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Abstract : Experimental Investigation of Pervaporation Membranes for Biobutanol Separation
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Abstract: Biotechnological production of chemical building blocks is one important step towards a more sustainable production. Unfortunately, the products to be separated are often highly diluted. Pervaporation has received increasing attention for the separation of small amounts of organic compounds from aqueous solutions, especially in the separation of butanol from water or from fermentation broth. To evaluate the potential of pervaporation for biobutanol recovery a consistent database is required, describing the dependency of permeate fluxes and selectivities on process variables like temperature, permeate pressure as well as feed concentrations and compositions. Therefore, within this work we investigated the separation behaviour of a commercially available polydimethylsiloxane (PDMS) membrane and membranes based on poly(ether block amide) (PEBA) fabricated in our own laboratory. The membranes were tested under varying operating conditions. Fermentation by-products or impurities may affect the pervaporation separation performance. Therefore, in addition, the permeate fluxes and the influence of acetone, ethanol, acetic and butyric acid and 1,3-propanediol have been investigated in detail as well. Several differences in the permeability and selectivity of PDMS and PEBA were observed during the experimental study. Swelling experiments were applied to further analyse the separation behaviour of PDMS and PEBA more in detail. Finally the influence of the observed separation performances on the overall butanol pervaporation process is discussed. It was found that especially well permeating by-products like acetone can drastically influence the subsequentdownstreaming process. Keywords: Polydimethylsiloxane (PDMS), PervapTM, poly(ether block amide) (PEBA), swelling, organic acid, Hansen Solubility Parameter.Download Full Article |
Abstract : Measures to Increase Recoveries and Avoid Concentrate Disposal: Principles to Control Scaling and Reduce Concentrate Disposal in Reverse Osmosis Applications
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Abstract: The present work is aimed at development of a new approach to reduce RO concentrate flow and to increase recovery. The described techniques enable us to remove calcium carbonate from RO concentrate by means of "seed" сrystallization. These proposed techniques use "open channel" spiral wound membrane modules that can directly treat water with high scaling and fouling potentials without pretreatment. The experimental procedure is described and experimental plots are presented that describe precipitation kinetics. The test membrane unit was operated in circulation mode and recovery values reach 95% or higher. RO concentrate constantly passed through the precipitation reactor where seed crystals were contained. Seed crystal formation was initiated by injecting caustic solution to RO concentrate. The driving force for crystal growth was constantly created by RO process due to increase of calcium and carbonate ion concentration values. Fouling control is achieved by providing sufficient cross flow velocities, flushings and cleanings. Coagulated suspended matter after membrane flushes is collected, sedimented and finally dewatered. The concentrated solution that contains rejected salts and impurities constitutes no more than 1 per cent of initial feed water volume and can be withdrawn together with wet sludge as a sludge moisture. The described technical procedure enables us to completely utilize concentrate and produce quality product water, softened water and sludge. Keywords: Reverse osmosis concentrate, concentrate utilization, calcium carbonate precipitation, seed crystallization.Download Full Article |
Abstract : Pilot Scale Hollow Fiber Pervaporation System for Phenol Recycling from Coal to Chemical Wastewater
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Abstract: Polydimethylsiloxane (PDMS)/Polyvinylidene fluoride (PVDF) hollow fiber composite membrane was prepared by dynamic negative pressure method to treat coal to chemical wastewater containing high concentration of phenol, in which PVDF hollow fiber membrane acts as base membrane and PDMS as modified membrane. In the pilot scale experiment, the influence of aeration rate, temperature, flow rate, pressure under membrane on phenol removal efficiency were investigated and operating parameter optimized. At temperature 70℃, flow rate of 150 L/h, pressure under membrane 5 KPa, gas-water ratio 0.3, 75 L coal to chemical wastewater containing phenol fluctuated between 1600 and 1800 mg/L was treated for 6h, and phenol removal efficiency reached 72%. The system ran stably for 120 h and performed well, phenol removal efficiency being kept more than 60%. Keywords: Hollow fiber composite membrane, dynamic negative pressure method, pilot scale pervaporation system, coal to chemical wastewater.Download Full Article |
Abstract : Purification of Olive Mill Wastewater Using Microfiltration Membrane Technology
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Abstract: Olive mill wastewater (OMWW), a by-product of the olive oil extraction process, is a severe polluting waste, but also a source of antioxidants; polyphenols, especially hydroxytyrosol. This study aimed at investigating the potential of microfiltration (MF) for separating the polyphenols from OMWW. OMWW treatment consisted of a preliminary centrifugation step, followed by MF for the separation of fats and polyphenols. Two types of ceramic MF membranes were used. MF flux ranged between 78 and 95 kg m-2 h-1, indicating the applicability of the described process on commercial scale. Better results were obtained with MF membrane of 50 nm pore size, due to its higher porosity compared to the membrane of 200 nm pore size. The optimum operative conditions were transmembrane pressure of 3.5 bar, flow rate of 10 m s-1, and temperature of approximately 55 °C. A 3-month storage of OMWW prior to treatment resulted in a 20% decrease in permeate flux, indicating that direct processing of the OMWW is necessary. Membrane pollution was not a problem for MF operation and did not affect membrane permeability significantly. Restoring the permeability of water to baseline levels after each use, confirmed the successful cleaning regime applied. The microfiltrate was an excellent antioxidant, which contained useful polyphenols, including hydroxytyrosol, tyrosol, p-coumaric acid, caffeic acid and catechin. Keywords: Permeate flux, polyphenols, membrane cleaning, OMWW storage, microfiltration.Download Full Article |
