Purification of Fuel Bioethanol by Pervaporation

Transcription

1 Digital Proceeding Of THE ICOEST , Cappadocia C.Ozdemir, S. Şahinkaya, E. Kalıpcı, M.K. Oden (editors) Nevsehir, Turkey, June 18 21, 2013 Purification of Fuel Bioethanol by Pervaporation Derya Ünlü* 1, Nilüfer Durmaz Hilmioğlu 1 1, Kocaeli University, Chemical Engineering Department, 41380, Kocaeli, Turkey ( derya.unlu@kocaeli.edu.tr, niluferh@kocaeli.edu.tr) Abstract Begin to be insufficient energy resources with increasing population growth, developed countries has led to search for alternative energy to increase energy diversity. For these reasons, searching to the availability of clean and renewable energy sources has increased. Bioethanol is biofuel which can be produced from different biomass feedstocks. Bioethanol must be a high concentration for using as fuel. Distillation process is usually used for the ethanol recovery from aqueous solutions, but azeotrope of ethanol/ water mixtures cannot be separated by distillation. Membrane aided separation techniques can be used for the separation of these azeotropes. Pervaporation is a membrane process used to separate azeotrope mixtures by using a dense polymeric film. In this study, ethanol was purified with pervaporation. For this purpose, in this article, we firstly reported the synthesis of hydrophilic cross-linked polyvinyl alcohol-chitosan blend membrane. The pervaporation performance of the blend membranes was studied by the dehydration of ethanol/water. Sorption and pervaporation tests were made. Flux and selectivity are analyzed how effecttiveness of different feed concentrations. The total flux and degree of swelling increased with increasing water concentration at feed. Selectivity decreased with increasing water concentration. Keywords: Bioethanol, Biofuel, Membrane, Pervaporation, Separation 1. Introduction Bioethanol which is produced from different types of biomass has a wide potential. Fuel ethanol has advantages over fossil fuels, because of environmental impact and economic benefits [1]. Bioethanol is produced from agricultural waste such as wheat stem, corn, potato, sugar beet. These sources are alternative raw materials for bioethanol production [2]. Bioethanol can be used to petroleum engines powered vehicles. For that, there is no need of any additive [3]. Bioethanol can be used purely (by volume 96% bioethanol and 4% water) or proportionately with gasoline (E85 volumetrically 85% bioethanol 15% gasoline, etc.) directly instead of petroleum [1]. Mixing ethanol with gasoline, not onyl gasoline emission quality is improved, but also oxygene in structure of gasoline is burn more cleanly and of good quality [4]. So ethanol is become important to obtained as pure. Result of fermentation, ethanol is obtained as dissolved water. Ethanol should be waterless to use as fuel [5]. Conventional purification process such as distillation is a cost effective process. Also ethanol and water form azeotrope. It is not possible to go beyond 95-96% purity [6,7]. When the pervaporation process is applied, both are better results and more economical operation

2 761 obtained. Product which is ethanol concentration is 99,9% can be obtained by using energy more efficiently [7]. Pervaporation is membrane aided process which is applied to separation azeotropes, close boiling mixtures [8]. Solution diffusion mechanism is mass transport mechanism of the pervaporation process. This mechanism involves selective sorption of a component from the feed into membrane, diffusion of selective component across the membrane, desorption of selective component as vapor at the permeate side [9]. Pervaporation process is shown schematically Fig. 1. Figure 1. Pervaporation process for bioethanol purification [10] Pervaporation process performance is determined with permeate flux and selectivity. The permeate flux (J) is dependent on the feed composition, permeate pressure and temperature of the process. Selectivity is related to solubility and diffusivity [11]. The result of the studies shows that, the membrane separation technique pervaporation consumes less energy than other separation techniques. Energy amount of bioethanol purification processes was given in Table 1. Pervaporation, due to the properties of low energy consumption, provides advantages for the purification of ethanol-water mixtures such as low investment cost, no pollution, no waste [12]

3 762 Table 1. Consumption of energy at different process [13] Purification(%) Energy Process Requirement (kj/kg EtOH) Distilation Azeotropic distilation Pervaporation In this study, ethanol was purified with pervaporation. For this purpose, membrane was developed, sorption and pervaporation tests were made and the effects of various factors studied the pervaporation process. 2. Material and Methods 2.1. Materials Chitosan (high molecular weight polymer) and polyvinyl alcohol was received from Sigma Aldrich. Acetic acid was purchased Merck Chemicals. Crosslink agent solutions acetone, hydrochloric acid were obtained from Merck Chemicals. Crosslink agent was supplied by Alfa Aesar Methods Membrane Preparation PVA (3% w) was dissolved in water at 90 o C temperature. After dissolution, chitosan (2% w ) was added polymeric PVA solution. After 30 minutes, 50 ml of % 1.5 w aqueous acetic acid solution was added in PVA/chitosan polymeric solution. When the dissolution was finished, crosslinking agent glutaraldehyde was added to polymeric solution. Blend membrane solution was casted to polymethylmethacrylate surface. Membrane was dried and then ready for use [14] Sorption Experiments

4 763 Before pervaporation tests, membrane s sorption characteristic was determined with swelling experimentals. Membranes were cut into small pieces and dry weightes was determined. Then membranes were released to different concentration of ethanol/water solutions in petri dishes. Then membrane weights were measured regularly. When membrane weight was constant, experiment was resulted. Degree of swelling is calculated to using Equation 2.1 [15]. Wwet - Wdry Degree of Swelling (%) = 100 W dry In this equation; W wet is wet membrane weight, W dry is dry membrane weight Pervaporation Experiments Different concentration of ethanol-water mixtures were prepared and fed to pervaporation unit. The vacuum in the downstream side of membrane cell was maintained about 0.5kPa using a vacuum pump. The effective membrane area was cm 2. The permeate was condensed and collected in a cold trap in liquid nitrogen, and the flux was determined from the amount of permeate sample collected for a given time. The analysis of concentrations of permeates concentrations were measured using Agilent GC-7820A installed with TCD and HP-FFAP capillary column. Permeate flux (J) and separation factor (α) were calculated according to the following equations (1.1) and (1.2): J = m A.t (1.1) y α = x i i / y / x j j (1.2) For flux, where m is the amount of the component in the permeate, A is the effective membrane area, t is the time. For selectivity, where x and y is the weight fraction of components in the feed and permeate liquid. For this study i and j is defined as respectively water and total of organic compounds [16].

5 Degree of swelling (%) Degree of swelling (%) Results and Discussion 3.1. Sorption Experimental Results Membranes performance is determined with swelling experiments. Fig shows that degree of swelling values of chitosan/pva blend membranes how change with time t (h) 5% (v/v) water/ethanol 10% (v/v) water/ethanol 15% (v/v) water/ethanol Figure 3.1. Change of degree of swelling by time on different water concentration fixed. It can be seen that when membrane saturated to water, degree of swelling can be % 2% 4% 6% 8% 10% 12% 14% 16% Water concentration (%v/v) Figure 3.2. Effect of water concentration on degree of swelling

6 Total flux (kg/m 2.h) 765 Fig.3.2. shows that when the water concentration increases, degree of swelling increases too. Also free volume of membrane is increased with this situation. Accordingly, membrane take on water to its structure. This is an expected results for blend membrane which has hydrophilic properties Pervaporation Experimental Results Fig shows effects of water volume fraction in feed on the pervaporation performance of chitosan-pva blend membrane at room temperature. The permeation flux of chitosan-pva blend membrane increases from 6.35 to 9.85 kg/m 2 h when water volume fraction in feed increases from 5 to 15 v% t (h) 5% (v/v( water/ethanol) 10% (v/v) water/ethanol 15% (v/v) water/ethanol Figure 3.3. Effect of water concentration on total flux Blend membrane has OH groups capable of binding with water. The increase in the concentration of water is resulted to increase in the flux. Because number of water molecules for sorption and diffusion were increased [17]. The interaction with water causes the membrane to swell due to free volume of membrane is increased. While the swelling increases, membrane selectivity reduces by increasing feed concentration. Fig shows effects of water volume fraction in feed on the selectivity. High selectivities obtained at low feed water concentrations.

7 766 Figure 3.3. Effect of water concentration on selectivity The decrease in selectivity is due to reduction of free volume in the blend membranes. Because the water content in the feed increases, membrane swells and allowes more ethanol transport through the membrane together with water, so it is resulted to a decrease of separation factor [18]. 4. Conclusion Blends of chitosan and PVA were prepared for pervaporation of ethanol water mixture. This blend membrane has good properties such as mechanical and thermal resistance, good flux and selectivity. Sorption studies showed that the blend had hydrophilic property, permate flux and selectivity of water was higher than other component. Diffusion coefficient was increased with water concentration at feed. Also total flux was increased with water concentration. The azeotropic of ethanol water mixture was easily separated by pervaporation and ethanol can be used as fuel. References [1] M. Balat, H. Balat and, C. Öz, Progress in bioethanol processing 34. Progress in Energy and Combustion Science. 34 (5) [2] C.N. Ibeto, A.U. Ofoefule and K.E. Agbo, A Global Overview of Biomass Potentials for Bioethanol Production: A Renewable Alternative Fuel 6. Trends in Applied Sciences Research. 6 (5) [3] A. Çolak, The effect of ethanol usage on performance and emissions at various compression ratios in spark ignition engine, Master Thesis, Department of Mechanical

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