Study On Dehydration Process Of Polymethoxy Dimethyl Ether Using Molecular Sieve

The paper studied the adsorption dehydration and formaldehyde removal performance of3A and 4A molecular sieves on polymethoxy dimethyl ether（PODEn）,and discussed the influence of adsorption air velocity and temperature on dynamic adsorption performance parameters.In addition,methanol was used as a regenerant to study the regeneration performance of 3A molecular sieve,and the influence of regeneration temperature and regeneration time on the regeneration effect,and molecular sieve regeneration stability experiments were also carried out.Finally,the preliminary design of the 30 kt/a PODEn dehydration industrial unit using molecular sieve was carried out.The experimental study was carried out on a 50 m L fixed-bed adsorption device with a diameter of 20 mm.The experiment uses a mixture of 4 components as a model of PODE_n.The content（mass）of each component is:about 86.0%methylal,about 10.5%methanol,about 1.5%formaldehyde,and about 2.0%water.This model compound is used to study the law of the adsorption and dehydration process of PODE_n by molecular sieve adsorbent.The experimental results show that under normal temperature and pressure,the total adsorption mass transfer coefficient K_f value increases with the increase of air velocity.so larger air velocity is beneficial to adsorption,within the experimental air velocity(3A molecular sieves1.5 h^-1～4.0 h^-1,4A molecular sieves 1.0 h^-1～4.0 h^-1),the air velocity at 4.0 h^-1 is the best.The experimental results show that under the condition of constant air velocity,the total mass transfer coefficient decreases with the increase of temperature,indicating that the adsorption process is suitable for lower temperature.So within the experimental temperature（50℃～80℃）,the adsorption effect is best at 50℃.Judging from the situation that the K_f value increases with the increase of air velocity and the K_f value decreases with the increase of temperature,the adsorption mass transfer process in this experiment is an adsorption process dominated by external diffusion control.Under normal temperature and pressure,the abilities of 3A and 4A molecular sieves for dehydration and formaldehyde removal by adsorption were investigated.The results show that in the entire adsorption process,the formaldehyde content in the material after adsorption treatment with 4A molecular sieve is about 0.1%higher than that with 3A molecular sieve,indicating that 3A molecular sieve has a stronger formaldehyde adsorption capacity.The comparison of the permeation curves shows that the dehydration effect of 4A molecular sieve is better than 3A molecular sieveIn the experiment,methanol was used as the regenerating agent,3A molecular sieve,normal pressure,and the regeneration time was 180 min.The regeneration effect under different regeneration temperature（140℃～240℃）was investigated.In terms of dehydration,it can meet the requirement within the experimental temperature range,just the time is different;but in terms of formaldehyde removal,when the temperature is below 180℃,the effect is poor.Therefore,taking into account the effects of dehydration,formaldehyde removal and energy saving,select 220℃as the best regenerationtemperatureIn the experiment,methanol was used as the regenerant,3A molecular sieve,normal pressure,fixed regeneration temperature at 220℃,and different regeneration times,to investigate the influence of regeneration time on the regeneration effect.The results show that when the liquide hourly air velocity of the regenerant methanol is 1.0 h^-1,and within the experimental regeneration time（60 min～90 min）,at 90 min,the regeneration effect is the best.In the experiment of investigating the regeneration stability of 3A molecular sieve,adsorption-desorption is a cycle,and a total of 10 experiments have been done.It shows that the degree of inactivation of the molecular sieve is very small,and it can be used continuously.