No abstract

At the bench scale, transfer of solid-liquid streams between reaction vessels or crystallizers that operate continuously poses a significant problem. Reduced equipment size of pumps and valves (i.e. approaching that on the microfluidic scale) means even further reduced orifices in which suspensions must attempt to flow. It forces bridging of solids and leads to blockages in flow.This study presents a new pressure-driven flow crystallizer (PDFC) with a custom-built suspension transfer pumping system. In the system, a dip tube is used to carry suspension between crystallizers by controlling the pressure differences of the crystallizers. This novel system has a small footprint on the scale of similar bench-top flow synthesis systems, and has been demonstrated to operate continuously with intermittent withdrawal for at least 24 hours.The system accommodates both cooling and antisolvent crystallization. It is compatible with a variety of solvents, can handle crystals with large and small aspect ratios, and it can also handle a large range of crystal sizes and suspension density. The miniature design of the system requires as little as 0.36 psig (0.025 bar(g)) pressure to operate and a design equation can be used to guide the estimation of the minimum pressure needed for the transfer of suspensions at larger scales.

In this work, the technical, economic, and environmental viability of the growth, harvest, drying, and extraction of oil from Chlorella vulgaris was evaluated. A flue stream from a rice husk processing plant was taken as the substrate for microalgae growth and the production of 1 ton/h of microalgae oil. The mass and energy balances were calculated using Aspen Plus Software. The economic assessment was developed using Aspen Process Economic Analyzer Software. The environmental impact evaluation was carried out using the waste reduction algorithm (WAR). The yields of the process were 0.37 kg of oil/kg of dry microalgae and 0.63 kg of cake/kg of dry microalgae. The production costs were 0.56 USD/kg of oil and 0.33 USD/kg of cake. The potential environmental impact was 0.003 PEI/kg of product. The results indicate significant mitigation of smog formation potential because gases are used to generated value-added products.

In this paper, fuel ethanol production from Chlorella vulgaris cake was evaluated by experimental and conceptual design techniques. Enzymatic hydrolysis and fermentation with Saccharomyces cerevisiae was performed to quantify the reducing sugars and ethanol from microalgae cake. Extractive distillation and molecular sieves were evaluated as alternative technologies for the dehydration of ethanol. The mass and energy balances were solved using the Aspen Plus software. The total ethanol production costs were evaluated using the Aspen Process Economic Analyzer software, and the Waste Reduction algorithm (WAR) was used to calculate the environmental impacts. Additionally, the effect of energy integration was included in the economic analysis and environmental assessment. The yields obtained for reducing sugars and ethanol were 0.55 and 0.17 g per g of cake, respectively. The global yield of ethanol was 211.9 L per tonne of cake, and the total production cost was 0.76 and 0.91 USD per liter using molecular sieves and extractive distillation, respectively. The most promising technology to produce ethanol from microalgae cake was dehydration by molecular sieves with full energy integration. For this technology, the production cost was 0.76 USD per liter, which resulted in an economic margin of 19.15%. From the environmental point of view, the potential environmental impact was 0.84 PEI/kg products. Additionally, bioethanol from microalgae was shown to be less harmful than bioethanol from corn and sugar cane.

In the pharmaceutical industry, it is often desired to produce seed crystals with an appropriate narrow size distribution of the desired polymorph. This study describes a system that generates such crystals continuously in a small-scale tubular crystallizer at low supersaturation via contact secondary nucleation. A response surface model was constructed by conducting a statistical design of experiment that models the nucleation rate as a function of contact force, area, and frequency. This model reveals that within a certain range the nucleation rate is linearly related to all three factors in this system. A combination of in-line video analysis and off-line microscope image analysis was used to determine the particle size distribution of seed crystals obtained in this system, and the majority of the crystals were found to be under 20 μm. This seems to be a feature of contact secondary nuclei in general and does not vary significantly with contact force, area, and frequency. Furthermore, the seed crystals generated are of the same polymorph as the parent crystals as a result of the attrition process. This study shows that generating seed crystals with a narrow size distribution using contact secondary nucleation for a continuous tubular crystallizer can be realized at a controlled rate by quantitative variation of certain design parameters.