Adsorptive Separation Of Difficult Separation Systems By Isocyanate-crosslinked Cyclodextrin Polymers

Acetophenone(AP)and 1-phenylethanol(PE)are the major by-products of the co-production of propylene oxide/styrene(PO/SM)in the petrochemical industry.They are both important organic chemicals used for the fine chemical industry,such as perfumes,fragrances,pharmaceuticals,etc.Cinnamyl acetate(CAc)and cinnamaldehyde(CA)are the majorly found in cinnamon oil which is a specialty resource in Guangxi,and they are two important fragrance chemicals widely used in perfumes,fragrances and cosmetics industries.Taking into account the environmental protection and economic benefits,it is necessary to separate the above two mixtures.However,due to the similar molecular structures and physical properties of AP and PE,CAc and CA,it is difficult to separate them using conventional separation methods.In order to separate the two groups of substances,a series of P-cyclodextrin polymers were synthesized using isocyanates as cross-linking agents,and their adsorption separation performances were studied from both the theoretical calculations and experiments.The specific research content is as follows:(1)Firstly,in order to separate the AP and PE of petrochemical by-products,?-cyclodextrin were cross-linked with four kinds of aromatic diisocyanates to get four water-insoluble ?-cyclodextrin polymers,CPP,CNP,CTOP and CMP.The structure and morphology of the polymers were characterized by FTIR,SEM and XRD,etc.The adsorption properties of polymers for AP and PE were investigated by binary-component adsorption experiments,then the CMP was screened out as the optimal adsorbent for adsorption separation of AP and PE.Next,the effects of different preparation conditions on the adsorption performances of CMP for separation of AP and PE were studied.The CMP obtained by the optimal preparation conditions was used in adsorption separation of equimolar ratio of AP and PE with a total concentration of 80 mmol·L-1.When the dosage of CMP was 15 g·L-1,the adsorption temperature was 25? and the time was 3.5 h,the adsorption capacities of AP and PE on CMP were 1.40 and 0.57 mmol ·g-1,respectively,and the separation factor was 3.95.Then the single-component adsorption kinetics,sigle-component isothermal adsorption and thermodynamic study,bianry-component isothermal adsorption and intermittent reusability were carried out to study CMP adsorbed AP and PE.The experimental results show that the adsorption process of AP and PE onto CMP is a spontaneous exothermic physical adsorption process,and the adsorption conforms to the pseudo-second-order kinetic model and Freundlich adsorption isotherm model.Finally,the mechanism of adsorption separation was analyzed by quantum chemistry calculation and FTIR of CMP before and after adsorption.The results showed that the different adsorption of AP and PE on CMP was mainly caused by weak intermolecular interaction forces with different intensities.(2)Then,four kinds of adsorbents,CTTP,CTTPP,CMTP and CMTTP,were prepared by the reaction of ?-cyclodextrin with four diisocyanate prepolymers containing multiple phenyl rings,and they were applied to the adsorption separation of AP and PE.The structure and morphology of the polymers were characterized by FTIR,SEM and XRD,etc.The adsorption properties of polymers for AP and PE were investigated by binary-component adsorption experiments,then the CTTP was screened out as the optimal adsorbent for adsorption separation of AP and PE.The CTTP obtained by the optimal preparation conditions was used in adsorption separation of equimolar ratio of AP and PE with a total concentration of 80 mmol·L-1.When the dosage of CTTP was 10 g·L-1,the adsorption temperature was 25? and the time was 3.5 h,the adsorption capacities of AP and PE on CTTP were 2.32 and 0.76 mmol·g-1,respectively,and the separation factor was 5.95.Then the single-component adsorption kinetics,single-component isothermal adsorption,thermodynamic study,binary-component isothermal adsorption,binary-component competing adsorption,batch reusability and continuous adsorption-desorption experiments were carried out to investigated CTTP adsorbed AP and PE.The experimental results show that the adsorption process of AP and PE onto CTTP is a spontaneous exothermic physical adsorption process,and the adsorption conforms to the pseudo-second-order kinetic model and Freundlich adsorption isotherm model.In addition,after two successive adsorption-desorption experiments on CTTP,the purity of AP in petrochemical by-products can be increased from 76.16%to 98.61%,which exceeds the purity of AP sold in the market(98%).Therefore,CTTP adsorbent has good industrial application potential for adsorption and separation of AP and PE.Finally,by analyzing the quantum chemical calculations and the FTIR of CTTP before and after adsorption,we speculated that ?-? interactions and intermolecular hydrogen bonding interactions may be the potential mechanisms for specific adsorption of AP and PE on CTTP.(3)Lastly,in terms of the adsorption separation of CAc and CA in cinnamon oil which is a special resource in Guangxi.The polymer CTP was synthesized by the cross-linking of toluene-2,4-diisocyanate and ?-cyclodextrin.The structure and morphology of CTP were analyzed by FTIR,SEM,XRD,TG-DSC and N2 adsorption-desorption.The CTP obtained by the optimal preparation conditions was used in adsorption separation of equimolar ratio of CAc and CA with a total concentration of 70 mmol·L-1.When the dosage of CTP was 20 g·L-1,the adsorption temperature was 25? and the time was 3.0 h,the adsorption capacities of CAc and CA on CTP were 1.18 and 0.57 mmol·g-1,respectively,and the separation factor was 4.05.By investigating the adsorption characteristics of CTP adsorbed CAc and CA,it was found that the adsorption process of CTP on the substrate is a spontaneous exothermic physical adsorption process,and this adsorption conforms to the pseudo-secondary adsorption kinetic model and the Freundlich adsorption isotherm model.By comparing the results of single and bianry-component adsorption,it was shown that the adsorption of CAc and CA on CTP showed cooperative adsorption behavior.Finally,the mechanism of adsorption separation was analyzed by quantum chemical calculation,FTIR,XPS and 13C NMR of CTP before and after adsorption.The results show that ?-? interaction and intermolecular hydrogen bond interactions are the reasons for the higher adsorption capacity of CAc on CTP than that of CA.In summary,the adsorption properties of AP and PE,CAc and CA onto isocyanate-crosslinked ?-cyclodextrin polymers were investigated in this work.According to these results,it is indicated that these ?-cyclodextrin polymers exhibit good performances for selective adsorption separation of the both mixtures.This research has provided several ?-cyclodextrin polymers,which can be used as potential adsorbents for separation of AP and PE,CAc and CA.