Aerial photo of the coal-based ethanol production project in Yulin, Shaanxi province. (Photo from the DICP website) 

By WANG Xiaoxia

Ethanol, a renewable fuel produced through grain fermentation or by hydration of ethylene derived from petroleum, is caught in a dilemma. Both production methods have flaws — the former threatens food security, while the latter is expensive and dependent on oil.

So, are there other ways to make ethanol on a large scale? Liu Zhongmin, academician at the Chinese Academy of Engineering, and his team from Dalian Institute of Chemical Physics (DICP), have explored a more economical and greener way of ethanol production from coal.

After years of technical optimization and scale-up verification, the technology is well ready for large-scale industrial production. Recently, based on Liu's research, the world's largest coal-based ethanol production project with an annual output of 500,000 tons was completed in Yulin, Shaanxi province.

High demand

Ethanol is one of the largest volume organic chemicals used in industrial and consumer products. Absolute ethanol can be used as a gasoline additive, namely fuel ethanol, which can effectively improve the quality of gasoline and greatly reduce the pollutant emissions.

Bioethanol is by far the most common biofuel worldwide, which mainly uses grain as raw material. China produced 9.87 million tons of bioethanol in 2020, of which about 2.74 million tons were fuel ethanol, far from meeting the country's demand, said Liu.

Therefore, increasing fuel ethanol production is of great significance to ensure energy security of the country. However, bioethanol production may not be widely promoted in China, given the large demand for food from its enormous population.

In view of China's large coal reserves, which account for 95 percent of the country's fossil fuel resources, it is feasible to develop coal -based ethanol production technology, which would serve both energy and food security of China. This is the prime reason why Liu and his team decided to develop this kind of technology.

New breakthrough technology

After years of research, DICP has come up with new technology to produce ethanol from coal -based syngas through methanol, dimethyl ether carbonylation and hydrogenation.

According to Liu, the dimethyl ether conversion reaction is very complex, as different catalysts can lead to completely different reactions, producing completely different products.

For a long time, the direct ethanol production from coal syngas has been stuck in the research and development stage, because it requires precious metals as catalysts and causes severe corrosion.

In order to develop a technology suitable for commercial use, researchers had to develop a proper catalyst for dimethyl ether carbonylation. After three years of testing and optimization, the research team achieved a breakthrough using a cheap catalyst with high activity and stability.

At the same time, the new technology requires no iodide methane and other halide additives in the production process, which avoids corrosion to equipment, and reduces the cost of corrosion-resistant materials.

This technology can directly produce absolute ethanol with no or very little water, requiring no further purification, which reduces the energy consumption and saves costs.

Apart from coal, natural gas, biomass and steel plant gas can also be used as raw material for the new technology to produce ethanol, providing strong technical support for the clean and efficient utilization of fossil fuels and the realization of carbon neutrality, said Liu.

From laboratory to factory

The fundamental purpose of research is to apply it into production, so the collaboration between laboratory and industry should be put high on the agenda.

In 2012, the DICP and Shaanxi Yanchang Petroleum Group jointly carried out the project on ethanol production technology from coal syngas.

On January 11, 2017, the 100,000-ton-capacity coal-based ethanol project with China's domestic technology was completed to produce qualified absolute ethanol.

From lab research to production line, it took only six years, "Which is very fast," said Liu, adding that the intermediate product methyl acetate is also a bulk chemical, which can help adjust the product structure in a timely manner according to the market demand.

On the basis of the 100,000-ton demonstration project, the technology upgrade has been constantly iterated. The 500,000-ton coal-based ethanol project began construction in June 2020. After more than two years of construction, the project is expected to be put into operation this September.

Using low-grade coal instead of grain to make ethanol, the world's largest coal-based ethanol project can save 1.5 million tons of grain every year after coming into operation, equivalent to 65 percent of Yulin's annual grain output, said Guo Zunli, general manager of Shaanxi Yanchang Petroleum Yushen Energy and Chemical Co., Ltd.