Youyuan Dai

In situ preparation of magnetic Fe3O4-chitosan nanoparticles for lipase immobilization by cross-linking and oxidation in aqueous solution.

A new and simple method has been proposed to prepare magnetic Fe(3)O(4)-chitosan (CS) nanoparticles by cross-linking with sodium tripolyphosphate (TPP), precipitation with NaOH and oxidation with O(2) in hydrochloric acid aqueous phase containing CS and Fe(OH)(2), and these magnetic CS nanoparticles were used to immobilize lipase. The effects on the sequence of adding NaOH and TPP, the reaction temperature, and the ratio of CS/Fe(OH)(2) were studied. TEM showed that the diameter of composite nanoparticles was about 80 nm, and that the magnetic Fe(3)O(4) nanoparticles with a diameter of 20 nm were evenly dispersed in the CS materials. Magnetic measurement revealed that the saturated magnetisation of the Fe(3)O(4)-CS nanoparticles could reach 35.54 emicro/g. The adsorption capacity of lipase onto nanoparticles could reach 129 mg/g; and the maximal enzyme activity was 20.02 micromol min(-1)mg(-1) (protein), and activity retention was as high as 55.6% at a certain loading amount.

Immobilization of lipase on methyl-modified silica aerogels by physical adsorption.

In this work, methyl-modified silica aerogels, a new kind of macro-porous material with high porosity, were used as carriers to immobilize lipase by adsorption. SEM, TEM, nitrogen adsorption device, and thermogravimetric analysis were used to characterize the properties of modified aerogels. The surface area was 395.6 m(2)/g, and the average pore diameter was 68.72 nm. The contact angle of aerogel particles increased from 20.9 degrees to 99.2 degrees after methyl modification. Reaction characteristics of the material after enzyme loading were also discussed. The results showed that adsorption capacity could reach 67.42 mg/g; and the maximal enzyme activity was 19.87 micromol min(-1)mg(-1) (protein), and activity retention could reach 56.44%. It is worth mentioning that the amount of modified aerogels added had significant effects on the diameter of droplets and the mass transfer behavior of substrates in the reaction emulsion. Online microscope was used to visualize the droplets in the emulsion, where the aerogel particles were observed locating at the interface of oil and water. The average diameter of droplets reached the minimum when 0.06 g of modified aerogels was added into the reaction emulsion which contained 10 ml of oil and 10 ml of phosphate buffer solution. The phenomenon was resulted from the wettability of methyl-modified silica aerogels.

Effect of random packing on shell-side flow and mass transfer in hollow fiber module described by normal distribution function

The residence time distribution (RTD) curves were measured to observe the shell-side flow status in hollow fiber modules (HFMs) with different packing densities, and with 30%TBP in kerosene/phenol/water as experimental system, the membrane extraction was carried out in three polypropylene HFMs in counter-current flow. A random distribution model described by the Voronoi tessellation method based on normal distribution function was proposed to determine the effect of random packing on the flow status and mass transfer characteristics. The standard deviation in normal distribution function represented the packing irregularity in commercial HFMs. So the random distribution model related the packing irregularity with the flow status and mass transfer performance in random packing modules. The theoretical calculation and experimental results indicated that the random packing of fibers caused the non-ideal flow and significant decrease in mass transfer performance; furthermore, the non-ideal flow in shell side had an influence not only on the mass transfer performance in shell side but also on that in lumen side.

Separation of phenol from aqueous solutions by polymeric reversed micelle extraction

Abstract Polyoxyalkylene block copolymers consisting of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO) or poly(butylene oxide) (PBO) have not attracted much attention until recent years. Variations of the molecular characteristics (PPO/PEO ratio, molecular weight) of the copolymer during the synthesis allows the production of molecules with optimum properties that meet the specific requirements in different areas. Our present interest is focused, on the formation of the reversed polymeric micelles, which are formed in ‘oil’ phases with PEO–PPO–PEO-type as well as PPO–PEO–PPO-type triblock copolymers. A novel process of polymeric reversed micelle extraction is subsequently proposed based upon the concepts of reversed micelle extraction and polymeric micelle extraction. Extraction equilibrium partition of phenol between polymeric reversed micelle solutions was investigated to study the extraction behaviors. PPO content, copolymer and co-surfactant types affected the extraction process.

Influence of alcohol treatments on the activity of lipases immobilized on methyl-modified silica aerogels.

The effects of alcohol treatment on the activity and loading amount of Candida rugosa lipase (CRL), Candida Antarctica lipase B (CALB) and Porcine Pancreas lipase (PPL) immobilized on methyl-modified silica aerogels were investigated, and the fluorescent analysis was used to explore the change of lipase hydrophobicity in aqueous solution caused by alcohols. It is found that alcohol types and the stages at which alcohol was added significantly influenced the performance of immobilized lipases through changing the hydrophobicity of the molecules. For CRL and PPL, five kinds of alcohol were added in the adsorption process, and n-butanol and isopropanol improved the apparent activity of CRL and PPL up to 2.5 times and 2 times those of the untreated ones, respectively; however, for CALB, it is better to activate the immobilized CALB after the adsorption process, and the apparent activity of CALB increased up to 2.76 times through n-butanol treatment.

A non-steady state model for the transport of iron(III) across n-decanol supported liquid membrane facilitated by D2EHPA

Abstract A non-steady state model to describe the permeation of iron(III) through a supported liquid membrane (SLM) based on n -decanol containing di-2-ethylhexyl phosphoric acid (D2EHPA) as a carrier is proposed. According to the model, two factors mainly contribute to the overall resistance for the iron(III) transport: the feed/organic interface chemical reaction and the diffusion of the complex Fe(III)-D2EHPA through the membrane liquid phase. The interface reaction is assumed first-order. The mole fractions of iron(III) in the three phases, the feed, the organic and the strip, were simulated by using a numerical method. Several series of experimental data were simulated and the simulated results fit very well the experimental data. The model accounts for the phenomenon of iron(III) retention in the organic phase and can simulate the iron(III) concentration in time in the membrane liquid phase. The rate controlling step for iron(III) transport from feed to strip is a combination between the interface reaction and the complex diffusion through the membrane.

Effect of solvents and precipitant on the properties of chitosan nanoparticles in a water-in-oil microemulsion and its lipase immobilization performance.

When chitosan nanoparticles were prepared in a water-in-oil (W/O) microemulsion by using 2% (wt) acetic acid (HAc) and 30% (wt) tri-n-octylamine (TOA) as solvent and precipitant, respectively, particle diameters of 7 nm were observed and the particles formed ovoid shaped aggregates. Using 0.05% HCl and 5.0M NaOH as solvent and precipitant produced nanoparticles 10nm in size that aggregated in the form of snowflakes. These two types of nanoparticles were used to immobilize lipase, the lipase adsorption capacity using nanoparticles 7 nm in size reached 156 mg/g and activity retention compared to free enzyme was as high as 66.7%, and the residual activity of the immobilized lipase was 91% after 5 runs of reaction. In additional, the activity retention of nanoparticles 10nm in size also could reach 62.8%. This indicated that the chitosan nanoparticles prepared in a W/O microemulsion were suitable for lipase immobilization.

Two-phase electrophoresis separation of dyestuffs from dilute solution

Abstract Dyestuffs are not efficiently removed by biological treatment or by conventional dye treatment techniques. New separation techniques are required. Two-phase electrophoresis, a coupled separation technique of solvent extraction with electrophoresis, can be used to remove dyestuffs from dye effluents. A study on the characteristics of the separation technique has been carried out with n -butanol–acid-chrome blue K–water, n -butanol–methyl blue–water and n -butanol–methyl red–water as working systems. Continuous separation equipment has been designed and used in this work. The influences of the two-phase flow rate, field strength and feed concentration on the recovery are studied. The results show that a high recovery with less solvent consumption can be achieved using this technique, especially for the separation of dilute solutions. As the field strength is increased, the recovery and mass flux increase. When the feed flow rate and the initial solute concentration in the feed are increased, the recovery decreases and the mass flux increases.

Extraction Mechanism and Behavior of Malic Acid with Tri‐octylamine (TOA)

Abstract Liquid–liquid equilibria of malic acid with tri‐octylamine (TOA) as extractant and 1‐octanol, methyl isobutyl ketone (MIBK) and chloroform as the diluents were investigated, and Fourier transform infrared spectrometer (FTIR) spectrum of the organic phase samples loaded with malic acid were taken to obtain the stoichiometry of complex. The extraction behavior depends on the concentration of malic acid in the equilibrium aqueous phase, species of diluent, and TOA concentrations in the organic phase. A large degree of extraction in protonated diluent appeared at low equilibrium malic acid concentration in the aqueous phase, while the sequence was as MIBK > 1‐octanol > chloroform at high equilibrium malic acid concentration. It has the same sequence as the degree of extraction at overloading region. Malic acid is bonded to TOA in three forms of (1,2), (1,1), and (2,1), and for the complex (1,2), one carboxyl on malic acid was bonded to TOA with ion‐pair association and another with hydrogen bond. By using mass action law, and taking some assumptions, an expression of extraction equilibrium was derived, and the apparent extraction equilibrium constants were evaluated. The predict equilibrium data agreed well with the experimental values.

Membrane extraction for sulfanilic acid removal from waste water

The flow characteristics in hollow fiber modules (HFMs) were studied using resident time distribution (RTD) curves, which showed that the actual flow was nonideal and conformed to neither the ideal plug flow nor the complete mixed-flow models. Axial dispersion was found to decrease with an increase in flow velocity on the tube side and to increase with an increase in flow velocity on the shell side. Good agreement between the curves calculated using an axial diffusion model and experimentally determined RTD curves showed that the diffusion model can be used to describe the mass transfer characteristics in HFMs. In the study using 20% trioctylamine+30% octanol+50% kerosene–sulfanilic acid–water as actual extraction process, it was found that axial dispersion was the cause of the significant decrease in mass transfer performance. The resistance to mass transfer is located mainly in the boundary layer of aqueous phase. The large amount of treatment suggested that sulfanilic acid removal from its wastewater by HFM was an efficient process.