Ethylene Glycol Production Technology Needs to Be Improved
Click:0    DateTime:Sep.22,2020


By Hu Shiming, China National Chemical Information Center


Ethylene glycol production routes

Ethylene glycol usually refers to monoethylene glycol (MEG), an important basic chemical raw material of polyester, which is for fiber and packaging applications. MEG is also used in the production of antifreeze and unsaturated polyester resin.
The industrial production routes of ethylene glycol are divided into two categories according to different raw materials: one is the ethylene route, with crude oil, ethane or methanol as raw materials; the other is the synthesis gas route, with coal, natural gas, and coke oven gas as feedstock.
The ethylene route is the most mature process with absolute market advantages. There are various raw material portfolios for ethylene plants, such as naphtha cracking to ethylene, shale gas based ethane to ethylene in North American, associated gas based ethane to ethylene in Middle East, imported natural gas to methanol to ethylene in China, and coal to methanol to ethylene in China (CTO/MTO).
In the synthesis gas route, CO and H2 in the synthesis gas, which is generated from coal, are used as raw materials to produce ethylene glycol. This route is suitable for China's producers as coal resources are abundant here. There are many kinds of synthesis gases, such as coal-based synthesis gas, natural gas-based synthesis gas, coke oven tail gas/calcium carbide tail gas, etc.
In addition, the new formaldehyde carbonylation route-based coal-to-ethylene glycol technology is about to be industrialized. Jiutai Inner Mongolia Hohhot 1 million t/a project and Erdos’ 500 kt/a project are under construction.

1. Ethylene route

Industrially, the ethylene-based ethylene oxide/ethylene glycol production route includes direct pressurized hydration process and ethylene carbonate process.
The basic process of the direct pressurized hydration method is as follows: in the first stage process, the ethylene is directly oxidized to EO in the presence of silver catalyst, methane stabilizer, and chloride inhibitor; in the second stage, EO and water are hydrated in a tubular reactor at a certain molar ratio to generate ethylene glycol; then the ethylene glycol solution is evaporated and refined to obtain MEG and by-products diethylene glycol (DEG) and triethylene glycol (TEG). No catalyst is used in the hydration reaction, and the process is mature. However, in order to maintain a high ethylene glycol selectivity, excessive water is often added during the hydration reaction, and a large amount of water needs to be evaporated in the later purified process, resulting in a long process flow and high energy consumption.
The ethylene carbonate process is the same as the direct pressurized hydration method as for the first stage. But in the second stage, EO is converted into ethylene glycol in two steps, first into ethylene carbonate (EC) and then EC is catalytically hydrolyzed to MEG (or catalytically alcoholzed via methanol to MEG and dimethyl carbonate). This process greatly reduces the consumption of water and steam, and the MEG selectivity can be increased to more than 99%, without the need to separate DEG or TEG.

The technology of direct pressurized hydration is monopolized by a few companies, including Dow, Scientific Design (abbreviated as SD), Shell, Nippon Shokubai, BASF, and SNAM. The industrial license of the ethylene carbonate hydrolysis technology is exclusively owned by Shell. See Table 1 for details.

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Since EO hydration process is almost a complete reaction, the research and development focus of EO and EG technology licensors has been on improving the silver catalyst for EO oxidation. According to the performance characteristics of the catalyst, the silver catalysts currently used in industrial EO/EG production lines are divided into four types: high activity, medium selectivity, high selectivity and high efficiency. See Table 2 for details.

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Shell's highly selective silver catalyst was the first to realize industrialization and the technology was relatively mature. SD company's highly selective catalysts are also used by many domestic units. The catalysts of the two companies have the highest market share internationally. Dow's catalysts have high selectivity and activity, and have the best overall performance; however, nitrogen-containing reaction accelerators need to be added in industrial production, and production lines using Dow's chemical process are forced to use its special silver catalyst.
Since its first industrial application in 1989, Yanshan Branch of Sinopec Beijing Research Institute of Chemical Industry has successively generated high-activity catalysts YS-4, 5, 6, and 7, medium-selectivity catalysts YS-8510, YS-8520, and high-selectivity catalysts YS-8810, YS-8830 and YS-9010. These catalysts are widely used in domestic EO plants.
At present, traditional high-activity silver catalysts have basically withdrawn from the market, and high- and medium-selectivity silver catalysts have become the mainstream of silver catalysts. The ethylene process is becoming more and more perfect. Companies are mainly committed to improving the selectivity of EO oxidation catalyst and the selectivity of EG to further reduce ethylene consumption and simplify the process.
The industrial technology owners of ethylene carbonate alcoholysis (transesterification) are Asahi Kasei Chemical Co., Ltd. and the Institute of Process Engineering, Chinese Academy of Sciences. Asahi Kasei has licensed Chimei-Asahi (a joint venture of Asahi Kasei and Chi Mei) and Lotte Chemical. The Institute of Process Engineering of Chinese Academy of Sciences has developed solid-supported ionic liquid catalyzed CO2 to produce DMC and MEG, and has licensed Jiangsu Aoke Chemical Company's 20 kt/a lithium battery electrolyte solvent project, which can switch production to EC/DMC.

2. Synthetic gas oxalate route

Syngas oxalate to MEG route includes 3 steps: methanol and nitric oxide (NO) oxidative esterification to generate methyl nitrite; CO and methyl nitrite carbonylation coupling reaction to generate dimethyl oxalate (DMO); DMO catalytic hydrogenation to produce ethylene glycol.
China’s industrialized oxalate route technology owners are shown in Table 3. In addition, Sinopec's technology is only used by its own units and not allowed for licensing. The key to this route is the performance of the carbonylation catalyst and the hydrogenation catalyst, which is closely related to the system energy consumption and product quality. The life cycle of the two catalysts has become the focus of production cost control.

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The first generation of synthesis gas to ethylene glycol carbonylation catalyst developed and produced by HighChem has a service life of more than 6 years in Xinjiang Tianye ethylene glycol plant.
Henan Energy Research Institute and Shangqiu Guolong New Material Company are also developing and producing carbonylation catalysts and hydrogenation catalysts and are conducting application tests in the ethylene glycol production lines of Henan Energy Chemical Group. Since the copper catalyst of the hydrogenation system of the ethylene glycol plant of Puyang Yongjin Company was put into use on April 3, 2018, it has been operating for a total of 14 150 hours as of March 16, 2020.
Xinjiang Tianye Group began to tackle key technical problems of ethylene glycol catalysts in 2013, and filed a total of 5 invention patent applications, and will promote the industrialization of catalysts in the future.
Henan Energy Puyang Yongjin Chemical Co., Ltd. and Hebei Kairui Environmental Protection Technology Co., Ltd. jointly undertake the “Ethylene Glycol Deep Refining Process Technology”. The R&D and application of this technology have greatly increased the light transmittance of ethylene glycol and have reached the polyester level by 100%.

The coal-to-MEG has become a hot spot for the development of China's ethylene glycol industry, but the technology of coal-to-MEG is not mature; products are yet qualified compared to ethylene-bases ones, not able to be applied to polyester production if not being blended. The blending ratio is generally 10%-20%, sometimes as high as 80%. The blending ratio is slightly high in conventional varieties of polyester staple fiber and polyester filament, low in polyester bottle chips and polyester high-end products, and zero in high-end filament products, especially those for export.
The oxalate route technology is almost mature, but there is still great potential to be tapped. The conversion rate, selectivity, stability and service life of hydrogenation catalysts have become the focus of attention.

3. Formaldehyde carbonylation route

The development of the formaldehyde carbonylation route began with Eastman, and Johnson Matthey Davy (JM Davy), which provides methanol and formaldehyde technologies, started later. In October 2013, the technology was successfully developed and is currently licensed by JM Davy. The basic process flow is getting glycolic acid from formaldehyde carbonylation, then getting methyl glycolate from glycolic acid esterification, and finally producing ethylene glycol from methyl glycolate catalytic hydrogenation.
Jiutai Company's Inner Mongolia Hohhot 1 million t/a ethylene glycol project and Erdos 500 kt/a ethylene glycol project, with Davy's formaldehyde carbonylation process package, are currently under construction and are expected to be put into operation in 2021.

Cost competitiveness

The production cost of traditional ethylene glycol producers is highly dependent on the price of the ethylene. In general, the ethylene glycol production cost is lowest in the United States (with the lowest ethylene prices), followed by the Middle East (with the lowest utility cost), China and Western Europe. Without considering the benefits of DEG and TEG, the cost of the OMEGA process is more competitive in all regions. In regions where the benefits of DEG and TEG are not good (such as China), the production cost of the OMEGA process is basically the same as that of the conventional process; while in regions with higher DEG and TEG benefits (such as Western Europe), the competitiveness of the OMEGA process is relatively weak.
Compared with the ethylene process, the complete cost of China's coal-to-MEG is higher, which is mainly due to the high unit capacity investment which leads to high depreciation and financial expenses. The advantage of coal-to-EG in areas rich in coal resources lies in its low coal price and extremely competitive variable costs. With the low oil prices, the original competitive advantage of coal-to-MEG has been severely weakened.
At present, China’s ethylene glycol manufacturers are facing tremendous pressure on profitability. The key to profitability lies in cost competitiveness, while improving ethylene glycol technology is the most effective means to reduce product costs. For the ethylene route, the focus is on improving the selectivity of the silver catalyst, increasing the selectivity of ethylene glycol, reducing ethylene consumption and simplifying the process flow. For oxalate route, the focus is on improving the stability and service life of hydrogenation catalysts, reducing power consumption and steam consumption, and improving the quality of ethylene glycol products.