Green Analysis And Optimization Of TDI Production Process

Toluene diisocyanate(TDI)is an important raw material for the synthesis of polyurethane.It is produced in the industry by the phosgenation of amines.With the rise of green chemistry,a variety of non-phosgenation TDI green production processes have been proposed,but industrialization has not yet been achieved.Based on the principles of green chemistry,this article analyzes the greening of the TDI production process,evaluates its current greening level,determines its shortcomings,and seeks optimization and improvement plans to improve greening.The main research contents and conclusions of this article are as follows:Based on atomic economy,the concept of by-product atomic recovery rate was proposed,and the concepts of effective value of atomic utilization and environmental factors were revised.On this basis,a multi-index resource comprehensive utilization efficiency(Multi Index Resource Comprehensive Utilization Efficiency(MRE)analysis method;this method is used in the four TDI synthesis pathways of phosgenation,one-step synthesis,two-step synthesis and dimethyl carbonate.2.3 times as much as the method;the scope of atomic economy is extended from the reaction stage to the entire production process,the concept of atomic economic effective value(VAE)is proposed and used in the TDI phosgenation synthesis route,and the raw materials are truly converted into sale The atomic ratio of products to achieve economic value is 35.12%.Based on the twelve green chemistry principles,the twelve green chemistry quantitative indexes(The 12-quantitative Indexes of green chemistry)and the green chemical quantitative evaluation method G12 method of chemical and chemical products are proposed.The twelve quantitative indexes include ten quantifiable green Chemical principles,two new indexes of by-products were added,and quantitative calculations were made from three aspects of resource utilization efficiency,energy consumption,and environmental hazards;a green radar chart was proposed to characterize twelve green quantitative indexes,and a total green degree was proposed.And the concept of relative total greenness;finally,the green evaluation method G12 of chemical processes is proposed.The G12 method was used to make green evaluations of the two TDI phosgenation production technologies using chlorobenzene or o-dichlorobenzene as the solvent;through the comparison of the green radar chart and the calculation of the total greenness,the photochemical with chlorobenzene as solvent The reaction process has a relatively high degree of greening.The total greenness of the process is 5.575.The improvement of the degree of greening can mainly be achieved by increasing the reaction yield,reducing the excess molar ratio of phosgene,and reducing the temperature of the photochemical reaction tower;The total greenness of the photochemical reaction process using o-dichlorobenzene as a solvent is 5.048.The main reason for its low greening degree is that the raw material phosgene is excessively large and the solvent o-dichlorobenzene is environmentally harmful.Two conversion and utilization methods are proposed for the by-product hydrogen chloride in the TDI process,which is converted into chlorine gas by catalytic oxidation and used in the production of PVC by the acetylene method.By calculating the quantification index P2 corresponding to the Green Principle 2,a comparative analysis of the resource utilization efficiency of the two conversion schemes is conducted.The extended process of catalytic oxidation of chlorine gas raises P2 from 0.3512 to 0.5627 in the original process,and the P2 of hydrogen chloride used in acetylene production of PVC to 0.5940,which has a relatively high degree of greenness in resource utilization efficiency.For the TDA synthesis and separation unit with large energy-saving potential in the phosgenation process,Aspen Plus software was used for simulation,and the operating parameters of the distillation column were optimized using sensitivity analysis.Based on the optimized process data,the Aspen Energy Analyzer software is used to design the heat exchange network,and a design scheme with better energy saving effect is obtained.The amount of heat utilities required for this program is 2030 k W,which is 37.33% energy saving compared with the original process flow;the amount of utilities required for cooling is 8350 k W,which is 12.64% energy saving;increase energy consumption index P6 from 0.78 to 0.96.In summary,this article uses the two important green chemistry principles of atomic economy and the twelve principles of green chemistry for the green analysis and optimization of TDI production processes,revising,supplementing and perfecting existing concepts,and proposing new concepts and indexes.The principle of green chemistry was promoted from a general qualitative concept to a quantitative concept,and a method that can be universally used in the green evaluation and analysis of chemical production processes was proposed and used in the existing TDI synthesis process.The method is accurate,reliable,intuitive and efficient,and can be used for the green level improvement and optimization analysis of the TDI production process or other process industries.