Continuous Fixed Bed CO2 Adsorption: Breakthrough, Column Efficiency, Mass Transfer Zone

The increased levels of carbon dioxide in the environment have incited the search for breakthrough technologies to lessen its impact on climate. The CO2 capture from a mixture of CO2/N2 was studied using a molecular sieve (MS) and silica gel type-III. The breakthrough behavior was predicted as a function of temperature, superficial velocity, and CO2 partial pressure. The breakpoint time reduced significantly with increased temperature and increased superficial velocity. The CO2 adsorption capacity increased appreciably with decreased temperature and increased CO2 pressure. The saturation CO2 adsorption capacity from the CO2/N2 mixture reduced appreciably with increased temperature. The molecular sieve contributed to higher adsorption capacity, and the highest CO2 uptake of 0.665 mmol/g was realized for MS. The smaller width of the mass transfer zone and higher column efficiency of 87.5% for MS signify the efficient use of the adsorbent; this lowers the regeneration cost. The findings suggest that a molecular sieve is suitable for CO2 capture due to high adsorption performance owing to better adsorption characteristic parameters.

Scale-Up of Self-Regenerating Semi-Batch Adsorption Cycles through Concurrent Adsorption and Reduction of Cr(VI) on Sheep Wool

A previous publication by our group reported that adsorption of Cr(VI) on sheep wool reached 99% when allowed a long residence time, with concurrent reduction to Cr(III). In this study, the process was scaled up by optimizing a pilot plant based on semi-batch adsorption cycles. This yielded Cr(III), which is about 300 times less toxic than Cr(VI), and can be precipitated using lime at high pH. Since the reduction step is slower than the adsorption one, an adsorption column was designed to perform semi-batch operation cycles, whereby the extended “off cycle” allows reduction to take place. Since reduction of Cr(VI) frees active sites on wool, the plant acts in lieu of in situ regeneration, accompanied by additional adsorption of Cr(VI). The results show that 97% of the column efficiency can be recovered within 24 h of “off cycle”. Wastewater from a local electroplating industry was treated by this method with high removal of Cr(VI), reaching the limit permitted by environmental standards. This study also reveals that typical concentrations of heavy metals, present in wastewater produced from electroplating, had no substantial antagonistic interference with Cr(VI) adsorption.

ACETONE RECOVERY USING BATCH DISTILLATION

This study focuses on determining the feasibility of obtaining maximum mole percentage of acetone (99 mole%) in the distillate stream from a 3 mole% acetone waste stream using batch distillation. The device which is used in this work has eight trays that will act as the stages of the batch distillation. The effects of varying reflux ratio and heat load (power) on acetone concentration were studied. Moreover, the operating conditions for the bath distillation column such as flooding and weeping with the extreme limits of operation were considered. The temperatures were also be recorded at each tray. The McCabe-Thiele method was used to determine the theoretical number of trays and compared with actual trays (column efficiency). For a chemical analysis of acetone/water compositions a refractometer was used for a chemical analysis, known acetone/water concentrations were analysed and used to construct a calibration curve. The results obtained showed that, the acetone concentration increases with increasing reflux ratio until a highest concentration was reached. Then, the concentration gradually decreases with increasing reflux ratio. However, the distillate stream with 99 mole % acetone was achieved at a reflux ratio of R=3 and at both powers 0.5 kw and 0.7 kw. Finally, the highest overall column efficiency reached by this work was about 75%.