A process for the catalytic one-step oxidative dihydroxylation of ethylene to produce ethylene glycol

Abstract

The application provides a method for preparing ethylene glycol by one-step oxidative double hydroxylation of ethylene, and relates to the technical field of ethylene glycol preparation. The method uses ethylene as a raw material, a halogen-containing compound as a catalyst, and water as a reaction medium, and carries out reaction in a high-pressure reaction kettle to prepare ethylene glycol through one-step oxidative double hydroxylation. The method can solve the problems in the traditional ethylene oxide hydration process, such as flammability and explosiveness of ethylene oxide, high water ratio, high energy consumption and environmental pollution in the hydration process. The catalyst of the method is simple and easy to obtain, the process is simple, the conversion rate and the selectivity are relatively high, and the method can be used in industrial production of ethylene glycol from ethylene.

Description

Technical Field

[0001] This invention relates to the field of ethylene glycol preparation technology, and more particularly to a method for the direct oxidation and dihydroxylation of ethylene / oxygen to produce ethylene glycol. Background Technology

[0002] Ethylene glycol is the simplest 1,2-diol and one of the most important chemical raw materials. It is widely used in the production of antifreeze, lubricants, solvents, and other chemical products, and plays a vital role in the synthetic fiber, textile, and plastics industries. Due to the booming development of the polyester industry in recent years, the production and demand of ethylene glycol have also increased rapidly. my country is a major producer and consumer of ethylene glycol; in 2023, my country's ethylene glycol production reached 16.535 million tons, indicating a huge market demand.

[0003] Currently, the most mature and widely used production route for ethylene glycol is the petrochemical route. This route consists of two steps: the first step uses ethylene as a raw material, converting it into ethylene oxide through an epoxidation reaction with oxygen; the second step involves the direct hydration or catalytic hydration of ethylene oxide to produce ethylene glycol. However, this process still has many drawbacks. The first step typically requires high temperatures and high oxygen partial pressures, which increases the energy consumption and hazard of the reaction. Furthermore, ethylene oxide has a low boiling point, is toxic, flammable, and explosive, making storage and transportation difficult. Ethylene oxide has a wide explosion limit; to prevent self-polymerization or explosion, a large water-to-ethylene oxide ratio (>20) is used in the second hydration step. Therefore, the resulting ethylene glycol solution is relatively dilute, and separation and purification require the evaporation of large amounts of water, making ethylene glycol production one of the most energy-intensive chemical projects.

[0004] In addition, the emerging coal-to-ethylene glycol route has also reached a considerable scale in recent years. The main processes of this route can be divided into direct synthesis, methanol process, and oxalate ester process. The direct synthesis method uses syngas, a product of coal gasification, as raw material to convert it into ethylene glycol in one step. This process still faces significant technical challenges. The methanol process uses syngas to produce methanol, methanol to produce ethylene, and then ethylene glycol is produced via the ethylene process. The oxalate ester process converts syngas into dimethyl oxalate, which is then hydrogenated to produce ethylene glycol. Given my country's energy structure of "abundant coal and scarce oil," this technical route has certain advantages. Green and sustainable ethylene glycol production routes have also received widespread attention. The Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has developed a biomass ethylene glycol process. This technical route uses biomass sugar as raw material, which is hydrocracking to produce ethylene glycol with high selectivity (close to 80%), and the produced ethylene glycol can reach polyester grade. Its techno-economic efficiency is superior to the existing bioethanol-bioethylene-bio-based ethylene glycol technical route. At the same time, the quality of the produced biomass ethylene glycol is superior to that of coal-based ethylene glycol. Since it does not use fossil fuels as raw materials, this technical route meets the industrial requirements under my country's "dual-carbon" background and has broad prospects. However, the new preparation route still faces problems such as lengthy processes, high energy consumption, and high costs.

[0005] Against this backdrop, shortening the process flow and reducing costs have become the research focus of the ethylene glycol industry. The ideal synthesis process is a one-step synthesis of ethylene glycol. Small-scale laboratory preparation of 1,2-diol can use osmium tetroxide as a catalyst to catalyze the oxidation of olefins, but the extremely high price and toxicity of osmium tetroxide make it difficult to scale up to industrial production. Recent studies have reported that using hydrogen peroxide as an oxidant and titanium silicate molecular sieves as a catalyst, ethylene glycol can be synthesized from ethylene in high yield. However, hydrogen peroxide is expensive and easily decomposes, increasing the production cost of ethylene glycol. From a green chemistry perspective, oxygen is cheap and readily available, and the atom utilization rate of the reaction is 100% when oxygen is used as an oxidant. Therefore, using oxygen as an oxidant and water as a solvent and reactant, a one-step oxidation and dihydroxylation of ethylene to ethylene glycol is a highly attractive production process. However, currently, there are few patents and literature reports on related research and inventions. Summary of the Invention

[0006] The purpose of this invention is to provide a one-step oxidative dihydroxylation method for preparing ethylene glycol using ethylene as a raw material, oxygen as an oxidant, a halogen-containing reagent as a catalyst, and water as a solvent and reactant. The selectivity of ethylene glycol in the product is 80-99%, and the reaction rate is fast, resulting in a high mass fraction of ethylene glycol in the solution and reducing energy consumption during the purification process.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] This invention provides a method for the one-step catalytic dihydroxylation of ethylene to prepare ethylene glycol, comprising the following steps:

[0009] Ethylene and oxygen are reacted in the presence of a catalyst and a reaction medium to produce ethylene glycol;

[0010] The catalyst is a halogen-containing reagent, and the reaction medium is water.

[0011] The reaction process for the direct oxidation dihydroxylation of ethylene / oxygen to produce ethylene glycol provided by this invention is as follows:

[0012]

[0013] The active ingredient of the catalyst is an element of Group VIIA or its compound, such as bromine, iodine, or chlorine or its compound. Preferably, it can be selected from one of the following:

[0014] A) One or more of elemental iodine, hydroiodic acid and its metal salts, hypoiodic acid and its metal salts, iodic acid and its metal salts, periodic acid and its metal salts, preferably one or more of elemental iodine, hydroiodic acid and its metal salts, such as HI, I2, KI, HIO3, KIO3, H5IO6, KIO4, etc.

[0015] B) One or more of elemental bromine, hydrobromic acid and its metal salts, such as: HBr, KBr, NaBr, FeBr3, CoBr2, NiBr2, CuBr2, ZnBr2;

[0016] C) One or more components of hydrochloric acid and its metal salts, such as HCl, KCl, CuCl2, FeCl3;

[0017] The cations of the metal salt are metal ions from the third, fourth, fifth, and sixth periods, with the fourth period transition metal ions being preferred.

[0018] Preferably, the amount of catalyst added per 1 mL of reaction medium is 10-100 mg, that is, the concentration of the catalyst is 10-100 g / L.

[0019] The reaction gas of this invention is a mixture of C2H4 and O2, the reaction medium is H2O, the reaction temperature is 100-240℃, the total reaction pressure is 0.5-6MPa, of which the pressure of C2H4 is 0.5-3MPa, the pressure of O2 is 0.5-4MPa, the reaction time is 0.5-12h, and the catalyst is a halogen-containing reagent.

[0020] Preferably, the reaction medium is ultrapure water.

[0021] Preferably, the reaction temperature is 140-200℃.

[0022] Preferably, the reaction stirring speed is 300-1500 rpm.

[0023] Preferably, the volume of the high-pressure reactor is 30mL-500L.

[0024] Preferably, the volume fraction ratio of C2H4 to O2 is 0.25-4.

[0025] In some specific implementations, the method includes the following steps:

[0026] 1) Add the catalyst to a high-pressure reactor equipped with a polytetrafluoroethylene liner and magnetic or mechanical stirring. After adding the reaction medium, introduce the reaction gases ethylene and oxygen. The partial pressure of ethylene is 0.5-3 MPa, the partial pressure of oxygen is 0.5-4 MPa, and the total reaction pressure is 0.5-6 MPa.

[0027] 2) Heat the reactor to 140-200℃ and react for 0.5-12 hours to obtain the product;

[0028] 3) The product was separated and qualitatively (quantitatively) analyzed by gas chromatography: using propylene carbonate as an internal standard, the conversion rate and selectivity were calculated by gas chromatography analysis.

[0029] The ethylene conversion number and product selectivity of the reaction are determined by the following formulas:

[0030]

[0031] Technical effects:

[0032] 1) This invention significantly reduces economic costs by using common halogen-containing reagents as catalysts.

[0033] 2) The synthesis method used in this invention is simple, easy to operate, and suitable for industrial production scale-up.

[0034] 3) The method used in this invention has good ethylene single-pass conversion rate, ethylene glycol selectivity and continuous reaction capability for the direct oxidation and dihydroxylation of ethylene / oxygen to ethylene glycol.

[0035] 4) The method used in this invention has good cycle performance for the direct oxidation of ethylene / oxygen to dihydroxylation to produce ethylene glycol.

[0036] 5) The catalytic reaction conditions of the present invention are relatively safe, and the reaction products are environmentally friendly and pollution-free. It can be used to replace the existing process for preparing ethylene epoxidation-ethylene oxide hydration and can be promoted and applied on a large scale.

[0037] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Attached Figure Description

[0038] Figure 1 This is a comparison chart of the reactivity of different catalysts. Detailed Implementation

[0039] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0040] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0041] Example 1

[0042] This embodiment investigates the effect of different halogen-containing catalysts on the oxidative dihydroxylation of ethylene. 100 mg of hydroiodic acid solution (47 wt%, containing 47 mg HI) was added to a high-pressure reactor lined with polytetrafluoroethylene. Subsequently, 4 mL of water was added to the reactor, and the reactor was purged three times with ethylene. A mixture of ethylene and oxygen (ethylene to oxygen volume ratio of 2:1) was introduced to bring the total pressure to 3 MPa. The reaction was carried out at 180 °C and 1000 rpm for 3 h, followed by rapid cooling of the reactor. The products in the reaction solution were analyzed by gas chromatography. The same experiment was conducted using other halogen-containing substances (iodine, potassium iodide, iodic acid, potassium iodate, periodic acid, potassium periodate, hydrobromic acid, potassium bromide) as catalysts, ensuring the same molar concentration of halogen in the reaction solution. The reaction evaluation results are shown in Table 1.

[0043] Table 1. Effect of different catalysts on the oxidative dihydroxylation of ethylene to prepare ethylene glycol.

[0044]

[0045] Table 1 shows that hydroiodic acid, elemental iodine, and iodic acid have the highest catalytic activity. The main product of the reaction is ethylene glycol, and the main byproducts are ethylene glycol dimer (diethylene glycol, 1,4-dioxane), as well as small amounts of acetaldehyde, acetic acid, and other products.

[0046] Example 2

[0047] This example investigates the effect of different temperatures on the catalytic activity of hydroiodic acid. 50 mg of hydroiodic acid solution (47 wt%, containing 23.5 mg HI) was added to a high-pressure reactor lined with polytetrafluoroethylene (PTFE). 2 mL of water was then added to the reactor, and the apparatus was purged three times with ethylene. A mixture of ethylene and oxygen (ethylene to oxygen volume ratio of 2:1) was introduced to bring the total pressure to 3 MPa. The reaction was carried out at 180 °C and 1000 rpm for 3 h. After the reaction, the reactor was rapidly cooled, and the products in the reaction solution were analyzed by gas chromatography. The same experiment was conducted at different reaction temperatures, and the reaction evaluation results are shown in Table 2.

[0048] Table 2. Effect of different reaction temperatures on the ethylene oxidation-dihydroxylation reaction to prepare ethylene glycol.

[0049]

[0050] The results in Table 2 show that the reaction is highly sensitive to temperature, with the reaction rate increasing rapidly with increasing temperature. Increasing the reaction temperature also leads to more ethylene glycol being converted into dimer products, thus reducing the selectivity of ethylene glycol.

[0051] Example 3

[0052] This embodiment investigates the catalytic performance during continuous reaction. 50 mg of hydroiodic acid solution (47 wt%, containing 3.5 mg HI2) was added to a high-pressure reactor lined with polytetrafluoroethylene (PTFE). 2 mL of water was then added to the reactor, and the apparatus was purged three times with ethylene. A mixture of ethylene and oxygen (ethylene to oxygen volume ratio 2:1) was introduced to bring the total pressure to 3 MPa. The reaction was carried out at 180 °C and 1000 rpm for 3 h. After the reaction, the residual gas was released, and the aforementioned mixture was re-introduced into the reactor to restart the reaction. Each reaction solution was collected, and the products were analyzed by gas chromatography. The reaction evaluation results are shown in Table 3.

[0053] Table 3. Effect of reaction number on the ethylene oxidation-dihydroxylation reaction to prepare ethylene glycol.

[0054]

[0055] The results in Table 6 show that as the reaction proceeds and the number of reactions increases, the ethylene conversion number gradually increases, and the selectivity of ethylene glycol gradually decreases. After four reactions, the selectivity of ethylene glycol is still 66.7%, and the mass fraction of ethylene glycol in the aqueous solution can reach 17%, which significantly reduces the energy consumption during concentration and purification.

[0056] Comparative Example 1

[0057] 2 mL of water was added to a high-pressure reactor lined with polytetrafluoroethylene (PTFE). The reactor was then purged three times with ethylene, followed by the introduction of a mixture of ethylene and oxygen (ethylene to oxygen volume ratio of 2:1) to bring the total pressure to 3 MPa. The reaction was carried out at 180 °C and 1000 rpm for 3 h. After the reaction, the reactor was rapidly cooled, and the products in the reaction solution were analyzed by gas chromatography. The reaction evaluation results are shown in Table 4.

[0058] Table 4 Comparative Experiments

[0059]

[0060] Comparative experiments showed that without the addition of a catalyst, ethylene and oxygen did not produce any target product, demonstrating the catalytic effect of halogenated compounds in this reaction.

[0061] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A method for the one-step catalytic dihydroxylation of ethylene to prepare ethylene glycol, characterized in that, Includes the following steps: Ethylene and oxygen are reacted in the presence of a catalyst and a reaction medium to produce ethylene glycol; The catalyst is a halogen-containing reagent, and the reaction medium is water; The catalyst is selected from: One or more of hydrobromic acid and its metal salts; The cations of the metal salts are metal ions from the third, fourth, fifth, and sixth periods; The concentration of the catalyst is 10-100 g / L; The reaction temperature is 140-240℃, the total reaction pressure is 3-6MPa, and the reaction time is 0.5-12h.

2. The method according to claim 1, characterized in that, The volume fraction ratio of ethylene to oxygen is 0.25-4, the pressure of ethylene is 0.5-3 MPa, and the pressure of oxygen is 0.5-4 MPa.

3. The method according to claim 1, characterized in that, The reaction temperature is 140-200℃.

4. The method according to claim 1, characterized in that, Includes the following steps: 1) Add the catalyst to the high-pressure reactor, add the reaction medium, and then introduce the reaction gases ethylene and oxygen. The partial pressure of ethylene is 0.5-3 MPa, the partial pressure of oxygen is 0.5-4 MPa, and the total reaction pressure is 3-6 MPa. 2) Heat the reactor to 140-200℃ and react for 0.5-12 hours to obtain the product.

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