Attasak Jaree

Amplification of inlet temperature disturbances in a packed-bed reactor for CO oxidation over Pt/Al2O3

Abstract The commonly used packed-bed catalytic reactor can exhibit complex dynamic features such as wrong-way behavior, differential-flow instability, different kinds of traveling waves and bifurcation behavior. Understanding these phenomena is essential for developing reliable reactor control systems. Of primary interest to the present study is the differential flow instability, which may cause amplification of small amplitude inlet perturbations of concentration, temperature, and flow rate into large temperature excursions. CO oxidation served as a model reaction to demonstrate resonance amplification of inlet temperature perturbations in a tubular reactor packed with 0.02 wt % Pt / Al 2 O 3 catalyst. Very low-frequency inlet perturbations did not cause large temperature increases in the reactor because the separation of thermal and concentration waves becomes insignificant when the system changes slowly between steady states. High-frequency perturbations, on the other hand, were attenuated as the waves propagated through the reactor bed. However, amplification at intermediate frequencies could be considerable. Amplification could be suppressed by increasing the axial thermal conductivity of the bed or by using highly concentrated catalyst.

Temperature excursions in reactors packed with segregated layers of catalyst and inert solids

Abstract A recent numerical studies by Yakhnin and Menzinger (Proc. 8th Int. Symp. on Catalyst Deactivation, Brugge, Belgium, 10tober, Vol. 126, 1999, pp. 291–298) suggests that activity inhomogeneity in a catalyst bed can create larger temperature excursions after changes in feed temperature than would be encountered in beds with homogeneous catalyst activity. Until now, this finding has not been confirmed experimentally. Inhomogeneous catalyst activity was simulated by constructing a packed bed reactor by successive layers of catalyst and the inert support. Oxidation of carbon monoxide (CO) with oxygen in a nitrogen carrier gas over an industrial 0.2 wt % Pt/ γ –alumina catalyst was employed. This reaction is exothermic and inhibited by CO. Step changes and periodically varying inlet temperature were used to generate disturbances. Both wrong-way behaviour and differential flow instability were observed. Temperature excursions in the layered bed significantly exceeded those in a bed of homogeneous activity at the same operating conditions.

Pork lard conversion to biodiesel using a microchannel reactor

Biodiesel was synthesized from pork lard via transesterification using a microchannel reactor. To investigate the effects of operating parameters, including reaction temperature (55–65 °C), residence time (5–20 s), methanol-to-oil molar ratio (4.5 : 1 to 9 : 1), and catalyst concentration (0.7–1.3 wt%), a series of full factorial experiments with a complete replicate were conducted. Results were statistically analyzed using MINITAB with the significance level of 0.05. A quadratic model was proposed for the prediction of %FAME from the specified operating conditions. High %FAME was obtained at low residence time due to the small size of droplets in the microchannel reactor. Evidence of droplets supported the presence of mass transfer limitation in this system. The optimal operating conditions provided %FAME of 95.41% were as follows: methanol-to-oil ratio of 6 : 1, temperature of 65 °C, residence time of 5 s, and KOH concentration of 1.3%w/w.

Synthesis of molecularly imprinted polymers from AnAc for the separation of γ-oryzanol

The selectivity of gamma-oryzanol (γ-oryzanol) was recognized by molecularly imprinted polymer (MIP). Polymeric materials were successfully synthesized via thermal polymerization method using γ-oryzanol as template, anacardic acid (AnAc) as functional monomer, toluene as porogen, benzoyl peroxide (BPO) as initiator and divinylbenzene as crosslinker. Binding performance of MIPs was evaluated by MINITAP 14 for variance of analysis, linear regression analysis and adequating model through full factorial experimental technique in terms of adsorption capacity. Analysis of variance with 95% confidence level suggested significant interaction effect (amounts of template, porogen, crosslinker) on adsorption capacity of MIPs. The strongest interaction is between the amount of porogen and the amount of crosslinker. It was also found that a linear regression model for adsorption capacity represents the experimental data with the correlation coefficients (R2) greater than 0.9. The MIP synthesis with 0.8 mmol of template, 6 ml of porogen and 10 ml of crosslinker provided the highest adsorption capacity of MIP (1.14 mg/g-adsorbent). The proposed method is relatively rapid and easy to perform for the separation of γ-oryzanol in non-aqueous systems.

Competitive effect of glucose–fructose adsorption in a fixed‐bed chromatographic column

A continuous separation system such as a simulated moving-bed process requires adsorption data with precise equilibrium and kinetic model parameters of a single chromatographic column. The adsorption of glucose and fructose in a fixed-bed chromatographic column was investigated to determine the competition effect of each component resulting from their initial molar ratios. The model parameters including bed porosity and axial dispersion coefficient were determined using the moment analysis method. The equilibrium isotherm parameters were estimated by conducting experiments at various molar ratios and initial sugar concentrations. The parameters obtained were then used for the simulation of dynamic breakthrough curves of glucose and fructose. The equilibrium isotherms revealed that the linear adsorption pattern provided good prediction for each molar ratio using the Henry equation. In addition, the modified Langmuir model was proposed to account for the competitive adsorption, due to the cooperative competition effect whereby glucose was promoted to the active sites by fructose to a greater degree than vice versa. A good agreement between the experimental and numerical data of the adsorption time profiles was also observed.

Carbon dioxide capture using monoethanolamine in a microchannel

Carbondioxide (CO2) capture has considerably gained the interest from industry and research. To reduce CO2 emission and utilize the purified CO2, many processes have been developed such as packed-bed, bubble column etc. This work applied micro-technology for the absorption of CO2 by using monoethanolamine (MEA). Factors for the investigation include pressure (1-3 atm) molar ratio between MEA and CO2 (2:1 4:1) and volumetric flow rate of liquid phase (3-5 ml/min). The variation of liquid phase volumetric flow rate while keeping the molar ratio constant did not significantly affect the CO2 absorption efficiency. For atmospheric pressure, increasing the molar ratio slightly improved the performance. Increasing the operating pressure caused this effect to markedly decrease the log-mean CO2 concentration. By comparing the mass transfer coefficient obtained from different types of unit operation, microchannel exhibited high potential due to the high value of