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Introduction
Published in S. T. Lee, Polymeric Foams, 2022
Polyurethane is made by reaction between hydroxyl and isocyanate groups to liberate CO2 in an exothermic reaction, which can heat up the thermoset matrix to about 140°C. The reaction rate can be controlled by catalyst. The product property is determined not only by degree of reaction and cell morphology but by raw material structure and the hard segment and soft segment distribution. No wonder, the same kinetics generates polyurethane foam rigid as refrigerator frame or soft as sponge. The origin of the raw material was mostly from fossil. As call for environmental accountability is getting stronger, more efforts have been dedicated to make raw material from plant-based products. Hydroxyl group chemicals can be extracted from plant seeds, for example palm seed. Although it is a partial solution, it paved the way for more progress in this front. In the last few years, major polyurethane foam producers have engaged in this area [40–42]. Since the process of turning plant-based material into the raw material to make PU foam is ongoing, the overall process will be gauged by the total carbon footprint.
General Chemistry
Published in Steven L. Hoenig, Basic Chemical Concepts and Tables, 2019
Kinetics deals with the rate (how fast) that a chemical reaction proceeds with. The reaction rate can be determined by following the concentration of either the reactants or products. The rate is also dependent on the concentrations, temperature, catalysts, and nature of reactants and products.
Fundamentals and Applications of Reaction Kinetics
Published in C. Anandharamakrishnan, S. Padma Ishwarya, Essentials and Applications of Food Engineering, 2019
C. Anandharamakrishnan, S. Padma Ishwarya
Rate law and rate constant: The rate law or rate equation for a reaction is defined as an equation that defines the relationship between reaction rate, the concentration of reactants, and certain constant parameters such as the rate constant and partial order of the reaction. If Eq. (8.1) corresponds to an elementary gas-phase reaction, then the rate law is simple of the form r=k[A]a[B]b
Studies of surface plasmon resonance of silver nanoparticles reduced by aqueous extract of shortleaf spikesedge and their catalytic activity
Published in International Journal of Phytoremediation, 2023
Norain Isa, Mohamed Syazwan Osman, Haslinda Abdul Hamid, Vicinisvarri Inderan, Zainovia Lockman
Methylene blue (MB) is among the most commonly used dyes in the textile industry owing to its vast availability and low cost. However, it is difficult to degrade MB under normal conditions due to its highly stable molecules (Mustafa et al. 2019). Therefore, a catalyst-based route is desired for MB degradation. Catalyst is a substance that increases reaction rate without modifying the overall standard Gibbs energy change in a reaction, and the process is called catalysis (Laidler 1996). Reduction using different catalysts is preferred for MB degradation. A suitable catalyst is needed for the reduction process, thus in this work, silver (Ag) in nanoparticles form was selected as the catalyst.
Oxidative degradation of inorganic sulphides in the presence of a catalyst based on 3,3’, 5,5'-tetra-tert-butyl-4,4'-stilbenequinone
Published in Environmental Technology, 2020
H. Y. Hoang, R. M. Akhmadullin, F. Yu. Akhmadullina, R. K. Zakirov, A. G. Akhmadullina, A. S. Gazizov, M. U. Dao
In general, the catalytic reaction rate depends on a number of factors: temperature, pH medium, catalyst nature and mechanism of catalyst action, etc. As the shown in Figure 3(a), when the sodium sulphide concentration is above 0.7 mol L−1, its oxidation in the presence of stilbenequinone occurs with a definite induction period. Furthermore, this period lengthens as the initial sulphide concentration increases. It is difficult to explain this phenomenon, but it might be related to the oxidation mechanism, that sulphide ion in water hydrolyses to form hydroxide and hydrosulphide anion (1st stage), as shown in Equation (4).
Catalysts used in biodiesel production: a review
Published in Biofuels, 2021
A catalyst is a substance that increases the chemical reaction rate without being consumed by the reaction itself. Theoretically, the catalyst is practically consumed in one stage and regenerated at a later stage, and this operation is continuously repeated without imposing a permanent change on the catalyst. Accordingly, the catalyst in a given reaction can be recycled unchanged at the end of the reaction. Catalysts change the speed of a chemical reaction that can be thermodynamically carried out. Therefore, they cannot perform reactions that are not thermodynamically feasible. Basically, a catalyst is considered a chemical compound capable of applying an accelerating effect on the reaction rate and a directional effect on the reaction progression which is thermodynamic in nature. In a reversible reaction, the catalyst evenly affects the rate of forward and backward reactions. Therefore, the equilibrium constant of the reaction is the same whether in the presence of a catalyst or without it. When there are several mechanisms available for the reaction, the catalyst must be selected. In principle, the catalyst should increase the ratio of the desired material to the unwanted material. Although ideally catalysts remain unchanged during the reaction, this is inaccurate in practice, since the catalyst itself is a reactive substance that undergoes irreversible physical and chemical changes during the reaction, reducing its ability to function. Over time, this reality may be vividly observed since the catalyst enters into billions of reactions [5]. In general, the catalysts used in the transesterification of vegetable oils and animal fats can be classified into three groups – homogeneous, heterogeneous and enzymatic catalysts [12] – as shown in Figure 1.