Effect of different additives on the physical and chemical CO 2 absorption in polyetherimide hollow fiber membrane contactor system

Porous asymmetric polyetherimide (PEI) hollow fiber membranes were fabricated via a phase-inversion method using ethanol, glycerol and acetone as the additives in the spinning dope. Also, hollow fiber PEI membrane without additives was fabricated. An aqueous solution of 1-methyl-2-pyrrolidone (80 wt.%) was used as bore fluid to prevent forming of an inner dense skin layer. The precipitation rate of the polymer dopes with the different additives was studied using cloud point measurement. The effect of the additives on the resulting membrane structure, surface porosity, pore size, critical water entry pressure, collapsing pressure and physical and chemical CO2 absorption performance by distilled water and NaOH (1 M) solution in a gas–liquid membrane contactor system were investigated and compared. Cloud point diagrams indicated that the precipitation rate of the polymer dopes increased following the trend of ethanol > acetone > glycerol. Results of gas permeation tests showed that ethanol and glycerol as additives provided the membranes with the largest and smallest pore size, respectively. Moreover, all the additives resulted in an increase in the effective surface porosity. The cross-section of the membranes was examined via a scanning electron microscopy. Ethanol in the spinning dope provided the membrane structure with a sublayer with finger-like macrovoids, originating from the inner and outer surfaces of the hollow fiber and extending to the middle section of the hollow fiber wall, which resulted in a larger pore size and higher CO2 absorption rate than the other PEI hollow fiber membranes

Effect of novel surface modifying macromolecules on morphology and performance of polysulfone hollow fiber membrane contactor for CO2 absorption

A novel surface modified Polysulfone (PSf) hollow fiber membrane was fabricated via dry–wet phased inversion process. surface modifying macromolecule (SMM) was used as additive in the spinning dope. The surface modified membrane showed large pore size, higher effective surface porosity, contact angle and porosity but lower critical water entry pressure (CEPw) compared to Polysulfone hollow fiber membrane without SMM. The performance of surface modified membrane in contactor application for CO2 absorption via distilled water as absorbent was studied. The results show that surface modified membrane has higher performance compared to plain Polysulfone membranes. With the membrane prepared from SMM in the spinning dope a maximum CO2 flux of 5.8 × 10-4 mol/m2 s was achieved at 300 ml/min of absorbent flow rate, which was almost 76% more than the other membrane. In a long-term stability study, the initial flux reduction was found to be about 18% within the 50 h of operation for surface modified membrane

A novel surface modified polyvinylidene fluoride hollow fiber membrane contactor for CO2 absorption

A novel surface modified polyvinylidene fluoride (PVDF) hollow fiber membrane was fabricated via a dry–wet phased inversion process. A surface modifying macromolecule (SMM) was used as an additive in the spinning dope. During phase inversion SMM migrates to the membrane surface and functions as both a pore former and surface modifier. The surface modified PVDF membrane showed large pore size, higher effective surface porosity, contact angle and porosity but lower critical water entry pressure compared to the PVDF hollow fiber membrane without SMM. The performance of the surface modified membrane in contactor application for CO2 absorption via distilled water as absorbent was studied. The results show that the surface modified PVDF membrane has higher performance compared to control PVDF membranes. With the membrane prepared from SMM in the spinning dope a maximum CO2 flux of 7.7×10−4 mol/m2 s was achieved at 300 ml/min of absorbent flow rate, which was almost 93% more than the other membrane. In a long-term stability study, CO2 flux was decreased only about 7.7% by using surface modified PVDF membrane during 150 h operation

Biosurfactant production for enhancing the treatment of produced water and bioremediation of oily sludge under the conditions of Gachsaran oil field

BACKGROUND: Gachsaran oil field is one of the largest oil fields in southern Iran and vast amounts of hydrocarbon contaminants are generated every year. Work is urgently required to devise effective methods to treat the produced water and high TPH content oily sludge under conditions that mimic the oil field. Bioremediation as an environmentally friendly and relatively cost-effective technique was examined in the present research. A continuous membrane bioreactor (CMBR) and bio-slurry processes were utilized to treat the produced water and oily sludge, respectively. RESULTS: The ability of consortium (GACH-1) for degradation of crude oil under extreme conditions revealed that GACH-1 is able to grow at crude oil concentrations up to 11.3% (w/v), temperatures up to 73 °C, salinities up to 15.4%, and in the pH range 4–10. The results obtained from the CMBR tests demonstrated that although the COD of influent changed from 1800–2100 mg L−1, the COD of permeate was maintained at less than 125 mg L−1, which was equivalent to a removal efficiency of 94%. In the case of oily sludge, TPH content was reduced by 31.2% after bioremediation for 90 days. CONCLUSION: Based on this approach, the consortium GACH-1 will be useful in clean-up of petroleum contamination in the Gachsaran oil field

Long-term study of CO2 absorption by PVDF/ZSM-5 hollow fiber mixed matrix membrane in gas–liquid contacting process

In order to fabricate hollow fiber mixed matrix membrane (HFMMM) for long-term CO2 absorption process, ZSM-5 (Zeolite Socony Mobil-5) zeolite was modified using hexadecyltrichlorosilane for increasing hydrophobicity and then added to the polyvinylidene fluoride (PVDF) spinning dope. The in-house made HFMMMs were characterized in terms of gas permeance, overall porosity, average pore size, effective surface porosity, surface roughness, mechanical stability, and wetting resistance. The morphology of the HFMMMs was studied using SEM. The cross-sectional SEM images indicated that the membrane structure has changed from sponge-like to finger-like by ZSM-5 loading. The surface roughness increased by increasing ZSM-5 concentration in the spinning dope. The HFMMM spun from the spinning dope with 0.5 wt % of ZSM-5 zeolite showed that the CO2 absorption flux decreased 18.9% in the initial 115 h of the operation and then the absorption flux remained constant until the end of the operation. For plain PVDF HFM the absorption flux decreased 36% from the initial value in the first 15 h of the experiment. Thus it could be concluded that the long term stability of HFM was improved by the incorporation of ZSM-5

Modification of membrane hydrophobicity in membrane contactors for environmental remediation

Membrane contactor is a well-developed, eco-friendly and waste-free technology that has been the subject of interest in both gas separation and water treatment. Despite the feasibility and advantages, one of the inherent issues with membrane contactor is the wetting of membrane which eventually leads to the increased mass transfer resistance and the deterioration of the membrane flux and overall long term stability performance. Various surface modification strategies which involve the alteration of surface chemistry and structure have been established to tackle this issue. The common goal of these strategies is to improve the surface hydrophobicity of the contacting membrane hence to prevent membrane wetting. This contribution reviews the state-of-the-art approaches that have been explored for membrane hydrophobic modifications. The recent progresses and performance evaluation of these surface modified hydrophobic membranes in both gas separation and wastewater treatment are presented. Finally, the challenges and future outlook of surface modified membranes for membrane contactors are highlighted

Modification of membrane hydrophobicity in membrane contactors for environmental remediation

Membrane contactor is a well-developed, eco-friendly and waste-free technology that has been the subject of interest in both gas separation and water treatment. Despite the feasibility and advantages, one of the inherent issues with membrane contactor is the wetting of membrane which eventually leads to the increased mass transfer resistance and the deterioration of the membrane flux and overall long term stability performance. Various surface modification strategies which involve the alteration of surface chemistry and structure have been established to tackle this issue. The common goal of these strategies is to improve the surface hydrophobicity of the contacting membrane hence to prevent membrane wetting. This contribution reviews the state-of-the-art approaches that have been explored for membrane hydrophobic modifications. The recent progresses and performance evaluation of these surface modified hydrophobic membranes in both gas separation and wastewater treatment are presented. Finally, the challenges and future outlook of surface modified membranes for membrane contactors are highlighted

Study on the effect of air-gap length on properties and performance of surface modified PVDF hollow fiber membrane contactor for carbon dioxide absorption

Surface modified polyvinylidene fluoride (PVDF) hollow fiber membranes (HFMs) were spun via dry-wet spinning technique at different air-gap lengths (0-20 cm). The morphology of prepared membranes was evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Membranes were also characterized in terms of gas permeation, overall porosity, collapsing pressure, critical water entry pressure (CEPw) and contact angle. To determine the CO2 absorption flux of HFMs, a gas-liquid membrane contactor system was used. Experimental results of this study revealed that by increasing the air-gap distance from 0 to 20 cm, wetting resistance and contact angle of fabricated membranes increased due to enhancement of membrane surface hydrophobicity. The highest helium (He) permeation was achieved for the spun fiber at the air-gap of 10 cm. From CO2 absorption experiment it was found that the hollow fiber spun at the air-gap of 10 cm had the maximum CO2 absorption flux of 1.41 x 10(-3) mol/m(2) s at the absorbent flow rate of 300 ml/min, which was significantly higher than CO2 absorption flux obtained by other researchers. It was also found that both highest He gas permeance and CO2 absorption flux were controlled by the surface porosity of the hollow fiber due to the maximum values obtained. Thus, the choice of an appropriate air-gap distance for fabrication of surface modified membranes was found to be a promising method to improve CO2 removal in membrane contactor systems