Research On Adsorbents Properties And Ptocess For Separation Of The Ethylene Glycol/1,2-butanediol Mixture

In the process of producing ethylene glycol(EG)from coal or biomass,mixed alcohol by-products will be produced,in which EG and 1,2-butanediol(1,2-BDO)are the typical components.However,EG and 1,2-BDO are easy to form azeotrope due to their similar boiling points,which makes it difficult to separate them effectively by ordinary distillation.For their molecular size and polarity differences,the selective adsorption separation of EG/1,2-BDO is an important research area.NaY zeolite or silica gel was selected as the adsorbent to study their adsorption thermodynamic properties and dynamic adsorption performance on EG/1,2-BDO separation,providing theoretical reference for industrial amplification.The main research contents and conclusions are as follows:Adsorption isotherms of NaY zeolite towards EG or 1,2-BDO were determined by static adsorption method,which were well fitted by Langmuir equation(R2>0.98).Meanwhile,the adsorption amounts of NaY towards the EG/1,2-BDO mixture were also determined,indicating that NaY owned different adsorption capacities towards EG and 1,2-BDO.Finally,the adsorption sites of EG and 1,2-BDO in NaY were determined by Grand canonical Monte Carlo(GCMC)simulation.It was found that EG and 1,2-BDO were adsorbed at different sites under low pressure(0.5 MPa).However,as the pressure increased to 3 MPa,EG was gradually adsorbed at both C and W site,while 1,2-BDO was still adsorbed at W site,which means that their adsorption sites gradually overlapped,resulting in stronger competitiveness.Dynamic breakthrough experiments were carried out in a fix-bed adsorption column using NaY as the adsorbent,to detemine breakthrough curves of EG/1,2-BDO solution,which were well fitted by Dose-Response model(R2>0.98).Meanwhile,breakthrough curves under different feed flow rate and operating temperature were determined.The results showed that with the increase of feed flow rate and temperature,the breakthrough curves of EG/1,2-BDO became steeper,and its adsorption selectivities(?EG/1,2-BDO)were also significantly increased,which indicated that increasing the temperature and feed flow rate was favorable for the purification of 1,2-BDO:the adsorption selectivity of EG to 1,2-BDO(?EG/1,2-BDO)reached 2.43 at the temperature of 313 K and the feed flow rate of 1.2 mL/min.Single-column pulse experiments were carried out using silica gel as the adsorbent and ethyl acetate as the eluent,to determine elution curves of EG/1,2-BDO and optimize its operating conditions.The optimal conditions for single-column pulse separation were:flow rate of eluent was 0.8 mL/min,elution direction was from top to bottom,silica gel particle size was 200-300 mesh,and adsorption column length was 30 cm,under which the resolution of EG/1,2-BDO was 0.48.Based on the above optimal single-column operating conditions,double-column shunt and double-column series experiments were carried out,to explore double-column technology for separation of EG/1,2-BDO.The results showed that the double-column shunt can make the adsorption column more fully utilized and the double-column series can significantly improve the resolution of EG/1,2-BDO to 1.32.