How can the refinement and diversification of downstream products derived from coal-based ethylene glycol be advanced?

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How can the refinement and diversification of downstream products derived from coal-based ethylene glycol be advanced? Author/Source: Huahua Net Coal Chemicals Date: 2018-01-22 Clicks: 19 With the rapid advancement of the industrialization of coal-based ethylene glycol production, the contradiction between the swift increase in domestic production capacity and the overly limited range of downstream applications for ethylene glycol has become increasingly apparent. The diversification of downstream products for ethylene glycol is of great significance for the healthy development of this industry. Using dimethyl oxalate and ethylene glycol in the coal-based ethylene glycol production process as benchmark compounds respectively, the development of downstream products and the progress of industrialization were analyzed. In recent years, the production capacity of coal-based ethylene glycol in China has grown rapidly. By the end of 2016, China’s production capacity for coal-based ethylene glycol was 2.12 million tons, with output of around 1.1 million tons; it is estimated that by 2020 this capacity will reach 10.46 million tons. China is the world’s largest consumer of ethylene glycol, accounting for over 50% of the world’s total consumption. In our country, over 90% of ethylene glycol is used in the polyester industry; the concentration of consumption in this downstream sector is too high, which is not conducive to the healthy development of the industry. At the same time, with the commissioning of new petrochemical production capacity in the Middle East and the continuous decline in international oil prices, China’s coal-based ethylene glycol industry is facing fierce competition from low-cost products from the Middle East, which is reducing the cost advantage of ethylene glycol produced through petrochemical routes and narrowing their profit margins. To enhance the competitiveness of coal-based ethylene glycol, it is crucial to intensify efforts in developing its applications in other fields. Some coal-based ethylene glycol manufacturers have achieved good results by using the by-products of their production facilities, namely dimethyl carbonate and ethanol. This paper takes dimethyl oxalate and ethylene glycol in the coal-based ethylene glycol industry chain as the platform compounds, and analyzes the development of downstream products as well as the progress in industrialization. 1 Analysis of the product chain based on the dimethyl oxalate platform. The derivatives of the dimethyl oxalate platform are shown in Figure 1. As can be seen from the diagram, there are numerous derivatives of dimethyl oxalate. In particular, the coal-based ethylene glycol production facilities established by existing enterprises can utilize these existing products along with dimethyl oxalate for further processing, thereby expanding the range of products offered by these enterprises and enhancing their resilience to risks. The analysis is carried out from 6 aspects below. http://img.yf116.cn/image/img/20180122/941583491846.jpg 1.1 Hydrolysis of dimethyl oxalate to produce oxalic acid. Oxalic acid is widely used in the separation and purification of rare earth metals, as well as in fabric bleaching; it can also be used in the production of antibiotics and drugs such as borneol, and its demand has been increasing in recent years. Our country is the world’s main producer of oxalic acid, accounting for over 60% of global production. Most oxalic acid manufacturers in China use the sodium formate method, which is costly and causes significant pollution. The industrialization of the technology for producing ethylene glycol from coal via oxalate esters enables the acquisition of low-cost dimethyl oxalate, which can be hydrolyzed to produce high-quality oxalic acid. Tongliao Jinmei Chemical Co., Ltd. has built an oxalic acid plant with a capacity of 100,000 t/a by using this method. Tianjin University’s Dou Wenjing determined that the hydrolysis reaction of dimethyl oxalate is a sequential reaction by examining the changes in the concentrations of various substances and the selectivity of each product in the dimethyl oxalate hydrolysis system, as well as the variations in the conversion rate of dimethyl oxalate. A hydrolysis mechanism for dimethyl oxalate was proposed, including the attack of hydrogen ions on the carbonyl oxygen, the addition of the nucleophilic water molecule to the protonated ester, proton transfer, and the elimination of methanol and protons; among these, the nucleophilic substitution reaction is the rate-determining step. The effects of process parameters such as temperature, water-to-ester ratio, stirring speed, and the addition of oxalic acid on the conversion rate of dimethyl oxalate and the yield of oxalic acid were investigated through experiments. The results show that higher reaction temperature and water-to-ester ratio are favorable for the formation of oxalic acid. 1.2 Hydrogenation of dimethyl oxalate to methyl glycolate and its derivatives In the hydrogenation reaction of dimethyl oxalate (DMO), besides ethylene glycol (EG), the products also include methyl glycolate (MG), ethanol, and 1,2-butanediol, etc. By controlling the hydrogenation process, MG can be produced with high selectivity. The main industrial method for MG production at present is the hydrolysis of chloroacetic acid; this method suffers from issues such as low MG yield and severe environmental pollution, making large-scale production impossible. Methyl glycolate is the simplest type of glycol ester, and its uses include hydrolysis to produce glycolic acid ； Synthesis of fully biodegradable biomaterials – polyglycolic acid ； Produced via air-catalyzed oxidation and carbonylation to malonate esters ； Ammonolysis is used to produce glycine, which is then used to manufacture glyoxalic acid ； Oxidative dehydrogenation to acetaldehyde esters can be used to produce vanillin and similar substances. 1.2.1 Methyl glycolate-Glycolic acid-Polyglycolic acid Glycolic acid, also known as hydroxyacetic acid, is primarily used in industries such as leather processing, cleaning agents, and cosmetics. There are currently over 10 production methods, but most of them have drawbacks such as strong corrosivity. The main production methods include hydrolysis of chloroacetic acid, formaldehyde carbonylation esterification, and hydrolysis of hydroxyacetonitrile. The main companies producing glycolic acid in the world include DuPont and Union Carbide in the United States, Marubeni Corporation in Japan, and Hoechst in Germany. The current technology used in China for producing glycolic acid is primarily the cyanidation method; the raw materials are highly toxic, and the quality of the product is not good enough to meet the demands of future markets. Huang Guangxiao et al. studied the reaction kinetics of the hydrolysis of methyl glycolate to glycolic acid under conditions without any added catalyst. They examined the effects of stirring speed, the initial molar ratio of water to ester, and temperature on the reaction rate. Based on the homogeneous model, the pre-exponential factor and activation energy were obtained through regression of experimental data. The standard reaction enthalpy for this reaction was estimated to be approximately 16.12 kJ/mol using the van’t Hoff equation. Studies by Zhang Huihui and others have found that the solubility of glycolic acid decreases as the temperature drops, and the metastable region for glycolic acid solutions with a mass fraction of 80% is quite wide, which facilitates the purification of glycolic acid through crystallization. By studying factors such as crystal growth time, end temperature, amount of seed crystals added, cooling rate, seed crystal addition temperature, and stirring speed, ethanol acid crystals with a purity of over 99% were obtained. In May 2014, Yangzi Petrochemical, in collaboration with the Shanghai Research Institute of Petrochemical Technology, utilized proprietary technology for producing glycolic acid from coal—developed based on a coal-to-glycolic acid pilot plant—to produce high-quality glycolic acid with a purity of 70%. Shanghai Pujing Chemical has built a 5,000 t/a facility for producing glycolic acid from syngas; the purity of the glycolic acid crystals produced is above 99.6%, and the technology is currently in the stage of technical industrial demonstration. The Technology Research Institute of Shanghai Huayi Group is conducting a hundred-ton-scale pilot test of this technology. Polyglycolic acid (PGA) is a novel polymer material with good biocompatibility, gas barrier properties, and machinability; it is the most direct downstream product derived from glycolic acid (ester). PGA is primarily obtained through the polycondensation of raw materials such as glycolic acid, glycolate esters, and lactide in the presence of catalysts. The most industrially valuable production methods are the condensation polymerization of glycolic acid (esters) and the ring-opening polymerization of lactide. In 1995, Wu Yu Company was the first in the world to develop industrial production technology for PGA, and in 2002 it built an industrial pilot plant for PGA with a capacity of 100 t/a in Iwaki City, Fukushima Prefecture, Japan. In 2008, Kuraray partnered with DuPont and invested $100 million at DuPont’s plant in West Virginia, USA, where glycolic acid is produced. This investment led to the construction of a PGA production facility with an annual capacity of 4,000 tons. Thus, a production system from raw material glycolic acid to PGA resin was established, enabling the comprehensive launch of various resin products for different applications and under multiple grades. 1.2.2 Methyl glycolate-glycolic acid-lactide: Lactide is the cyclic dimer of glycolic acid, that is, a cyclic compound formed by the dehydration condensation of two molecules of glycolic acid. The ring-opening polymerization of glycolide is a relatively mature method for preparing polyglycolic acid; this method can yield polyglycolic acid products with a relatively high molecular weight. Currently, the most mature and widely used method for synthesizing lactide at home and abroad is the polycondensation-depolymerization method using glycolic acid as a raw material. Du Xiguang et al. used industrial glycolic acid as a starting material; after purification to 70% via solvent extraction, catalytic prepolymerization followed by depolymerization was carried out to produce lactide with a yield of 70%. Wu Qingyun et al. used polyglycolic acid (PGA) as a raw material; first, it was prepolymerized into low-molecular-weight polyglycolic acid and then depolymerized to produce glycolide. Studies have found that the depolymerization temperature rise rate has a significant impact on the yield of lactide; meanwhile, the effects of various reaction conditions on the lactide yield were also examined. The results showed that the best depolymerization effect was achieved at a polymerization temperature of 180 °C, with a catalyst (Sb2O3) addition amount of 0.75% based on the mass of the oligomer PGA, and by raising the temperature to 290 °C at a rate of 15 °C/min. The yield of the crude lactide product was as high as 87.5%, and after 3 recrystallizations, the purity exceeded 99.9% with a yield of 78.0%. Sun Zheng and others used methyl glycolate as a starting material to synthesize methyl glycolate oligomers through melt polycondensation, and then depolymerized these oligomers to produce lactide. Studies show that under the conditions of a mass ratio of catalyst tin dichloride to methyl glycolate of 0.4%, a polycondensation temperature of 200°C, a nitrogen flow rate of 150 mL/min, a polycondensation time of 6 hours, and a depolymerization temperature of 240°C, the yield of crude lactide is 85.6%, and the purity reaches 99.95% after 3 recrystallizations. 1.3 Hydrogenation of dimethyl oxalate to ethanol Ethanol is an important clean energy source that can be used as a fuel substitute or an oxygen-containing additive, offering great market potential. The carbonylation of CO to produce dimethyl oxalate, and the hydrogenation of dimethyl oxalate to yield ethanol, are new ethanol synthesis processes that have attracted considerable attention in recent years. These processes feature high selectivity, mild reaction conditions, and catalysts that are inexpensive and readily available. Zhao Yujun from Tianjin University used a Ni-modified Cu/SiO2 catalyst. Under the reaction conditions of a volumetric liquid hourly space velocity of 1.0 h−1, a pressure of 2.5 MPa, a reaction temperature of 280 °C, and a hydrogen-to-ester ratio of 200, the conversion rate of DMO reached 100%, while the selectivity to ethanol attained 90%. Zhu Yulei and colleagues from the Shanxi Coal Chemistry Institute of the Chinese Academy of Sciences found that the Cu/ZrO2/Al2O3 catalyst baked at 750°C could operate stably for 200 hours under reaction conditions of 270°C temperature, 4 MPa pressure, a volumetric liquid space velocity of 0.2 h-1, and a hydrogen-to-ester ratio of 150, achieving an ethanol yield as high as 97.4%. The authors attribute this to the synergistic effect of copper active sites together with more Cu+, as well as the ZrO2 crystal phase formed during high-temperature baking and the increased number of acidic sites. Chen Jiangang and colleagues from the Shanxi Coal Chemistry Institute of the Chinese Academy of Sciences used a Cu-modified Mo2C catalyst to achieve ethanol yield of 67.2% through the low-temperature hydrogenation of dimethyl oxalate under reaction conditions of 200°C temperature, 2.5 MPa pressure, a hydrogen-to-ester ratio of 200, and a volumetric space-time velocity of 0.2 h−1. In April 2014, the pilot-scale plant for producing ethylene glycol and ethanol from yellow phosphorus exhaust gas, developed through a partnership between Tianjin University and Guizhou Xinchen Coal Chemical Industry Group Co., Ltd., passed the on-site inspection and evaluation conducted by an expert panel organized by the China Petroleum and Chemical Industry Federation. This project uses the same apparatus and catalyst, and by merely changing the operating conditions, it can produce ethylene glycol and ethanol with high selectivity respectively. Through switching operations—producing ethylene glycol at a hydrogenation temperature of 200°C and ethanol at 270°C—the same plant is able to produce two different important chemical products: ethylene glycol and ethanol. 1.4 Ammonolysis of dimethyl oxalate to produce oxamide: The most promising use of oxamide is as a slow-release fertilizer. The existing nitrogen fertilizer industry is unable to synthesize slow-release nitrogen fertilizers on a large scale, and converting fast-acting nitrogen fertilizers into secondary slow-release forms does not meet the requirements of modern agricultural development. The utilization rate of oxamide nitrogen is as high as 65–80%, which is twice that of urea. The solubility of oxamide in water is only 0.016%. By using oxamide instead of urea as a nitrogen fertilizer, it is possible to **reduce the waste and loss of nitrogen fertilizers, thereby helping to conserve resources and protect the environment. There are various methods for synthesizing oxamide, including the HCN method, thermal decomposition method, and the CO coupling followed by ammonolysis of dimethyl oxalate. The CO coupling followed by ammonolysis of dimethyl oxalate process has advantages such as easy availability of raw materials, rational use of resources, and low energy consumption. CN102267921A, CN103242188A, and CN103288666A each disclose a continuous oxalamide production process. In 1981, the Japanese company Ube Industries built a plant with a capacity of 600 t/year for the production of oxamide via the ammonolysis of dioxalate esters, thereby finding a convenient and inexpensive method for oxamide production. In China, the Fujian Institute of Research on the Structure of Matter under the Chinese Academy of Sciences, as well as the Southwest Chemical Engineering Research and Design Institute Co., Ltd., have carried out experimental research on continuous production processes for oxalamide. 1.5 Transesterification of dimethyl oxalate and phenol to produce diphenyl carbonate Diphenyl carbonate (DPC) is a low-toxicity and environmentally friendly organic carbonate. It can be used in the synthesis of polycarbonates, methyl parahydroxybenzoate, monoisocyanates, etc., and is widely applied in industries such as plastics, pesticide synthesis, and pharmaceuticals. Currently, there are mainly three methods for synthesizing diphenyl carbonate: the phosgene method, the transesterification method, and the oxycarbonylation method. Among these, the transesterification of phenol and dimethyl oxalate to synthesize DPC has become a research hotspot due to its mild reaction conditions, high atom utilization rate, and ease of separation of by-products. The research group led by Ma Xinbin at Tianjin University and the research group led by Wang Gongying at Chengdu Organic Chemicals Co., Ltd. of the Chinese Academy of Sciences have carried out extensive work in this field. China is the fastest-growing market for polycarbonate demand**, with an annual growth rate of 8% to 12%. In 2016, China’s apparent consumption of polycarbonate was approximately 1.7 million tons. Although China’s polycarbonate production capacity is nearly 900,000 tons per year, with output of around 600,000 tons, its net import volume is close to 1.1 million tons, resulting in a self-sufficiency rate of less than 40%. With the rapid development of China’s polycarbonate industry, the market demand for DPC is increasing steadily. The synthesis of DPC via transesterification of phenol with DMO holds great promise. To meet industrial requirements, it is necessary to improve its catalytic performance by conducting in-depth research on the mechanism of catalyst action, optimizing its preparation methods, and combining it with other catalysts. 1.6 Decarboxylation of dimethyl oxalate to dimethyl carbonate Dimethyl carbonate can replace halomethanes as a methylating agent in the synthesis of pesticide and pharmaceutical intermediates, antioxidants, plastic processing stabilizers, etc. It is also an excellent solvent; as a high-performance solvent, it boasts advantages such as good solubility with other organic compounds, low toxicity, and rapid evaporation rate. Meanwhile, dimethyl carbonate is also an important component of lithium-ion batteries; lithium-ion batteries containing DMC have a higher capacitance. As a gasoline additive, DMC can increase the oxygen content in gasoline and improve combustion efficiency. Currently, there are various methods for synthesizing dimethyl carbonate. These include the synthesis method using phosgene and methanol, the oxidative carbonylation of methanol in a gas-liquid phase, and the oxidative synthesis from carbon monoxide and methanol. However, all these methods have significant drawbacks; they may cause environmental pollution or lead to waste of raw materials. Through thermodynamic calculations, Zhang Haoyang from Shanghai Normal University demonstrated that the reaction of decarboxylation of dimethyl oxalate to yield dimethyl carbonate is feasible. On this basis, they used alkali metal carbonates as active components and prepared a series of carbon-based catalysts via the equal-volume impregnation method; these catalysts were used to catalyze the decarboxylation of dimethyl oxalate to produce dimethyl carbonate, achieving high yields, but the catalysts had poor stability. 2 Analysis of the product chain based on the ethylene glycol platform. Figure 2 shows the derivatives of ethylene glycol; it can be seen that there are numerous such derivatives, which provide ideas for the development of downstream products based on ethylene glycol. The analysis is carried out from 7 aspects below. http://img.yf116.cn/image/img/20180122/943163499668.jpg 2.1 Ethylene glycol-glyoxal-glycolic acid 2.1.1 Oxidation of ethylene glycol to glyoxal Glyoxal is the simplest aliphatic dialdehyde in terms of molecular structure, and it has wide applications in areas such as textile printing and dyeing, building materials, leather manufacturing, pharmaceuticals, pesticides, coatings, and environmental protection; its main uses are in the pharmaceutical and textile industries. There are mainly two industrial production methods for glyoxal: the acetaldehyde oxidation method and the ethylene glycol oxidation method. The ethylene glycol oxidation process has become the development trend for producing high-quality glyoxal, owing to its advantages such as simple process equipment, environmental friendliness, high concentration of the crude product, easy post-treatment, and suitability for continuous production. Shanghai Huayi Group’s Shangliu Chemical Industry has utilized this process to construct and put into operation a production facility capable of manufacturing 28,000 tons per year of 40% glyoxal with low color content. The main domestic producers of glyoxal include Shanghai Huayi Group Shangliu Chemical Co., Ltd. (58,000 t/a), Jiangsu Taicang Guangze Fine Chemicals Co., Ltd. (50,000 t/a), and Hubei Luotian Hongyuan Pharmaceutical Technology Co., Ltd. (120,000 t/a). Currently, domestic glyoxal production capacity exceeds demand; therefore, efforts should be made to actively explore new application areas for glyoxal so as to promote the healthy development of the industry. 2.1.2 Production of glyoxylic acid from glyoxal Glyoxylic acid is an important fine chemical product and organic synthesis intermediate that contains both an aldehyde group and a carboxyl group within its molecule. It has a wide range of applications in fields such as food additives, fragrances, pharmaceuticals, papermaking, biochemistry, spectroscopic research, and anti-corrosion. Currently, the main methods for glyoxylic acid production include the oxidation of glyoxal, the electrolytic oxidation of oxalic acid, and the enzymatic oxidation of glycolic acid. Among these, the oxidation of glyoxal is the predominant production method. Depending on the oxidant used, the glyoxal oxidation method can be further divided into nitric acid oxidation, air or oxygen oxidation, and hydrogen peroxide oxidation, among others. The development of a series of chemical products derived from ethylene glycol, glyoxal, and glyoxylic acid provides an environmentally friendly and pollution-free method for producing glyoxylic acid. Currently, the main acetaldehyde acid producers in China include Jiangsu Taicang Guangze Fine Chemical Co., Ltd. (30,000 t/a), Hubei Luotian Hongyuan Pharmaceutical Technology Co., Ltd. (10,000 t/a), and Cangzhou Sangtian Chemical (5,000 t/a), among others. 2.2 Production of ethylene glycol ethers from ethylene glycol: The series of ethylene glycol monoether products are versatile green solvents. Due to their structure, which contains ether bonds, hydroxyl groups, and various alkyl groups, they can dissolve organic substances, polymers, and natural polymers; at the same time, they possess a certain degree of water solubility. As a result, they are widely used in industries such as industrial solvents, antifreeze, and surfactants ； The ethylene glycol diether series of products are a class of potential oxygenated ether liquid fuels. These compounds possess a high cetane number and energy density, are miscible with diesel, have stable properties, and can effectively reduce emissions from diesel engines. Ethylene glycol ethers are typically produced through a catalytic reaction between ethylene oxide and corresponding anhydrous alcohols. Jiangsu Dena Chemical Co., Ltd. uses this process to manufacture a range of diol ether and ester products, and it currently has the largest production capacity in China. Given issues such as the production cost of ethylene oxide, market demand, and transportation, synthesizing ethylene glycol ethers using ethylene glycol as a raw material offers mild reaction conditions and low risk, thus holding great potential for practical application. A patent filed by Di Wei and others from the Beijing Institute of Low-Carbon Clean Energy states that ethylene glycol can react with methanol to produce ethylene glycol monomethyl ether; this hydrogenation reaction takes place under mild conditions, yields high selectivity for ethylene glycol monomethyl ether, and achieves high space-time yields. CN105585455A discloses a method for preparing ethylene glycol monomethyl ether via continuous etherification, using ethylene glycol and methanol as raw materials; in a fixed-bed reaction apparatus, under the action of a multiphase etherification catalyst, high-selectivity ethylene glycol monomethyl ether product is continuously produced. CN105585459A discloses a method for the continuous etherification of ethylene glycol to produce dimethyl ethylene glycol, with an ethylene glycol conversion rate of over 90% and a selectivity for dimethyl ethylene glycol of over 74%. The laboratory-scale tests and the design of pilot plant scale of 10,000 tons have been completed for the reaction of highly chemically modified ethylene glycol with methanol to produce ethylene glycol monomethyl ether and ethylene glycol dimethyl ether. 2.3 Ammoniation of ethylene glycol to produce fine chemicals such as ethylenediamine and its derivatives. Ethylenediamine is primarily used in the production of pesticides, pharmaceuticals, and various chemical auxiliaries; the global annual consumption is approximately 450,000 tons. China’s consumption of ethylenediamine is growing rapidly at an annual rate of 5% to 10%; before 2011, China’s demand for ethylenediamine was met mainly through imports from abroad. The main methods for synthesizing ethylenediamine include the dichloroethane method, the ethanolamine method, the ethylene oxide method, the ethylene amination method, and the diglycol amination method. Among these, the industrial synthesis methods are the dichloroethane (EDC) method and the ethanolamine method; however, the EDC method has drawbacks such as poor product quality, severe equipment corrosion, and high emissions of waste substances. The ethanolamine method uses ethylene oxide as a raw material, and this core technology has for a long time been held in control and monopolized by a few foreign companies, which refuse to transfer it to other firms. In 2011, an industrial plant with a capacity of 10,000 t/a was built in Shandong Lianmeng, utilizing the patented hydrogenation ammonia synthesis technology for ethanolamine developed by the Dalian Institute of Chemical Physics; this plant has been operating steadily since then. In 2015, the company constructed another industrial plant with a capacity of 30,000 t/a. To date, there are no reports of industrial-scale production of ethylenediamine via the ammonia synthesis of ethylene glycol. From a reaction principle perspective, the aminoalkylation of ethylene glycol is the most ideal route for preparing ethylenediamine. Zhang Hualiang et al. used a supported bicomponent composite metal oxide catalyst NiO/CuO/Al2O3 to determine the optimal process conditions for the synthesis of ethylenediamine: the molar ratio of the active components of the catalyst, n(Ni):n(Cu), was 3:1; the amount of catalyst used was 3%; the mass ratio of ammonia to alcohol was 4:1; the reaction temperature was 180 °C; the reaction pressure was 0.6 MPa; and the reaction time was 4 hours. The selectivity for ethylenediamine reached 56.7%, while the conversion rate of ethylene glycol was 68.6%. CN101384542B discloses a method for the direct amination of ethylene glycol to produce ethylenimine and ethylenediamine. Each hydroxyl group of ethylene glycol undergoes three steps: hydroxyl dehydrogenation to form an aldehyde, imine formation via ammonia addition and dehydration, and imine hydrogenation to form an amine; among these, dehydrogenation and hydrogenation are the key steps in this reaction. CN 105503613A discloses a method for preparing polyamines from polyhydroxyl compounds via direct amination, using a carrier-supported liquid-phase reduced transition metal as a catalyst to enable the amination of polyhydroxyl compounds under milder conditions, with the catalyst being recyclable. 2.4 Ammonolysis of ethylene glycol to produce ethylenecyanide Ethylenecyanide is an important intermediate used in the synthesis of polyamides, pharmaceuticals, and fuels; in the known methods, it is synthesized from hydrocyanic acid in the presence of oxygen, nitrates, and copper catalysts. Ethylene glycol can be converted into ethylenecyanide through oxidation, amination, and dehydrogenation processes; the oxygen source is air or oxygen, while the nitrogen source is ammonia, ammonium hydroxide, urea, or ammonium salts. This process is green and environmentally friendly. CN104945279A discloses a method for preparing dicnitriles from diols via ammoxidation, which enables the synthesis of dicnitriles from diols under mild conditions using an efficient heterogeneous catalyst. This approach offers advantages such as high ammoxidation efficiency, high product yield, easy separation of the product from the catalyst, and ease of catalyst reuse. 2.5 The reaction of ethylene glycol with formaldehyde to produce 1,3-dioxolane: 1,3-dioxolane is a key material for lithium battery electrolytes and the main raw material for the engineering plastic polyoxymethylene (POM). The traditional synthesis method for 1,3-dioxolane involves the reaction of paraformaldehyde or concentrated formaldehyde with ethylene glycol; this approach results in a low conversion rate of the raw materials, with a large amount of unreacted material being discharged from the reactor, leading to environmental pollution and waste of raw materials ； The product has many by-products, the purification process for the crude product is complicated, and it requires high energy consumption. Guo Xiaoying’s research on the purification of dioxolane products showed that the combined method of sodium chloride salting out and molecular sieve dehydration is the most suitable purification technique. When the amount of sodium chloride used is 7.5%, and the appropriate ratio of molecular sieve to the purified product is 1:1, the purity of the product can reach 99.9%, meeting the quality requirements for dioxolane products. In 2016, Sichuan Zhijiang High-Tech Materials Co., Ltd. successfully overcame the challenge of continuous production of 1,3-dioxolane, achieving a product purity of 99.99%, which was widely recognized by downstream lithium battery manufacturers. 2.6 The reaction of ethylene glycol with dimethylamine yields N,N,N’,N’-tetramethylethylenediamine (TMEDA), which is used in the preparation of spherical non-ionic hydrogels. It can serve as a foaming catalyst with moderate activity, and it is also a raw material for the synthesis of water treatment agents, pesticides, and pharmaceuticals. There are generally 3 methods for synthesizing TMEDA: ① Reacting formic acid and formaldehyde as methylating agents with ethylenediamine, which causes significant environmental pollution ； ② The process involves reacting an excess of sodium hydroxide with 1,2-dichloroethane and dimethylamine; this is currently the main method used by domestic companies to produce TMEDA, but it incurs high costs for wastewater treatment and dimethylamine recovery ； ③Dimethylamine is used as a methylation reagent to react with dichloroethane; this reaction takes place in the presence of N-propylmorpholine. There are numerous by-products generated, and hydrogen chloride gas is produced as well, resulting in significant environmental pollution. By using dimethylamine to react with ethylene glycol, the raw materials are readily available; this process is environmentally friendly, and the only by-product is N,N-dimethylethanolamine, which is relatively easy to control. Zhang Tao et al. used a copper-nickel-based catalyst to react dimethylamine with ethylene glycol in a hydrogen atmosphere; under the optimal reaction conditions, the yield reached 79.84%. 2.7 Reaction of ethylene glycol with aniline to produce indole. As a fine chemical, indole is an important raw material for the production of pharmaceuticals, pesticides, fragrances, dyes, and feed additives. Before the 1990s, the industrial production of indole mainly relied on methods involving the separation and purification of indole from coal tar, as well as multi-step synthesis using o-toluidine and formic acid as raw materials; these methods had drawbacks such as numerous production steps, complex operational processes, and high costs associated with indole production. The synthesis of indole from aniline and ethylene glycol is a new one-step method for producing indole that was developed in Japan in the mid-1990s. This method not only features low costs for raw materials and a simple operational process, but also avoids the generation of waste such as inorganic salts that can be harmful to the environment during the reaction; it is thus the most economical among various indole synthesis methods. To date, this process has been industrialized only in Japan. The key to this method lies in the research on catalysts. The Cu/SiO2 catalyst reported by Sun Junming et al. achieved an indole yield of 88%, but the catalyst had poor stability. To overcome this drawback, Shi Lei prepared a Cu/SiO2-ZnO catalyst by first loading the additive ZnO and then the active component Cu; after a reaction time of 2 hours, an indole yield of 75% was achieved. Wei Chenglin employed a method of first loading Cu and then ZnO, and prepared Cu/SiO2-ZnO catalysts through equal-volume impregnation, calcination, and in-situ reduction. It was found that with the addition of a 1.0% by mass ZnO additive, the yield of indole could reach 91%. 3 Conclusions In recent years, with the rapid advancement of the industrialization of ethylene glycol, domestic production capacity for coal-based ethylene glycol has increased significantly. The issue of monotony in the downstream application areas of coal-based ethylene glycol has become increasingly prominent, posing a serious constraint on the economic viability and long-term development of this industry. Using dimethyl oxalate and ethylene glycol, which are key compounds in the process of producing ethylene glycol from coal, fine chemical products such as glycolic acid, polyglycolic acid, glyoxalic acid, ethylene glycol ethers, ethylenediamine/ethanolamine, and indole can be synthesized. This approach provides new ideas for the further development and diversification of downstream products derived from coal-based ethylene glycol. By establishing effective connections between ethylene glycol and the company’s existing products and by carrying out further processing, it is possible to achieve a deep integration of modern coal chemistry with traditional coal chemistry, thereby supporting the healthy development of the enterprise.