Korean Journal of Chemical Engineering

The carbon dioxide reforming of methane under periodic operation over a commercial Ni/SiO2·MgO catalyst was investigated at two different temperatures, 923 and 1,023 K. According to this operation, pure methane and carbon dioxide were alternately fed to the catalyst bed where methane cracking and the reverse Boudouard reaction took place, respectively. Therefore, hydrogen and carbon monoxide products appeared separately in different product streams. The performance of this operation was compared to that of the steady state operation with simultaneous feed of both carbon dioxide and methane. At 1,023 K, the methane conversion and hydrogen yield from the periodic operation initially decreased with time on stream and eventually leveled off at values about half of those obtained in the steady state operation with co-feed of both reactants. The decreased catalytic activity was due to the accumulation of carbonaceous deposit and loss of metal active sites. However, a different trend was observed at 923 K. The methane conversion and hydrogen yield were almost constant over the time on stream, although more carbonaceous deposit was progressively accumulated on the catalyst bed during the reaction course. At this temperature, the periodic operation offered the equivalent hydrogen yield to the steady state operation. The observed behavior could be due to the different mechanisms of carbon formation over the catalyst. Finally, it was found that cycle period and cycle split did not influence the reaction performance within the ranges of this study.

We examined the conversion of HFC-134a over five catalysts, Na2CO3, CaO, CaCO3, and two types of γ-Al2O3 with different surface areas, between 300 and 600 °C. HFC-134a was barely converted via the non-catalytic reaction, even at the highest temperature (600 °C). The operating temperatures for the catalytic conversion of HFC-134a were reduced dramatically and its efficiency increased with increasing temperature. Among the catalysts used, γ-Al2O3 with the larger surface area showed the highest conversion rate of HFC-134a, which was followed, in order, by γ-Al2O3 with the smaller surface area, CaCO3, CaO, and Na2CO3. The conversion rate of γ-Al2O3 decreased rapidly due to catalyst deactivation. The catalytic efficiency of γ-Al2O3 was maintained for a longer period by water addition. Water acted as a hydrogen donor for the dehydrofluorination reaction.

Four strains of yeast with reduction activity of chloroacetophenones were screened, in which Saccharomyces cerevisiae B5 showed best reduction activity and stereoselectivity. High optical purity (R)-2′-chloro-1-phenylethanol can be obtained with Saccharomyces cerevisiae B5 as biocatalyst. The influence of several co-substrates on the enantiometric excess (ee%) and yield of (R)-2′-chloro-1-phenylethanol was evaluated. 5% (v/v) ethanol is optimal cosubstrate for (R)-2′-chloro-1-phenylethanol formation. The optimal bioconversion conditions of 2′-chloroacetophenone catalyzed by Saccharomyces cerevisiae B5 are as follows: pH 8.0, 25 °C and 24 h. The yield and the enantiometric excess of (R)-2′-chloro-1-phenylethanol can both reach more than 99% with 10.75 g/l Saccharomyces cerevisiae B5 (the cell dry weight) and 1 g/l 2′-chloroacetophenone used in the biotransformation.

A chattering-free sliding mode controller (CFSMC) is proposed to realize level position control of liquid level system for two coupled water tanks, as is often encountered in practical process control. The controller is used due to its robustness against large parameter variation, disturbances rejection and reduction in chattering. Experimentation of the coupled tank system is realized in two different configurations: configuration 1 and configuration 2. In configuration 1, the water level in the top tank is controlled by a pump. In 2, the water level in the bottom tank is controlled by the water flow coming out of the top tank. The validity of the proposed controller is verified by means of a practical testing on an experimental liquid level control device.

The interaction of an electric field with a dielectric liquid film is investigated as it drains under gravity down an inclined plane electrode emitting uniform positive ions into the liquid region. By applying long-wave approximation to the governing equations, the evolution equation for the free surface is derived up to the first order of a thin film parameter ξ To investigate the space charge effect on the development of a finite-amplitude surface wave, a neutral stability condition is obtained as a critical Reynolds number through a linear stability analysis, and the amplitude and velocity of a periodic disturbance are also calculated within a supercritically stable flow region. The presence of a unipolar space charge in the fluid makes a steady surface wave take on even higher amplitude and faster wave speed compared with the case of no space charge.

A cascade control strategy is proposed to the benchmark simulation model 1 (BSM1) to enhance the treatment performance of nitrogen removal in a biological wastewater treatment plant. The proposed control approach consists of two control loops, a primary outer loop and a secondary inner loop. The method has two controllers of which the primary loop has a model predictive control (MPC) controller and the secondary loop has a proportional-integralderivative (PID) controller, which is a cascade MPC-PID controller. The primary MPC controller is to control the nitrate concentration in the effluent, and the secondary PID controller is to control the nitrate concentration in the final anoxic compartment. The proposed method controls the nitrate concentrations in the effluent as well as in the final anoxic reactor simultaneously to strictly satisfy the quality of the effluent as well as to remove the effects of disturbances more quickly by manipulating the external carbon dosage rate. Because the control performance assessment (CPA) technique has the features of determining the capability of the current controller and locating the best achievable performance, the other novelty of this paper is to suggest a relative closed-loop potential index (RCPI) which updates the CPA technology into a closed-loop cascade controller. The proposed method is compared with a cascade PID-PID control strategy and the original PID controller in BSM1 and an improved performance of the suggested cascade MPC-PID controller is obtained by using the CPA approach.

Colloidal silver nanoparticles were obtained by chemical reduction of silver nitrate in water with sodium borohydride (NaBH4) in the presence of sodium dodecyl sulfate (SDS) as a stabilizer. The obtained nanoparticles were characterized by their UV-vis absorption spectra and transmission electron micrograph (TEM) images. The UV-vis absorption spectra showed that NaBH4 served not only as a reducing agent but also as a stabilizer, which protects the aggregation of silver nanoparticles. The TEM images showed that the particles were dispersed better with increasing the NaBH4 concentration.

A series of thermosetting shape memory epoxy polymers (SMEPs) were prepared using the epoxy resin diglycidyl ether bisphenol A E-51 with varying content of curing agent 4,4′-diaminodiphenyl methane (DDM). The chemical, thermal and mechanical properties of the SMEPs were systematically investigated via Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic and static mechanical analysis, and thermogravimetric analysis. The results indicate that the shape-memory temperature (Tg) of the SMEPs varies within the range of 33.9 °C to 140.0 °C with DDM content increasing from 12% to 25%, and the Tg values exhibit a good linear correlation, with a correlation coefficient of more than 0.999. This indicates that SMEPs with tunable shape-memory temperatures can be realized by controlling the content of the curing agent. When the DDM content is 17–19%, the shape fixity and shape recovery ratio of the SMEPs reaches approximately 100%. In addition, the shape recovery time decreases as temperature increases. This work also highlights the effect of DDM curing agent content on the thermal, mechanical and shape-memory properties of SMEPs, and it is in favor of extending their further applications.