Enzymes are able to perform reactions under mild conditions, e.g., pH and temperature, with remarkable chemo-, regio-, and stereoselectivity. Because of this feature, the number of biocatalysts used ...in organic synthesis has rapidly increased during the last decades, especially for the production of chiral compounds. The present review highlights biotechnological processes for the production of chiral alcohols by reducing prochiral ketones. These reactions can be catalyzed by either isolated enzymes or whole cells that exhibit ketone-reducing activity. The use of isolated enzymes is often preferred because of a higher volumetric productivity and the absence of side reactions. Both types of catalysts have also deficiencies limiting their use in synthesis of chiral alcohols. Because reductase-catalyzed reactions are dependent on cofactors, one major task in process development is to provide an effective method for regeneration of the consumed cofactors. In this paper, strategies for cofactor regeneration in biocatalytic ketone reduction are reviewed. Furthermore, different processes carried out on laboratory and industrial scales using isolated enzymes are presented. Attention is turned to process parameters, e.g., conversion, yield, enantiomeric excess, and process strategies, e.g., the application of biphasic systems or methods of in situ (co)product recovery. The biocatalytic production of chiral alcohols utilizing whole cells is presented in part II of this review (Goldberg et al., Appl Microbiol Biotechnol, 2007).
Direct liquid fuel cells: A review Ong, B.C.; Kamarudin, S.K.; Basri, S.
International journal of hydrogen energy,
04/2017, Letnik:
42, Številka:
15
Journal Article
Recenzirano
Direct liquid fuel cells (DLFCs) are one of the most promising types of fuel cells due to their high energy density, simple structure, small fuel cartridge, instant recharging, and ease of storage ...and transport. Alcohols such as methanol and ethanol were the most common types of fuel used, although glycols and acids are also used. The main problem that arose in direct liquid fuel cells (DLFCs) was the high cost of the catalyst and the high catalyst loading. Other issues, such as fuel crossover, cathode flooding, the generation of various side products, fuel safety and unproven long-term durability, must also be solved to improve the performance of DLFCs. More research studies were required to increase its performance and foster commercialization. Currently, there were some commercial products using direct methanol fuel cells (DMFCs) and direct ethanol fuel cells (DEFCs), but the other types of DLFCs were generally still in the research stage. This paper aims to review the different types of liquid fuels directly used in fuel cells and identify their properties, challenges and applications.
•DLFCs are one of the most promising types of fuel cells.•DLFCs still have problems to be solved before commercialization.•Thus this paper presents different types of DLFC and applications.•It also highlights the properties, challenges and prospects of DLFC.
This study, as an observation, put its utmost effort to emphasize on the development of various physicochemical properties using multiple alcohols (C2 to C6) at different ratios compared to that of ...the conventional ethanol–gasoline blend. To optimize the properties of multiple alcohol–gasoline blends, properties of each fuel were measured first. An optimization tool of Microsoft Excel “Solver” was used for obtaining the optimum blend. Using optimizing tool, three optimum blend ratios were selected which possessed maximum heating value (MaxH), maximum research octane number (MaxR) and maximum petroleum displacement (MaxD). These blends were used for testing in a four cylinder gasoline engine at the wide open throttle condition with varying speeds and compared obtained outcomes with that of E15 (15% ethanol and 85% gasoline) as well as gasoline. Optimized blends have shown higher brake torque and brake thermal efficiency (BTE) but lower brake specific fuel consumption (BSFC) than E15. MaxR, MaxD and MaxH blends produced mean 4.4%, 1.8% and 0.4% increased BTE and mean 4.39%, 1.8% and 2.27% lower BSFC than that of E15. On the other hand, MaxR, MaxD, MaxH and E15 reduced 4.46%, 8.37%, 12.4% and 17.2%, mean CO emission and 4.5%, 11.81%, 8.19% and 16% mean HC emission respectively than that of gasoline. NOx emission of optimized blends was higher than gasoline. However, MaxR, MaxD, MaxH reduced 4%, 14.57% and 20.76% NOx than that of E15.
•Optimized C2–C6 alcohols–gasoline blends achieved better properties than E15.•Optimum blends improved BTE and torque and reduced BSFC than that of E15 fuel.•Compared to gasoline, optimum blends reduced CO and HC emission.•Optimum fuels reduced NOx emission than E15 fuel.
n-Butanol is an important industrial chemical usually produced by the oxo process, an expensive, energy-consuming set of reactions over metal catalysts, using petrochemical raw materials at high ...pressure. We developed nonstoichiometric hydroxyapatite (HAP), a highly active calcium phosphate compound and found it catalyzed selective conversion of ethanol to n-butanol in a single reaction at atmospheric pressure and low temperature, with maximum selectivity of 76%. Higher alcohols were also formed. We postulate that ethanol is adsorbed and activated on HAP as CH3CH2OH(a) and that a C−C bond was formed between β-C in the CH3CH2OH(a) and α-C in n-C n H2 n +1OH to produce n-C n H2 n +1CH2CH2OH. We further postulate that, by successive propagation, part of this n-C n H2 n +1CH2CH2OH is then adsorbed and activated on HAP as n-C n H2 n +1CH2CH2OH(a) and that C−C bond was formed between β-C in the n-C n H2 n +1CHCH2OH(a) and α-C in n-alcohol to produce branched alcohols. Reaction simulation supported this hypothesis, suggesting that efficient, environmentally friendly production of n-butanol might be possible in future using bioethanol as raw material.
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•Carbon/hydrocarbon assisted water electrolysis reviewed for clean hydrogen production.•Reviewed different electrochemical technologies using carbon fuels under development.•This ...technology has been progressed to different levels of maturity for different carbon sources.•This route of hydrogen production can lower the electric input and CO2 emissions from the carbon sources.
Hydrogen is mainly produced by natural gas reforming, which is a highly efficient process with low feedstock costs. However, the rising interest in clean technologies will increase the demand for hydrogen, meaning that other sources will need to be explored. Although coal is currently the major source of power generation, its demand appears to be declining due to the rise in electricity generated from renewable energy sources and the worldwide quest for low-emission power generation. Coal reserves worldwide are abundant, but new technologies would be needed to produce hydrogen from this feedstock. Coal gasification is one well-established technology for this purpose, but it is inefficient and produces high CO2 emissions. An alternative technology that has been investigated over the past few decades is carbon assisted water electrolysis. The basic process is water/steam electrolysis, with part of the energy required for the electrolysis provided by the chemical energy of coal, which reduces the overall electrical energy input. In addition to coal, the process can also use other carbon sources, such as biomass, alcohols or gaseous hydrocarbons. Several studies have investigated this electrochemical route of hydrogen production, employing different electrolytes in a wide temperature range (room temperature to 850 °C) under different process conditions. This paper presents a comprehensive review of carbon assisted water electrolysis, associated materials used and the challenges for the development of the technology at the commercial scale.
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•ZSM-5 was synthesized from the synthetic gels containing various alcohols.•The impact of the alcohols on the Al distribution was investigated.•Al distribution was considered by ...constrain index and Co2+ exchange properties.•The impact of the Al distribution on the catalytic properties was clarified.
The distribution of Al atoms in ZSM-5 has been recognized as an important factor in catalytic activity. Here, ZSM-5 zeolites were synthesized from synthetic gels containing various alcohols, including straight- and branched-chains alcohols. The effect of the alcohols in the synthetic gel on the Al distribution in the MFI framework was investigated based on 27Al MAS NMR, Co(II) ion UV−vis DRS, and constraint index value. Thus synthesized ZSM-5 zeolites were applied to catalysts for the cracking of n-hexane and the methanol-to-olefins (MTO) reactions in order to investigate the impact of the Al distribution on the catalytic properties. A unique Al distribution in the MFI framework was achieved by the use of trimethylolethane (TME) in combination with Na cations, and thus-prepared ZSM-5 catalyst showed a long catalytic life for both the cracking of n-hexane and the MTO reaction.
Enzymes are able to perform reactions under mild conditions, e.g., pH and temperature, with remarkable chemo-, regio-, and stereoselectivity. Due to this feature the number of biocatalysts used in ...organic synthesis has rapidly increased during the last decades, especially for the production of chiral compounds. The present review highlights biotechnological processes for the production of chiral alcohols by reducing prochiral ketones with whole cells. Microbial transformations feature different characteristics in comparison to isolated enzymes. Enzymes that are used in whole-cell biotransformations are often more stable due to the presence of their natural environment inside the cell. Because reductase-catalyzed reactions are dependent on cofactors, one major task in process development is to provide an effective method for regeneration of the consumed cofactors. Many whole-cell biocatalysts offer their internal cofactor regeneration that can be used by adding cosubstrates, glucose or, in the case of cyanobacteria, simply light. In this paper, various processes carried out on laboratory and industrial scales are presented. Thereby, attention is turned to process parameters, e.g., conversion, yield, enantiomeric excess, and process strategies, e.g., the application of biphasic systems. The biocatalytic production of chiral alcohols utilizing isolated enzymes is presented in part I of this review (Goldberg et al., Appl Microbiol Biotechnol, 2007).
Pada penelitian ini, kami memanfaatkan pasir zirkon (ZrSiO4) yang kesediaannya cukup melimpah (174,22 juta ton) sebagai bahan baku pembuatan katalis zirkonia (ZrO2). Pasir zirkon dicampur dengan NaOH ...(rasio massa 1 : 1,5) kemudian dikalsinasi pada suhu 700 ºC selama 1 jam. Ekstraksi menggunakan HCl dan presipitasi menggunakan NH4OH menghasilkan endapan putih Zr(OH)4 yang dapat ditransformasi menjadi ZrO2 melalui kalsinasi. Hasil XRD menunjukkan bahwa Zr(OH)4 yang dihasilkan bersifat amorf, kemudian berubah fase menjadi ZrO2 setelah kalsinasi dengan kristalinitas 35,8%). Katalis dari pasir zirkon ini memiliki aktivitas katalitik yang relatif tinggi untuk reaksi transfer hidrogenasi (CTH) senyawa turunan biomassa furfural (FFald) menjadi furfuril alkohol (FFalc). Reaksi CTH senyawa FFald menggunakan katalis ZrO2 pada 150 ºC , 350 rpm, 1 jam menghasilkan konversi 19,6% dan selektivitas >99%, sedangkan Zr(OH)4 menghasilkan konversi 37,1% dan selektivitas >99%. Katalis ini memiliki aktivitas yang lebih tinggi dibanding Al2O3 komersial (konversi 20,2%) berdasarkan hasil analisa kromatografi gas (GC). Terbentuknya produk FFalc juga dikonfirmasi melalui analisis FTIR dengan munculnya vibrasi O-H pada bilangan gelombang sekitar 3.355,32 cm-1.
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