Chao Song,Xuejun Hu,Shuang Yang,Jinxiao Xu,Chang Chen,Guangqing Liu
Due to the low density and hydrophobicity, the corn straw (CS) particles tend to float on the liquid surface in the anaerobic digester, deteriorating the bioconversion efficiency and process stability. Although the mechanical mixing is widely used in digesters, the drawdown and suspension of CS in the non-Newtonian slurry have not been sufficiently studied. This paper investigated the effect of particle size, liquid viscosity, solid phase mass fraction, impeller type and off-bottom distance on the just-drawdown rotational speed ( N jd ), complete drawdown rotational speed ( N cd ) and cloud depth ( CD ) of dry and wet straw particles in the stirred tank. The results showed that the distribution of dry and wet straw in the stirred tank significantly differed due to differences in density and wettability. The models built by dimensional analysis and machine learning were suitable for accurate predictions of specific variables. Based on the model analysis, the N jd of dry straw was mainly affected by the liquid viscosity, impeller type and off-bottom distance, as these factors determined the flow field of liquid phase for its drawdown. N jd of wet straw was related to the liquid viscosity and N cd was influenced by impeller off-bottom distance. The CD of dry and wet straw particles were both affected by rotational speed, impeller type, and liquid viscosity related to the mean flow and turbulence intensity in the tank. The results provide valuable references for the design and operation of mixing configurations for low-density feedstocks in the anaerobic digester.
Pharmaceutical cocrystals consist of an active pharmaceutical ingredient and a coformer in a fixed stoichiometric ratio. They can improve the manufacturability and properties of a drug powder. However, the manufacture of cocrystals is often more complicated compared to crystals of an active ingredient due to the possible formation of different solid-state forms. Cocrystallization through anti-solvent addition is a commonly used technique. However, the risk of nucleation of multiple solid-state forms is often high due to the high supersaturation levels achieved during anti-solvent crystallization. Therefore, intensifying a solution-mediated phase transformation is important. In this work, the ability of tubular flow crystallizers to intensify the phase transformation process in the carbamazepine-saccharin cocrystal system is characterized and compared to a conventional stirred tank crystallizer. The influence of the flow rate, tubular crystallizer type, and ratio of residence time in the tube to that in the tank are documented. The phase transformation process is substantially faster with the tubular crystallizers compared to that in a stirred tank crystallizer, which we explain through increased nucleation rates. We show that such intensification can be achieved either by recirculating the slurry through a static mixer or by installing a tubular crystallizer upstream of a stirred tank crystallizer.
In this work, the effect of activated carbon particles on the production of xylonic acid from xylose by Gluconobacter oxydans in a stirred tank bioreactor was investigated. The enhancement of the oxygen transfer coefficient by activated carbon particles was experimentally evaluated under different solids volume fractions, agitation and aeration rates conditions. The experimental conditions optimized by response surface methodology (agitation speed 800 rpm, aeration rate 7 L min −1 , and activated carbon 0.002%) showed a maximum oxygen transfer coefficient of 520.7 h −1 , 40.4% higher than the control runs without activated carbon particles. Under the maximum oxygen transfer coefficient condition, the xylonic acid titer reached 108.2 g/L with a volumetric productivity of 13.53 g L −1 h −1 and a specific productivity of 6.52 g/g x /h. In conclusion, the addition of activated carbon particles effectively enhanced the oxygen mass transfer rate. These results demonstrate that activated carbon particles enhanced cultivation for xylonic acid production an inexpensive and attractive alternative.
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