The Simulation Analysis Of Phosgenation Of TDI In A Reactive Distillation Process

As a kind of important isocyanate, toluene diisocyanate （TDI） is one of the mostimportant materials of polyurethane. Hot and cold phosgenation are widely used inindustry, hot reactor could be the reactive distillation column. The process ofreactive distillation （RD） is an operation process coupling chemical reaction andrectification in one column. It has the advantages of low energy consumption andhigh conversion rate. Using reactive distillation to produce TDI has beenindustrialized, but the simulation analysis which considers reactive kinetics has noreports so far. Aimed at the uncertain parameters of phosgenation of amine salt, thispaper puts forward a method to simulate it. Applying the method above, a reactivedistillation column is simulated, the effection of various factors on the column isanalysised and the operating conditions is optimized too.1. Based on the available literature, this paper builds a mathematical model ofphosgenation of amine salt and calculate its reaction activation energy （31.77KJ/mol）and pre-factor (9.78×10^-4). Due to the reaction condition in this paper is different fromthe literature, kinetic parameters are uncertain, so this paper puts forward a method tosimulate the reactive distillation column. This method uses Aspen Plus to estimate theexponential factor and analysis the simulated results under different conditions of thereactive distillation column by supposing the99%completion of amine salt. Someconclusions can get as following：（1） The minimum consumption of amine salt occurs at the N-1stage；（2）.The temperature distribution of reaction stages changes little；（3） Mole fraction of liquid amine salt changes a lot and phosgene changes little.No matter how exponential factor changes, the conclusions are the same. So themethod this paper proposed is available.2. A reactive distillation column （30000t/y） is simulated using the method above. This paper changes the alterable factors and fixes others, then find the law of effectionof every factor on the reactive distillation column. These specific results are asfollowing:（1） As the reflux ratio gets bigger, the temperature of reactive distillation columnwill be higher and separation effects will be better. But bigger reflux ratio means theincremental cost of the operation, so this paper chooses the mass reflux ratio as8afterall these comprehensive considerations.（2） Operating pressure has a positive effect on the liquid mass fraction of COCl2and the temperature profile. But the material requirement of high pressure is stricter,so this paper chooses1.8MPa as the operating pressure.（3） Feed ratio is in direct proportion to the liquid mass fraction of reactants andreactant selective. But too big feed ratio will increase the load of subsequent workingprocedure. So this paper chooses it as1:3:9after all these comprehensiveconsiderations.（4） The mass flow of side-draw and the side-draw stage have an effect on massfraction of production and reactant selective, this paper chooses the mass flow ofside-draw as17000kg/h and the fifth stage as side-draw stage after all thesecomprehensive considerations.（5） The rectification stage number has an effect on separating effect of theproduction and the reactive stage number has an effect on the conversion of reactants.Due to the simulated result, this paper chooses five reactive stages and sixrectification stages.Applying the method above, this paper carries on the simulation and analysis onthe reactive distillation column. The consequences are in line with the situation ofindustrial production, that is to say, the method is feasible. In addition, the followingconclusions can play a guiding role in the practical production of TDI.