture of methyl imidazolium sulfonate and oxalic acid.

2. The method according to claim 1, characterized in that, The eutectic solvent is a mixture of methyl imidazolium sulfonate and oxalic acid in a molar ratio of 1:1 to 1:

5.

3. The method according to claim 1, characterized in that, The eutectic solvent is obtained by the following method: methyl imidazole sulfonate is mixed with oxalic acid and stirred continuously at 60-150°C for 30-90 minutes until a uniform transparent liquid is formed, and then cooled for later use.

4. The method according to claim 1, characterized in that, The amount of eutectic solvent used is 5%-30% of the mass of glycerol.

5. The method according to claim 1, characterized in that, The space velocity relative to the volume of the microchannel reactor is 1-10 h⁻¹, based on the volume of the glycerol and eutectic solvent mixture. -1 .

6. The method according to claim 1, characterized in that, The olefin is isobutylene and / or isopentenene.

7. The method according to claim 1, characterized in that, Olefins and glycerol are introduced into a microchannel reactor at a gas-liquid molar ratio of 10-20:

1.

8. The method according to claim 1, characterized in that, The reaction conditions in the microchannel reactor are as follows: reaction temperature is 20-100℃, and reaction pressure is 0.2-2MPa.

9. The method according to claim 1, characterized in that, The inner diameter of the microchannel reactor is 0.2-1.2 mm.

10. The method according to claim 1, characterized in that, After gas-liquid separation of the product flowing out of the microchannel reactor, the gaseous portion is unreacted olefins, which can be selectively reused as olefin feedstock.

11. The method according to claim 1, characterized in that, After the product gas-liquid separation from the microchannel reactor, the liquid portion passes through a separation tower and is separated by at least one method selected from water washing, extraction, and distillation. The bottom of the tower contains unreacted trace amounts of glycerol, eutectic solvent, and glycerol monoether, which can optionally be recycled. The top of the tower contains a small amount of glycerol monoether and the main products of glycerol diether and glycerol triether.

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