Daijia Zhang

Stoichiometric analysis and experimental investigation of glycerol bioconversion to 1,3-propanediol by Klebsiella pneumoniae under microaerobic conditions

In this study, the glycerol metabolism by Klebsiella pneumoniae is stoichiometrically analyzed according to energy (ATP), reducing equivalent and product balances. The theoretical analysis reveals that a microaerobic condition is more perfect for the production of 1,3-propanediol (1,3-PD) from glycerol by K. pneumoniae than anaerobic and aerobic conditions. The yields of 1,3-PD, biomass and ATP to glycerol under microaerobic conditions depend not only on the molar fraction of reducing equivalent oxidized completely by molecular oxygen in tricarboxylic acid (TCA) cycle (δ), but also on the molar fraction of TCA cycle in acetyl-CoA metabolism. The maximum theoretical yield of 1,3-PD to glycerol could reach to 0.85 mol/mol rather than 0.72 mol/mol if all acetyl-CoA entered into TCA cycle instead of acetic acid pathway under anaerobic conditions. The yield of 1,3-PD is still higher than 0.72 mol/mol in a range of δ between 0.11 and 0.48, which corresponds to respiratory quotient (RQ) between 11.34 and 2.66. In the same range of δ or RQ, the biomass under a microaerobic condition is more than that of an anaerobic culture. The experimental results of batch cultures demonstrate that microaerobic cultivations are favorable for cell growth, reduction of culture time and ethanol formation, and enhancement of volumetric productivity of 1,3-PD. In addition, no aeration could improve the yield of 1,3-PD to glycerol in comparison with that of an anaerobic or aerobic culture.

Theoretical and experimental investigations on the size of alginate microspheres prepared by dropping and spraying

In order to produce functional microspheres with different ranges of sizes for various applications, the size of alginate droplets prepared by dropping and spraying was studied. It was shown that the mean diameter could be controlled by liquid flow velocity and applied voltage as operating parameters using a conventional dropping and an electrostatic dropping method, separately. The formation mechanism of alginate droplets could be categorized into two different modes: Dripping mode and jetting mode. By employing an effective force analysis, the diameters in each modes showed to be well agreed with the numerical simulation within 7% deviations. It was testified that the initial amount of surface charges had a high impact on droplet diameter and the liquid flow velocity played a more important role on mean diameter of alginate droplets by electrostatic dropping method in dripping mode than in jetting mode. Then, an empirical equation and a semi-empirical model were used to simulate the diameter of droplets obtained by spraying and spraying with electrostatic field (SEF) method, respectively. The decrease in diameter was more sensitive to the increase of gas flow rate than to the decrease of liquid flow rate, and the results of two models fitted well with experimental values. The simulations showed that SEF yielded a 20% lower on droplet diameter than simple spraying method.

Partition behavior of hydrophilic diols in an ethanol/ammonium sulfate salting-out extraction system

It is important to investigate the partition behavior of hydrophilic alcohols at different process parameters in order to have a deep understanding of the salting‐out extraction technique and to design suitable downstream processes. First, phase diagram data of ethanol/ammonium sulfate at 293.15 K were obtained, and the reliability of binodal curve and tie line data were proved by Merchuk, Othmer–Tobias, and Bancroft equations, respectively. Then, the partition behavior of five short‐chain diols was studied. For different tie lines, the partition coefficient changed linearly with an increase in tie line length. The concentration of diols also had a significant effect on the partition behavior due to the similarity between diols and ethanol. Further, the effect of temperature was increased as the hydrophobicity of the diols increased, and the partition behavior of diols was correlated with their hydrophobicity, implying that the solutes with higher hydrophobicity could be extracted more effectively. These findings are useful for designing an economic and efficient salting‐out extraction process for diverse products.