1.Project Background
a certain chemical enterprise adopted the transesterification method to build a 100,000-ton/year dimethyl carbonate (DMC) plant (2×50,000t/a). Using ethylene oxide, carbon dioxide and methanol as raw materials, DMC was synthesized through the transesterification reaction between ethylene carbonate (EC) and methanol and co-produced ethylene glycol. The traditional process has problems such as high energy consumption and low separation efficiency. To achieve green production, the project integrates reactive distillation + differential pressure thermal coupling distillation + heat pump distillation technology, significantly improving energy efficiency and product quality.
2.Processing technology
（1）Reactive distillation system
A continuous reaction distillation column was adopted, with acidic ion-exchange resin catalysts filled inside to achieve the integrated transesterification reaction of EC and methanol and the separation of products. The reaction heat is directly used in the distillation process to reduce the demand for external heating. The gas phase at the top of the tower is compressed and then enters the differential pressure thermal coupling system.
（2）Differential pressure thermal coupling distillation system
The reaction distillation column is divided into the high-pressure section (operating pressure 1.2-1.5MPa) and the low-pressure section (0.3-0.5MPa). The high-temperature steam (110-125℃) at the top of the high-pressure section tower is used as the heat source for the reboiler at the bottom of the low-pressure section tower to achieve heat integration. The latent heat of steam in the high-pressure section is recovered through a thermal coupling heat exchanger, reducing the external steam consumption by approximately 40%.
（3）Heat pump distillation system
The heat pump renovation was carried out on the DMC refining tower. The steam containing methanol and DMC at the top of the tower was pressurized and heated by the compressor (with a temperature increase of 12℃), and then used as the heat source for the reboiler at the bottom of the tower. After the transformation, it can replace 12.5t/h of industrial steam, save 900m³/h of circulating cooling water, and save more than 16 million yuan in operating costs annually.
3.Treatment effect
Production capacity and purity: Annual output of DMC 100,000 tons, product purity ≥99.9% (national standard superior grade), ethylene glycol by-product purity ≥99.9% (polyester grade).
Energy consumption optimization: The comprehensive energy consumption is reduced by more than 30% compared with the traditional process. The steam consumption per ton of DMC is reduced from 3.0 tons to 0.8 tons, and the electricity consumption is controlled within 125kWh. The energy-saving rate reaches 78%-85%.
Environmental benefits: Reduce CO₂ emissions by approximately 25,000 tons per year, achieve high-value utilization of CO₂ from raw materials, and comply with the requirements of the "dual carbon" goals.
4.Equipment advantages
（1）Main material design
The distillation column is made of CS+304 composite material: the middle and lower parts of the column body (including the reaction section) are made of carbon steel (CS), which can withstand high pressure and mechanical stress. The top of the tower and the condenser are made of 304 stainless steel, which is resistant to corrosion by media such as methanol. This design reduces the equipment cost by approximately 15% while ensuring corrosion resistance.
（2）Optimization of super-large tower equipment
The maximum tower size is DN4000×50000mm. It adopts high-efficiency structured packing and liquid distributors, reducing the pressure drop of the internal components of the tower by 20%. The tower body structure was optimized through finite element analysis to ensure stability under high pressure difference (1.2MPa), and at the same time facilitate modular installation and maintenance.
（3）Intelligent control and safety design
Integrate advanced control systems (such as QR/F temperature - forming cascade control) to achieve multi-tower collaborative operation and parameter self-optimization. The compressor adopts explosion-proof motors and special sealing structures to meet the safe operation requirements of flammable and explosive media such as methanol and DMC.
5.Technological innovation and industry value
This project is the first transesterification DMC unit in China that integrates three advanced distillation technologies. Through the full-process optimization of reaction - separation - energy integration, it has broken through the energy consumption bottleneck of traditional processes. Its successful operation not only brings significant economic benefits to the enterprise (saving over 20 million yuan in costs annually), but also provides a green transformation model for the domestic DMC industry, promoting the development of transesterification methods towards large-scale and low energy consumption. In the future, this technology can be further extended to polycarbonate supporting projects, facilitating the upgrading of the new energy materials industry.
