China 
Africa 
Explore chapters and articles related to this topic
Visbreaking
Published in Mark J. Kaiser, Arno de Klerk, James H. Gary, Glenn E. Hwerk, Petroleum Refining, 2019
Mark J. Kaiser, Arno de Klerk, James H. Gary, Glenn E. Hwerk
Another type of free radical initiation reaction that can take place is molecule-induced homolysis. Molecule-induced homolysis leads to hydrogen transfer between two non-radical molecules to produce two radical species (Payan and De Klerk 2018). This is a reaction class that may help to explain initiation of free radical reactions at lower temperatures. In refineries, where corrosion products might be present, free radical formation by redox reactions could also be a source of free radical initiation.
Biological Effects of Static Magnetic Fields
Published in Charles Polk, Elliot Postow, CRC Handbook of Biological Effects of Electromagnetic Fields, 2019
Magnetic fields of the order of 10-3 to 10-2 T can affect chemical reactions by influencing the electronic spin states of reaction intermediates.50 53 These effects can have biological consequences.54,55 A relatively simple chemical illustration of the effect involves homolytic cleavage of a chemical bond to produce two radicals.* Since the electrons in the chemical bond are spin-paired in an S = 0 or singlet state,55a these electrons on the nascent radicals will also have overall singlet character as the radicals separate. Separation is a diffusion-controlled process and there is a high probability that the two radicals will recncountcr each other. If the electrons retain their overall singlet character, a reencounter is likely to produce recombination. If the electrons have overall triplet (S = 1) character, the bond will not reform and the radicals will eventually separate and perhaps participate in other chemical reaction. The transition from singlet to triplet can result from the interaction of the odd electrons of the radicals with the nuclear magnetic moment(s) of the atom(s) on which they have high probability density. This interaction, the magnetic hyperfine interaction, is equivalent to a local magnetic field at the electrons produced by the nuclei. Different local magnetic fields cause the electrons on the radicals to precess at different rates, which destroys singlet phasing and results in triplet formation. However, an applied magnetic field will decouple the electrons and the nuclei, suppressing formation of the triplet state. This enhances the recombination rate and suppresses the other chemical reactions. The decoupling of the electrons and the nuclei will occur when the intensity of the applied field exceeds the effective magnetic field produced by the hyperfine interaction. Then the electrons will precess in phase about the applied field rather than at different rates about the local field. This condition is typically satisfied for fields of the order of 10-3 to 10-2 T.
Mechanistic Study of the Inhibition of Active Radicals in Coal by Catechin
Published in Combustion Science and Technology, 2021
Zhilin Xi, Ke Gao, Xiangyu Guo, Meitong Li, Changxing Ren
As part of in-depth studies on the mechanism of the spontaneous combustion of coal, the free radical chain reaction has received extensive attention. Under the influence of external conditions (mechanical fracture, heating, illumination, etc.), the homolysis of covalent bonds generates a large number of free radicals. Free radicals are atoms or groups with unpaired electrons, which are very reactive and highly aggressive toward other substances. The activation energy for the reaction between radicals is zero, and bond-forming reactions can occur rapidly (Li et al. 2018a). The free radical chain reaction of the spontaneous combustion of coal is generally divided into three stages: chain initiation, chain growth, and chain termination. The reaction process has been widely recognized (Li et al. 2016b; Li et al. 2018a).
Degradation of benzotriazole by sulfate radical-based advanced oxidation process
Published in Environmental Technology, 2021
Jie Ma, Yi Ding, Liping Chi, Xin Yang, Yingjie Zhong, Zhiheng Wang, Quan Shi
Low concentration of (1–10 mM) promoted the BTA oxidation while high concentration of (100 mM) inhibited the reaction (Figure 7(d)). A recent study shows that can activate PS and promote its oxidation of acetaminophen [50]. The reactions between and PS lead to the formation of peroxymonocarbonate (). undergoes homolysis of the O-O bond that generates a series of active species including superoxide radical () and singlet oxygen (1O2). Therefore, 1-10 mM of promoted the BTA oxidation. However, it is well-known that can scavenge active species [49]. When the concentration was high (≥100 mM), the scavenging effects may become much stronger. This may significantly reduce the overall oxidation strength and decrease the BTA degradation rate.