The literature overview presents the newest accomplishments in pervaporation and comparing different types of pervaporation membranes in separation H2O and ethanol mixture. Besides this literature reappraisal includes a brief theoretical footing of membrane procedures and describes recent membrane market.
After agitation in the production of bioethanol, the following measure is desiccation of aqueous mixture 5 – 12 wt % of ethyl alcohol, which is called ‘broth ‘ or ‘beer ‘ [ 1 ] . To divide this ethanol-water mixture in bioethanol production mills is normally used two phases:
The first phase is conventional distillment, which is involved desiccation ethyl alcohol from 10 wt % to 92.4wt % ethyl alcohol. However farther distillment, up than 92.4 wt % , became impossible because of nearing azeotrope point ( at 95.6wt % ) , which makes simple distillment absurd as the azeotrope boiling temperature lower than boiling temperature of pure ethyl alcohol [ 1 ] . Breaking azeotrope is one of the chief jobs in bioethanol industry, by David P. Brayant [ 2 ] to sublimate bioethanol from aqueous mixture by one phase distillment is possible until 95 % . The simple diagram of bring forthing 95 wt % bioethanol from biomass is presented in figure 2.1.
2.1. The simple strategy of bring forthing 95 wt % aqueous bioethanol mixture.
The 2nd phase ( bring forthing anhydrous bioethanol ) is fundamentally more power-intensive procedure. To bring forth anhydrous intoxicant it is necessary to add excess alteration into distillment procedure and it normally consumes 40 % – 60 % of whole works energy ingestion [ 2 ] . Therefore at this measure of desiccation are used more sophisticated setup and methods than at the first measure to cut down energy ingestion and bring forth pure bioethanol. Basically, to divide water-ethanol mixture at azeotrope point ( see figure 2.2 ) is used cyclohexane but the disadvantage of this method is cyclohexane will ne’er let go of from intoxicant. This drawback of cyclohexane as a ledgeman of azeotrope mixtures makes it unsuitable to bring forth intoxicant of high pureness [ 3 ] . Other the most widely used methods are azeotropic distillment ( AD ) , different types of extraction distillment and pervaporation or other membrane processes [ 1 ] .
Figure 2.2. Vapour-liquid equilibrium curve
To sublimate ethyl alcohol and do it cheaper in this thesis will be advised to utilize membrane separation procedure, which is alleged membrane pervaporation procedure.
2.1.2 Membrane market.
Membranes are one of the fast developing scientific Fieldss in chemical industry. They have successfully been applied in dairy industries and nutrient industry. Today membranes are widely used in H2O intervention and in medical specialty to assist people, who are enduring with kidney disease [ 4 ] .
In all industries where there are distillment, desiccation and vaporization, membranes could replace or modify classical methods thereby cut down energy ingestion. By a study in 1986 the one-year energy usage in the USA, which was spent on desiccation, distillment and vaporization, formed 4.2 quads ( 1 quad about equal to 2,93A-1011 Kilowatt-hours ( kWh ) ) . This study noted that by debut of membranes into gasoline, chemical and nutrient industries and utilizing them in the above-named procedures, it is possible to cut down expended energy more than 0.8 quads [ 5 ] .
Today the sale of membrane is a really fast developing market, one-year gross revenues in 1998 amounted more than US $ 4.4 billion dollars [ 4 ] . The biggest consumers are: the USA around 45 % of all gross revenues in 1996 and 29 % Europe and the Middle East. However the Asiatic and South American markets are lifting quickly and in the nearest hereafter will show large portion of membrane consumers [ 4 ] . Besides it was noted that farther grow of this market will go on and organize 10 % /year [ 4 ] .
2.1.3 Types of membrane and membrane procedures.
By and large all membrane procedures could be explained like separation of a flow into two streams one of them is permeate and another one is retentate, a conventional diagram of membrane procedure is showed in fig. 2.3. Even it could be seen really simple procedure, the most of import thing in a membrane processes is control of pervasion and separation through a membrane [ 6 ] . Therefore the chief end of applied scientists and scientist is to accomplish the best separation of a mixture, which will be economically profitable.
Figure 2.3. The basic circuit of the membrane procedure.
At the recent clip, there are six chief types of membrane procedures: microfiltration ( MF ) , ultrafiltration ( UF ) , nanofiltration ( NF ) , rearward osmosis ( RO ) , pervaporation ( PV ) and electrodialysis.
The first four of them microfiltration, ultrofiltration, nanofiltration and hyperfiltration ( rearward osmosis ) are developed and widely used by companies around the universe. Microfiltration, ultrafiltration and nanofiltration differ from each other by the diameter of pores in the membrane, therefore all three methods are based on filtration technique, which is consisted in separation dissolved or suspended solutes from a flow, by utilizing porous membrane with different diameters. The Forth type, rearward osmosis, uses membranes, which virtually do non hold pores, because diameter of pores 3 – 5 A ( 1 angstrom equal to 10-10 metres ) , therefore the driving force of the contrary osmosis is differences in solubility and mobility of solutes [ 5, 6 ] . Basically electrodialysis was designed to obtain fresh H2O by desalinization of sea salt H2O by utilizing as a thrust force electrical potency, today this procedure is widely used in the nutrient industry, for illustration to deionise cheese whey [ 6 ] . However to divide azeotropic ethanol-water mixture all these types of membrane can non be used, hence they will non be discussed in this literature reappraisal.
Although pervaporation is still developing procedure, the first clip when was published the term of pervaporation was in 1917 in the Journal of the American Chemical Society [ 7 ] . Nowadays it has immense potency in desiccation of ethanol-water mixture and interrupting azeotrope, the latter one makes large energy ingestions by utilizing distillment procedures. Basically pervaporation based on separation a liquid mixture by one constituent selective membrane, where the drive force is differential force per unit area between upstream flow ( retantate side ) and downstream flow ( permeate side ) . The advantage of pervaporation over conventional distillment is ability to divide close bowling mixture or azeotrope mixtures. In the pervaporation procedure a membrane represents the 3rd stage, which selectively passes H2O molecules through it, therefore boiling point of azeotropic mixture does non act upon on separation.
Basically principle strategy of pervaporation seems like other membrane procedures ( see figure 2.4 ) , nevertheless difference from the latter 1s is that one constituent of water-organic or organic-organic mixture preferentially extracted through a nonporous permeate selective membrane by partial vaporisation. In the pervaporation procedure a provender is in liquid stage contacts with membrane ‘s active bed, while on the opposite side of the membrane there is a vacuity, which makes driving force through membrane mass. Equally shortly as molecules of permeate are approached the opposite side of the membrane, pervade evaporates with the vacuity aid [ 8 ] . Whole procedure could be described in tree stairss:
Discriminatory sorption of a needed constituent by selective membrane
Diffusion of the fastest constituent through the membrane
Desorption of permeate and vaporisation by vacuity.
Figure 2.4. The basic circuit of the membrane procedure.
There are two chief parametric quantities which describe pervaporation procedure. The first parametric quantity, which shows pervasion ratio, can be defined by the undermentioned equation
( 2-1 )
Where, – pervasion flux ( ) , – the mass of the permeate ( ) , – the country of the membrane in contact with the provender mixture ( ) , – the pervasion clip ( ) .
The 2nd parametric quantity shows selectivity of a membrane and efficiency of separation, it can be besides found by equation 2-2 [ 9 ] :
( 2-2 )
where, – dimensionless separation factor, and – the mass fractions of H2O and ethyl alcohol in the permeate side, severally, and – the mass fractions of H2O and ethyl alcohol in the feed side, severally.
As higher a separation factor of a membrane, so better separation could be achieved in a pervaporation procedure, therefore superselectivity can be at [ 3 ] . Basically, in the pervaporation procedure there is reverse proportionality between flux ratio ( J ) and separation factor ( I± ) , alleged ‘trade off ‘ phenomenon, nevertheless, some membranes show exclusion of regularity [ 10, 11 ] . By R.Y.M. Huang et Al. [ 12 ] tradeoff phenomenon is non common for perfectly all types membrane but, fundamentally, membranes without strong polar interaction show this regularity.
Variation of the flux and separation factor to bring forth the best membrane makes really difficult to happen good membrane with first-class pervaporation belongingss. Therefore scientists have introduced new equation ( see equation 2-3 ) for comparing different membranes, which is alleged ‘pervaporation separation factor ‘ ( PSI ) [ 13 ] .
( 2-3 )
Although a batch of scientists are utilizing this equation to analyze different types of membrane, by Peter D. Chapman this equation has one disadvantage that the same PSI could be achieved either by membrane with jurisprudence separation factor and high pervasion rate or membrane with high separation factor and jurisprudence pervasion rate. Therefore, in some instances the highest Pounds per square inch does non bespeak a membrane with the best pervaporation belongingss.
Experimental informations of temperature dependance of entire pervasion flux by and large exhibits an Arrhenius relationship [ 13 ] :
( 2-4 )
where is pervasion flux, R – gas invariable, T – operating temperature, and are the pre-exponential factor and the evident activation energy of pervasion, severally, at the same clip the latter described by the undermentioned equation [ 12 ] :
( 2-5 )
where and are the activation energy of diffusion and the heat content of sorption if the permeant in the membrane, severally.
Another of import parametric quantity, which can do impact on pervaporation belongingss, is swelling degree, normally it is really difficult to foretell the puffiness of membrane at a different procedure conditions. Swelling grade is really of import as puffiness of a membrane exert alterations in flux and separation factor, the equation to find the swelling grade is 2-5.
Membranes ‘ over swelling lead to increasing pervasion flux of both constituents, hence separation factor of membrane could be decreased dramatically. Although that over puffiness is non good for membrane, un-swollen active bed and/or excessively much dry underneath support bed cause membrane deformation and as the consequence membrane lose ain separation belongingss [ 14 ] . Therefore it is really of import to command swelling grade of a membrane by adding crosslinking component into membrane, therefore polymer became more jammed. By other words crosslinking cut down molecular ironss ‘ motion and free volumes in a membrane.
Membranes for pervaporation procedure.
For the last two decennaries there were written a batch of scientific articles and books about pervaporation membranes. Different types of surveies have investigated the following followers parametric quantities, which required membranes to be used in industry [ 15 ] :
Economic profitableness of bring forthing membranes ;
Damage and leaking opposition ;
Bettering efficiency of separation and cut downing energy waste ;
Increasing of pervasion through a membrane ;
Be easy to clean.
Satisfaction to all these parametric quantities makes a membrane high effectual in pervaporation procedure. However, to bring forth a good membrane, which will content to all above demands, it depends to a big extent on natural stuff for a membrane.
184.108.40.206 Categorization of membranes by type of stuffs.
In pervaporation procedure there are three types of membrane which are differed from each other by type of stuffs. The first type is organic membranes normally they are made from polymers ; they became widely used after developing polymer production industry. The 2nd type is inorganic membranes, they are much expensive than polymers membranes, but have better belongingss. The 3rd type is inorganic-organic membranes, which are alleged intercrossed membranes ( or composite membrane ) . Basically intercrossed membranes seem like polymer base with little inorganic atoms inside the mass or inorganic porous base with polymer selective bed on top of it [ 3, 15 ] .
I™ . Inorganic membranes.
Two chief inorganic stuffs zeolite and ceramic [ 16 ] provide membrane with high permeableness ( flux ratio ) and separation factor, because of these belongingss they are widely used to bring forth inorganic membranes. As a consequence the pervaporation belongingss of inorganic membranes are rather good to utilize them in industry and do commercial membranes. However, the disadvantages of inorganic membranes are high monetary value of feedstock for this type of membrane and physical failing.
In ain article about pervaporation alcohol-water and organic aqueous mixtures D. Shah et Al. [ 16 ] tested commercial NaA-zeolite membranes and in item investigated mechanism of pervaporation through NaA-zeolite membranes. The pervaporation procedure was under following temperature conditions 40oC, 60oC and 70oC and feed intoxicant concentration varied from 0 wt % to 100 wt % . Therefore it was found that during the pervaporation of ethanol-water mixture ( from 0 wt % to 70 wt % ) at 60oC the pervasion flux about did non vary, by writers ‘ sentiment it is because of high hydrophilicity of the zeolite membranes. In malice of the high H2O affinity of NaA-zeolite membranes, flux reduced after increasing intoxicant concentration up to 100 wt % . D. Shah et Al. supposed that raised solvent concentration reduces H2O activity and as a consequence chemical potency reduces every bit good. In add-on writers explained zeolite construction, sorption mechanism and motion through the membranes by dipole minute and molecules interaction. By D. Shah et Al. molecular size is non complete for the best separation through zeolite membranes and as illustration of this theory writers compared two different mixtures one of them is ethanol-water and another one is dimethylformamide ( DMF ) -water. Despite the fact that molecules of DMF bigger than ethyl alcohol, molecules of dimethylformamide crossed through the membranes faster than ethyl alcohol ‘s. Scientists described this behavior by high polar activity of dimethylformamide molecules, which makes a contention to H2O molecules, therefore H2O flux reduced. Therefore, separation factor of the NaA-zeolite membranes for dimethylformamide-water mixture is lower than for ethanol-water. To back up ain premise scientists compared H2O sorption during the pervaporation of the same concentration ethanol-water and DMF-water mixtures, hence it was found that H2O sorption in the latter mixture 30 % lesser than ethanol-water mixture. Another interesting point is that interior of zeolite membranes there are non-zeolitic pores, which are similar to polymer membranes ‘ free volumes, but by D. Shah et Al. these pores are non decently studied. In add-on scientists compared these NaA-zeolite membranes with PVA membrane, so it was found that flux and separation features of PVA membranes are much less than NaA-zeolite membranes ( table 1 ) .
Comparison of selected solvent/water PV consequences for zeolite and PVA membranes [ 16 ] .
Feed dissolver ( wt % )
Temperature ( oC )
Permeate ( dissolver ) concentration ( wt % )
Entire flux ( kg/m2h )
Another survey about the zeolite membrane was late written by Y. Hasegava et Al. [ 17 ] , where scientists in their article about NaA-type zeolite membranes investigated ‘the influence of the acid ‘ on membrane public presentation. All alterations in separation of water-ethanol mixture were supervising in a real-time by a mass spectrometer. In ain experiments Y. Hasegawa et Al. used acetic acid as an add-on to the ethanol-water mixture, the value of acid varied from 0.1 milliliters – 1.0 milliliter. Therefore it was observed that acetic acid destroys NaA-zeolite membranes and as a consequence the fluxes of ethyl alcohol and H2O through the membranes increased significantly but separation factor dramatically dropped. Whole 100 infinitesimal experiment was conditionally divided into three stairss, where at the first measure flux decreased instantly, so on the following measure somewhat raised and at the last measure membrane was non able to divide mixtures, as separation factor aggressively dropped. After the experiment the membrane was wholly destroyed, hence it lost its separation ability.
Robert W. Van Gemert and F. Petrus Cuperus [ 18 ] investigated public presentation of ceramic membrane by pervaporation separation following mixtures: methanol-water, ethanol-water, and 2-propanol-water. The chief purpose of their research was to make the first satisfying dense membrane, which will be sufficient for industrial applications. By writers these new ceramic membranes, which were based on I?-Alumina with deposited silicon oxide by sol-gel technique showed preparedness to divide different types of mixtures. The membranes had been proving for a period of 3 months and during this clip flux and separation factor did non alter significantly.
I™I™ . Organic membranes.
During the literature research, it was found that chief stuffs to bring forth organic membranes are: poly ( vinyl ) intoxicant, chitosan, different types of alginates, polyimides and polyamids. All of them have really good H2O selective belongingss, which are really of import for ethanol-water separation. However the chief job of these stuffs and membranes, which were made from them, is over swelling. In this instance different scientists tried to modify membrane construction by adding some particular complexs, which can keep the puffiness.
Jing Ma et Al. [ 14 ] created and examined chitosan/polyacrylonitrile membranes with added mussel adhesive-mimetic molecule, carbopol. By Jing Ma et Al. carbopol increased pervaporation belongingss of chitosan/polyacrylonitrile membranes by increasing separation factor. It was interesting to detect that to fix this membrane was used layer-by-layer technique, hence, bulk of carbopol molecules were located in intermediate bed between chitosan and polyacrylonitrile. However with increasing carbopol content in the membrane flux lessenings, by the writers ‘ sentiment the ground of flux lessening is influence of carbopol on thickness of intermediate bed. Another interesting fact that is these membranes showed ‘anti-trade-off ‘ behavior but this consequence was achieved while pervaporation of 90 wt % ethanol-water mixture. Though membranes broke usual ‘trade-off ‘ , with increasing H2O content in the feed side swelling grade enhanced and caused decrease of separation factor. Therefore, with increasing H2O content membranes proved general behavior, by other words with increasing flux separation factor decreases. But the most interesting fact that during 150 hours of pervaporation membrane ‘s belongingss reduced somewhat and it was found any mechanical defects, therefore these membranes showed good long-run pervaporation abilities.
P. Kanti et Al. [ 19 ] tested crosslinked chitosan and Na alginate membrane by pervaporation of ethanol-water mixtures. In contrast to the research of Jing Ma et al. , where chitosan and alginate presented independent beds, in this survey membranes were made by intermixing deacetylated chitosan with Na alginate and further this solution was crosslinked by add-on glutaraldehyde to cut down inordinate puffiness. P. Kanti et Al. investigated H2O provender concentration influence on membrane pervaporation belongingss, hence it has been found that with increasing H2O content in the provender from 5 wt % to 45 wt % , the flux increased from 0.55 kg/m2h to 2.12 kg/m2h, while the selectivity aggressively dropped from 436.3 to 16.6. Besides the writers examined influence of membrane thickness to pervaporation conditions, therefore, it was mentioned that significantly dropped from 0.22 kg/m2h to 0.07 kg/m2h, while thickness increased from 25 I?m to 190 I?m. However selectivity increased from 436.3 to 2118.5 with an addition at the same thickness. The last point, which P. Kanti et Al. described in the article is influence of permeate force per unit area on membrane features ; hence, it was found that with increasing permeate force per unit area pervaporation flux and selectivity decreased.
R. Jiraratananon et Al. [ 13 ] investigated chitosan/hydroxylethylcellulose ( CS/HEC ) composite hydrophilic membranes based on porous cellulose ethanoate. They found that porous cellulose ethanoate improved chitosan/hydroxylethylcellulose membranes public presentation during pervaporation of ethanol-water mixture. As a consequence, for 90 wt % and 95 wt % ethanol aqueous mixture these membranes showed higher flux and separation factor than dense chitosan/hydroxylethylcellulose at the same intoxicant concentrations and temperature 60oC. For illustration for dense CS/HEC membrane at 90 wt % ethanol-water mixture and temperature 60oC flux and separation factor were 112 g/m2h and 10491. However, the same parametric quantities for CS/HEC on top of porous ethanoate cellulose showed 424 g/m2h – of the membrane and 5469 – separation factor. To compare these two types of membranes R. Jiraratananon et Al. used pervaporation separation index ( PSI ) , which is showed in equation 2-3. Harmonizing to this equation dense CS/HEC has PSI equal to 1,178,278 but CH/HEC-AC ‘s PSI is 2,332,188. However, by R. Jiraratananon et Al. other chitosan membranes, which were made by other scientists, showed much lower PSI. Besides writers described influence of temperature, permeate force per unit area and H2O provender concentration on separation conditions, hence it was found that these CS/HEC membrane based on porous cellulose ethanoate, showed general ‘trade-off ‘ . Although these membranes showed usual ‘trade-off ‘ behavior, separation factor and flux was really high at high intoxicant concentration and 60oC procedure temperature.
Tcrosslinking = 80 min Jp = 700 I± a‰? 315, therefore harmonizing to equation 2-2 PSI = 219800
Tcrosslinking = 85 min Jp a‰? 630 I± = 400, therefore harmonizing to equation 2-2 PSI = 251370
The writer besides mentioned information about influence of temperature and ethanol provender content but did non take into history swelling grade. In the 2nd portion of this research [ 20 ] writers continued probe of belongingss chitosan/hydroxylethylcellulose ( CS/HEC ) composite membranes, the chief point of this research was analyzing of mass conveyance through these membranes and besides affects of procedure conditions on membranes pervaporation belongingss. Scientists by mathematical equation proved that H2O molecules can be selectively extracted through membranes ; nevertheless ethyl alcohol has negative opposition, by R. Jiraratananon et Al. it means that ethyl alcohol molecules ‘ ‘ … conveyance of ethyl alcohol was in opposite way to H2O ‘ [ 20 ] .
R.Y.M. Huang et Al. [ 12 ] besides investigated belongingss of new alginate/chitosan membranes based on top of polyvinylidene fluoride ( PVDF ) . Alginate membranes show strong hydrophilic belongingss, nevertheless there are two chief jobs of alginate membranes they are H2O solubility and mechanical failing. Therefore, scientists investigated possibility of membrane betterment by adding other stuffs. The over H2O solubility of alginate bed was prevented by ionic crosslinking. Mechanical belongingss are ameliorated by utilizing chitosan bed and do membranes by projecting method bed after bed. The experiment was traveling under 50oC and concentration of ethyl alcohol in the provender varied from 50 wt % – 95 wt % . During the survey there were investigated different alterations of alginate/chitosan membranes and their ability to divide ethanol-water and isopropanol-water mixtures under different temperature conditions. In ain research R.Y.M. Huang et Al. examined swelling grade of the membranes and so after swelling experiments scientists compared Na alginate membrane with alginate/chitosan. Therefore, it was found that swelling grade of latter one was lower than Na alginate membrane at high intoxicant concentrations, by writers ‘ sentiment, better H2O suppress due to strong H bonding of alginate/chitosan membrane.
R.Y.M. Huang et Al. [ 21 ] examined sodium alginate membranes, which were prepared for desiccation of ethanol-water and isopropanol-water mixtures, by pervaporation procedure. The writers investigated that alginate membrane, which was crosslinked by Ca2+ ions, exhibited the best relationship between flux and separation factor comparison to alginate membranes with another divalent and trivalent ions like Zn2+ , Mn2+ , Co2+ , Fe2+ and Al3+ . R.Y.M. Huang et Al. noticed that the highest separation factor was achieved for 90 wt % ethanol-water and isopropanol-water with the same concentration at 50. However, writers compared Ca alginate membrane with another one, which was crosslinked with Na+ ions. To look into the best membrane research workers varied two runing parametric quantities the first is H2O content in the provender from 5 wt % to 30 wt % and the 2nd is temperature of the procedure from 40oC to 70oC. Sodium alginate membrane showed higher pervaporation public presentation than Ca except the pervaporation of 95 wt % ethanol-water and isopropanol-water mixtures mixture. It is really interesting to detect that for Na alginate membrane with increasing in H2O content in the provender, concentration of permeate H2O additions. By R.Y.M. Huang et al. this behavior of the membrane can non be described by usual swelling theory, because with increasing swelling degree flux of ethyl alcohol would increase as a consequence separation factor would diminish. Therefore, writers supposed that this phenomenon could be explained by strong communicating between H2O molecules in the provender and Na ethanoate and hydroxyl groups in the alginate membrane. Another interesting fact that these Ca2+ and Na+ alginate membranes showed “ anti-trade-off ” behavior, where with increasing in temperature separation and flux addition, by R.Y.M. Huang et Al. it could be explained by relaxation behavior of a polymer membrane.
Recently, Wulin Qiu et Al. [ 9 ] tested to different membranes, which were made from two types of commercial polyimide, the first 1 was Matrimid and the second was Torlon. The purpose of this research was to see how these polyimide membranes separate ethanol-water mixture by changing temperature and provender intoxicant concentration. It is really interesting to detect that Wulin Qiu et Al. tested polyimide membranes for a long term period of clip at different intoxicant concentrations, hence, these membranes showed addition in flux and lessening in separation factor or alleged general ‘trade-off ‘ . At first clip both types of polyimide membranes showed really low separation factor, for case, membranes which were made from Matrimid at 85 wt % ethanol-water mixture these membranes ‘ separation factor was around three. Low separation factor of these polyimide membranes could be explained by plasticization procedure of the membranes, by John D. Wind et Al. [ 22 ] , fundamentally, glassy polymeric membranes ‘ plasticization prolongs concatenation relaxation, hence pervaporation flux additions and separation factor decreases. Therefore, to better pervaporation belongingss and cut down plasticization of polyimide membranes, it was decide to tempering hollow fiber membranes and as a consequence separation public presentation increased significantly. However, temperature and clip of tempering procedure is really of import, for illustration the best temperature and clip conditions for Matrimid membrane is 260oC and 5 hours, severally. At these conditions this hollow storyteller membrane achieved the best separation factor, which consequently equal to around 200. There were three different temperatures of pervaporation procedure 30oC, 40oC and 75oC and it was found that at 30oC the separation factor was the highest, where after farther increasing of temperature the separation factor decreased. By Wulin Qiu et Al. lessening in separation factor was explained like with temperature addition ironss motion and free volume of membrane besides addition, therefore, H2O and ethanol fluxes increased. To look into membrane stableness scientists made four twenty-four hours pervaporation trial for Matrimid and Torlon membranes with 95 wt % and 15 wt % ethanol-water mixtures. As a consequence it was found that
Matrimid membranes showed dramatic bead in separation factor at 95 wt % alcohol- H2O mixture from 240 at the beginning of the experiment to 10 after three yearss, writers explained this extremist alteration due to fast plasticization of the membranes. However, during the pervaporation of 15 wt % ethanol-water mixture membrane showed more stable separation public presentations.
Torlon membrane showed better separation factor at higher ethyl alcohol concentration but besides like Matrimid reduced separation factor dramatically in three yearss. Decrease in separation factor in this instance besides was explained by plasticization of polymer.
During this research it was found that the Matrimid polyimide membranes were plasticized by ethyl alcohol but Torlon membranes showed high suppression the membrane swelling. Despite the fact that in this survey explained hydrophilicity and hydrophobicity of membrane and besides temperature influence, these membranes need farther probe, for illustration influence of crosslinking on membranes belongingss.
Another article about pervaporation of alcohol-water mixture through polyimide membrane was written by Jeong-Hoon Kim et Al. [ 23 ] , where scientists dehydrated ethanol-water mixture through polyimide membrane. In this research Jeong-Hoon Kim et Al. used different diamines as monomers for polyimide membranes, such as hexamethylene diamine ( HXDA ) , ethylene diamine ( EDA ) and m-phenylene diamine ( m-PDA ) . Besides polyimide membranes were based on polysulfone porous ultrafiltration membrane, which was as a support bed, but farther experiments included membranes without polysulfone support. During pervaporation trial scientists investigated influence of imidization temperature on belongingss of membranes. Therefore, it was found that polyimide membranes, which were made from EDA and HXDA, had higher flux and separation factor than m-PDA. Writers supposed that better flux and separation factor could be explained by physical construction instead than chemical construction. In instance of EDA and HSDA, EDA showed higher flux and lower separation factor than HXDA, this state of affairs was clarified by high hydrophilicity of EDA than HXDA. In add-on, writer mentioned that with increasing imidization temperature of polyimide membranes higher than 150oC, flux and separation factor decreased, for EDA and HXDA separation factor dramatically dropped.
2.2.3. Hybrid membranes.
Nowadays intercrossed membranes became more popular, as this sort of membranes has comparatively lower monetary value than inorganic membranes, while has better pervaporation and mechanical belongingss than polymer membranes.
Tadashi Uragami et Al. [ 24 ] investigated membranes, which were made from organic and inorganic stuffs. Organic portion of the membrane was presented by chitosan ( q-Chito ) and inorganic portion of the membrane was presented by tetraethoxysilane ( TEOS ) . During this research Tadashi Uragami et Al. found that q-Chito membranes with TEOS showed higher pervaporation belongingss than pure q-Chito membranes. By the writers better water/ethanol selectivity was achieved by cross linked construction of the membrane, hence swelling grade of the organic inorganic membrane decreased. However it was noticed that, with increasing in TOES content more than 45 mol % , water/ethanol selectivity of the membranes decreased significantly, therefore selectivity was lower than q-Chito membranes. This membranes ‘ behavior was described by altering in construction of the membranes, where at the concentration of TEOS less than 45 % construction was homogenise and at higher concentration of TEOS it was changed to heterogenous.
Another work, where were studied organic-inorganic intercrossed membranes was written by Dong Yang et Al. [ 25 ] . Dong Yang et Al. explored the influence of Ti oxide on an alginate membrane belongingss, such as flux and separation factor. It is interesting to observe, that under the same conditions CS/TiO2 membranes made by situ sol-gel engineering showed higher flux and separation factor than CS/TiO2 intercrossed membranes made by intermixing method. The optimum concentration of Ti oxide is 6 wt % , at which membranes showed mean pervasion flux and separation factor 0.340 kg/m2h and 196 for 90 wt % ethanol-water mixture. Just increasing the content of Ti oxide by more than 6 wt % increases the puffiness of the membrane, thereby cut downing the separation factor and increasing pervasion flux. Besides the writers mentioned information about influence of the pervaporation temperature on pervasion flux and separation factor, hence with increasing in temperature flux additions every bit good, nevertheless, separation factor decreases with lifting in temperature. By Dong Yang et Al. with lifting temperature, concatenation motion additions, hence free volume widens and as a consequence handiness of go throughing bigger radius molecules of ethyl alcohol. Another interesting fact that was noticed by writers is that diffusivity of H2O and ethyl alcohol through membrane, where it was found that with temperature lifting diffusion coefficient of ethanol grows faster than H2O ‘s.
Harmonizing to the purpose of this survey bring forthing of membrane is non necessary. Therefore in this research will be used commercial organic membrane based on poly ( vinyl ) intoxicant and polyimide, which was made by Heggemann company. Nowadays surveies in polymer and membrane industry allow us to bring forth good organic membranes with acceptable pervaporation belongingss. This organic membrane has two advantages, which will be of import for mill usage, like ability to run at temperature up to 150oC and force per unit area 5 Barr and comparatively inexpensive monetary value. High H2O selective poly ( vinyl ) intoxicant bed was crosslinked by polyimide to avoid an overswelling of the membrane.
220.127.116.11. Categorization of membranes by provender mixtures.
To take membrane for pervaporation procedure it is really of import to take into history a compound of a provender and constituents content. In practise, there are two types of existed mixtures, which can be of involvement for membrane pervaporation procedure: organic-water and organic-organic. However, aqueous organic mixtures are divided into two subgroups, where difference between the first subgroup and the 2nd is occurred in varied concentration of organic portion. Therefore, scientists assign free types of membrane: hydrophilic, hydrophobic and organophilic [ 8 ] .
I™ . Hydrophilic membranes.
This type of membranes was found for desiccation of aqueous organic solution. Hydrophilic stuffs like poly ( vinyl ) intoxicant or chitosan have high flux and separation factor but inordinate hydrophilicity of this stuffs leads to its swelling. Despite the fact that with the swelling increases the flux of membrane, The chief job of all hydrophilic polymer membranes such as chitosan or poly ( vinyl ) intoxicant [ 19, 21 ] is high swelling grade, which causes increasing speed of concatenation motion and turning free volume in membrane. The disadvantage of inordinate puffiness is fast increasing of the flux of all constituents and as a consequence decrease of separation factor. In order to forestall inordinate puffiness of a membrane is used the method of cross-linking [ 10, 11, 19, 21, 24, 25 ] . Besides different sorts of crosslinking agents provide hydrophilic membranes by more mechanical strength and better flux [ 8 ] .
By P.A. Peters et Al. [ 11 ] , who examined organic-inorganic intercrossed membranes based on poly ( vinyl ) intoxicant and I?-Al2O3, some pervaporation membranes are ‘ … beliing the flux-selectivity paradigm ‘ . In this article P.A. Peters et Al. compared flux ratio and separation factor of each membrane by fluctuation procedure conditions and types of intoxicants, such as ethyl alcohol, 1-propanol, 2-prpopanol and 1-butanol. Therefore, it was been found that during pervaporation of ethyl alcohol and 1-propanol aqueous mixtures at the same conditions membrane showed typical trade-off proportionality between the pervasion rate and separation factor. It means with increasing temperature of the procedure the flux ration was increased and the separation factor was decreased. However, during of purification of 2-propanol-water and 1-butanol-water mixtures membranes showed anti-trade-off paradigm, where both the pervasion rate and the selectivity of membranes were increased. The same phenomenon was observed by Qiu Gen Zhang et Al. [ 10 ] , who tested intercrossed membranes based on top of the I?-amino propyltriethoxysilane ( APTEOS ) and poly ( vinyl ) intoxicant ( PVA ) . By the writers the fresh PVA/APTEOS membrane showed increasing separation factor with increasing temperature of a procedure. The cardinal point of this research was happening an optimum concentration of APTEOS to better flux rate and separation factor, therefore the best APTEOS content was consisted 5 wt % besides it was mentioned that selectivity was decreased significantly, while concentration of APTEOS exceeded 5wt % . By Qiu Gen Zhang et Al. aggressively bead of separation factor could be explained by increasing in hydrophobicity of a membrane. In add-on the writers wrote that pervasion and separation of these PVA/APTEOS membranes depends on H2O provender concentration. With increasing H2O content in the provender was observed the usual tradeoff.
Young Moo Lee et Al. [ 26 ] examined crosslinked hydrophylic chitosan membranes and compared with poly ( vinyl ) intoxicant membranes. Chitosan membranes were made by projecting solution method based on top of a porous polyethersulfone ultrafiltration membrane. Crosslinking component was sulfuric acid, therefore acerb residue SO4-2 and NH3+ of chitosan molecule made strong ionic connexion. In this article scientists figure out an optimum crosslinking clip for chitosan membranes. It was found that ethanol-water mixture required much longer crosslinking clip than isopropanol-water mixture. Young Moo Lee et Al. described a ground of different crosslinking clip by molar volumes of solutes, where the molar volume of isopropyl alcohol and ethanol constitute 76 cm3/mol and 41 cm3/mol, severally. The consequence of this research was that chitosan membranes showed better pervaporation belongingss and less temperature-dependency than poly ( vinyl ) intoxicant. Besides it is really interesting to detect that at 80oC and 90oC, poly ( vinyl ) intoxicant membranes lager alterations in free volume than chitosan membranes.
I™I™ . Hydrophobic membranes in pervaporation membrane procedures.
In add-on to the on-going procedures of pervaporation by hydrophilic membranes, there are some surveies of pervaporation procedures, which are used hydrophobic membranes. This type of membranes is widely used to pull out organic constituent from aqueous mixture. In bioethanol industry hydrophobic membranes are widely used at the phase of agitation to pull out intoxicant from agitation ‘broth ‘ [ 27-29 ] . Membrane for this procedure is made from hydrophobic stuffs, which are organic selective. It is non common procedure but developing hydrophobic polymer membranes cause new chances in forepart of fermentation/pervaporation procedure.
Leland M Vane [ 27 ] in ain reappraisal about merchandise recovery from agitation stock, writer identified and discussed possible alterations in the procedure to do it more competitory public presentation in comparing with distillment. He observed the undermentioned parametric quantities of pervaporation, which are really of import for equal comparing pervaporation with other types of biofuels recovery systems. The first parametric quantity is energy efficiency theoretically membrane procedure should be less energy-consuming procedure. The cost of pervaporation system and integrating of pervaporation unit with agitation procedure are really of import as to be competitory it is really of import to be economically profitable. By the Leland M Vane utilizing pervaporation procedure for pull outing ethyl alcohol from agitation stock has several jobs to be used alternatively of usual distillment procedures. The first ground is energy efficiency, where the chief jobs are commercial hydrophobic membranes does non hold high separation factor. The 2nd ground is membranes still has low flux, hence it is required to utilize bigger membrane country but to cut down the capital cost it is really of import to better permeableness of the membrane. The following ground is importance of utilizing long tally experiments with membranes to look into stableness of a membrane unit. Besides writer noticed that to utilize pervaporation membrane it is really of import to utilize micro or extremist filtration as in agitation stock there are solid atoms like enzymes and micro-organisms, which could cut down efficiency of the pervaporation membranes and foul up whole rig.
I™I™I™ . Organophilic membranes in pervaporation procedure.
Organophilic membranes are developed and made to pull out peculiar types of organic elements from organic-organic mixture. These membranes preferentially sorb indispensable sorts of molecules, while other molecules are rejected by membrane surface. The rule of separation the same as other types of pervaporation procedures, where diffusion through a membrane traveling by vacuity on a permeate side. The common illustration of organic-organic separation is extraction of aromatic elements from aliphatics.
In the thesis will be investigated ethanol H2O separation, which is can be separated by two ways the first 1 is utilizing hydrophilic membrane and another one is separation through hydrophobic membrane. However harmonizing to the searched stuffs there are non many good hydrophobic membranes, which has satisfactory flux ratio and selectivity. Large accomplishments in analyzing of hydrophilic membranes lead to utilize this type of membrane.
2.3. Pervaporation research lab works design.
During the literature hunt it was noticed that there are non a batch of narrow information about works design, it is due to a commercial secretness of pervaporation works. However each research, which was found, included simple works strategy and operation conditions of a procedure.
The design of the pervaporation rig or works does non vary significantly, as schematically they are really similar to each other. The chief principium of pervaporation is separation of provender flow into two flows the first 1 is a renetate and other one is permeate. On the permeate side is required a vacuity force per unit area, to keep a diffusion of permeate through membrane mass. The force per unit area on the permeate side should be maintained low than 10-20Torr ( 1Torr a‰?1 mmHg ) [ 16, 23 ] . Then due to vaporization of diffused constituent, there should be existed capacitor which has to be plenty effectual to distill whole sum of vaporised permeate, fundamentally as a capacitor is used a cold trap. The retentate side normally recycled to a provender armored combat vehicle, hence it seems like batch operation system. The feed mixture should be heated by temperature accountant and monitored by thermocouples. The temperature of the provender depends on membrane pervaporation belongingss, for illustration for ethanol-water mixture the temperature varies from 40 oC to 80oC. The principle strategy of pervaporation works is shown in figure 2.5 [ 9, 16, 19, 21, 23, 30 ] .
Figure 2.5 Principle strategy of pervaporation.
2.3.1. Membranes geometry.
Design of the pervaporation works evidently depends on membranes geometry which divides into three chief groups: planar, which is besides alleged plate-and-frame, coiling lesion and capillary [ 15, 31 ] .
I™ . Planar membranes in membrane industry.
Basically the simplest type of membrane, by Robert H. Perry ‘it is a really much like a filter imperativeness ‘ [ 15 ] . Although schematically two-dimensional membranes ‘ conceptually is really simple, their sealed building requires a batch of sealers. A two-dimensional membrane is shown in figure 2.6a [ 15 ] .
I™I™ . Spiral wound membranes.
Another cheap membrane faculty is called coiling lesion membrane. This type of membranes consist of permeate pipe, which has aggregation holes, and sheets, which are rounded of cardinal pipe. Feed comes into a membrane from one of cylindrical membrane and leaves it through an opposite side, while permeate goes into permeate pipe and so collected from it. By Daniel Bernal, coiling lesion membranes require competitively less certain stuffs than two-dimensional membranes but they are really hard to clean. The coiling lesion membrane is shown on the figure 2.4b [ 15 ] .
I™I™I™ . Hollow fibber membranes.
This type of membranes consist a batch of little capillaries, hence in some beginnings it is besides called like capillary membranes. Normally a diameter of each capillary for pervaporation procedure varies from 250 Aµm up to 6 millimeters [ 15 ] and by Robert H. Perry ‘there is no obvious bounds for the hereafter ‘ for self-supported hollow storyteller membranes ( see figure 2.6c ) [ 15 ] .
a ) B )
degree Celsiuss )
Figure 2.5. Different types of pervaporation polymer membranes classified by membrane geometry. ( a ) Planar membrane ; ( B ) Hollow fibber membrane ; ( degree Celsius ) Spiral membrane [ 15 ] .
In this research will be used commercial polymer hydrophilic membrane with hollow storytellers geometry based on poly ( vinyl ) intoxicant and polyimide. Crosslinking construction of a membrane will stamp down puffiness of membrane and hollow storyteller geometry will let easy installing and operation. In add-on in this research at that place will non be a recycle cringle, which is used to return permeate to a provender armored combat vehicle. Therefore, by other words the pervaporation works will stand for a uninterrupted operation system alternatively of usual batch system, therefore all experiences will be required less clip and will be higher efficient.
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