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- Volume 19, Issue 2, 2014
South African Journal of Chemical Engineering - Volume 19, Issue 2, 2014
Volume 19, Issue 2, 2014
Source: South African Journal of Chemical Engineering 19, pp 1 –17 (2014)More Less
The influence of temperature on the solubility of 27 volatile organic compounds (VOCs) representing seven VOC families in biodiesel esters was investigated. Phase equilibrium data in the form of infinite dilution activity coefficients were predicted for a temperature range of 30° to 50°C using the Modified UNIFAC Dortmund Group Contribution Model. The desired phase equilibrium data were computed using a Microsoft Excel spreadsheet designed for this purpose. It was found that alkane activity coefficients decreased with increasing temperature, but do not approach ideality with increasing temperature. With the exception of the acroleins, activity coefficients of the aldehydes decreased with increasing temperature, approaching ideality. Activity coefficients of organic acids in unsaturated esters tended towards ideality whilst interactions with unsaturated esters deviated from ideality. With the exception of tetrahydrofuran and tetrahydropyran, ether interactions with ester solvents generally tended towards ideality. It was also observed that the activity coefficients of formates and carbonates particularly ethyl formatein biodiesel generally tended towards ideality with increasing temperature. The interactions in this study show that ester/solute interactions yielding activity coefficients greater than 1 favour higher absorption temperatures whilst those with coefficients less than 1 favour lower absorption temperatures.
Process simulation and parametric study of a biogas upgrading plant using gas permeation technique for methane enrichmentSource: South African Journal of Chemical Engineering 19, pp 18 –31 (2014)More Less
An operational biogas upgrading plant with cleaning process and methane (CH4) enrichment has been presented in this study. Parametric study was carried out to investigate the effect of varying the operating conditions on CH4 recovery, product purity and gas processing cost (GPC). Double stage with permeate recycle gave a good approximation of the plant upgrading result. An increase in %CO2 in the feed composition from 10-60% reduces the CH4 recovery by 4.1%. Increase in membrane selectivity from 5.6 to 33.33 increased CH4 recovery by 7.11% and reduced the membrane area required for separation by 47.73%. Pressure increase also increased CH4 recovery up to the module design configuration limit. Increasing feed flow rate from 80-140m3/h increased CH4 recovery by 6.2% with 2.6% increase in membrane area. The GPC at optimal condition was $0.36/Nm3 with 96% CH4 recovery and 91% product purity.
Statistical experimental design for the optimisation of dilute sulphuric acid hydrolysis of oil palm empty fruit bunchSource: South African Journal of Chemical Engineering 19, pp 32 –41 (2014)More Less
Dilute acid hydrolysis was applied for the pretreatment of oil palm empty fruit bunch (OPEFB) to produce fermentable sugars. Chemical composition analysis of the OPEFB used in this study revealed that the major components were cellulose, hemicellulose and lignin which accounted for 40.2, 22.1 and 19.2% of the material respectively. The OPEFB was subjected to dilute sulphuric acid hydrolysis and the effect of temperature (100-150 °C), acid concentration (0.5-3.0 %w/w), time (10-40 min) and liquid to solid ratio (30-40 mL/g) on the hydrolysis pr°Cess was quantitatively evaluated using a four variable Box-Behnken design. Response surface methodology (RSM) was used to optimise the hydrolysis pr°Cess in order to obtain maximum fermentable sugar yield. The optimum hydrolysis temperature, acid concentration, time and liquid to solid ratio were obtained as 150 °C, 3 %w/w, 30 minutes and 40 mL/g respectively. Under these conditions, the maximum sugar yield was obtained to be 94.74%.
Source: South African Journal of Chemical Engineering 19, pp 42 –56 (2014)More Less
A two-bed pressure swing adsorption (PSA) system for nitrogen separation from air using carbon molecular sieve is studied. The effects of feed flow rate, purge-to-feed ratio (P/F), and adsorption step pressure as well as adsorption step time on the product purity and recovery are also investigated. The energy, mass and momentum balances are included in the model. The coupled PDEs are solved using fourth order Runge-Kutta scheme. Results showed that nitrogen purity decreases with feed flow rate. As the P/F and adsorption pressure are increased the nitrogen purity also increases. The simulation results also have very good agreement with the experimental data.