Experimental survey of temperature, time and cross-linking agent effects on polydimethylsiloxane composite membranes performances in sulfur removal

Experimental survey of temperature, time and cross-linking agent effects on polydimethylsiloxane... Four types of the multi composite membranes were fabricated to decrease the sulfur content in diesel fuel, which the inves- tigated polymers are polydimethylsiloxane (PDMS), polyethyleneglycol (PEG), polyethersulfonic (PES) and cross-linked polyacrylonitrile (PAN) with tetra-ethyl-ortho-silicate (TEOS). The effects of the operating parameters such as the cross- linking temperature (65–85 °C) and cross-linking time (0.5–2.5 h) were studied on the membranes performances. The results showed that the sulfur selectivity of PDMS/PEG/PES/PAN membranes were improved through increasing temperature and time. In addition, most of the total flux and the lowest amount of sulfur in the back flow is related to composite membranes of PEG + PDMS. Keywords Composite membrane · Sulfur content removal · Cross-linking agent · PDMS · PEG · PAN Introduction layer of polydimethylsiloxane and base layer of polyethersul- fone by the aminosilane and amino propyl trimethoxysilane The used membrane materials for removing sulfur are [3]. Their results showed that with increase of cross-linking mostly including hydrophobic membranes such as polyu- agent penetration flux is uniformly reduced. The effect of rethane, polyurea/polyurethane, polyamide, natural rubber, tetraethyl ortho silicate on the increasing selectivity in the polystyrene–butadiene and polydimethylsiloxane. Hydro- Polydimethylsiloxane membrane has been studied by Xu philic properties of the membranes clearly increase the et al. [4]. In another study, manufacturing of polydimethyl- selectivity to the sulfur compounds which usually are more siloxane and polyamide composite membrane in separation polar than hydrocarbons. The most common methods for of heptane from thiophene was studied [5]. The transport making membranes with high selectivity and flux include properties of gases in polydimethylsiloxane (PDMS)/zeolite cross-linking, blending, filling and copolymerization. Lin a mixed matrix membranes (MMMs) were determined based et al. studied the solubility of gasoline blending in polyeth- on pure gas permeation experiments in study of Rezakazemi ylene glycol [1]. They concluded that sulfur recovery rate et al. 2012. The permeation rates of C H, CH, CO , and H 3 8 4 2 2 by increasing the amount of cross-linking agent and the were evaluated through a dense homogeneous pure PDMS cross-linking time increases. Lin et al. used polyethylene membrane and PDMS/4A MMMs to assess the viability of glycol and polyurethane polymers for fluidized bed cata - these membranes for natural gas sweetening and hydrogen lytic cracking unit gasoline desulfurization [2]. Wu et al. purification. SEM investigations showed good adhesion improved the stability of the interface between the active of the polymer to the zeolite in MMMs. Permeation per- formance of the membranes was also investigated using a laboratory-scale gas separation apparatus and effects of * Amir Heydarinasab feed pressure, zeolite loading and pore size of zeolite on amir.heydarinasab@hotmail.com the gas separation performance of the MMMs were evalu- 1 ated [6]. Rezakazemi et  al. cross-linked polydimethylsi- Department of Chemical Engineering, Science and Research loxane (PDMS) membranes supported on cellulose acetate Branch, Islamic Azad University, Tehran, Iran 2 (CA) and polyamide (PA) microfiltration membranes were Department of Chemical Engineering, Marvdasht Branch, prepared by pre-wetting technique for pervaporation (PV) Islamic Azad University, Marvdasht, Iran Vol.:(0123456789) 1 3 178 International Journal of Industrial Chemistry (2018) 9:177–183 dehydration of ethanol. The experiments were carried out Fourier-transformed infrared spectroscopy (FTIR). The to investigate the effects of support layer and permselec - results showed that the thermal stability of these novel nano- tive thickness on the separation performance of membranes composite membranes was much better than that of the neat at different operating conditions particularly initial ethanol membrane thermodynamically, dipole–dipole interaction concentrations and temperatures. The results revealed that between the functional groups is the main parameter lead- increasing feed concentration and temperature increases ing to better dispersion and thermal stability [11]. Further- total permeation flux. PDMS/PA membrane showed bet- more, it was found that the separation properties of different ter overall performance than PDMS/CA membrane [7]. gases (H, C H, CO and CH ) across the nanocomposite 2 3 8 2 4 Chen et  al. investigated cross-linked polydimethylsilox- membranes were enhanced with increasing FS content. All ane (PDMS)–polyetherimide (PEI) composite membranes the improvements observed can be attributed to synergistic preparation, in which asymmetric microporous PEI mem- interactions between FS and POSS [12]. Rajesha et al. syn- brane prepared with phase inversion method acted as the thesized oxide–zeolite composite membranes for benzophe- microporous supporting layer in the flat-plate composite none-3 removal from water. They concluded that membrane membrane. Membrane characterization was conducted by performances were significantly improved after the addi- Fourier-transform infrared and scanning electronic micros- tion of ZnO–zeolite in the cellulose acetate solution [13]. copy analysis. The composite membranes were employed Ghasemian et al. used polyvinylidene fluoride (PVDF) and in pervaporation separation of n-heptane–thiophene mix- nano-porous silica particle. Their results show that PVDF/ tures. Effect of amount of PDMS, cross-linking temperature, SiO nano-composite membranes exhibited enhanced anti- amount of cross-linking agent, and cross-linking time on the fouling property compared to neat PVDF membrane [14]. separation efficiency of n -heptane–thiophene mixtures was Xu et al. manufactured a gradient cost-efficient composite investigated experimentally [8]. membrane. They concluded that when the additive amount Rostamizadeh et  al. investigated Gas permeability of OMWCNTs was 1 wt%, the composite membranes pre- through synthesized polydimethylsiloxane (PDMS)/zeo- sented an excellent flux [15]. lite 4A mixed matrix membranes (MMMs) with the aid of In this study, the total sulfur in diesel product of an artificial neural network (ANN) approach. Kinetic diameter oil refinery was reduced from 6380  ppm to 1700  ppm and critical temperature of permeating components (e.g., using composite membranes of PDMS, PDMS + PEG, H, CH, CO and C H ), zeolite content and upstream pres- PDMS + PES and PDMS + PAN, as well as the cross-linking 2 4 2 3 8 sure as input variables and gas permeability as output were technique by TEOS in a module of flat sheet membranes. inspected. Collected data of the experimental operation was The effect of operational variables such as cross-linking used to ANN training and optimum numbers of hidden lay- temperature and cross-linking time on the total flux of the ers and neurons were obtained by trial–error method. As a stream and total sulfur in the retentate stream was evaluated. result, ANN can be recommended for the modeling of gas transport through MMMs [9]. Rezakazemi and Mohammadi developed robust artifi- Materials and methods cial neural network (ANN) to forecast sorption of gases in membranes that comprised porous nanoparticles dispersed Materials homogenously within polymer matrix. The main purpose of this study was to predict sorption of light gases (H, CH , 2 4 To manufacture the composite membranes, the following CO ) within mixed matrix membranes (MMMs) as function of critical temperature, nanoparticles loading and upstream laboratory material were used: pressure. The prediction results were remarkably agreed with the experimental data with MSE of 0.00005 and cor- 1. Tetraethyl ortho-silicate (TEOS) with an average molecular weight of approximately 208 g/mol (Merk, relation coefficient of 0.9994 [10]. In other work of Rezakazemi et al., a facile strategy for Germany). 2. Oligomers of Polydimethylsiloxane (PDMS) with an the synthesis of binary fillers nanocomposite membranes containing fumed silica (FS) and octatrimethylsiloxy poly- average molecular weight of approximately 40,000 g/ mol and viscosity 5000 MPa s (Aldrich, USA). hedral oligomeric silsesquioxane (POSS) nanoparticles was proposed to prepare high-performance PDMS–FS–POSS 3. Polyethylene glycol (PEG) with an average molecu- lar weight of approximately 4000 g/mol (BASF, Ger- nanocomposite membranes. To fully explore the syner- gistic effect between POSS and FS nanoparticles, thermal many). 4. Polyethersulfone (PES) with an average molecular stability by thermo-gravimetric analysis (TGA) and disper- sion quality by scanning electron microscopy (SEM) were weight of about 58,000  g/mol (flakes, BASF, Ger - many). investigated, while the crosslinked network was studied by 1 3 International Journal of Industrial Chemistry (2018) 9:177–183 179 5. Polyacrylonitrile (PAN) with an average molecular layer and the film device is used. The solution to build a weight of about 45,000 g/mol (Merk, Germany). base film by deposition technique made by immersion; 6. Polyvinylpyrrolidone (PVP) k90 as a filler with an therefore, a 15% the mass of solution polyethersulfone average molecular weight of approximately 360,000 g/ and 3% the mass of the Polyvinylpyrrolidone as filler in mol (Merk, Germany). the dimethylacetamide solvent is made. This solution is 7. Dimethyl acetamide (DMac) as a solvent (Merk, Ger- built on the base of nano-filter asymmetric polyester, and many). after using the film immersed quickly in distilled water to 8. Dibutyltin dilaurate (fluka, Switzerland). remove residual dimethylacetamide. Membranes initially 9. Ammonia (Merk, Germany). are placed in the open air for 24 h and then to complete the 10. Asymmetric nano filter based membrane of polyester cross-linking process and evaporate the remaining solvent (plasmachemGmbH, Germany). at the time of cross-linking (0.5–2.5 h) determined and at 11. N-heptane (Romil, UK). the time of cross-linking time (65–85 °C) placed inside 12. SPAN 80 (MERK, Germany). an electric furnace. Finally, the membranes are washed 13. Distilled water. with distilled water and placed between sheets of filter paper and dried. All membranes before used in the mem- Composite membrane preparation brane module and the membrane performance be measured should be placed in a free of dust and dry environment. A certain amount of span 80 as surfactant, silicone propul- Laboratory devices for research is shown in Fig. 1. sion (tetraethyl-ortho-silicate) with weight percentages of Feed tank (position 1) is containing about three liters 8% with oligomers of polydimethylsiloxane and polyeth- of diesel with the total sulfur content of 6380 ppm. After ylene glycol in n-heptane (solvent) at room temperature using any appropriate membrane, the remaining diesel is for making homogeneous solution mixed together. Ammo- poured inside the feed tank and the feed will be replaced nia in water (anti-solvent) with half the molar concentra- with new diesel to experiment with new membrane. In tion of the solution is solved to build a solution with pH position 2, the pump has been used that leads diesel with 9. However, a certain amount of this solution is added different flow rates and pressures set (5–9 times) into the into a homogeneous solution under difficult conditions membrane module (position 5). Membrane modules is of stirring. Mass ratio between solvent and polymer is manufactured from stainless steel and membranes used about 3.5 and the mass ratio between the polymers used with active area of 2100 cm . The pressure gauges repre- in this study is equal. The use of ammonia as catalyst sents (position 4 and 6) the diesel and backflow pressures, cause agglomerate silica has been done at the interface of respectively. Needle valves are installed at 7 positions to water/homogeneous solution. After mixing for 30 min, a control the backflow and a valve is inserted in position 3 small amount of Dibutyltin dilaurate as bubble removing for the input flow to the module. The membranes in the is added to this mixture. The mass ratio between the poly- input feed to the modulus to be kept wet approximately 1 h mer, Dibutyltin dilaurate, Span 80 and the solution with before the start of each test to achieve steady state condi- pH 9 is 10/0.1/0.3/1, respectively. After removing bubbles tions. For each test approximately 3 h were taken and the in homogeneous solution, the solution is laying the base operating temperature range is between 65 and 85 °C. Fig. 1 Schematic diagram of experimental apparatus 1 3 180 International Journal of Industrial Chemistry (2018) 9:177–183 Fig. 2 The cross section morphology of the PDMS composite mem- Fig. 4 SEM images of the cross-section of composite PDMS mem- brane brane Fig. 5 The surface morphology of the PDMS composite membrane Fig. 3 Scanning electron microscope image of the composite mem- brane of PDMS PDMS with TEOS as agent, consisted of an ultrathin skin layer and a porous finger-like structure. The top dense layer is clearly demonstrated in Figs.  2 and 4. Using Soaking method, porosity of the membrane, 33.308%, Results and discussion was obtained. Furthermore, the thickness of the PDMS top layer was determined to be about 4.5 μm from the SEM Figures 2, 3, 4, 5 are scanning electron microscope images photograph by the scale tab. Note that, top-layer thickness of PDMS composite membrane at a temperature of cross- increased as the PDMS concentration increased. Also, the linking 75 °C and cross-linking time of one hour and the thickness of membrane support obtained as 130 μm. amount of TEOS 8% by weight. These images show the The surface morphology of the composite membrane porosity in internal layer of membrane. As demonstrated is shown in Fig. 5. From this figure, the originally porous in the SEM photographs, there is a clear boundary between surface was covered by a flat featureless PDMS layer, and the PDMS top layer and support layer. Meanwhile, the the top PDMS layer, functioning as the basis of selectiv- cross-sectional structure of the composite membrane of ity, had a nonporous and tight structure. The surface of the 1 3 International Journal of Industrial Chemistry (2018) 9:177–183 181 composite is dense and there is no pinhole or crack, which is important for practical application. Figure 6 shows that the total flux changes with the use of TEOS as cross-linking agent in the manufacture of mem- branes, which in accordance with Fig.  6 with increasing consumption of TEOS output flux from retentate stream is reduced. This result implied that, when the TEOS content increased, more TEOS chains occurred in cross-linking reaction, and the top membrane layer, functioning as the basis of permselectivity, became a nonporous and very tight structure. Accordingly, the free volume of PDMS composite membrane decreased, which led to the flux decrease. Mean- while, top-layer thickness increased as the TEOS concen- tration increased. By all given reasons, the flux decreased as TEOS content increased. According to Fig. 6, it can be seen that the highest flux is related to the blending polymers PDMS + PEG, which it uses the technique of blending poly- Fig. 7 Sulfur changes in the back flow using mass percentage of mers with the PDMS as a hydrophobic polymer and PEG as crosslinking agent, at 70 °C, crosslinking time of 1 h and membrane a hydrophilic polymer. module pump pressure in 7 bar Figure 7 shows sulfur is reduced in the back flow with the use of TEOS as a cross-linking agent. According to Fig. 7, As cross-linking temperature (65–85 °C) increases, the increasing the amount of TEOS in manufacturing composite membranes reduces the amount of sulfur in the return flow. degree of equilibrium swelling decreases and thus the selec- tivity of the composite membrane increases. Some obser- Because by increasing the amount of TEOS as cross-linking agent, the selectivity of composite membrane increased and vations show reducing the chain length between the cross- linking. Reducing chains between cross-linking increases the consequently total sulfur in retentate flow decreases. Figure  8 shows sulfur changes in the back flow with elastic resistance of swelling stress in composite membranes and thus the swelling degree of the membrane reduces. cross-linking temperature that 8% weight of TEOS is used as cross-linking agent in the construction of composite mem- Thereby, reducing the degree of swelling increases the selec- tivity of the composite membranes to sulfur compounds and branes, which according to Fig. 8 increasing cross-linking temperature reduces total sulfur flux. ultimately the amount of sulfur in the backflow reduces. Fig. 6 Total flux changes with consuming value of mass percentage Fig. 8 Total flux changes with crosslinking temperature at 8% mass of crosslinking agent at 70 °C and crosslinking time of 1 h and mem- of the cross-linking agent and crosslinking time of 1 h and membrane brane module pump pressure in 7 bar module pump pressure in 7 bar 1 3 182 International Journal of Industrial Chemistry (2018) 9:177–183 Fig. 11 Sulfur enrichment factor as a function of time Fig. 9 Total flux changes with crosslinking time at 8% mass of cross- linking agent and crosslinking temperature of 70  °C and membrane module pump pressure in 7 bar Fig. 12 Sulfur enrichment factor as a function of temperature ratio of total sulfur content of permeate to total sulfur con- Fig. 10 Sulfur enrichment factor as a function of TEOS percentage tent of feed samples. Figure 9 shows total flux changes with cross-linking time in the case of 8% weight TEOS as a cross-linking agent is Conclusion used in the construction of composite membranes. Accord- ing to Fig. 9, the total flux is reduced with increasing cross- In this work, PDMS, PEG, PES and PAN composite mem- linking time from 0.5 to 2.5 h. branes have been prepared to reduce sulfur diesel fuel using The effects of crosslinking dosage, crosslinking time and cross-linking technique by TEOS cross-linking agent in vari- temperature are illustrated in Figs. 10, 11, 12. As can also ous mass percentages. According to results it can be seen be seen in these figures, the blended PDMS + PEG polymer that most of the total flux is related to composite membranes shows a higher enrichment factor than other cases. In con- of PEG + PDMS (0.7732 L/h). In addition, it is observed that sequence to previous descriptions, when the total sulfur in the lowest amount of sulfur in the back flow related to the retentate flow decreases so the enrichment factor will be state in which the composite membranes PEG + PDMS had increased. The sulfur enrichment factor is defined as the been used (1780 ppm). Increasing use of TEOS reduces the 1 3 International Journal of Industrial Chemistry (2018) 9:177–183 183 composite membranes. Desalination. https ://doi.org/10.1016/j. total flux passing retentate stream, however, the amount of desal .2010.03.035 sulfur in the return flow is also reduced. It can be noted that 5. Lin L, Zhang Y, Li H (2010) Pervaporation and sorption behavior by increasing the amount of TEOS from 8 to 22 wt%. in the of zeolite filled polyethylene glycol hybrid membranes for the case of composite membranes PDMS + PAN, PDMS + PES, removal of thiophene species. J Colloid Interface Sci. https ://doi. org/10.1016/j.jcis.2010.06.031 PDMS + PEG, PDMS, the flux changed from 0.5412 to 6. Reza Kazemi M, Shahidi K, Mohammadi T (2012) Hydrogen 0.5217 L/h, 0.6215 to 0.6033 L/h, 0.7583 to 0.6211 L/h separation and purification using crosslinkable PDMS/zeolite A and 0.6813 to 0.6314 L/h, respectively; while, the differ - nanoparticles mixed matrix membranes. Inter J Hyd Energy. https ences between the total flux passing through the composite ://doi.org/10.1016/j.ijhyd ene.2012.06.104 7. Reza Kazemi M, Shahidi K, Mohammadi T (2015)  Synthetic membranes are too much in the range of 1–8 wt% relative PDMS composite membranes for pervaporation dehydration to 15–22 wt%. Also by increasing use of TEOS from 8% to of ethanol. Desal Water Treat. https :// doi.o r g/10. 1080/1 9443 22 wt% in the case of composite membranes PDMS + PAN, 994.2014.88703 6 PDMS + PES, PDMS + PEG, PDMS, the amount of sulfur 8. Chen J, Li J, Qi R, Ye H, Chen C (2010) Pervaporation separa- tion of thiophene–heptane mixtures with poly dimethyl siloxane in the back flow is changed from 2035 to 1982 ppm, 1933 (PDMS) membrane for desulfurization. App Biochem Biotech. to 1921 ppm, 1825 to 1811 ppm, 2011 to 1972 ppm, respec- https ://doi.org/10.1007/s1201 0-008-8368-z tively; while, the differences between the amount of sulfur 9. Rostamizadeh AM, Reza Kazemi M, Shahidi K, Mohammadi T in the back flow is too much in the range of 1–8 wt% relative (2013) Gas permeation through H2-selective mixed matrix mem- branes: experimental and neural network modeling. Inter J Hyd to 15–22 wt%. Energy. https ://doi.org/10.1016/j.ijhyd ene.2012.10.069 10. Reza Kazemi M, Mohammadi T (2013) Gas sorption in H2-selec- Acknowledgement The authors gratefully acknowledge the scientific tive mixed matrix membranes: Experimental and neural network institutes and companies that they sincerely helped to this research. modeling. Inter J Hydro Energy. https ://doi.org/10.1016/j.ijhyd Among them can be mentioned the following: 1-Esfahan Oil Refining ene.2013.08.062 Company, 2-Iran Polymer and Petrochemical Institute (IPPI), 3-Chem- 11. Reza Kazemi M, Vatani A, Mohammadi T (2016) Synthesis and istry & Chemical Engineering Research Center of Iran (CCERCI), gas transport properties of crosslinked poly(dimethylsiloxane) 4-Razi University. nanocomposite membranes using octatrimethylsiloxy POSS nanoparticles. J Nat Gas Sci Eng. https ://doi.org/10.1016/j.jngse Open Access This article is distributed under the terms of the Crea- .2016.01.033 tive Commons Attribution 4.0 International License (http://creat iveco 12. Reza Kazemi M, Vatani A, Mohammadi T (2015) Synergistic mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- interactions between POSS and fumed silica and their effect on tion, and reproduction in any medium, provided you give appropriate the properties of crosslinked PDMS nanocomposite membranes. credit to the original author(s) and the source, provide a link to the RSC Adv. https ://doi.org/10.1039/C5RA1 3609A Creative Commons license, and indicate if changes were made. 13. Rajesha BJ, Halali V, Geetha R, Padakia M, Nazri NAM (2017) Effective composite membranes of cellulose acetate for removal of benzophenone-3. J Water Proc Eng. https ://doi.org/10.1016/j. jwpe.2017.06.003 References 14. Ghasemian S, Sahari M, Ali Barzegar M, Ahmadi G (2017) Omega-3 PUFA concentration by a novel PVDF nano-composite 1. Lin L, Kong Y, Xie K (2008) Polyethylene glycol/polyurethane membrane filled with nano-porous silica particles. Food Chem. blend membranes for gasoline desulphurization by pervaporation https ://doi.org/10.1016/j.foodc hem.2017.02.135 technique. Sep Purif Technol. https ://doi.or g/10.1016/j.seppu 15. Xu Z, Li X, Teng K, Zhou B, Ma M, Shan M, Jiao K, Qian X, r.2007.10.020 Fan J (2017) High flux and rejection of hierarchical composite 2. Lin L, Kong Y, Zhang Y (2008) Poly ethylene glycol/polyurethane membranes based on carbon nanotube network and ultrathin elec- blend membranes for gasoline desulphurization by pervapora- trospun nanofibrous layer for dye removal. J Mem Sci. https://doi. tion technique. J Member Sci. https ://doi.org/10.1016/j.memsc org/10.1016/j.memsc i.2017.04.029 i.2008.08.019 3. Wu H, Zhang X, Xu D, Li B, Jiang Z (2009) Enhancing the Publisher’s Note Springer Nature remains neutral with regard to interfacial stability and solvent-resistant property of PDMS/PES jurisdictional claims in published maps and institutional affiliations. composite membrane by introducing a bifunctional aminosilane. J Membr Sci. https ://doi.org/10.1016/j.memsc i.2009.03.043 4. Xu R, Liu G, Dong X, Jin W (2010) Pervaporation separation of n-octane/thiophene mixtures using poly dimethyl siloxane/ceramic 1 3 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Industrial Chemistry Springer Journals

Experimental survey of temperature, time and cross-linking agent effects on polydimethylsiloxane composite membranes performances in sulfur removal

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Abstract

Four types of the multi composite membranes were fabricated to decrease the sulfur content in diesel fuel, which the inves- tigated polymers are polydimethylsiloxane (PDMS), polyethyleneglycol (PEG), polyethersulfonic (PES) and cross-linked polyacrylonitrile (PAN) with tetra-ethyl-ortho-silicate (TEOS). The effects of the operating parameters such as the cross- linking temperature (65–85 °C) and cross-linking time (0.5–2.5 h) were studied on the membranes performances. The results showed that the sulfur selectivity of PDMS/PEG/PES/PAN membranes were improved through increasing temperature and time. In addition, most of the total flux and the lowest amount of sulfur in the back flow is related to composite membranes of PEG + PDMS. Keywords Composite membrane · Sulfur content removal · Cross-linking agent · PDMS · PEG · PAN Introduction layer of polydimethylsiloxane and base layer of polyethersul- fone by the aminosilane and amino propyl trimethoxysilane The used membrane materials for removing sulfur are [3]. Their results showed that with increase of cross-linking mostly including hydrophobic membranes such as polyu- agent penetration flux is uniformly reduced. The effect of rethane, polyurea/polyurethane, polyamide, natural rubber, tetraethyl ortho silicate on the increasing selectivity in the polystyrene–butadiene and polydimethylsiloxane. Hydro- Polydimethylsiloxane membrane has been studied by Xu philic properties of the membranes clearly increase the et al. [4]. In another study, manufacturing of polydimethyl- selectivity to the sulfur compounds which usually are more siloxane and polyamide composite membrane in separation polar than hydrocarbons. The most common methods for of heptane from thiophene was studied [5]. The transport making membranes with high selectivity and flux include properties of gases in polydimethylsiloxane (PDMS)/zeolite cross-linking, blending, filling and copolymerization. Lin a mixed matrix membranes (MMMs) were determined based et al. studied the solubility of gasoline blending in polyeth- on pure gas permeation experiments in study of Rezakazemi ylene glycol [1]. They concluded that sulfur recovery rate et al. 2012. The permeation rates of C H, CH, CO , and H 3 8 4 2 2 by increasing the amount of cross-linking agent and the were evaluated through a dense homogeneous pure PDMS cross-linking time increases. Lin et al. used polyethylene membrane and PDMS/4A MMMs to assess the viability of glycol and polyurethane polymers for fluidized bed cata - these membranes for natural gas sweetening and hydrogen lytic cracking unit gasoline desulfurization [2]. Wu et al. purification. SEM investigations showed good adhesion improved the stability of the interface between the active of the polymer to the zeolite in MMMs. Permeation per- formance of the membranes was also investigated using a laboratory-scale gas separation apparatus and effects of * Amir Heydarinasab feed pressure, zeolite loading and pore size of zeolite on amir.heydarinasab@hotmail.com the gas separation performance of the MMMs were evalu- 1 ated [6]. Rezakazemi et  al. cross-linked polydimethylsi- Department of Chemical Engineering, Science and Research loxane (PDMS) membranes supported on cellulose acetate Branch, Islamic Azad University, Tehran, Iran 2 (CA) and polyamide (PA) microfiltration membranes were Department of Chemical Engineering, Marvdasht Branch, prepared by pre-wetting technique for pervaporation (PV) Islamic Azad University, Marvdasht, Iran Vol.:(0123456789) 1 3 178 International Journal of Industrial Chemistry (2018) 9:177–183 dehydration of ethanol. The experiments were carried out Fourier-transformed infrared spectroscopy (FTIR). The to investigate the effects of support layer and permselec - results showed that the thermal stability of these novel nano- tive thickness on the separation performance of membranes composite membranes was much better than that of the neat at different operating conditions particularly initial ethanol membrane thermodynamically, dipole–dipole interaction concentrations and temperatures. The results revealed that between the functional groups is the main parameter lead- increasing feed concentration and temperature increases ing to better dispersion and thermal stability [11]. Further- total permeation flux. PDMS/PA membrane showed bet- more, it was found that the separation properties of different ter overall performance than PDMS/CA membrane [7]. gases (H, C H, CO and CH ) across the nanocomposite 2 3 8 2 4 Chen et  al. investigated cross-linked polydimethylsilox- membranes were enhanced with increasing FS content. All ane (PDMS)–polyetherimide (PEI) composite membranes the improvements observed can be attributed to synergistic preparation, in which asymmetric microporous PEI mem- interactions between FS and POSS [12]. Rajesha et al. syn- brane prepared with phase inversion method acted as the thesized oxide–zeolite composite membranes for benzophe- microporous supporting layer in the flat-plate composite none-3 removal from water. They concluded that membrane membrane. Membrane characterization was conducted by performances were significantly improved after the addi- Fourier-transform infrared and scanning electronic micros- tion of ZnO–zeolite in the cellulose acetate solution [13]. copy analysis. The composite membranes were employed Ghasemian et al. used polyvinylidene fluoride (PVDF) and in pervaporation separation of n-heptane–thiophene mix- nano-porous silica particle. Their results show that PVDF/ tures. Effect of amount of PDMS, cross-linking temperature, SiO nano-composite membranes exhibited enhanced anti- amount of cross-linking agent, and cross-linking time on the fouling property compared to neat PVDF membrane [14]. separation efficiency of n -heptane–thiophene mixtures was Xu et al. manufactured a gradient cost-efficient composite investigated experimentally [8]. membrane. They concluded that when the additive amount Rostamizadeh et  al. investigated Gas permeability of OMWCNTs was 1 wt%, the composite membranes pre- through synthesized polydimethylsiloxane (PDMS)/zeo- sented an excellent flux [15]. lite 4A mixed matrix membranes (MMMs) with the aid of In this study, the total sulfur in diesel product of an artificial neural network (ANN) approach. Kinetic diameter oil refinery was reduced from 6380  ppm to 1700  ppm and critical temperature of permeating components (e.g., using composite membranes of PDMS, PDMS + PEG, H, CH, CO and C H ), zeolite content and upstream pres- PDMS + PES and PDMS + PAN, as well as the cross-linking 2 4 2 3 8 sure as input variables and gas permeability as output were technique by TEOS in a module of flat sheet membranes. inspected. Collected data of the experimental operation was The effect of operational variables such as cross-linking used to ANN training and optimum numbers of hidden lay- temperature and cross-linking time on the total flux of the ers and neurons were obtained by trial–error method. As a stream and total sulfur in the retentate stream was evaluated. result, ANN can be recommended for the modeling of gas transport through MMMs [9]. Rezakazemi and Mohammadi developed robust artifi- Materials and methods cial neural network (ANN) to forecast sorption of gases in membranes that comprised porous nanoparticles dispersed Materials homogenously within polymer matrix. The main purpose of this study was to predict sorption of light gases (H, CH , 2 4 To manufacture the composite membranes, the following CO ) within mixed matrix membranes (MMMs) as function of critical temperature, nanoparticles loading and upstream laboratory material were used: pressure. The prediction results were remarkably agreed with the experimental data with MSE of 0.00005 and cor- 1. Tetraethyl ortho-silicate (TEOS) with an average molecular weight of approximately 208 g/mol (Merk, relation coefficient of 0.9994 [10]. In other work of Rezakazemi et al., a facile strategy for Germany). 2. Oligomers of Polydimethylsiloxane (PDMS) with an the synthesis of binary fillers nanocomposite membranes containing fumed silica (FS) and octatrimethylsiloxy poly- average molecular weight of approximately 40,000 g/ mol and viscosity 5000 MPa s (Aldrich, USA). hedral oligomeric silsesquioxane (POSS) nanoparticles was proposed to prepare high-performance PDMS–FS–POSS 3. Polyethylene glycol (PEG) with an average molecu- lar weight of approximately 4000 g/mol (BASF, Ger- nanocomposite membranes. To fully explore the syner- gistic effect between POSS and FS nanoparticles, thermal many). 4. Polyethersulfone (PES) with an average molecular stability by thermo-gravimetric analysis (TGA) and disper- sion quality by scanning electron microscopy (SEM) were weight of about 58,000  g/mol (flakes, BASF, Ger - many). investigated, while the crosslinked network was studied by 1 3 International Journal of Industrial Chemistry (2018) 9:177–183 179 5. Polyacrylonitrile (PAN) with an average molecular layer and the film device is used. The solution to build a weight of about 45,000 g/mol (Merk, Germany). base film by deposition technique made by immersion; 6. Polyvinylpyrrolidone (PVP) k90 as a filler with an therefore, a 15% the mass of solution polyethersulfone average molecular weight of approximately 360,000 g/ and 3% the mass of the Polyvinylpyrrolidone as filler in mol (Merk, Germany). the dimethylacetamide solvent is made. This solution is 7. Dimethyl acetamide (DMac) as a solvent (Merk, Ger- built on the base of nano-filter asymmetric polyester, and many). after using the film immersed quickly in distilled water to 8. Dibutyltin dilaurate (fluka, Switzerland). remove residual dimethylacetamide. Membranes initially 9. Ammonia (Merk, Germany). are placed in the open air for 24 h and then to complete the 10. Asymmetric nano filter based membrane of polyester cross-linking process and evaporate the remaining solvent (plasmachemGmbH, Germany). at the time of cross-linking (0.5–2.5 h) determined and at 11. N-heptane (Romil, UK). the time of cross-linking time (65–85 °C) placed inside 12. SPAN 80 (MERK, Germany). an electric furnace. Finally, the membranes are washed 13. Distilled water. with distilled water and placed between sheets of filter paper and dried. All membranes before used in the mem- Composite membrane preparation brane module and the membrane performance be measured should be placed in a free of dust and dry environment. A certain amount of span 80 as surfactant, silicone propul- Laboratory devices for research is shown in Fig. 1. sion (tetraethyl-ortho-silicate) with weight percentages of Feed tank (position 1) is containing about three liters 8% with oligomers of polydimethylsiloxane and polyeth- of diesel with the total sulfur content of 6380 ppm. After ylene glycol in n-heptane (solvent) at room temperature using any appropriate membrane, the remaining diesel is for making homogeneous solution mixed together. Ammo- poured inside the feed tank and the feed will be replaced nia in water (anti-solvent) with half the molar concentra- with new diesel to experiment with new membrane. In tion of the solution is solved to build a solution with pH position 2, the pump has been used that leads diesel with 9. However, a certain amount of this solution is added different flow rates and pressures set (5–9 times) into the into a homogeneous solution under difficult conditions membrane module (position 5). Membrane modules is of stirring. Mass ratio between solvent and polymer is manufactured from stainless steel and membranes used about 3.5 and the mass ratio between the polymers used with active area of 2100 cm . The pressure gauges repre- in this study is equal. The use of ammonia as catalyst sents (position 4 and 6) the diesel and backflow pressures, cause agglomerate silica has been done at the interface of respectively. Needle valves are installed at 7 positions to water/homogeneous solution. After mixing for 30 min, a control the backflow and a valve is inserted in position 3 small amount of Dibutyltin dilaurate as bubble removing for the input flow to the module. The membranes in the is added to this mixture. The mass ratio between the poly- input feed to the modulus to be kept wet approximately 1 h mer, Dibutyltin dilaurate, Span 80 and the solution with before the start of each test to achieve steady state condi- pH 9 is 10/0.1/0.3/1, respectively. After removing bubbles tions. For each test approximately 3 h were taken and the in homogeneous solution, the solution is laying the base operating temperature range is between 65 and 85 °C. Fig. 1 Schematic diagram of experimental apparatus 1 3 180 International Journal of Industrial Chemistry (2018) 9:177–183 Fig. 2 The cross section morphology of the PDMS composite mem- Fig. 4 SEM images of the cross-section of composite PDMS mem- brane brane Fig. 5 The surface morphology of the PDMS composite membrane Fig. 3 Scanning electron microscope image of the composite mem- brane of PDMS PDMS with TEOS as agent, consisted of an ultrathin skin layer and a porous finger-like structure. The top dense layer is clearly demonstrated in Figs.  2 and 4. Using Soaking method, porosity of the membrane, 33.308%, Results and discussion was obtained. Furthermore, the thickness of the PDMS top layer was determined to be about 4.5 μm from the SEM Figures 2, 3, 4, 5 are scanning electron microscope images photograph by the scale tab. Note that, top-layer thickness of PDMS composite membrane at a temperature of cross- increased as the PDMS concentration increased. Also, the linking 75 °C and cross-linking time of one hour and the thickness of membrane support obtained as 130 μm. amount of TEOS 8% by weight. These images show the The surface morphology of the composite membrane porosity in internal layer of membrane. As demonstrated is shown in Fig. 5. From this figure, the originally porous in the SEM photographs, there is a clear boundary between surface was covered by a flat featureless PDMS layer, and the PDMS top layer and support layer. Meanwhile, the the top PDMS layer, functioning as the basis of selectiv- cross-sectional structure of the composite membrane of ity, had a nonporous and tight structure. The surface of the 1 3 International Journal of Industrial Chemistry (2018) 9:177–183 181 composite is dense and there is no pinhole or crack, which is important for practical application. Figure 6 shows that the total flux changes with the use of TEOS as cross-linking agent in the manufacture of mem- branes, which in accordance with Fig.  6 with increasing consumption of TEOS output flux from retentate stream is reduced. This result implied that, when the TEOS content increased, more TEOS chains occurred in cross-linking reaction, and the top membrane layer, functioning as the basis of permselectivity, became a nonporous and very tight structure. Accordingly, the free volume of PDMS composite membrane decreased, which led to the flux decrease. Mean- while, top-layer thickness increased as the TEOS concen- tration increased. By all given reasons, the flux decreased as TEOS content increased. According to Fig. 6, it can be seen that the highest flux is related to the blending polymers PDMS + PEG, which it uses the technique of blending poly- Fig. 7 Sulfur changes in the back flow using mass percentage of mers with the PDMS as a hydrophobic polymer and PEG as crosslinking agent, at 70 °C, crosslinking time of 1 h and membrane a hydrophilic polymer. module pump pressure in 7 bar Figure 7 shows sulfur is reduced in the back flow with the use of TEOS as a cross-linking agent. According to Fig. 7, As cross-linking temperature (65–85 °C) increases, the increasing the amount of TEOS in manufacturing composite membranes reduces the amount of sulfur in the return flow. degree of equilibrium swelling decreases and thus the selec- tivity of the composite membrane increases. Some obser- Because by increasing the amount of TEOS as cross-linking agent, the selectivity of composite membrane increased and vations show reducing the chain length between the cross- linking. Reducing chains between cross-linking increases the consequently total sulfur in retentate flow decreases. Figure  8 shows sulfur changes in the back flow with elastic resistance of swelling stress in composite membranes and thus the swelling degree of the membrane reduces. cross-linking temperature that 8% weight of TEOS is used as cross-linking agent in the construction of composite mem- Thereby, reducing the degree of swelling increases the selec- tivity of the composite membranes to sulfur compounds and branes, which according to Fig. 8 increasing cross-linking temperature reduces total sulfur flux. ultimately the amount of sulfur in the backflow reduces. Fig. 6 Total flux changes with consuming value of mass percentage Fig. 8 Total flux changes with crosslinking temperature at 8% mass of crosslinking agent at 70 °C and crosslinking time of 1 h and mem- of the cross-linking agent and crosslinking time of 1 h and membrane brane module pump pressure in 7 bar module pump pressure in 7 bar 1 3 182 International Journal of Industrial Chemistry (2018) 9:177–183 Fig. 11 Sulfur enrichment factor as a function of time Fig. 9 Total flux changes with crosslinking time at 8% mass of cross- linking agent and crosslinking temperature of 70  °C and membrane module pump pressure in 7 bar Fig. 12 Sulfur enrichment factor as a function of temperature ratio of total sulfur content of permeate to total sulfur con- Fig. 10 Sulfur enrichment factor as a function of TEOS percentage tent of feed samples. Figure 9 shows total flux changes with cross-linking time in the case of 8% weight TEOS as a cross-linking agent is Conclusion used in the construction of composite membranes. Accord- ing to Fig. 9, the total flux is reduced with increasing cross- In this work, PDMS, PEG, PES and PAN composite mem- linking time from 0.5 to 2.5 h. branes have been prepared to reduce sulfur diesel fuel using The effects of crosslinking dosage, crosslinking time and cross-linking technique by TEOS cross-linking agent in vari- temperature are illustrated in Figs. 10, 11, 12. As can also ous mass percentages. According to results it can be seen be seen in these figures, the blended PDMS + PEG polymer that most of the total flux is related to composite membranes shows a higher enrichment factor than other cases. In con- of PEG + PDMS (0.7732 L/h). In addition, it is observed that sequence to previous descriptions, when the total sulfur in the lowest amount of sulfur in the back flow related to the retentate flow decreases so the enrichment factor will be state in which the composite membranes PEG + PDMS had increased. The sulfur enrichment factor is defined as the been used (1780 ppm). Increasing use of TEOS reduces the 1 3 International Journal of Industrial Chemistry (2018) 9:177–183 183 composite membranes. Desalination. https ://doi.org/10.1016/j. total flux passing retentate stream, however, the amount of desal .2010.03.035 sulfur in the return flow is also reduced. It can be noted that 5. Lin L, Zhang Y, Li H (2010) Pervaporation and sorption behavior by increasing the amount of TEOS from 8 to 22 wt%. in the of zeolite filled polyethylene glycol hybrid membranes for the case of composite membranes PDMS + PAN, PDMS + PES, removal of thiophene species. J Colloid Interface Sci. https ://doi. org/10.1016/j.jcis.2010.06.031 PDMS + PEG, PDMS, the flux changed from 0.5412 to 6. Reza Kazemi M, Shahidi K, Mohammadi T (2012) Hydrogen 0.5217 L/h, 0.6215 to 0.6033 L/h, 0.7583 to 0.6211 L/h separation and purification using crosslinkable PDMS/zeolite A and 0.6813 to 0.6314 L/h, respectively; while, the differ - nanoparticles mixed matrix membranes. Inter J Hyd Energy. https ences between the total flux passing through the composite ://doi.org/10.1016/j.ijhyd ene.2012.06.104 7. Reza Kazemi M, Shahidi K, Mohammadi T (2015)  Synthetic membranes are too much in the range of 1–8 wt% relative PDMS composite membranes for pervaporation dehydration to 15–22 wt%. Also by increasing use of TEOS from 8% to of ethanol. Desal Water Treat. https :// doi.o r g/10. 1080/1 9443 22 wt% in the case of composite membranes PDMS + PAN, 994.2014.88703 6 PDMS + PES, PDMS + PEG, PDMS, the amount of sulfur 8. Chen J, Li J, Qi R, Ye H, Chen C (2010) Pervaporation separa- tion of thiophene–heptane mixtures with poly dimethyl siloxane in the back flow is changed from 2035 to 1982 ppm, 1933 (PDMS) membrane for desulfurization. App Biochem Biotech. to 1921 ppm, 1825 to 1811 ppm, 2011 to 1972 ppm, respec- https ://doi.org/10.1007/s1201 0-008-8368-z tively; while, the differences between the amount of sulfur 9. Rostamizadeh AM, Reza Kazemi M, Shahidi K, Mohammadi T in the back flow is too much in the range of 1–8 wt% relative (2013) Gas permeation through H2-selective mixed matrix mem- branes: experimental and neural network modeling. Inter J Hyd to 15–22 wt%. Energy. https ://doi.org/10.1016/j.ijhyd ene.2012.10.069 10. Reza Kazemi M, Mohammadi T (2013) Gas sorption in H2-selec- Acknowledgement The authors gratefully acknowledge the scientific tive mixed matrix membranes: Experimental and neural network institutes and companies that they sincerely helped to this research. modeling. Inter J Hydro Energy. https ://doi.org/10.1016/j.ijhyd Among them can be mentioned the following: 1-Esfahan Oil Refining ene.2013.08.062 Company, 2-Iran Polymer and Petrochemical Institute (IPPI), 3-Chem- 11. Reza Kazemi M, Vatani A, Mohammadi T (2016) Synthesis and istry & Chemical Engineering Research Center of Iran (CCERCI), gas transport properties of crosslinked poly(dimethylsiloxane) 4-Razi University. nanocomposite membranes using octatrimethylsiloxy POSS nanoparticles. J Nat Gas Sci Eng. https ://doi.org/10.1016/j.jngse Open Access This article is distributed under the terms of the Crea- .2016.01.033 tive Commons Attribution 4.0 International License (http://creat iveco 12. Reza Kazemi M, Vatani A, Mohammadi T (2015) Synergistic mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- interactions between POSS and fumed silica and their effect on tion, and reproduction in any medium, provided you give appropriate the properties of crosslinked PDMS nanocomposite membranes. credit to the original author(s) and the source, provide a link to the RSC Adv. https ://doi.org/10.1039/C5RA1 3609A Creative Commons license, and indicate if changes were made. 13. Rajesha BJ, Halali V, Geetha R, Padakia M, Nazri NAM (2017) Effective composite membranes of cellulose acetate for removal of benzophenone-3. J Water Proc Eng. https ://doi.org/10.1016/j. jwpe.2017.06.003 References 14. Ghasemian S, Sahari M, Ali Barzegar M, Ahmadi G (2017) Omega-3 PUFA concentration by a novel PVDF nano-composite 1. Lin L, Kong Y, Xie K (2008) Polyethylene glycol/polyurethane membrane filled with nano-porous silica particles. Food Chem. blend membranes for gasoline desulphurization by pervaporation https ://doi.org/10.1016/j.foodc hem.2017.02.135 technique. Sep Purif Technol. https ://doi.or g/10.1016/j.seppu 15. Xu Z, Li X, Teng K, Zhou B, Ma M, Shan M, Jiao K, Qian X, r.2007.10.020 Fan J (2017) High flux and rejection of hierarchical composite 2. Lin L, Kong Y, Zhang Y (2008) Poly ethylene glycol/polyurethane membranes based on carbon nanotube network and ultrathin elec- blend membranes for gasoline desulphurization by pervapora- trospun nanofibrous layer for dye removal. J Mem Sci. https://doi. tion technique. J Member Sci. https ://doi.org/10.1016/j.memsc org/10.1016/j.memsc i.2017.04.029 i.2008.08.019 3. Wu H, Zhang X, Xu D, Li B, Jiang Z (2009) Enhancing the Publisher’s Note Springer Nature remains neutral with regard to interfacial stability and solvent-resistant property of PDMS/PES jurisdictional claims in published maps and institutional affiliations. composite membrane by introducing a bifunctional aminosilane. J Membr Sci. https ://doi.org/10.1016/j.memsc i.2009.03.043 4. Xu R, Liu G, Dong X, Jin W (2010) Pervaporation separation of n-octane/thiophene mixtures using poly dimethyl siloxane/ceramic 1 3

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International Journal of Industrial ChemistrySpringer Journals

Published: Jun 6, 2018

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