Separations Technology最新文献

The competitive adsorption isotherms of praziquantel enantiomers on microcrystalline cellulose triacetate were determined by concentration pulse chromatography. A model comprising a non-selective linear term and a selective first order improved Langmuir term was found to fit the data excellently. It is postulated that this chiral stationary phase consists of two types of binding sites: one responsible for the chiral, selective interactions and one responsible for the achiral, non-selective interactions of the enantiomers with the stationary phase. The selective sites are easily saturated compared to the non-selective sites, accounting for the experimental observation of lower separation efficiency at higher enantiomer concentrations.

Separation of pseudocumene from the C₉ aromatic raffinates found in naphtha cracking by thiourea adduction was studied. For the trimethylbenzene isomers, the tendency for adduct formation with thiourea was found to be pseudocumene > hemimellitene /ggr/ mesitylene, and for the ethyltoluene isomers, p-ethyltoluene>o-ethyltoluene >m-ethyltoluene. From the eight cases of binary mixtures of C₉ aromatic compounds studied, separation by adduction with thiourea was more efficient than either distillation or extractive crystallization. Specifically, one adduction stage was approximately 5.4–58.0 times greater than one theoretical distillation stage. Similarly, the entrapping capacity by one adduction stage was approximately six times greater than that of extractive crystallization. Pseudocumene of purity of 99.7 wt% may be obtained from C₉ aromatic mixtures with the use of four thiourea adduction stages.

Investigations have been carried out for purification of oily wastewater by a combination of ultrafiltration/reverse osmosis processes. A tubular ultrafiltration system using cellulosic and non-cellulosic membranes was tested with typical oily wastewater collected from harbour and simulated emulsion without any pretreatment. Both membrane types produced a permeate with an oil content generally less than 10 mg/dm³. Rejection of chemical oxygen demand (COD) is 80% for ultrafiltration treatment. The permeate is generally of acceptable quality for direct sewer discharge. For further treatment of UF permeate, reverse osmosis was applied with tubular B1 PCI modules using cellulose acetate membranes. The rejection of COD after ultrafiltration/reverse osmosis treatment increased up to 98.5% and total dissolved solids (TDS) to 95.7%. Reverse osmosis treatment will permit reuse of the treated water as process water.

An experimental and theoretical study was performed for bulk separation of two binary systems — $\text{H}{}_2\text{CO}{}_2$ and $\text{H}{}_2\text{CO}$ mixture ($\text{70}\text{30}$ volume %) — by one-column PSA with zeolite 5A, a process widely used commercially in conjunction with catalytic steam reforming of natural gas or naphtha. In order to establish the optimal adsorption/desorption conditions of the PSA process, the dynamics of the adsorption/desorption process were studied through breakthrough and desorption experiments under various conditions. The purge-to-feed ratio was found important to H₂ product purity for cases with long adsorption step time. By cycling the pressure of a bed of zeolite between 1 atm and 11 atm and at ambient temperatures, H₂ could be concentrated from 70% in the feed to a product of 99.99% with a H₂ recovery of 67.5% for $\text{H}{}_2\text{CO}{}_2$ mixture and 97.09% with a H₂ recovery of 65.35% for $\text{H}{}_2\text{CO}$ mixture. Information concerning the function of each step in the cyclic process was given. The performance of all the five steps of the PSA process can be predicted by the LDF model together with the energy balance and equilibrium relationships. In applying the LDF model, the effective diffusivities (D_e) were obtained independently from up take curves of H₂, CO₂, and CO by zeolite. The Langmuir-Freundlich isotherm was used to correlate the experimental equilibrium data and was very well fitted to the results.

Coal fly ash, a solid waste from thermal power stations was used to successfully remove 2,4-dimethyl phenol by adsorption from aqueous solutions. The rate of adsorption follows first order kinetics before attaining equilibrium. Both diffusional and kinetic resistances affect the rate of adsorption and their relative effects vary with operating temperatures. Equilibrium adsorption data satisfied both Langmuir and Freundlich isotherms.

Pervaporative separation of aqueous solutions of propionic, butyric and iso-butyric acid has been studied using plain and filled silicone rubber membranes. All the three acids can be conveniently separated using plain silicone rubber membranes.

The application of the conventional flotation column to wastewater treatment has failed to realize its full. potential, mainly because of inadequate mixing (or backmixing) and non-uniform dispersion of bubbles in the column. Thus, the challenge lies in the development of a mechanical design, which can provide proper hydrodynamic conditions that will result in efficient separation, with high throughput. This paper describes a new column design, in which multiple draft tubes were used. Test results demonstrate that this new design is superior to that of the conventional flotation column for wastewater treatment.

Studies were conducted to evaluate potential applications of collagen dispersions in liquid-solid separation processes for water treatment and sludge dewatering. The collagen dispersion was prepared from fibrillar type I bovine hide buffered with organic acid. The results indicate that the collagen dispersion was effective as a coagulant for removing turbidity caused by colloidal clay particles and as a sludge conditioner for thickening and dewatering sludge from a water treatment plant. Coagulation of kaolin suspensions using the collagen reduced the initial turbidity of the suspension by 92%. Additions of collagen to sludge from a water treatment plant improved the settling rate during gravity thickening by a factor of five and improved the specific cake resistance of the sludge during filtration by a factor of three. Research is continuing on the mechanisms and kinetics of collagen dispersions in coagulation and sludge dewatering.