Study On The Reaction Process Of Carboxylation Of Sodium Phenoxide To Sodium Salicylate

Sodium salicylate is a synthetic raw material or intermediate of many kinds of antipyretic and analgesic medicine,among which it is widely concerned as an intermediate of aspirin.At present,the main method of industrial production of sodium salicylate is to add sodium phenoxide solution into the stirred tank and dry it to solid particles in vacuum,introduce carbon dioxide gas,and carry out carboxylation reaction under certain temperature and pressure.The existing process has problems such as long production cycles,low energy utilization and low effective conversion rates.In order to overcome the related problems,the process conditions,thermodynamic data and reaction kinetics of the carboxylation reaction of sodium phenoxide particles were studied in this paper so as to provide basic data for the development of a continuous and efficient production process of carboxylation of sodium phenoxide.Firstly,single factor experiments were carried out in a batch autoclave with selfmade dry sodium phenoxide particles,the effects of temperature,pressure,reaction time,stirring speed and material moisture content on the yield of sodium salicylate were investigated during the reaction.The experimental results show that the carboxylation reaction is more suitable when the temperature is 160?,the pressure is 0.55 MPa,the reaction time is 40 min,the stirring speed exceeds 50 rpm,and the material moisture content is less than 2%,and the maximum yield is 76.85%.Secondly,by using Guassian 09 software,the heat of carboxylation of sodium phenoxide particles was calculated at B3LYP/6-311G(d,p)level.It was found that the enthalpy of carboxylation of sodium phenoxide changed to-16KJ/mol at 130-180?.At the same time,specific experiments were carried out to determine the heat of carboxylation reaction.First,the combustion heat values of pure sodium phenoxide and sodium salicylate were measured with an oxygen bomb calorimeter,and the specific heat capacity at constant pressure of sodium phenate and sodium salicylate was measured using a differential scanning calorimeter DSC204F1.It is calculated that the reaction heat of the main carboxylation reaction of sodium phenoxide at 160 ? is-59.68KJ/mol.The second is to use the adiabatic calorimeter VSP2 to measure the reaction temperature change of the carboxylation reaction between sodium phenoxide and carbon dioxide.Through the temperature change during the adiabatic reaction,the heat of carboxylation reaction under the reaction conditions of 160? and 0.5MPa is calculated as-17.43KJ/mol.Finally,a kinetic nucleation model was established for the carboxylation of solid sodium phenoxide particles and carbon dioxide gas.By analyzing the experimental data,it was determined that the control steps at the reaction temperatures of 150? and 160? are all controlled by ash diffusion,and the reaction is affected by the diffusion rate of carbon dioxide to the ash.When a certain reaction time is exceeded,due to the formation of a dense product layer and coking phenomenon,the ash diffusion control is deviated in the later stage of the reaction.