How can coal complete the magnificent transformation from "black" to "white"?

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Against the backdrop of an increasingly severe global environmental crisis and the imperative of green transformation, China is promoting the sustainable development of the energy and chemical industries with unprecedented determination and action. Yulin City, Shaanxi Province, located in the heart of the Loess Plateau, is not only a treasure trove of rich resources, but also a place with extremely fragile ecology. Here, coal is not only an energy source, but also an important lifeline for driving the dual development of energy transformation and environmental protection. Recently, the reporter went to the Yulin Industrial Park to see how scientific and technological workers use the power of science and technology to compose the magnificent transformation of coal from "black" to "white".

Coal to Ethylene Glycol

108 hours of magical transformation

In our minds, coal is often seen as an energy source, but in the modern chemical industry, it can also be transformed into an important chemical raw material - ethylene glycol. As a multifunctional compound, ethylene glycol's unique properties and chemical reactivity make it an indispensable component in many products and processes, adding many conveniences and possibilities to our lives.

"Ethylene glycol has two main functions. The first is to make polyester resin and the second is polyester fiber." Xu Weiwei, manager of the ethylene glycol plant of the new material branch of Guoneng Yulin Chemical Co., Ltd., introduced that polyester resin has good optical properties, such as our eyeglass lenses and medical syringes. The downstream of polyester fiber is mainly textiles. It has some excellent properties. If a certain amount of ethylene glycol polyester fiber is added to the textile material, its fabric will not be easy to wrinkle.

Yulin Industrial Park. Photo provided by the interviewee

From coal to ethylene glycol, the entire production process only takes 108 hours, but the technology development took several years. In November 2021, Yulin Chemical's 400,000 tons/year ethylene glycol project completed the entire process at one time and successfully produced qualified ethylene glycol products. The project cleverly utilized the surplus synthesis gas and public facilities of the coal-to-methanol project that has been completed and put into production, and recycled the tail gas generated by the ethylene glycol unit as a raw material for the coal-to-methanol project, realizing the clean recycling of coal, and significantly improving the economic benefits and environmental protection effects.

Relying on the ethylene glycol project, Yulin Chemical also carries out deep processing of some intermediate products and builds a new PGA project to produce polyglycolic acid degradable materials, further extending the industrial chain and enhancing the value chain. This material has many advantages such as full biodegradability, high biocompatibility, high mechanical properties and high barrier properties. It can be completely harmlessly degraded in soil, seawater and other environments. It can be widely used in food packaging fields such as disposable plastic bags, lunch boxes, and straws. It can also be used in medical surgical sutures and bone scaffold materials. It provides a new path for my country to control white pollution, serve people's livelihood needs and tackle "stuck neck" technologies, and promote the transformation and development of the national coal chemical industry towards high-end, diversified and low-carbon development.

Starting from zero

Green technology brings wastewater back to life

If coal-to-ethylene glycol is a process of changing from "black" to "white", water treatment is a magical process of changing from dirty to clean. Coal chemical wastewater discharge is large, the water quality is complex, and contains a large number of pollutants. Developing coal chemical industry in the ecologically fragile areas of Northwest China will not only pollute local water resources, but also aggravate the shortage of water resources. The "water gate" has become a difficult hurdle that coal chemical industry must overcome, and zero wastewater discharge has become a key way to solve this problem.

Salt separation and crystallization pretreatment plant. Photo provided by the interviewee

In the process of developing zero wastewater discharge technology, how to extract the main salt from high-salt wastewater and achieve the reduction of crystalline mixed salt and its resource-based circular economic utilization has become a difficulty and key point.

"Through independent innovation, we have developed a low-temperature critical freezing plus vacuum thermal salt separation technology. We separate high-purity salts through a low-temperature freezing crystallization process. At the same time, we recover the heat in the process through thermal methods to achieve energy reuse, which greatly reduces operating costs." said Hu Huagui, deputy manager of the Environmental Storage Plant of Guoneng Yulin Chemical Co., Ltd.

The salt separation crystallization device produces qualified sodium chloride and achieves continuous and stable operation. It not only achieves a "zero" breakthrough in the low-temperature critical freezing and vacuum thermal salt separation technology in coal chemical wastewater treatment, filling the domestic technical gap, but also brings significant environmental and economic benefits. It can save 2.94 million tons of water and 25 million yuan in costs each year, reduce the amount of miscellaneous salt by about 32,000 tons, and save about 110 million yuan in hazardous waste disposal costs. These remarkable achievements have witnessed an important step taken by my country in the pursuit of green and low-carbon development, and inspired more people to devote themselves to this sustainable development plan.

Silicon's Nemesis

Young scientific research team **** unlocks magical purification technique

In the wastewater generated by coal chemical industry, common impurities that are difficult to remove, in addition to salt, are silicon, which mainly exists in the wastewater in the form of silicon dioxide. The removal of silicon is crucial for zero discharge of coal chemical wastewater. It can greatly slow down the scaling of key equipment such as reverse osmosis membranes and evaporators, and ensure the efficient operation of subsequent treatment processes. However, it is not easy to remove silicon from wastewater. It requires precise control of chemical reaction conditions to avoid new problems caused by inappropriate reagents or excessive addition of chemicals. Faced with this difficult problem, Lu Chaochao, a "national technical expert" born in 1995, and his team conducted repeated experimental studies.

Lu Chaochao is recording on-site operation data. Photo provided by the interviewee

"In the process of removing silicon from sodium aluminate, the most important and difficult task we do is to study its reaction pH. We made a pH gradient from acidic pH 3 to pH 14, and determined its reaction conditions and hydraulic conditions, including the order of dosing, through preliminary beaker experiments to determine its optimal pH. Finally, we found out that the optimal pH value is about 8.5, which has the best silicon removal effect." Lu Chaochao, the team leader of the Environmental Protection Team 1 of the Water Treatment Plant of the Environmental Storage Plant of Guoneng Yulin Chemical Co., Ltd., told reporters.

In this process, the research team not only solved technical challenges, but also deeply realized the significance of their work. In the eyes of these young scientific and technological workers, dealing with wastewater every day and restoring the clarity of wastewater through their participation is not only the realization of their personal values, but also a contribution to the realization of green production. "The black water produced by coal chemical industry has been processed by our process and turned into high-quality recycled water for reuse in our factory as production water. I am very proud of it." Lu Chaochao said.

Yulin, a city that thrives on coal, is realizing its own magnificent transformation through scientific and technological innovation. From the technological innovation of coal-to-ethylene glycol, to the industrial production of polyglycolic acid biodegradable materials, to the zero-discharge treatment of coal chemical wastewater, this path of green transformation and development has witnessed that Yulin Chemical is taking practical actions to promote the transformation and upgrading of the coal chemical industry to "high-end, diversified, and low-carbon" while effectively ensuring national energy security. "Green" has been injected into the development gene of coal chemical industry, making the transformation and upgrading of coal consumption more and more practical, and also showing the world the infinite possibilities of green chemistry and a green future.