Wanhua Chemical Group Co., Ltd. has been granted an invention patent related to toluene diisocyanate (TDI) production, according to the China National Intellectual Property Administration. Titled "Toluene Diisocyanate Production System and Toluene Diisocyanate Production Method," the patent was granted under publication number CN121338372B. Application No. 202511495652.1 was filed on October 20, 2025 and granted on July 24, 2026.
The patent describes a TDI production system comprising a rectification column, a dividing-wall column and related piping. The dividing-wall column includes sections for light-component removal, isomer ratio control and heavy-component concentration, enabling purification, impurity removal and isomer ratio adjustment.
Improving TDI Purification and Product Quality Control
TDI is an important polyurethane raw material. Commercial products mainly contain 2,4-TDI and 2,6-TDI, and their relative proportions affect reaction behaviour and final material performance.
As polyurethane applications become more specialised, downstream users are demanding greater TDI purity, stability and grade flexibility. The patent identifies limitations in conventional purification, including inefficient impurity separation, limited isomer ratio adjustment, complex equipment and high energy use.
Wanhua therefore proposes combining a rectification column with a dividing-wall column. Crude TDI is first separated in the rectification column, while the dividing-wall column further removes light and heavy impurities and produces TDI with a controllable isomer ratio.
Three Technical Highlights: Purity, Isomer Control and Energy Efficiency
The patent focuses on improvements in three areas.
First, it raises TDI purity and reduces impurity levels.
Different functional zones in the dividing-wall column jointly treat light and heavy impurities to improve separation efficiency. The patent states that the process can achieve TDI purity of at least 99.95 wt% and hydrolysable chlorine content of no more than 10 ppm.
Hydrolysable chlorine is an important TDI quality indicator. Lower levels can support better product stability and downstream performance.
Second, it improves isomer ratio adjustment flexibility.
This is one of the patent's main technical features.
An isomer ratio control section is installed in the dividing-wall column, with several withdrawal points arranged along the column height. Multi-level withdrawal allows TDI products with controllable isomer ratios to be collected.
The process can adjust the ratio of 2,4-TDI to 2,6-TDI and produce different isomer compositions, improving flexibility when switching between product grades.
Third, it simplifies equipment and lowers production energy use.
By integrating rectification, stripping and isomer ratio control in the dividing-wall column, the process can reduce equipment requirements and energy consumption.
From Capacity Competition to Technology-Based Competition
China's TDI industry has expanded rapidly, with domestic producers increasing plant scale and supply capability. As competition intensifies, production stability, product quality and differentiated product development are becoming more important. Wanhua's patent does not change the basic TDI production route; instead, it optimises downstream purification and separation to improve purity control and isomer ratio adjustment. Patent approval confirms the technical solution, but industrial application still requires verification of operating stability, economics and product performance.
Overall, the patent reflects Wanhua's continued investment in isocyanate purification and flexible manufacturing. As downstream applications become more specialised, higher TDI quality and greater production flexibility may become important directions for future industry upgrading.