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Oxidative desulfurization of fuels using ionic liquids: A review? ?
Hua Zhao,Gary A. Baker
Front. Chem. Sci. Eng.. 2015, 9 (3): 262-279.
https://doi.org/10.1007/s11705-015-1528-0
Extractive oxidation, wherein aromatic sulfur-containing compounds are extracted and subsequently oxidized to their corresponding sulfones, has proven to be one of the most effective desulfurization methods for producing ultra-low sulfur content fuels. As non-volatile and highly designable solvents, ionic liquids (ILs) have attracted considerable attention for the oxidative desulfurization of fuels. In this review, we systematically discuss the utility of ILs in catalytic and extractive oxidation, including their role as extractant, catalyst, or both. We also discuss the challenges facing the use of ILs in this regard, including their relatively high cost and excessive viscosity, as well as their efficiency and stability as catalyst.
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Metal-free, carbon-based catalysts for oxygen reduction reactions
Zhiyi Wu,Zafar Iqbal,Xianqin Wang
Front. Chem. Sci. Eng.. 2015, 9 (3): 280-294.
https://doi.org/10.1007/s11705-015-1524-4
Developing metal-free, carbon-based catalysts to replace platinum-based catalysts for oxygen reduction reactions (ORRs) is an emerging area of research. In recent years, different carbon structures including carbon doped with IIIA-VIIA heteroatoms (C−M site-based, where M represents the doped heteroatom) and polynitrogen (PN) compounds encapsulated in carbon nanotubes (CNTs) (N−N site-based) have been synthesized. Compared to metallic catalysts, these materials are highly active, stable, inexpensive, and environmentally friendly. This review discusses the development of these materials, their ORR performances and the mechanisms for how the incorporation of heteroatoms enhances the ORR activity. Strategies for tailoring the structures of the carbon substrates to improve ORR performance are also discussed. Future studies in this area will need to include optimizing synthetic strategies to control the type, amount and distribution of the incorporated heteroatoms, as well as better understanding the ORR mechanisms in these catalysts.
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Valorisation of protein waste: An enzymatic approach to make commodity chemicals? ?
Madura B. A. Kumar, Yuan Gao, Wei Shen, Lizhong He
Front. Chem. Sci. Eng.. 2015, 9 (3): 295-307.
https://doi.org/10.1007/s11705-015-1532-4
Protein-rich waste is an abundantly available resource that is currently used mainly as animal feed and fertilizers. Valorisation of protein waste to higher value products, particularly commodity chemicals such as precursors for polymers, has attracted significant research efforts. Enzyme-based approaches, being environmentally-friendly compared to their chemical counterparts, promise sustainable processes for conversion of protein waste to valuable chemicals. This review provides a general overview on valorisation of protein waste and then further summarises the use of enzymes in different stages of the valorisation process—protein extraction and hydrolysis, separation of individual amino acids and their ultimate conversion into chemicals. Case studies of enzymatic conversion are presented for different amino acids including glutamic acid, lysine, phenylalanine, tyrosine, arginine and aspartic acid. The review compares the different enzyme reactors and operation modes for amino acid conversion. The emerging opportunities and challenges in the field are discussed: engineering powerful enzymes and integrating innovative processes for industrial application at a low cost.
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Cyanobacterial photo-driven mixotrophic metabolism and its advantages for biosynthesis
Ni Wan,Mary Abernathy,Joseph Kuo-Hsiang Tang,Yinjie J. Tang,Le You
Front. Chem. Sci. Eng.. 2015, 9 (3): 308-316.
https://doi.org/10.1007/s11705-015-1521-7
Cyanobacterium offers a promising chassis for phototrophic production of renewable chemicals. Although engineered cyanobacteria can achieve similar product carbon yields as heterotrophic microbial hosts, their production rate and titer under photoautotrophic conditions are 10 to 100 folds lower than those in fast growing E. coli. Cyanobacterial factories face three indomitable bottlenecks. First, photosynthesis has limited ATP and NADPH generation rates. Second, CO2 fixation by ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) has poor efficiency. Third, CO2 mass transfer and light supply are deficient within large photobioreactors. On the other hand, cyanobacteria may employ organic substrates to promote phototrophic cell growth, N2 fixation, and metabolite synthesis. The photo-fermentations show enhanced photosynthesis, while CO2 loss from organic substrate degradation can be reused by the Calvin cycle. In addition, the plasticity of cyanobacterial pathways (e.g., oxidative pentose phosphate pathway and the TCA cycle) has been recently revealed to facilitate the catabolism. The use of cyanobacteria as “green E. coli” could be a promising route to develop robust photo-biorefineries.
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High butanol production by regulating carbon, redox and energy in Clostridia? ?
Jianfa Ou,Chao Ma,Ningning Xu,Yinming Du,Xiaoguang (Margaret) Liu
Front. Chem. Sci. Eng.. 2015, 9 (3): 317-323.
https://doi.org/10.1007/s11705-015-1522-6
Butanol is a promising biofuel with high energy intensity and can be used as gasoline substitute. It can be produced as a sustainable energy by microorganisms (such as Clostridia) from low-value biomass. However, the low productivity, yield and selectivity in butanol fermentation are still big challenges due to the lack of an efficient butanol-producing host strain. In this article, we systematically review the host cell engineering of Clostridia, focusing on (1) various strategies to rebalance metabolic flux to achieve a high butanol production by regulating the metabolism of carbon, redox or energy, (2) the challenges in pathway manipulation, and (3) the application of proteomics technology to understand the intracellular metabolism. In addition, the process engineering is also briefly described. The objective of this review is to summarize the previous research achievements in the metabolic engineering of Clostridium and provide guidance for future novel strain construction to effectively produce butanol.
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HDS of dibenzothiophenes and hydrogenation of tetralin over a SiO2 supported Ni-Mo-S catalyst? ?
Qiang Wei, Jinwen Chen, Chaojie Song, Guangchun Li
Front. Chem. Sci. Eng.. 2015, 9 (3): 336-348.
https://doi.org/10.1007/s11705-015-1535-1
A one-step synthesized Ni-Mo-S catalyst supported on SiO2 was prepared and used for hydrodesulphurization (HDS) of dibenzothiophene (DBT), and 4,6-dimethyl-dibenzothiophene (4,6-DMDBT), and for hydrogenation of tetralin. The catalyst showed relatively high HDS activity with complete conversion of DBT and 4,6-DMDBT at temperature of 280 °C and a constant pressure of 435 psi. The HDS conversions of DBT and 4,6-DMDBT increased with increasing temperature and pressure, and decreasing liquid hourly space velocity (LHSV). The HDS of DBT proceeded mostly through the direct desulphurization (DDS) pathway whereas that of 4,6-DMDBT occurred mainly through the hydrogenation-desulphurization (HYD) pathway. Although the catalyst showed up to 24% hydrogenation/dehydrogenation conversion of tetralin, it had low conversion and selectivity for ring opening and contraction due to the competitive adsorption of DBT and 4,6-DMDBT and insufficient acidic sites on the catalyst surface.
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Facile synthesis and enhanced visible-light photocatalytic activity of Ti3+-doped TiO2 sheets with tunable phase composition? ?
Xiaojie Zhang,Lei Wang,Shuqing Chen,Yi Huang,Zhuonan Song,Miao Yu
Front. Chem. Sci. Eng.. 2015, 9 (3): 349-358.
https://doi.org/10.1007/s11705-015-1523-5
Ti3+-doped TiO2 nanosheets with tunable phase composition (doped TiO2 (A/R)) were synthesized via a hydrothermal method with high surface area anatase TiO2 nanosheets TiO2 (A) as a substrate, structure directing agent, and inhibitor; the activity was evaluated using a probe reaction-photocatalytic CO2 conversion to methane under visible light irradiation with H2 as an electron donor and hydrogen source. High-resolution transmission electron microscope (HRTEM), field emission scanning electron microscope, UV-Vis diffuse reflectance spectra, and X-ray diffraction (XRD) etc., were used to characterize the photocatalysts. XRD and HRTEM measurements confirmed the existence of anatase-rutile phase junction, while Ti3+ and single-electron-trapped oxygen vacancy in the doped TiO2 (A/R) photocatalyst were revealed byelectron paramagnetic resonance (EPR) measurements. Effects of hydrothermal synthesis temperature and the amount of added anatase TiO2 on the photocatalytic activity were elucidated. Significantly enhanced photocatalytic activity of doped TiO2 (A/R) was observed; under the optimized synthesis conditions, CH4 generation rate of doped TiO2 (A/R) was 2.3 times that of Ti3+-doped rutile TiO2.
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Fluoroalcohol-mediated reductive iodonio-Claisen rearrangement: Synthesis of complex ortho-substituted-allyl iodoarenes? ?
Hem Raj Khatri,Hai Nguyen,James K. Dunaway,Jianglong Zhu
Front. Chem. Sci. Eng.. 2015, 9 (3): 359-368.
https://doi.org/10.1007/s11705-015-1530-6
Reductive iodonio-Claisen rearrangement (RICR) involving λ3-iodanes and allyl or substituted-allyl silanes in fluoroalcohols, such as 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) and 2,2,2-trifluoroethanol (TFE), was studied for the synthesis of complex ortho-allyl or substituted-allyl iodoarenes. In comparison to the previously reported condition involving boron trifluoride diethyl etherate, the RICR mediated by fluoroalcohols was found to proceed more effectively. The resulting complex ortho-allyl iodoarenes are useful synthetic intermediates and can be readily converted to various heterocyclic compounds.
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High production of butyric acid by Clostridium tyrobutyricum mutant? ?
Chao Ma,Jianfa Ou,Matthew Miller,Sarah McFann,Xiaoguang (Margaret) Liu
Front. Chem. Sci. Eng.. 2015, 9 (3): 369-375.
https://doi.org/10.1007/s11705-015-1525-3
The objective of this study was to improve the production of butyric acid by process optimization using the metabolically engineered mutant of Clostridium tyrobutyricum (PAK-Em). First, the free-cell fermentation at pH 6.0 produced butyric acid with concentration of 38.44 g/L and yield of 0.42 g/g. Second, the immobilized-cell fermentations using fibrous-bed bioreactor (FBB) were run at pHs of 5.0, 5.5, 6.0, 6.5 and 7.0 to optimize fermentation process and improve the butyric acid production. It was found that the highest titer of butyric acid, 63.02 g/L, was achieved at pH 6.5. Finally, the metabolic flux balance analysis was performed to investigate the carbon rebalance in C. tyrobutyricum. The results show both gene manipulation and fermentation pH change redistribute carbon between biomass, acetic acid and butyric acid. This study demonstrated that high butyric acid production could be obtained by integrating metabolic engineering and fermentation process optimization.
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Real time monitoring of bioreactor mAb IgG3 cell culture process dynamics via Fourier transform infrared spectroscopy: Implications for enabling cell culture process analytical technology
Huiquan Wu, Erik Read, Maury White, Brittany Chavez, Kurt Brorson, Cyrus Agarabi, Mansoor Khan
Front. Chem. Sci. Eng.. 2015, 9 (3): 386-406.
https://doi.org/10.1007/s11705-015-1533-3
Compared to small molecule process analytical technology (PAT) applications, biotechnology product PAT applications have certain unique challenges and opportunities. Understanding process dynamics of bioreactor cell culture process is essential to establish an appropriate process control strategy for biotechnology product PAT applications. Inline spectroscopic techniques for real time monitoring of bioreactor cell culture process have the distinct potential to develop PAT approaches in manufacturing biotechnology drug products. However, the use of inline Fourier transform infrared (FTIR) spectroscopic techniques for bioreactor cell culture process monitoring has not been reported. In this work, real time inline FTIR Spectroscopy was applied to a lab scale bioreactor mAb IgG3 cell culture fluid biomolecular dynamic model. The technical feasibility of using FTIR Spectroscopy for real time tracking and monitoring four key cell culture metabolites (including glucose, glutamine, lactate, and ammonia) and protein yield at increasing levels of complexity (simple binary system, fully formulated media, actual bioreactor cell culture process) was evaluated via a stepwise approach. The FTIR fingerprints of the key metabolites were identified. The multivariate partial least squares (PLS) calibration models were established to correlate the process FTIR spectra with the concentrations of key metabolites and protein yield of in-process samples, either individually for each metabolite and protein or globally for all four metabolites simultaneously. Applying the 2nd derivative pre-processing algorithm to the FTIR spectra helps to reduce the number of PLS latent variables needed significantly and thus simplify the interpretation of the PLS models. The validated PLS models show promise in predicting the concentration profiles of glucose, glutamine, lactate, and ammonia and protein yield over the course of the bioreactor cell culture process. Therefore, this work demonstrated the technical feasibility of real time monitoring of the bioreactor cell culture process via FTIR spectroscopy. Its implications for enabling cell culture PAT were discussed.
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