| In the synthesis of coal to ethylene glycol,due to the complexity of the catalytic reaction,in addition to the main product ethylene glycol,by-products such as 1,2-butanediol and1,2-propanediol are also produced.Especially,the boiling points of ethylene glycol and1,2-butanediol are close to each other and they form azeotropes,so there is a problem of difficult distillation and high energy consumption to separate them.Therefore,how to separate ethylene glycol and 1,2-butanediol efficiently has received much attention.In this paper,the gas-liquid phase equilibrium data of ethylene glycol and 1,2-butanediol missing within 0-100k Pa were firstly measured supplementally,and the overall data were correlated with thermodynamic equations,and the reliability of the calculated model was further verified by using distillation experiments,which finally resulted in a 10,000-ton high-efficiency separation process of coal to ethylene glycol by-products.The main research contents are as follows.The vapor-liquid equilibrium data for the ethylene glycol-1,2-butanediol binary system at1,10,19,29,39,60,80 and 100.4 k Pa were measured using a modified Othmer vapor-liquid equilibrium kettle to fill the data gaps at different vacuum levels and the data passed the thermodynamic consistency test by the Herington area method.The Wilson,NRTL and UNIQUAC equations were used to correlate the vapor-liquid equilibrium data at different pressures,and the results showed that the calculated values of the three equations were in good agreement with the experimental data,and the UNIQUAC equation was more accurate and applicable to the phase equilibrium calculation at 1-100 k Pa.The UNIQUAC equation was used to calculate the azeotropic composition of ethylene glycol-1,2-butanediol at different pressures,and the content of ethylene glycol in the azeotropic composition increased nonlinearly with the decrease of pressure.The content of ethylene glycol in the azeotropic composition increased slowly with decreasing pressure when the operating pressure was greater than 20k Pa;the content of ethylene glycol in the azeotropic composition increased rapidly with decreasing pressure when the operating pressure was less than 20k Pa.When the operating pressure is reduced from 100k Pa to 1k Pa,the change value of ethylene glycol in the azeotropic composition can reach 12%,which can separate ethylene glycol and 1,2-butanediol by differential pressure distillation.The UNIQUAC equation modified by correlation parameters was used for the calculation of phase equilibrium parameters,and the specifications of the experimental distillation column were used as the basic input parameters to establish the calculation models of intermittent and continuous distillation of ethylene glycol-1,2-butanediol by Aspen Plus process simulation software.The distillation separation process of ethylene glycol-1,2-butanediol at different pressures was simulated,and the experimental verification of distillation was carried out based on the simulations.The maximum error between the simulated results and the experimentally obtained values was 5%,which further verified the reliability of the UNIQUAC equation and the distillation calculation model after the correlation parameter correction.A full process simulation for the extraction of ethylene glycol and 1,2-butanediol from 10,000-ton coal to ethylene glycol by-product variable heat distillation was established,and parameters such as reflux ratio,theoretical plate number and feed position were optimized with the objective of minimum TAC,and the TAC of the better process was obtained as2.716×10~6$/year.In order to reduce the operating energy consumption,the heat-integrated energy-saving optimization of the variable-pressure distillation process was carried out according to the thermal pinch point technology,and the TACs of the partially heat-integrated and fully heat-integrated pump processes were obtained as 1.948×10~6$/year,1.836×10~6$/year and 1.73×10~6$/year,respectively.Compared with the traditional variable-pressure distillation process,the TAC of partially heat-integrated variable-pressure distillation,fully heat-integrated variable-pressure distillation and heat pump process are reduced by 28.3%、32.4%and 36.3%,respectively,which can generate obvious economic and social benefits and lay the foundation for the resource utilization of coal to ethylene glycol by-products. |
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