Raw Material of TTA: Short of Supply

By Chen Shuxia

Byproduct OTD (o-toluene diamine) generated from the TDI (toluene diisocyanate) hydrogenation can be used as raw material to produce a very important fine chemical TTA (tolyltriazole). Many downstream products with high added value can then be produced. With the completion of China's large-scale TDI units, the development of TTA and its downstream products has already acquired remarkable economic advantage.

Industrial applications are yet to be further developed

Corrosion inhibitors commonly used both at home and abroad today include mono-functional varieties, multi-functional varieties, low-polymerized varieties and polycondensation varieties. Multi-functional varieties have the most extensive applications and the consumption accounts for over 30% of the total. Azole corrosion inhibitors such as TTA and BTA (benzotriazole) are the largest category of multi-functional varieties and the consumption accounts for around 10% of the total.    Other important application sectors for TTA include engine anti-freezing fluids, high-grade coatings, high-grade cleaning agents, hydraulic press oils, special lubricants and cultural relic protection. TTA can also be used in the mechanical processing of copper and other alloys to protect the surface color of metals. Many important fine chemicals can also be synthesized from TTA. For example, TTA has been used in great quantities in stabilizers for polymer materials (rubber antioxidants), synthetic dyestuffs, UV-ray absorption agents and plant growth regulators.    The production of corrosion inhibitors has always been the most important application sector for TTA in China. The consumption in this sector accounted for over 55% of the total in 2005. Other major application sectors included high-grade cleaning agents, anti-freezing fluids and mechanical/electric devices and the consumption accounted respectively for 15%, 12% and 8% of the total. As the BTA production in China has no large scale, great quantities of BTA are for export and the application market is yet to be expanded, the consumption proportion of TTA in China is quite high compared with foreign countries. Besides, the demand of TTA in cleaning agents and anti-freezing fluids is increasing fast. A great number of cleaning agent and anti-freezing fluid producers have started to use TTA produced in China.

Production and demand maintain rapid growth

China started the TTA production in the early 1990s. The capacity of TTA in China was only 1 000 t/a in 1999 and the output was around 600 tons. Most of the product was for export and there was almost no consumption in China's market. Both the production and the demand of TTA in China started a rapid growth after 2000. The total capacity of TTA reached around 12 000 t/a in 2005, the output was around 11 000 tons and China's consumption increased to around 1 900 tons. There were 9 TTA producers in China in 2005. Most of them are located in Jiangsu and Zhejiang provinces and their capacity is mostly less than 1 000 t/a.

Production processes make constant improvement

China mainly uses two methods for the TTA production. They are the low-pressure process and the high-pressure process, both modified from the BTA process. The low-pressure process has long process flow, complicated operation, high consumption and low yield. There are also great hazards of TTA decomposition explosion in vacuum distillation. The low-pressure process is no longer used in new units and renovated units.    The high-pressure process has short process flow, simple operation, relatively great safety, high product quality, few side reactions and high yield. Continuous production can be made after renovation and the comprehensive cost is over 50% lower than the low-pressure process. The 400 t/a TTA unit using the high-pressure process constructed by Cangzhou Dahua Group Xinxing Industrial Trade Co., Ltd. started production in 2005 and is in smooth operation today.    Enterprises in China have also basically mastered the commercial process for the purification of crude OTD and crude TTA, increased the raw material utilization rate and improved the product quality. The distillation tower designed by Cangzhou Dahua Group Xinxing Industrial Trade Co., Ltd. itself can process crude OTD and crude TTA with a purity of around 80% into products with a purity of over 99%. Besides, accident risks are reduced and the facilities are safe and reliable.

Raw material bottlenecks are hard to remove

Most of OTD used as raw material for the TTA production is from rectified byproducts in the TDI hydrogenation. The output of crude OTD is 2 - 2.5% of the TDI output on average. With the completion of large TDI units constructed by BASF and Bayer in China, the capacity of TDI in China can hopefully reach 270 000 t/a in 2006 and 600 000 t/a in 2009. The output of byproduct OTD (100%) will be around 4 800 tons in 2006 and 10 800 tons in 2009. The proportion of imported OTD will come down at that time. As the TTA market has a bright prospect, however, the capacity of TTA will be further pushed by the demand. The dependence on raw material import in the TTA production can hardly be changed in future. It is expected that more than 50% of OTD will still have to be imported from abroad in 2010.      TTA producers in China usually have small scale, low technical level, high accident risks and high production cost. The product quality is also different with different producers and lots. This is also a major factor for the low export price of TTA. TTA producers should therefore make greater efforts to make technical innovation, achieve large-scale operation, reduce production cost and improve product quality.

Major TTA Producers in China   (t/a)Producer        Capacity        Raw material source     Major product marketing channel        Process                                    Cangzhou Dahua Group Xinxing Industrial Trade Co.       400        self-produced   export  high-pressure processNanjing Trust Chemical Co.                              500        imported        export  n.a.Nanjing Shenbai Far East Chemical Co.                   500         imported        export  high-pressure processNanjing Xincheng Additive Plant                         500        imported        export  n.a.Jiangyin Huaya Chemical Co.                             500        imported        export  n.a.Nanjing Bohan Industry Trade Co.    &n