Why is the cost of 1,4-cyclohexanedimethanol high after localization?

After 1,4-cyclohexanedimethanol (CHDM) was produced domestically, the production cost was high, and the sales price was close to 30,000 per ton. The high cost constrained the application and directly affected the cost-effectiveness of the downstream products.


DMT two-step hydrogenation synthesis


  CHDM is a white waxy solid, is an important organic chemical material, molecular formula for C8H16O2, molecular weight of 144.21, there are cis, trans two structures cis isomer melting point of 43 ℃, the trans isomer 70 ℃, 1,4 - cyclohexanedimethanol (CHDM) is a coatings, printing ink, adhesives, insulating materials, and some special uses of saturated polyester and unsaturated polyester intermediates, intermediates of 1,4 - cyclohexanedimethanol (CHDM) is an important organic chemical material. CHDM is an intermediate of saturated polyester and unsaturated polyester for coatings, inks, adhesives, insulating materials and some special applications, and its most important use is in the synthesis of new polyesters such as PCT, PETG and PCTG, which have good transparency, impact resistance, abrasion resistance and corrosion resistance. The annual demand for CHDM for the production of resin-based coatings, high-performance film, and highly sophisticated liquid crystal materials has been growing in Japan, while the demand in other European countries is also growing.


  CHDM is mainly produced from dimethyl terephthalate (DMT) by a two-step hydrogenation reaction, in which the saturated benzene ring of DMT is hydrogenated to produce dimethyl 1,4-cyclohexanedicarboxylate (DMCD), and then through ester hydrolysis by the intermediate product of 4-(carbonylmethoxy)cyclohexanemethanol (CMCHM), CHDM is finally produced.


Formulation of DMT hydrogenation for CHDM production


  As early as 1959, the United States Eastman Company used Pd/Al2O3 catalyst to catalyze the hydrogenation of DMT, in order to avoid the reduction of catalyst activity by trace CO, the reaction needs to be carried out under high-pressure hydrogen conditions, hydrogen pressure of 30MPa or more, the company in the 1990s to improve the catalyst, add Ni, Pt, Ru and other second active components, the reaction of hydrogen pressure can be reduced to 12.5MPa, the reaction temperature 180-200 ℃, the reaction temperature 180-200 ℃. The reaction pressure of hydrogen can be reduced to 12.5MPa, and the reaction temperature is 180～200℃. Palladium catalyst has high reaction yield, but it needs to be carried out under high pressure, with high equipment cost and operation cost. Highly dispersed nano Ru/C catalyst has been used to prepare DMCD under low-pressure condition, and the product yield is up to 95%, but the catalyst is still expensive. The use of rhodium, ruthenium or ruthenium-M bimetallic catalysts can significantly reduce the reaction pressure, but the yield is low. In recent years, modified Pd or Ru-loaded catalysts have reduced the operating pressure of DMT hydrogenation to a certain extent, but the target product yield is also unsatisfactory.


  China has been in the development and production of co-polyester PETG or PCTG is still a blank, the main reason is that the raw material CHDM production technology is not mastered, the domestic can not be produced, foreign imports of products at a higher price.


Industry analysis, CHDM localization, high production costs, the main about three factors:


High cost of raw materials for production


  CHDM for DMT by two different steps of hydrogenation reaction, the current domestic production units have been built into the DMT purchased or imported, the current market price, the production of 1 ton of CHDM, the required DMT raw material costs accounted for 14,000 yuan.


Two-step hydrogenation consumes a large amount of hydrogen, due to DMCD and CHDM saturated vapor pressure is low, the gas phase reaction requires a huge amount of hydrogen cycle, generally need hydrogen oil molar ratio of 600 or more, a huge amount of hydrogen cycle not only greatly increase energy consumption, but also limit the production capacity, the liquid phase hydrogenation production of CHDM, hydrogen oil molar ratio from the gas phase of 600 down to 80-200, although a significant reduction in the amount of hydrogen cycle, but at present, the liquid phase hydrogenation production of CHDM, the hydrogen oil molar ratio from the gas phase of 600 to 80-200, although significantly reduced the hydrogen Although it greatly reduces the amount of hydrogen recycling, at present, the cost of producing 1 ton of CHDM hydrogen consumption is also 3,000 RMB.


High catalyst cost


  1,4-Cyclohexanedimethanol has cis and trans isomer structure, trans ratio structure is more symmetrical, the lattice structure is regular, lattice energy is high, it has higher melting point and good heat resistance, when used in the production of PETG and other polyester products, the higher the ratio of trans, the higher the heat resistance of the polyester, the better the performance of the product, but the catalyst selectivity is high, the catalyst is a precious metal, if the selectivity is not high, the cost of producing 1 ton of CHDM is 3,000 yuan. If the catalyst selectivity is not high, the catalyst cost is high.


  At present, the industrial DMT hydrotreating process reduces the hydrotreating operation pressure to a certain extent, but the target product yield is low. Therefore, in order to minimize the catalyst dosage and reduce the catalyst cost, it is necessary to develop new catalysts with high activity and high selectivity, so as to reduce the operating pressure of DMT hydrogenation and increase the yield of the target product DMCD, which is the direction of the development of DMT hydrogenation process.


Process design and optimization issues


  At present, the domestic CHDM production unit is not a DMT-CHDM full-flow setup and design, full-flow setup and optimization of process and equipment design is still insufficient, or will result in high energy consumption and cost, like the liquid-phase hydrogenation, to improve the conversion rate and selectivity is the core technology, after the completion of the hydrogenation of DMCD, when the DMCD is converted to CHDM, as far as possible, to reduce the residence time of the material in the reaction system, the other hand is to reduce the temperature to a temperature that is not easy for the target product, DMCD. On the other hand, the temperature is lowered to a temperature that is not easy to generate high-boiling substances, however, this is contradictory to the requirement of improving the conversion of DMCD. This requires a unique approach to process setup, process equipment design, and experience in production operation.


DMT-CHDM integrated production flow chart






CHDM localization optimization and improvement direction:


  Expand production scale and reduce production cost


  At present, the domestic CHDM production unit is small in scale, high in production cost, constrained in market application, low in production load, forming a vicious circle.


DMT-CHDM integrated design is the direction


  Integrated design, there is the use of process setup optimization, due to the preparation of terephthalic acid DMT, methanol, and the preparation of CHDM will by-products of methanol, through the hydrogenation of by-product methanol recycling, avoiding the purification of methanol, reducing the energy consumption of the system, and at the same time, the use of some of the by-products of the 4-methylcyclohexanemethanol recycling to inhibit the generation of 4-methylcyclohexanemethanol by-products to improve the selectivity of CHDM, and the full process design and optimization determines the direction of DMT-CHDM production plant. And the design and optimization of the whole process determines the lower energy consumption and higher selectivity.