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- Volume 18, Issue 2, 2013
South African Journal of Chemical Engineering - Volume 18, Issue 2, 2013
Volume 18, Issue 2, 2013
Source: South African Journal of Chemical Engineering 18, pp 1 –13 (2013)More Less
In this study the separation of two alkenes, ethene and butene, which have similar physical properties, was attempted for industrial gas purification. Using both inorganic (ceramic and zeolite NaA) and polymeric (Teflon AF 2400) coated ceramic membranes, a mixture of 70 % ethene and 30 % butene was separated. Both membranes showed promising single gas permeation, where the best inorganic ideal selectivity (α = 9), was obtained for the NaA coated ceramic membrane. The Teflon AF 2400 coated ceramic membrane had an ideal selectivity of 31. For the binary mixture, the NaA coated ceramic membrane was however not able to separate the mixture satisfactorily, probably due to intercrystalline boundary diffusion. The Teflon coated membrane yielded a selectivity o 4 with a permeate permeance of 1.98x10-3 mol.s-1.m-2.bar-1.
Source: South African Journal of Chemical Engineering 18, pp 14 –28 (2013)More Less
The oxidative desulphurization followed by catalytic adsorption method was used for desulfurization of diesel oil. The diesel fuel was oxidized at temperature range of 70-80°C with hydrogen peroxide (H2O2) in the presence of formic acid. The effectiveness of the process mainly depends on (1) Efficient decomposition of (H2O2) in the diesel to oxidize various Organic sulfur compounds (sulfones, sulfoxides) and to extract them via polar solvent (2). Developing and analyze the catalytic adsorbent for the adsorption of unextracted aromatic sulphur compound (DBT). A porous Zeolite catalytic support mainly composed of Alumina and Silica was synthesized, and the said catalytic support loaded with Single walled carbon Nanotubes (SWNT's) to enhance the catalyst adsorption capability. FTIR spectral images of diesel and SEM "Scanning electron microscopic images"/EDX "Energy-dispersive X-ray" studies of catalyst provided a better qualitative approach as visual assessment of porosity and surface behavior. The proposed method can remove complex sulfur compounds from diesel fuel of high sulphur contents up to 80% in total.
Difference of hydrodynamics for a VPE with and without mass transfer and effect of agitation level on extent of mass transferSource: South African Journal of Chemical Engineering 18, pp 29 –39 (2013)More Less
Liquid-liquid extraction offers an alternative separation technique, other than distillation, that uses a solvent for the separation of liquid constituents (Pratt, 1983). The vibrating plate extractor (VPE) is a mechanically agitated column that offers many advantages to conventional extraction equipment. Besides the dimensions of the column (diameter and height) and plate design, the VPE has many variables that may be appropriately adjusted to achieve the desired results viz. amplitude and frequency of vibrations, tray spacing, individual flow rates and the final throughput. The first part of the paper investigates the difference in hydrodynamics of the column due to the mass transfer process showing that the hydrodynamics (dispersed phase holdup, droplet size and size distribution) cannot be investigated without mass transfer in order to predict the behaviour during mass transfer. The second part of this paper is devoted to the investigation of the effect of agitation level on the extent of mass transfer.
Source: South African Journal of Chemical Engineering 18, pp 40 –51 (2013)More Less
The discharge of heavy metals into aquatic ecosystem has become a matter of concern in South Africa over the last few decades. These pollutants are introduced into the aquatic systems significantly as a result of various industrial operations. Conventional methods for metal removal such as ion exchange, reverse osmosis, etc. have proven to be expensive. Due to the increasing awareness of ecological effects of heavy toxic metals, a research on new and cheap technologies involving the removal of heavy toxic metals from wastewater on the principle of adsorption was investigated in this study. The aim of the study was to investigate the adsorption characteristics of marine algae on copper solution as an alternate cheaper option with emphasis on its adsorption efficiency, stability and regeneration. In this study, the rate and extent for removal of copper is subjected to parameters such as pH, initial metal concentration, biosorbent size, contact time, temperature and the ability of the biomass to be regenerated in sorption-desorption experiments. The metal adsorption was found to be rapid within 25 minutes. The maximum copper uptake of 30 mg of copper / g of biomass has been observed, in the following conditions: 100 mg / L, 0.1 g of biomass, pH 4 and at temperature of 25°C. Metal biosorption behaviour of raw seaweed Sargassum in six consecutive sorption-desorption cycles were also investigated in a packed-bed column, during a continuous removal of copper from a 35 mg/l aqueous solution at pH 4. The sorption and desorption was carried out for an average of 85 and 15 hours, respectively, representing more than 40 days of continuous use of the biosorbent. The weight loss of biomass after this time was 13.5%. The column service time decreased from 25 hrs in the first cycle to 10 hrs for the last cycle. From this study, it was found that copper uptake is increasing with increase in pH, with optimum being pH 4. The biomass of the marine algae Sargassum species demonstrated a good capacity of copper biosorption, highlighting its potential for effluent treatment processes.
Source: South African Journal of Chemical Engineering 18, pp 52 –68 (2013)More Less
Refinery processes undergo periodic changes of operating conditions in response to changes in the composition of process streams, and to satisfy product specifications while compensating for the loss of catalyst activity. Multi-period hydrogen management approach may be employed to account for changing operating conditions of refinery processes in the design of refinery hydrogen networks at a conceptual level (Ahmad et al. 2010). In this work the short-cut models of Liu and Zhang (2004), of purification processes employed in refineries for recovery of hydrogen, are modified to account for the changing operating conditions of a hydrogen network. Results indicate reduced total annualised costs compared to previous design optimisation methodologies.
The ozone technology to reduce the concentration of polychlorinated biphenyls (PCBs) in contaminated soil-order of chemical reactionSource: South African Journal of Chemical Engineering 18, pp 69 –79 (2013)More Less
Polychlorinated Biphenyls (PCBs) are hazardous and toxic chemicals to both humans and animals. In the late 1960's PCBs were discovered to be a harmful pollutant which could cause environmental contamination due to its slow degradation. PCBs were added into transformer oil in the past to increase its insulating properties. Oil spills are a frequent occurrence at Eskom substations which may contain PCBs. The contaminated sediments which are easily carried away by rain and wind can further contaminate the environment and aquatic bodies. Eskom, the world's 11th largest power utility has put a phase out plan in place to remove PCBs from the environment by the year 2025 since South Africa is a party to the Stockholm Convention. Eskom currently disposes of soil contaminated with PCBs by thermal destruction. This is a costly process as PCBs are regarded as hazardous materials and needs to be safely transported and disposed of at a licensed disposal facility. Based on literature, ozone has been used on a laboratory scale to treat soil contaminated with PCBs with the addition of chemicals such as hexane and acetone which assist in breaking down PCBs. The objective of this study was to evaluate whether ozone without the addition of chemicals could reduce the levels of PCBs present in contaminated soil. In this study, two soil samples were contaminated with 5ml of transformer oil which contained different PCB ranges (50 ppm, 200 ppm and 600 ppm) of PCBs and then exposed to 0.4, 0.5 and 0.6 l/min of ozone for a period of 60 minutes to examine the effects of increasing ozone flow rates on PCB destruction in soil. The results of the experimental tests showed that ozone gas reduced the concentration of PCBs in the soil samples for the different total gas flow rates. The literature study identified that the final products of the ozonation of PCBs are carbon dioxide and water and that any products formed after this process could possibly be degraded by the soil natural microorganisms. Calculations based on the Shin et al. (2004) model proved that ozone was in excess after the ozonation process. The results of the experiments also confirmed this, as the PCB residuals were similar for all three total gas flows, which showed that there was no dependence on the gas flow rates hence, ozone was in excess. The experimental data was then trended with zero, first and second order reaction equations, which showed that the best fit was obtained with the first-order reaction equation.