Increasing Feed Pressure Research Articles

Computational simulation of gas separation using nonporous polymeric membranes: Experimental and theoretical studies

In this study, preparation and simulation of polydimethylsiloxane (PDMS) membranes for gas separation is carried out. The membranes are synthesized by solution‐casting method via silicon oil as precursor. Gas permeation experiments for single gases of CH4 and N2 were conducted at different feed pressures (2–10 bars). PDMS membrane as a rubbery polymer showed that are more permeable toward more condensable gases, i.e., CH4 compared to N2. It was indicated that increasing feed pressure enhances permeability of CH4 through the membrane slightly, but the permeability of nitrogen was almost constant over enhancement of feed pressure. Moreover, a mathematical model was developed to predict the permeation of gases across PDMS membrane. The model is based on solving conservation equations for gases in the membrane phase. Finite element analysis was utilized for numerical simulation of the governing equations. The simulation results were used to predict the concentration of gases inside the membrane. POLYM. ENG. SCI., 55:54–59, 2015. © 2014 Society of Plastics Engineers

Preparation, characterization and gas permeation properties of PDMS/PEI composite asymmetric membrane for effective separation of hydrogen from H2/CH4 mixed gas

In this work, PDMS/PEI membranes were synthesized and sorption and permeation of H2/CH4 mixture were studied. The influence of pressure, temperature and feed composition were investigated. It was shown that permeances increased and selectivity decreased with an increment in the feed temperature. Increasing feed pressure caused a decline in gas permeance and increased selectivity. Higher concentrations of hydrogen in the feed declined the selectivity. The effect of different non-solvents was explained by their effect on precipitation time and it was concluded that water made the membrane denser while isopropanol forms a sponge-like structure. Coagulation bath temperature made the membrane denser. Film casting and dip-coating techniques were used to prepare selective membranes. Obtained selectivity results introduced dip-coating as a better method than film casting. Sequential coating improved selectivity of the prepared membrane. Finally, sequential coating with different concentrations was applied and enhanced selectivity significantly from about 22 to more than 70.

Use of dynamic membranes for the preparation of vitamin E-loaded lipid particles: An alternative to prevent fouling observed in classical cross-flow emulsification

Solid lipid particles (SLP) were introduced at the beginning of the 1990s as an alternative to encapsulation systems such as emulsions and liposomes used in cosmetic and pharmaceutical preparations. The present paper investigated for the first time the preparation of SLP based on premix emulsification with packed beds of micron-sized glass beads. A coarse pre-emulsion was prepared by mixing the aqueous phase (water and Tween 80) and the lipid phase (Precirol and vitamin E) under magnetic stirring at 1200rpm during 15min, followed by passing the premix through the glass beads layer. SLP were formed by cooling to room temperature of the final emulsion.SLP were successfully produced under various conditions, but was most optimally carried out by extruding a coarse O/W emulsion 6 times under a pressure of 2bar through a dynamic membrane. For example, when a 2mm layer of glass beads sized 63μm was used, the premix size of 5μm was reduced to 1.5μm. It was found that particle size tended to decrease with increasing feed pressure, increasing number of passes, decreasing glass bead size and decreasing bed height. Even more importantly, the dynamic membrane was hardly prone to fouling compared to the membranes used in traditional cross-flow emulsification which typically need small pore size for the production of particles of similar size. In addition, the small beads could be easily cleaned by disintegrating the bed. The preparation process developed was easy to use, easy to scale-up, and the particle size could be controlled by appropriate choice of process parameters.

Analysis of permeate pressure build-up effects on separation performance of asymmetric hollow fiber membranes

The study rectifies some perceptions about pressure build-up in hollow fiber membranes. It is a general intuition that operating at higher pressures permeates more gases, and sometimes the membrane module is tested or characterized at lower pressures to reduce gas consumption. It is also perceived that higher pressure build-up occurs at higher feed pressures, and membrane performance deteriorates at higher feed pressures. In this study, the apparent and intrinsic permeances of H2 and N2 in asymmetric cellulose acetate-based hollow fiber membranes were evaluated from gas permeation experiments and numerical analysis. It was shown that though the permeate pressure build-up increases as the feed pressure increases, the effect of the permeate pressure build-up on the membrane performance is actually reduced at higher feed pressures. Membrane performs close to its intrinsic separation properties if it is operated at high feed pressures, under which conditions the effect of pressure build-up on the membrane performance is minimized. The pressure build-up effect was further investigated by evaluating the percentage loss in the driving force due to permeate pressure build-up, and it was found that percentage loss in driving force is less at higher feed pressures than that at lower feed pressures.

Preparation and Characterization of (PVC-Blend-SBR) Mixed Matrix Gas Separation Membrane Filled with Zeolite

Polyvinylchloride (PVC)/Styrene-Butadiene-Rubber (SBR) (PVC:SBR, (95:5) (w/w)) blend gas separation membrane filled with zeolite was prepared by solution-casting method using tetrahydrofuran (THF) as solvent. Zeolite was also applied as inorganic filler additive in membrane preparation. The zeolite loading and pressure effects on the gas separation performance of the membranes were studied for pure He, N2, CH4, CO2 gases. The obtained results indicated that permeability was increased and (CO2/N2), (CO2/CH4) and (N2/CH4) selectivities all were decreased by the increase of zeolite loading ratio. Moreover, it was found that increase of feed pressure led to an increase in membrane gas permeability for all of prepared membranes. Results showed that the (CO2/N2) and (CO2/CH4) gas pair selectivities were decreased by the increase in feed pressure for all prepared membranes. Conversely, opposite trend was found for (N2/CH4) selectivity at 50 wt} zeolite loading ratio. The (N2/CH4) selectivity was improved from 1.41 to 2.33 by increase in pressure force from 2 to 8 bar. Differential scanning calorimetry was also utilized for the membrane thermal stability investigation. The results showed the glass temperature (Tg) and melting temperature (Tm) obviously were improved from 340.1 to 467.1 K and from 359.5 to 516.9 K, respectively, by the increase in zeolite loading ratio from 0 to 50 % wt in prepared membranes.

Facilitated transport by amine-mediated poly(vinyl alcohol) membranes for CO2 removal from natural gas

The drive toward greater application of membrane has resulted in its rapid development in natural gas processing industry. In this work, amine-mediated membranes were tailored for CO2 removal from CO2/CH4 stream. The effects of various parameters such as amine concentration, microporous support, feed pressure and composition were examined to study the permeation behavior of pure and mixed gases. Generally, CO2 transport through the DEA-PVA membranes was higher than that of MEA-PVA membranes for approximately 70%. The membrane containing 15 wt% DEA and 35 wt% MEA revealed higher permselectivity. CO2 permeance enhancement of amine-PVA membranes in comparison with neat PVA membrane, confirmed that CO2-amine reaction was the dominant transport mechanism. Additionally, with increasing feed pressure, CO2/CH4 permselectivity decreased due to carrier saturation. However, lower partial pressure of CO2 was in favor of reaction mechanism in pure and mixed gas tests. On the other hand, CH4 is not significantly affected by feed pressure confirming that solutiondiffusion is the governing transport mechanism. Additionally, PTFE support with higher wettability showed better performance (18%) regardless of amine type, concentration and feed pressure. DEA-PVA membrane has exhibited good stability during 2 weeks, unlike MEA-impregnated membrane, which was probably due to carrier degradation over time. POLYM. ENG. SCI., 54:1268–1279, 2014. V C 2013 Society of Plastics Engineers

Fabrication and modification of cellulose acetate based mixed matrix membrane: Gas separation and physical properties

[Cellulose acetate (CA)-blend-multi walled carbon nano tubes (MWCNTs)] mixed matrix membranes (MMMs), [CA/polyethylene glycol (PEG)/MWCNTs] and [CA/styrene butadiene rubber (SBR)/MWCNTs] blend MMMs were prepared by solution casting method for gas separation applications using Tetrahydrofuran (THF) as solvent. Both raw-MWCNTs (R-MWCNTs) and functionalized carboxylic-MWCNTs (C-MWCNTs) were used in membrane preparation. The MWCNTs loading ratio and pressure effects on the gas separation performance of prepared membranes were investigated for pure He, N2, CH4 and CO2 gases. Results indicated that utilizing C-MWCNT instead of R-MWCNTs in membrane fabrication has better performance and (CO2/CH4) and (CO2/N2) selectivity reached to 21.81 and 13.74 from 13.41 and 9.33 at 0.65wt% of MWCNTs loading respectively. The effects of PEG and SBR on the gas transport performance and mechanical properties were also investigated. The highest CO2/CH4 selectivity at 2bar pressure was reached to 53.98 for [CA/PEG/C-MWCNT] and 43.91 for [CA/SBR/C-MWCNT] blend MMMs at 0.5wt% and 2wt% MWCNTs loading ratio respectively. Moreover, increase of feed pressure led to membrane gas permeability and gas pair selectivity improvement for almost all prepared membranes. The mechanical properties analysis exhibited tensile modules improvement with increasing MWCNTs loading ratio and utilizing polymer blending.

Development of matrimid/zeolite 4A mixed matrix membranes using low boiling point solvent

Pure matrimid and matrimid/zeolite 4A MMMs were prepared using dichloromethane as a low boiling point solvent combined with control evaporation. The prepared membranes were characterized by FESEM, DSC, TGA, XRD and single gas permeation. FESEM results show that zeolite 4A particles upto 20wt% are homogeneously dispersed and adhered within the polymer without aggregation. The semi-crystalline structure of matrimid is modified by the addition of zeolite 4A. The addition of 4A particles have improved the thermal stability of matrimid in the MMMs as depicted by an increase in the glass transition temperature (Tg) and TGA results. In single gas permeation of N2, H2, O2 and CO2, the effect of zeolite 4A loading, operating temperature, feed pressure and membrane annealing temperature on the separation properties were investigated. As the loading of zeolite 4A is increased, permeability of the membranes increases but at the expense of losing selectivity over N2. The MMMs were annealed at a higher temperature of 250°C for 3h and permeation was carried out as before. Comparison of the results show that the selectivity has been recovered much with a little expense of permeability such that the overall separation properties of the MMMs have improved. The increase of feed pressure from 2 to 8bars has little effect such that the permeability and selectivity of the MMMs can be considered to remains constant. As the operating temperature is increased from 30°C to 70°C, permeability of all the gases increases with N2 by 632%, O2 by 168%, H2 by 162% and CO2 by 62%. The corresponding decrease in the selectivity of gas pairs O2/N2, H2/N2 and CO2/N2 has been observed as 63%, 64% and 78% respectively.

Investigation on Delamination Factor in Drilling Medium Density Fiberboards with Variable Feed Pressure Using Multi-Spindle Drill

Abstract．Drilling quality in manufacturing medium density fiberboards (MDF) is greatly affected by delamination. In multi-spindle drill machine, the feed is provided by feed pressure generated by air compressor. This study focus on relation between delamination and machining parameters in drilling MDF with variable feed pressure. The relation is investigated by establishing second order polynomial models using response surface methodology, and the analysis of variance (ANOVA) is employed to verify the validity of the models. It is found that the delamination factor increases with the decrease of drill hardness and with the increase of feed pressure both at entry and exit of MDF. However, at low level hardness and high level feed pressure, the delamination factor is insensitive with variation of drill hardness and feed pressure.

Preparation and Characterization of Polycarbonate-Blend-Raw/Functionalized Multi-Walled Carbon Nano Tubes Mixed Matrix Membrane for CO2 Separation

Membrane composed of PC as base of polymer matrix with different ratio of multiwall carbon nano tubes (MWCNTs) as nanofillers and poly ethylene glycol (PEG) as second polymer was prepared by solution casting method. Both raw-MWCNTs (R-MWCNTs) and functionalized carboxyle-MWCNTs (C-MWCNTs) were used in membrane preparation. The MWCNTs loading ratio and pressure effects on the gas transport properties of membranes were examined in relation to pure He, N2, CH4, and CO2 gases. Results showed that the use of C-MWCNT instead of R-MWCNTs in mixed matrix membranes (MMMs) fabrication with base of PC provides better performance and also it increases (CO2/CH4) and (CO2/N2) selectivities to 27.38 and 25.42 from 25.45 and 19.24, respectively (at 5 wt% of MWCNTs). PEG as the second rubbery polymer was utilized to improve the separation performance and mechanical properties. In blend MMMs, highest (CO2/CH4) selectivity at 2 bar pressure increased to 35.64 for PC/PEG/C-MWCNT blend MMMs which was 27.28 for PC/MWCNTs MMMs at 10 wt%. Increase of feed pressure led to gas permeability and gas pair selectivity improvement in approximately all of membranes. Analysis of mechanical properties showed improvement in tensile modules with the increase of MWCNTs loading ratio and use of PEG in prepared MMMs.

Optimization of continuous phase in amino-functionalized metal–organic framework (MIL-53) based co-polyimide mixed matrix membranes for CO2/CH4 separation

Nano-size non- and amino-functionalized flexible crystalline metal-organic frameworks (MOFs) MIL-53(Al) and NH2-MIL-53(Al), two co-polyimides 6FDA/ODA-DAM (1 : 1 and 1 : 4) and cross-linked co-polyimide 6FDA-ODA-DAM (1 : 1, 2% agent cross-linking APTMDS) were used to prepare mixed matrix membranes (MMMs) whilst membranes consisting of MIL-53(Al) and commercial polyimides (Matrimid 5218 and Ultem 1000) were also fabricated for comparison. Pure gases and blends of CO2 and CH4 permeation tests showed enhanced separation performance of MMMs with relatively high NH2-MIL-53(Al) loadings (CO2 permeability up to 65 Barrer, ideal selectivity up to 36.5). A detailed study of the relation between MMM properties and their morphology as affected by the nature of continuous polyimide phase was performed. The separation factor increased with MOF loading. Furthermore, these materials showed stable CO2/CH4 selectivity at increasing feed pressure, in contrast to the traditional polymer membranes. The separation performances as functions of operation temperature and composition of gas mixture were also studied. Experimental permeation data of MMMs with 6FDA-ODA-DAM (1 : 1, 2% agent cross-linking APTMDS) and up to 35 wt% NH2-MIL-53(Al) loading are in excellent agreement with the modeling predictions by both the Maxwell model and the modified Maxwell model. An approximately ideal morphology was reached when preparing MMMs. A computational optimized process was proposed in order to estimate simultaneously three independent parameters, including gas permeability of dispersed filler, interphase thickness and polymer chain rigidification factors, which would be applied for non-ideal MMM systems.

Separation of pentane isomers using MFI zeolite membrane

A BZSM-5 zeolite membrane layers supported on a porous tubular alpha alumina support were prepared by hydrothermal synthesis. Permeation of single and binary mixture of normal pentane (nC5) and 2-methylbutane (2MB) through BZSM-5 zeolite membrane was studied as a function of total pressure, temperature and feed composition using total pressure difference and concentration gradient methods. The nC5/2MB selectivity decreased with increasing of temperature. The rapid decrease in separation selectivities with increase in temperature indicated that preferential adsorption was responsible for the selectivity. The selectivity decreased as the feed pressure increased in total pressure difference method. The performance of membrane in concentration gradient method is higher than that in total pressure drop method. It can be addressed by decreasing of non-zeolite effect on membrane permeation in the concentration gradient method. In addition, in contrast of pressure drop method, the nC5/2MB selectivity of membrane increased with increase in feed pressure for concentration gradient method.

Mathematical Modeling of CO2/CH4 Separation by Hollow Fiber Membrane Module Using Finite Difference Method

Removal of CO2 in landfill gas recovery processes and fractured wells as well as its application in enhanced oil recovery and its environmental aspects are of interest. Also separation of CO2 from CH4 in Ethylene Oxide plant is an environmental policy of Marun Petrochemical Company. In the present work, a shell-fed hollow fiber module was modeled mathematically for CO2 separation from CH4. Finite difference method was used for solving the equations. Comparison between co-current and counter-current flow patterns showed that for all conditions, counter current pattern had better efficiency for CO2/CH4 separation. Influence of operating parameters such as feed pressure, permeate pressure, feed flow rate, fiber length and CO2 concentration of feed on separation efficiency of CO2/CH4 mixture was investigated. Also the effect of feed and permeate pressures on required membrane area showed that the membrane area increases by increasing permeate pressure and decreases by increasing feed pressure. The modeling offers valuable data about feasibility study and economical evaluation of a gas separation unit operation as a helpful unit in the industry.

Preparation and characterization of polyvinylchloride based mixed matrix membrane filled with multi walled carbon nano tubes for carbon dioxide separation

Poly vinyl chloride/multi wall carbon nano tubes (PVC/MWCNTs) mixed matrix membranes (MMMs) were prepared for gas separation. Raw and functionalized MWCNTs (R-MWCNTs and C-MWCNTs) were utilized in membranes preparation. The C-MWCNT shows better performance compared to raw ones. Membrane (CO2/CH4) selectivity was increased from 39.21 to 52.18 at 2bar pressure by MWCNT loading ratio. The modified membranes with styrene butadiene rubber (SBR-MMMs) showed 63.52 and 34.70 selectivity for (CO2/CH4) and (CO2/N2) at 2bar pressure. Mechanical properties analysis exhibited tensile module improvement utilizing blending modification. Increase of feed pressure led to membrane gas permeability decreasing. But gas pair selectivity follows a nearly constant behavior for MMMs and increasing behavior for blend MMMs.

CFD numerical simulation of flow velocity characteristics of hydrocyclone

A CFD based numerical simulation of flow velocity of hydrocyclone was conducted with different structural and operational parameters to investigate its distribution characteristics and influencing mechanism. The results show there exist several unsymmetrical envelopes of equal vertical velocities in both upward inner flows and downward outer flows in the hydrocyclone, and the cone angle and apex diameter have remarkable influence on the vertical location of the cone bottom of the envelope of zero vertical velocity. It is also found that the tangential velocity isolines exist in the horizontal planes located in the effective separation region of hydrocyclone. The increase of feed pressure has almost no effect on the distribution characteristics of both vertical velocity and tangential velocity in hydrocyclone, but the magnitude and gradient of tangential velocity are increased obviously to make the motion velocity of high density particles to the wall increased and to make the cyclonic separation effect improved.

Characterization of Natural Zeolite Membranes for H2/CO2 Separations by Single Gas Permeation

Natural zeolite membranes can be used as a model for the development of robust molecular sieve membranes with superior separation characteristics. We describe the characterization of natural clinoptilolite membranes made from dense mineral deposits by single gas H 2 and CO 2 permeation. Permeability values as a function of temperature and pressure were analyzed on the basis of mass transport fundamentals of gas permeation through zeolite and nonzeolite pathways. H 2 and CO 2 fluxes through the membranes were fitted with a model based on a combination of zeolitic, Knudsen, and viscous transports so that the selective and nonselective flux fractions could be quantified. An increase in feed pressure increased the total permeance especially at low temperatures. The membranes were also characterized by XRD, SEM, and EDX analysis.

Natural gas dehydration by desiccant materials

Water vapor in a natural gas stream can result in line plugging due to hydrate formation, reduction of line capacity due to collection of free water in the line, and increased risk of damage to the pipeline due to the corrosive effects of water. Therefore, water vapor must be removed from natural gas to prevent hydrate formation and corrosion from condensed water.Gas dehydration is the process of removing water vapor from a gas stream to lower the temperature at which water will condense from the stream; this temperature is called the “dew point” of the gas. Molecular sieves are considered as one of the most important materials that are used as desiccant materials in industrial natural gas dehydration.This work shows a study of natural gas dehydration using 3A molecular sieve as a type of solid desiccant materials, the scope of this work was to build up a pilot scale unit for a natural gas dehydration as simulation of actual existing plant for Egyptian Western Desert Gas Company (WDGC). The effect of different operating conditions (water vapor concentration and gas flow rate) on dehydration of natural gas was studied.The experimental setup consists of cylinder filled with 3A molecular sieve to form a fixed bed, then pass through this bed natural gas with different water vapor concentration, The experimental setup is fitted with facilities to control bed pressure, flow rate, measure water vapor concentration and bed temperature, a gas heater was used to activate molecular sieve bed.Increasing water vapor concentration in inlet feed gas leads to a marked decrease in dehydration efficiency. As expected, a higher inlet flow rate of natural gas decrease dehydration efficiency. Increasing feed pressure leads to higher dehydration efficiency.

Post-treatment of biologically treated wastewater of agrochemical industry by sulfated chitosan composite nanofiltration membrane

The objective of this study is to treat the biologically treated wastewater using sulfated chitosan/ polyacrylonitrile (PAN) composite nanofiltration (NF) membrane to improve agrochemical industry wastewater quality for reuse. Although biological treatment is quite efficient, the wastewater does not meet the reuse criteria. Hence, further treatment to improve the water quality is investigated. Sulfated chitosan composite NF membranes, having a PAN ultrafiltration membrane as the substrate, are prepared by coating and cross-linking methods. The effects of membrane preparation conditions on the rejection and permeation performance of the membranes are studied. The new membranes are characterized by NMR and scanning electron micrograph. Wastewater from agrochemical industry contains high concentrations of organic matter, color, heavy metals and other toxic substances. The operating variables studied are applied pressure (3-15 atm) and feed flowrate (4-16 L/min). It is found that the observed rejection (R(o)) increases with increase in feed pressure at constant feed flowrate. The rejection of cations follows the sequence: R(o)(Zn2+) > R(o)(Ni2+) > R(o)(CU2+) > R(o)(Cd2+) for wastewater. It is observed that the order of solute rejection sequence is inversely proportional to the diffusion coefficients.

Intrinsic properties and performances of NF270 and XLE membranes for water filtration

Nanofiltration and low pressure reverse osmosis membranes are well-known in the field of drinking water production and their separation performance is very strongly related to their intrinsic characteristics. The membrane characterization (scanning electron microscopy (SEM), atomic force microscopy (AFM), zeta potential …) was realized on a NF270 and extra-low energy (XLE) membrane. SEM results of virgin NF270 and XLE membranes show that both are about the same thickness whereas that of the active layer of NF270 membrane is weaker than that of the XLE. The AFM measurements show that the roughness of the low pressure reverse osmosis membrane (XLE) is almost 20 times as high as that of nanofiltration (NF270). Zeta potential measurements showed that both membranes are negatively charged in pH (4–12) range. An increase in permeability by increasing feed pressure and temperature was also noted for the two types of membrane; but the permeability evolution for XLE membrane according to the volume factor reduction reveals a fall faster than that of NF270.

Olefin Gas Dehydration Using Carbon Hollow Fiber Membranes Derived from Sulfonated Poly(phenyl oxide)

Selective membrane separation of saturated water vapor from olefin gas such as ethylene and propylene has been investigated using two types of carbon hollow fiber membranes. One is prepared by the pyrolysis of sulfonated poly(phenylene oxide) (H-SPPO) at 600°C of which pore size is 0.4-0.45 nm, and another is prepared using sodium substituted SPPO (Na-SPPO) of which pore size is 0.3-0.35 nm. The membrane pore size was found to have a significant effect on the olefin gas dehydration performance and the latter carbon membrane showed superior performance due to the higher ideal selectivity of water vapor with respect to ethylene or propylene. This carbon membrane selectively permeated 95% of water vapor in feed stream (4.4 vol%) at a feed flow rate of 30 L · m−2 · min−1. It was revealed that the permeation amount of water vapor increased with increasing feed pressure. At a feed pressure of 0.5 MPa, more than 97% of the propylene gas dehydration ratio was obtained with good resistance against olefin gases.