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An Overview of Catalytic Bio-oil Upgrading, Part 2:
Published in Ozcan Konur, Biodiesel Fuels, 2021
Jianghao Zhang, Junming Sun, Yong Wang
The desired product with high selectivity can be gained by controlling the reaction pathway using catalysts. Similar to the HDO of aromatic oxygenate, oxophilicity is also correlated with the performance of a catalyst. Readers are referred to Kepp (2016) for the oxophilicity index of a specific metal. Goulas et al. (2019) conducted kinetic and extensive characterization studies on the C–O bond cleavage of furfuryl alcohol. The reaction rate for C–O bond cleavage in furfuryl alcohol displayed a volcano-type dependence on the ‘Gibbs free energy’ of metal oxide formation (another way to evaluate the oxophilicity of metal). This correlation (Goulas et al., 2019) for oxide catalysts originated from the reverse ‘Mars-van Krevelen C–O bond activation mechanism’, which requires the balancing of the activation of the O abstraction from furanic oxygenates and its further elimination from the vacancy site. Therefore, the optimum catalyst is the one with moderate oxophilicity (Xiong et al., 2014) or a combination of both low and high oxophilic metals (Huang et al., 2014) to achieve high activity and selectivity.
2 Reduction: A Density Functional Approach
Published in Aneeya Kumar Samantara, Satyajit Ratha, Electrochemical Energy Conversion and Storage Systems for Future Sustainability, 2020
As discussed earlier, highly efficient electrocatalyst should be developed, which could enhance the electrochemical reduction of CO2 to form electro-fuels. At the electrode surface, the ET reaction should take place in the presence of an electrocatalyst, which also accelerates the electrochemical reaction on the electrode surface (Benson et al., 2009; Simakov, 2017). For an efficient catalyst, both the reactions must be accelerated simultaneously. The redox potentials, (E0), of both the processes, should be matched thermodynamically to get an optimal electrocatalyst. The ideal catalyst should have a few desired characteristics, which could help to reduce CO2 even under ambient conditions (Vasileff et al., 2017). The catalysts should show low activity towards the competing HER and high activity towards CO2 reduction reaction. High selectivity is another important characteristic in which desired chemicals should be obtained at the end of the reaction, suppressing the production of other possible chemicals. Besides these, the catalysts must be strong enough to be stable for a longer period and should be of non-precious origin, which would make the cell suitable for practical use and commercialization.
Homogeneous Reactors
Published in Salmi Tapio, Mikkola Jyri-Pekka, Wärnå Johan, Chemical Reaction Engineering and Reactor Technology, 2019
Salmi Tapio, Mikkola Jyri-Pekka, Wärnå Johan
The quantity that we refer to here as yield is often denoted as selectivity by synthetic chemists. Last but not the least, the reader ought to be reminded of the fact that the term “yield” is used in another context with a different meaning: yield is defined as the amount of product formed per total amount of the reactant—naturally normalized with the stoichiometric coefficients. This “yield” (yR/A) would thus assume the following form for the product R: yR/A=νA1(cR−c0R)νRc0A.
A review on solid base heterogeneous catalysts: preparation, characterization and applications
Published in Chemical Engineering Communications, 2022
Diksha K. Jambhulkar, Rajendra P. Ugwekar, Bharat A. Bhanvase, Divya P. Barai
In the last few years, there has been a rapid increase in development of both fundamental research and chemical industry mainly in the area of petroleum refining due to the impact of solid acid catalysis. Similarly, many vital reactions are being catalyzed by using solid base catalysts as they are capable of attaining high levels of activity and selectivity (Tanabe 1970). Recently, solid heterogeneous catalysts with several industrial applications have attracted widespread attention because of characteristics like large specific surface area, simple separation processes, uniform pore size distribution, and strong alkalinity. Due to these specified properties, various industrial processes are catalyzed by solid base catalysts that include dehydration, condensation, isomerization, alkylation, polymerization, hydrogenation, esterification, amination, etc. The basic properties of solid base catalysts are activity, selectivity, and stability. Activity is the ability of catalyst to use energy and processing time effectively for conversion of feedstock reactants into desired products. Selectivity is the ability to accelerate the conversion of reactants into specific desired product and reduce the growth of by-products. Whereas, stability is the ability of catalyst to avoid deactivation and maintain activity and selectivity during extended processing time (Védrine 2017). A long catalyst life and easy recovery are highly desirable properties for industrial applications. Even for prolonged use, the catalyst should poses high activity, selectivity, stability and should have low environmental impact.
Sustainability of biodiesel production in Malaysia by production of bio-oil from crude glycerol using microwave pyrolysis: a review
Published in Green Chemistry Letters and Reviews, 2018
Saifuddin Nomanbhay, Refal Hussein, Mei Yin Ong
Pyrolysis of agricultural residues and waste glycerol from the biodiesel industry can help to meet renewable energy targets by displacing fossil fuels and, thereby, deal with concerns about global warming. Besides the use of bio-oil and syn-gases, the other pyrolysis product, which is bio-char, can also be used for soil amendment and as a carbon-sequestering agent. With the growing production of biodiesel in the coming years, managing crude glycerol produced will become an increasingly difficult task. Although the development of glycerol-free biodiesel production is making progress significantly, implementation of these processes at a large scale still faces a number of challenges such as high costs, low efficiency, and lack of relevant technologies. It is crucial to utilize this waste stream generated from biodiesel production efficiently. Most of the current methods of utilization of crude glycerol are only able to uptake small volumes of the waste glycerol. Furthermore, the real costs of its utilization are uncertain. Pyrolysis of glycerol is a viable process for clean energy production. Liquid bio-oils, produced from the pyrolysis process, are a promising route to utilize large quantities of the waste glycerol. However, several key technical barriers must be addressed – (a) optimization of process conditions and catalyst performance to maximize bio-oil yield and quality while reducing the impact of feedstock variability and impurities; (b) improving the thermal stability of bio-oil and impurities be removed to facilitate economical upgrading to biofuels, and (c) maximizing carbon efficiency during bio-oil deoxygenation. One of the promising technologies for enhancement of bio-oil quality and quantity is by using the microwave-assisted pyrolysis process. Only few literatures are available on the microwave-assisted pyrolysis of waste glycerol. A more detailed study on the production of bio-oil from waste glycerol by microwave-assisted pyrolysis is needed in order to have a better understanding of the process parameters. Further research and development on microwave-assisted pyrolysis should focus on: (i) the types of microwave absorbents since it is necessary to achieve desired temperatures, (ii) improving catalyst selectivity, (iii) optimizing reaction conditions such as flow rate of inert gas to improve yield, (iv) study of the reaction kinetics of the overall process, and (v) study on the mechanism for microwave-assisted crude glycerol pyrolysis. The raw glycerol may also present some difficulties in feeding since it is liquid. For this reason, further studies must be done to reduce the water content in order to obtain a smaller concentrated volume of waste glycerol. The concentrated waste could be blended with a small portion of sawdust or similar waste to make the glycerol into a semi-solid paste. Finally, it can be concluded that the utilization of waste glycerol into higher value products through pyrolysis can potentially improve the issue of excess glycerol within the biodiesel industry. More work is needed to extend the existing understanding of the microwave technology for pyrolysis in order to improve the process and ultimately to transform it into a commercially viable route to recover energy from waste materials.