Naoto Ohmura

Emulsion polymerization of styrene in a continuous Taylor vortex flow reactor

Abstract A continuous emulsion polymerization of styrene was tried in a Taylor vortex flow reactor which has characteristics of a plug flow reactor. The Taylor vortex flow reactor has the mixing characteristics appropriate for this reaction system. The steady-state conversion, the average molecular weight and the size distribution of latex particles can be controlled by the flow condition as well as by the reaction temperature.

Effective mass diffusion over cell boundaries in a Taylor-Couette flow system

Abstract Effective mass diffusion over cell boundaries in a Taylor-Couette flow system was investigated ranging from singly periodic wavy vortex flow to weakly turbulent wavy vortex flow by a salt-solution tracer technique. In order to determine experimentally the intercell mixing coefficient k CB between the neighbouring pairs of vortices, an appropriate model was formulated. As a result, k CB depends not only on Taylor number but also on axial wavelength with fluid viscosity. In the singly periodic wavy vortex flow region, the intermixing is enhanced by periodic fluctuations resulting from azimuthally travelling waves on the cell boundaries. With increasing Taylor number in the doubly periodic wavy vortex flow and weakly turbulent wavy vortex flow regions, the mixing characteristics go toward axial turbulent diffusion. In these two flow regions, the correlation between k CB and effective diffusion coefficient D z based on an axial diffusion model has been obtained as D z = 2 λk CB .

Construction of a xylose-metabolizing yeast by genome integration of xylose isomerase gene and investigation of the effect of xylitol on fermentation.

A yeast with the xylose isomerase (XI) pathway was constructed by the multicopy integration of XI overexpression cassettes into the genome of the Saccharomyces cerevisiae MT8-1 strain. The resulting yeast strain successfully produced ethanol from both xylose as the sole carbon source and a mixed sugar, consisting of xylose and glucose, without any adaptation procedure. Ethanol yields in the fermentation from xylose and mixed sugar were 61.9% and 62.2% of the theoretical carbon recovery, respectively. Knockout of GRE3, a gene encoding nonspecific aldose reductase, of the host yeast strain improved the fermentation profile. Not only specific ethanol production rates but also xylose consumption rates was improved more than twice that of xylose-metabolizing yeast with the XI pathway using GRE3 active yeast as the host strain. In addition, it was demonstrated that xylitol in the medium exhibits a concentration-dependent inhibition effect on the ethanol production from xylose with the yeast harboring the XI-based xylose metabolic pathway. From our findings, the combination of XI-pathway integration and GRE3 knockout could be result in a consolidated xylose assimilation pathway and increased ethanol productivity.

Controlling particle size by self-sustained oscillations in continuous emulsion polymerization of vinyl acetate

This work examined the controllability of the size of polymer particles and its distribution by taking advantage of the self-sustained oscillations of monomer conversion in continuous emulsion polymerization of vinyl acetate in a CSTR. The emulsifier concentration was primarily varied as a control parameter of the experimental condition below the critical micelle concentration. Regularly periodical oscillations in monomer conversion occurred with a long period as compared to the mean residence time of the CSTR. Time-dependent size distribution of polymer particles observed by TEM varied in form synchronously with the periodical oscillations of monomer conversion. These results suggest that particles can be formed intermittently owing to the temporal variation of the concentration of free emulsifier in the condition below CMC. It has also been confirmed that the particle size distribution (PSD) is made quite narrow in the condition for regularly periodical oscillations but considerably wide in the condition for irregular oscillations. It has been successfully indicated that the self-sustained oscillations in continuous emulsion polymerization will be profitable not only for controlling the size of latex particles but also for raising the monomer conversion.

Sugar consumption and ethanol fermentation by transporter-overexpressed xylose-metabolizing Saccharomyces cerevisiae harboring a xyloseisomerase pathway.

Four kinds of transporters, HXT1 and HXY7 from Saccharomyces cerevisiae, and GXF1 and GXS1 from Candida intermedia, were overexpressed in xylose-metabolizing S. cerevisiae harboring a xyloseisomerase-based pathway. Overexpression of transporter enhanced sugar consumption and ethanol production, and GXF1 was efficient for ethanol fermentation from both glucose and xylose.

Particle classification in Taylor vortex flow with an axial flow

Particle classification phenomenon in Taylor vortex flow with an axial flow was investigated experimentally and numerically. The flow-visualization experiment by a laser-induced fluorescence method clearly revealed that there existed two distinct mixing regions at low Reynolds numbers. The tracer near the vortex cell boundary was rapidly transported axially owing to the bypass flow effect. On the other hand, the fluid element was confined to the vortex core region without being exchanged with the outer flow region. In order to observe particle classification phenomenon, polymethyl methacrylate (PMMA) particles suspended in the same aqueous solution of glycerol as the working fluid were fed into the top of the apparatus. Particle size was initially ranging from 10 to 80 ?m. The ratio of the particle density to the fluid density was 1.04?1.05, which means the density difference between particle and fluid is very small. The suspended solution was withdrawn using a hypodermic needle every a certain time period at 30 mm above the bottom of apparatus. The fluid was sampled both near the outer wall and in vortex core. The particles sampled at 42 min having the size of 20?50 ?m were mainly observed in the vortex core region. On the other hand, a large population of particles having the size of about 50?80 ?m could be seen in the outer region of vortex. It was found that large particles located near the outer edge of vortices were quickly transported axially owing to the bypass flow effect. Numerical simulation also revealed that the loci of particles depended on the particle size.

Intercellular mass transfer in wavy/turbulent Taylor vortex flow

Abstract Axial mass transfer or mixing through trains of cellular vortices has been observed in the range of time-dependent wavy vortex flow with the aid of visualization technique of wave motion, salt-tracer response technique, and spectral analysis of fluctuating velocity-gradients. There appear multiple stable flow states even at the same Reynolds number owing to the hysteresis of the flow system, depending upon the start-up operation. Intercellular mass transfer depends upon the axial wavelength and wave motion as well as the Reynolds number in the range of singly (SPWVF) and doubly periodic wavy vortex flow (DPWVF) whereas it is controlled mainly by turbulent motion in the range of weakly turbulent wavy vortex (WTWVF) and fully turbulent Taylor vortex flows (TTVF). Intracellular mixing increases monotonically with Reynolds number, regardless of the flow state.

Characterisation of Isolated Mixing Regions in a Stirred Vessel

An experimental study of isolated mixing regions (IMRs) in a cylindrical vessel stirred by three different impellers (a six-blade Rusthon turbine, a four-blade Lightnin A315 impeller and an axial CPE RTF4 impeller) has shown the existence of IMRs in all three systems at low Reynolds numbers. Calculations of the Re ranges in which IMRs exist, torque measurements and flow visualizations enabled the analysis of the effects of impeller type and the flow structures when IMRs were present. Particular attention was given to the case of the Rushton turbine, where digital image analysis revealed that the mechanism of IMR disappearance can be described as a period-doubling locus in the physical space, in which IMRs completely disappear at a critical Re, resulting in global mixing.

Prediction of onset of Taylor-Couette instability for shear-thinning fluids

AbstractThe definition of Reynolds number (Re) in a Taylor-Couette flow for a shear-thinning fluid is discussed in this paper. Since the shear-thinning property causes spatial distribution of fluid viscosity in a Taylor-Couette flow reactor (TCFR), a method to determine Re by using a numerical simulation is suggested. The effective viscosity (ηeff) in Re was the average viscosity using a weight of dissipation functionηeff=∑i=1Nγ⋅i2ηiΔVi/∑i=1Nγ⋅i2ΔVi,