Investigating and understanding CO2 levels in school classrooms

 It is a reported fact that a high CO2 concentration is a problem in school classrooms. However, the mere reporting of such results stops short of investigating causes; understanding is often missing. Steady-state results are often used in situations where changes occur frequently, such as varying student numbers, opening and closing classroom doors and windows and changing weather conditions. We revisit the mass balance model commonly used to predict or track CO2 concentrations in enclosed spaces as these factors change over time under varying conditions. This has prompted the study in several classrooms of actual air exchange rates, student exhalation rates, room volumes and ventilation design. In these cases, student numbers, room ventilation conditions (open and closed doors), room volume and the CO2 concentration have been recorded throughout the day. By fitting the model equation to the data, unknown parameters such as actual air change rates and CO2 exhalation rates per student can be determined. Having verified that the data can be modelled, we can predict behaviour in other cases such as a realistic rate of CO2 increase. This allows designers to size classrooms and ventilation systems to achieve a desired CO2 characteristic for known usages while saving energy.

Wool powders used as sorbents to remove Co2+ ions from aqueous solution

The Co2+ sorption of two wool powders was investigated using its radioisotope 57Co (T1/2=271.8 days and γ=122.1 and 136.5 keV) as a tracer. The effects of the type of buffer, the pH value, the contact time and the initial concentration of Co2+ on the sorption behaviour of wool powders were studied. The Co2+ releasing ability of wool powders and the re-use of wool powders to sorb Co2+ were also examined. The optimum sorption of Co2+ by the powders occurred at pH 8 in phosphate buffer and pH 10 in ammonium sulphate buffer. Fourier-transform infrared spectroscopy (FTIR) was used to study the changes in chemical structure of the wool after exposure to both buffer solutions. Compared to the untreated wool fibre, the fine wool powders showed rapid sorption rates and high sorption capacities for Co2+. Co2+ ions were recovered after exposing the Co2+ loaded wool to HCl (0.1 M) and buffer at pH 3 (glycine/sodium chloride). After releasing Co2+ ions from wool powders, the efficiency of wool powders re-used to sorb Co2+ was 80% of that of the fresh wool powders. It is concluded from this study that wool powder can be used as an efficient sorbent to remove and release Co2+ from solution.

Nanofiltration for the concentration of heat stable salts prior to MEA reclamation

While monethanolamine has shown great potential as a solvent for the capture of carbon dioxide, impurities can build within the solution over time, leading to increased viscosity and corrosivity. Classically, these impurities are removed by a combination of neutralization and either thermal reclamation, ion exchange or electrodialysis. In this work, we evaluate the use of nanofiltration to concentrate the heat stable salts within the solution prior to such reclamation. This allows the recirculating solvent to operate with low concentrations of these impurities, while providing a low volume, concentrated solution for reclamation. Results show that nanofiltration can reject greater than 80% of the heat stable anions, while allowing the monoethanolamine to permeate through the membrane, for return to the process. Rejection of the MEA itself is less than 7%. The nanofiltration operation is only effective on lean solvent with CO2 loadings of less than 0.2 and neutralization would be required upstream to deprotonate the amine. The two membranes tested (Koch MPF-34 and MPF-36) appeared stable to exposure to the solvent for over four months.