Formulation Optimization And Experimental Evaluation Of ZIF-8 Slurry For Efficient N-/i-butane Separation

A large amount of butane and isobutane will be produced in catalytic cracking and other devices in oil refineries,and their efficient separation is beneficial to subsequent processing into high value-added chemical products.However,butane and isobutane have similar properties such as boiling point and polarizability.Conventional rectification has high energy consumption and low selectivity,and requires a large amount of equipment and operation costs.Due to these limitations,most of them are used as fuels and do not exert maximum economic value.In this thesis,the absorption-adsorption coupling method was adopted to form suspension slurry with ZIF-8 and solvents,and dynamic separation of n-/i-butane mixtures was carried out,which not only took advantage of the large difference in adsorption rate of ZIF-8 for butane isomers,but also took advantage of the good fluidity and uniform dispersion brought by appropriate solvents.The formed slurry is beneficial to continuous operation in industrialization,and has the advantages of fast separation speed,high selectivity,and low energy consumption.The research contents of this thesis are as follows:（1）By examining the state change of the slurry before and after standing,the pressure drop curves of n-butane and the XRD of the recovered adsorbent,the organic solvent that can form a stable slurry with ZIF-8 was screened out:hexylene glycol.However,the ZIF-8/hexylene glycol slurry has low selectivity to n-/i-butane,and the selectivity could be greatly improved by adding a certain proportion of water on the premise of ensuring the excellent kinetic properties of the slurry.The effects of different water contents in the solvent on the sorption kinetics of the slurry was investigated,and the optimal slurry composition taking into account the sorption speed and selectivity was tested for separation of n-/i-butane gas mixtures.The effects of water content,separation time,solid content and temperature on the separation results were systematically investigated.The results showed that for the ZIF-8/hexylene glycol-water system,the higher the water content in the solvent,the higher the separation selectivity,up to 1673,but increasing the water content also reduced the kinetic properties of the slurry.Considering the slurry viscosity,sorption speed,and separation selectivity,the slurry system was finally determined to be 30 wt%ZIF-8 and 60 wt%MPD+40 wt%H₂O solvent system,and the suitable separation temperature and time were 30℃and 40 min,respectively.Finally,the stability regeneration experiment of the slurry was carried out,the results showed that the slurry had good stability,and the n-/i-butane separation selectivity could be stable at about 180.（2）The slurry system was further improved by adding solvent M to the ZIF-8/hexylene glycol-water slurry.ZIF-8/hexylene glycol-water-M slurry had a faster asorption rate than ZIF-8/M-water slurry;and it had lower viscosity,better separation selectivity and stability than ZIF-8/hexylene glycol-water slurry.For example,at the same solid content,the separation factor of ZIF-8/hexylene glycol-water-M slurry（β:583）was doubled compared with that of ZIF-8/hexylene glycol-water slurry（β:237）,while the viscosity was reduced by 20.88%at the same temperature of 30℃.In order to further reduce the viscosity of the slurry system to be suitable for industrial separation,the final composition formula of the new slurry was:ZIF-8 content is 25 wt%,solvent composition:20 wt%MPD+30 wt%H₂O+50 wt%M,the stability experiments of the slurry showed that the separation selectivity of the regenerated slurry was even better than that of the fresh slurry.After several cycles,the separation factor of the n-/i-butane mixtures were stable at about 550.And the breakthrough tests of butane isomers mixtures were carried out with this slurry.The effects of different inlet flow rates,temperatures,operating pressures,and the presence or absence of packing on gas penetration were investigated.Breakthrough tests further verified the excellent kinetic selectivity of the slurry.The results showed that the breakthrough separation effect increased with the decrease of the inlet flow and operating temperature,and the increase of the operating pressure,and proved the beneficial effect of adding packing in the column.