Study On The Application Of Membrane Separation Technology In The Concentration Of Tobacco Extracts Liquid

Tobacco extracts liquid(TEL)is the main component of reconstituted tobacco sheet,the main factors affecting the quality of TEL are the content of impurities and the content of aromatic substances.Multi-step centrifugation and sieve shaker are usually adopted to achieve the separation of solid-liquid,but it is not effective to remove the tiny particles and macromolecular substances.Also,its vacuum evaporation concentration results in a large loss of neutral aromatic substances which are positively related to the flavor.These problems make the production process of domestic reconstituted tobacco deficient.Membrane separation is a kind of high-efficiency technique widely applied in the process of purification and concentration,and makes it potential to be applied to purify and concentrate TEL.However,the complex composition of TEL is very prone to serious membrane fouling,which limits the application of membrane separation technology in the tobacco industry.This study aims to develop a set of membrane separation and concentration processes for TEL,study the membrane fouling mechanisms and effective cleaning methods to provide technical support for its industrial application.Firstly,the component analysis of TEL was carried out and membranes were selected based on its characteristics.Results showed that the total dry solid(TDS)of TEL were in the range of 6.76-7.49%,the percentages of protein,pectin,and starch were 8.55%,1.88%,and 0.4%,respectively.Sugar accounted for the largest proportion of 41.48%and the average particle size was 13 14 nm.Based on these results,two inorganic tubular membranes and three commercial nanofiltration(NF)membranes were selected.Results showed that CF-NF1 system demonstrated best performance,the average flux and the flux recovery of CF membrane were 90.0 LMH and above 94%.During the concentration process of NF1 membrane,the VCR,TDS,average flux,and rejection rate were 5.05,18.3%,4.24 LMH,and 94.9%,respectively.Compared with the traditional process,the concentrating efficiency increased 1.4 times and the increased amount of various neutral aromatic substances were between 0.85%and 560.82%.The total amount of neutral aromatic substances increased by 29.2%,while the membrane treatment process did not have a large impact on the proportion of various neutral aromatic substances.Secondly,the operating parameters of selected CF and NF membranes were optimized.Results showed that the optimized operating condition of CF membrane was a TMP of 0.1 MPa,the temperature of 40-50?,and the feed flow rate of 32-34 L/min.Concentration experiments were conducted under the optimized conditions,the rejection rates of protein,pectin,and starch were above 60%,80%,and 80%,respectively,and the retention rate of TDS was 83.4-90.5%.The optimized operating conditions of NF membrane were a TMP of 16 bar,the temperature of 35-40?,and crossflow velocity of 0.84 m/s.The optimized process improved the increment of neutral aromatic substance from 29.2%to 34.8%.Thirdly,the fouling mechanism of the CF membrane was investigated,which was the major constraint of the double membranes system's efficiency.Results showed that it was involved multiple pore-blocking and they could be coupled or occurred simultaneously.The fouling mechanism did relate to the operating conditions.To this end,a multistage Hermia model was developed.A ternary plot was proposed to cluster the different operating conditions with respect to the types of pore-blocking and visualized the contribution of different pore-blocking to membrane fouling.The operating points located in the C region could be selected to minimize the irreversible fouling during the initial period of the filtration and improve the operating efficiency of membrane system.Results of FTIR and EDS demonstrated that foulants on membrane surface were mainly composed of protein,polysaccharides,and fatty acids.The presence of calcium and magnesium ions contributed to form a layer of inorganic foulants.A cleaning protocol that included 1 wt%NaOH and 0.5 wt%SDS cleaning for 1 h and 0.5%(v/v)HNO3 cleaning for 0.5 h could lead to a flux recovery rate of more than 95.3%.By establishing a double membrane system,the content of macromolecular impurities in TEL was reduced and the loss of neutral aromatic substances was reduced,thus further improving the quality of tobacco sheet.The present study provides technical support and a good basis for industrial application for the development of new separation and concentration technology of TEL.