The Synthesis And Process Optimization Of HDI Curing Agents

Hexamethylene diisocyanate(HDI)is an important category of aliphatic polyisocyanates.Due to the monomer's large volatility and toxicity,HDI is usually prepared into its derivatives(such as: HDI biuret,HDI trimer,etc.).Boasting their most notable features including weather resistance,gloss and color retentio,HDI curing agents are widely used in various sectors of the national economy.In recent years,HDI has become one of the high-end raw materials in polyurethane industry,its application rapidly expanding to various fields such as aviation,textiles,foams,paints,rubber and high protective coating,therefore HDI derivatives is an important direction for the future development of polyurethane coatings.As raw materials,HDI monomers are synthesized to HDI biuret curing agents and HDI trimer curing agents.By researching feeding method,reaction temperature and heating temperature control,reaction time and other factors,the impacts on the HDI biuret curing agent reaction and the optimal reaction condition have been confirmed.By researching the impacts of the amount of catalysts,reaction time,reaction temperature,terminator,post-treatment conditions on the HDI trimer structure and yield,the optimum formula and process for the synthesis of HDI trimer curing agents have been obtained.By repeated synthetic tests of HDI biuret curing agents,the molar ratio of HDI and water compound has been determined as 5:1;the reaction temperature was140 ? and reaction time was 5.0h,at which conditions the synthesis of the curing agents was the most stable.Meanwhile,the treatment of free monomers in HDI biuret with molecular distillation process as well as the influence of factors including feed rate,rotating speed,distillation temperature,absolute pressure of distillation and distillation times etc.have been determined.Finally,the most satisfying conditions of treatment process have been determined as follows: feed rate 5ml/s,rotating speed 300rad/min,distillation temperature 130? and absolute pressure of distillation 0.85mbar;after one separation step,the content of free HDI in HDI biuretreaches 1.41%.The film of the coating prepared with HDI biuret curing agent after the removal of free HDI has shown adequate excellent properties to meet downstream customers' application requirements.By HDI trimer curing agent synthesis experiment,the catalytic activity of the Octanoic tetramethylammonium salt was found strong and had short reaction time.Among three termination agents which were selected,benzoyl chloride had the minimal impact on product transparency.Molecular film evaporation was the optimal method in removing free HDI monomer in HDI trimer.Finally,the best conditions of preparation HDI trimer have been determined as follows: temperature 65?,reaction time 6h,the conversion rate was controlled within 25%.For HDI monomer separation process,a 2-step separation has been proven as the best: temperature160 ? and absolute pressure 0.2mbar-0.1mbar at stage 1 while temperature185 ?and absolute pressure 0.1-0.05 mbar at stage 2,whereby the product HDI trimer with national standard quality has been obtained.