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Advanced Oxidation Processes for Wastewater Treatment
Published in Sreedevi Upadhyayula, Amita Chaudhary, Advanced Materials and Technologies for Wastewater Treatment, 2021
Gunjan Deshmukh, Haresh Manyar
Transition metals have been widely studied as homogeneous catalytic systems in AOPs. The activity of homogeneous catalysts is well known, and these catalysts are mainly involved in Fenton's process, photo-Fenton's process and electrochemical oxidations integrated with O3 and UV. The most commonly studied transition metals involved in the above mentioned AOPs are Fe, Zn, Mn, Ti, Cr, Cu, Co, Ni, Cd, and Pb salts in their possible multivalent forms [5]. Among these elements, Fe is the most extensively studied element in Fenton and photo-Fenton processes to generate hydroxyl radicals. Further, Fe salts are widely used in catalytic ozonolysis processes, which help to enhance the activity of overall process [6]. An ideal homogeneous photocatalyst should be effective in a wide range of pH, and it was observed that the degradation efficiency of pollutants is higher at acidic pH with Fe as a catalyst compared to a catalyst-free process [7]. Further, it can also be noted that higher Fe catalyst concentration leads to Fe3+ ion formation, which increases the scavenging effect and decreases the efficiency of the catalyst. There are disadvantages of homogeneous catalysts, which can be listed as narrow pH range, short life span of the catalyst, difficult isolation and recovery cost, scavenging effect, no reusability, formation of by-products, and use of large excess of oxidants. To overcome these barriers, heterogeneous catalysts are advantageous in current science for water purification.
Introduction to Catalysts
Published in Qingmin Ji, Harald Fuchs, Soft Matters for Catalysts, 2019
In a spontaneous reaction, catalysts have multi-forms, varying from atoms, molecules and larger supermolecules. In addition, the catalysis may occur in various mediums, in liquids, in gases, or at the surface of solids. According to the states of phases during catalysis, catalysts can be classified as homogeneous and heterogeneous. In homogeneous catalysis, both the catalyst and the reactants are in the same phase, gas phase or liquid phase. An advantage of homogeneous catalysis is that it allows a very high degree of interaction between catalyst and reactant molecules. One of the simplest examples is ozone destruction in atmospheric chemistry, which is important for the prediction of the ozone hole. Via chlorine (Cl) atoms as catalysts, the decomposition of ozone can be accelerated tremendously to produce oxygen as shown in Scheme 1.1. In the gas phase, the reaction can occur spontaneously in cycles unaltered. Industry also uses a multitude of homogenous catalysts to produce chemicals.
Synthesis Of 1,4-Cis Polybutadiene By The Heterogenized Dithiosystem On Base Of Nanosize Montmorillonite
Published in A. K. Haghi, Lionello Pogliani, Devrim Balköse, Omari V. Mukbaniani, Andrew G. Mercader, Applied Chemistry and Chemical Engineering, 2017
Fizuli A. Nasirov, nazil F. Janibayov, sevda R. Rafiyeva, gulara N. Hasanova
The processes of oligomerization, polymerization of olefins and dienes processed with application of the homogeneous catalytic systems of Ziegler-Natta type. The homogeneous catalysis has a number of advantages concluding in high selectivity, large reaction proceeding rate, etc. But simultaneously it has a number of essential defects: single use of the catalysts, application of a large quantity of solvent, necessity of washing of purposeful products by water from catalysts owing to what a large number of quantities of waste waters containing ions of heavy metals, deteriorating ecological situation of production in formed. In addition, it is extremely difficult to create a continuous technology or production, to carry out a process in the gas phase, etc.
Study on obtaining high performance diesel/biodiesel fuel by using heterogeneous catalysts
Published in Petroleum Science and Technology, 2019
Liming Sun, Mengmeng Li, Xiaoou Ma, Zhenyuan Ma, Changfeng Ma, Ping Li
At present, the synthesis of alkyl esters is commonly carried out by using homogeneous catalysts (Dias, Alvim-Ferraz, and Almeida 2008; Miao, Li, and Yao 2009; Brito et al. 2012; Soriano, Venditti, and Argyropoulos 2009), due to their wide availability and low cost. However, homogeneous catalysis can lead to difficult separation of products, side reactions, costly neutralization, equipment corrosion and environmental pollution. So, this technique is unsatisfactory when considering cost and environmental issues. In order to overcome these drawbacks associated with homogeneous catalysis, heterogeneous catalysts are prepared and used in the synthesis of alkyl esters. This catalyst possesses good catalytic activity and is quite effective in facilitating the conversion of alkyl esters.
Effects of MgO as an additive in canola oil – an experimental study
Published in International Journal of Ambient Energy, 2020
S. Ganesan, K. S. Sridhar Raja, J. Senthil Kumar
Biodiesel, monoalkyl ester of fatty acids derived from vegetable oils or animal fats, is known as a clean and renewable fuel. Biodiesel is usually produced by the transesterification of vegetable oils or animal fats with methanol or ethanol (Ganesan and Elango 2013). When methanol is used, the transesterification reaction is referred to as methanolysis. The transesterification reaction can be catalysed by both homogeneous and heterogeneous catalysts (Ganesan et al. 2014, 2015). The homogeneous catalysts include alkalis and acids. The most preferable alkali catalysts are sodium hydroxide and potassium hydroxide (Ganesan et al. 2017; Varatharajan and Cheralathan 2012).
Comparative analysis of various waste cooking oils for esterification and transesterification processes to produce biodiesel
Published in Green Chemistry Letters and Reviews, 2021
Ikram ul Haq, Ayesha Akram, Ali Nawaz, Xin Zohu, Syed Zaghum Abbas, Yong Xu, Mohd Rafatullah
For transesterification, triglycerides in oil are converted into fatty acid methyl esters and glycerol using various acids, alkali and enzyme catalysts along with short chain alcohols (12). Multiple heterogeneous catalysts calcined animal bones and biocatalysts are being utilized to produce biodiesel, for reducing energy input and increasing feasibility of product, in modern day research. The advantage of homogenous catalysis over heterogeneous is that the process can occur even under slight operational parameters and thus have escalated specificity as well as reactivity. However, this specificity has proved to be one of its limitation particularly for FFA concentration (13). Methanol, as an acyl receptor, is preferred among other alcohols due to its low cost and fast reaction. Glycerol is a main byproduct of transesterification reaction which requires complete separation from biodiesel through different purification processes (14). There are multiple techniques for quantitative and qualitative characterization of biodiesel, but chemical composition analysis of the purified biodiesel is performed with gas chromatography mass spectrometry (GCMS), while the fuel characteristics are measured by ASTM protocols and compared with the standard ranges provided for biodiesel (15). The main objective of the paper is to provide comparison of different waste cooking oil samples processed through esterification and transesterification procedures along with parameter optimization for its efficient utilization in biodiesel production. The present work also focuses on the chemical characterization and fuel properties analysis of the final product by GCMS and ASTM standard protocols, respectively. The novelty of the current study is the economical biodiesel production from second generation feedstock i.e. waste cooking oil by employing cheap pretreatment of waste oil and reusability strategy of indigenously synthesized microbial lipase.