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Instability and Incompatibility
Published in James G. Speight, Refinery Feedstocks, 2020
Briefly, and by way of explanation, an induction period in chemical (or physical) reactions is an initial stage of the reaction (or a slow stage of a reaction) in which the reaction does not appear to occur after which the reaction may accelerate, even leading to (in some reactions) an explosion. Typically, the end of the induction period marks the end of the period of low (or no) chemical or physical activity and the onset of the reaction. For example, in the coking process, there is an induction period during which coke is not formed but the chemistry of coke formation as already started and coke depletion is manifested after a period of time that is dependent upon the feedstock composition and the temperature of the process (Chapter 7) (Magaril and Akensova, 1967, 1968; Magaril and Ramazaeva, 1969; Magaril and Aksenova, 1970a,b; Magaril et al., 1970, 1971; Magaril and Aksenova, 1972; Wiehe, 1994; Speight, 2014a). In another case, in the deasphalting procedure, there is an induction volume during which time the amount of precipitant does not cause any asphaltene constituents to separate. Again, the appearance of the asphaltene phase is dependent upon the feedstock composition and the temperature of the process (Speight, 2014, 2015).
2 to Low-Carbon Compounds
Published in Fangming Jin, Hydrothermal Reduction of Carbon Dioxide to Low- Carbon Fuels, 2017
Ge Tian, Chao He, Ziwei Liu, Shouhua Feng
Kinetic studies were carried out in the system. Figure 6.1 shows a kinetic curve for the reaction. The yield was obtained by comparing a calibration curve of peak area with the peak area of the product. In the first 10 h of the reaction, the yield of phenol increased slowly. With the increasing of reaction time from 10 to 120 h, the phenol yield increased rapidly. This is typical of a self-catalytic reaction, with a fast formation reaction after a short induction period. In the short induction period, some compounds that can further catalyze the reaction (such as formaldehyde, formic acid, and others) are formed. At this stage, several organic molecules could be identified by GC-MS, including the main product phenol and trace amounts of formic acid and formaldehyde. After 120 h, the phenol yield reached a maximum value of 1.21 mol% according to carbon dioxide and then remained nearly constant. The final product was phenol.
Creep Models of Nanocomposites Deterministic Approach
Published in Leo Razdolsky, Phenomenological Creep Models of Composites and Nanomaterials, 2019
The first section (I) is the induction section. It is characterized by low speed reaction. In this case, small stable particles are formed that have catalytic activity. Next is the acceleration section (II). In the third section (III) with the consumption of reagents and the stabilization of particles, the reaction rate decreases. The activation energy for the formation of stable nuclei of the new phase is sufficiently large, since the induction period proceeds under homogeneous conditions. The duration of the induction period depends on the nature of the reagents, their concentration and ratio, temperature, the presence of various catalytic impurities, etc. For many systems, the conversion of metal ions for the induction period is usually not more than 5%. Strong reducing agents (alkali metal tetrahydroborates, hypophosphite, hydrazine, hydroxylamine, etc.) reduce the induction period, while weaker ones (formaldehyde, glucose, alcohols, etc.) increase it. Stable particles have a size of at least 1 nm and are formed by successively increasing small particles with reduced atoms metal [18]. In the transition from a homogeneous regime to a heterogeneous one (formation of nuclei new phase), at which the activation energy of the reaction is much lower, acceleration of oxidation-reduction reaction is observed. Homogeneous nucleation becomes energetically unstable, and the reduction of metal ions proceeds mainly on the already formed clusters (the growth stage). The clusters serve as carriers of electrons from the molecules (ions) of the reducing agent to the metal ions that are reconstructed on their surface, thereby catalyzing the reduction process.
Investigation and improvement on storage stability of pyrolysis oil obtained from Aegle marmelos de-oiled seed cake
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Baranitharan Paramasivam, Ramesh K., Sakthivel R.
Rancimat is a computer-controlled measuring device for determining the oxidation stability of bio-oil/bio-oil blends according to the standards EN 14112 and EN 15751 (Sakthivel et al. 2018). Natural oils possess relatively low level of storage stability, as they are oxidized by atmospheric oxygen. These oxidation processes, which progress slowly at ambient temperatures, are referred to as auto-oxidation. In this method, the sample (5 g) is exposed to airflow at a constant temperature of 110ºC. Highly volatile, secondary oxidation products are transferred into the measuring vessel with airflow (10 l/hr), where they are absorbed in the measuring solution (distilled water of 50 ml). Here the conductivity is continuously registered. The organic acids can thus be detected by an increase in the conductivity (Pinto et al. 2015). The time until these secondary reaction products occur is referred to as the induction time or induction period, which is a good characteristic for the oxidation stability. With respect to time, the conductivity curve raised increasingly regarding enhanced oxidation, parallel to the exponential growth curve. This curve declines after reaching a maximum rate of degradation. Meanwhile, incorporated Rancimat software assesses the Induction period time through analyzing the maximum second derivative curve, it is corresponding to time and conductivity (Shameer and Ramesh 2017).
Effect of alcohol on the crystallization process of MgCO3·3H2O: an experimental and molecular dynamics simulation study
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Xingfu Song, Chaoyan Dai, Guilan Chen, Chunhua Dong, Jianguo Yu
An induction period, namely, the period from the start of the reaction to the formation of the crystal, is crucial in measuring the transformation rate from Mg(HCO3)2 to MgCO3 · 3H2O. The rate can be measured by the induction period, and the length of the induction period is closely related to the temperature and concentration (Hu 2004). A decline of the solution temperature and concentration results in a longer induction period, and vice versa. The key to determining the induction period is to accurately detect the time when the first nuclei appear. Methods including visual method (Söhnel and Mullin 1988), Coulter counter method (Kind and Mersmann 2010), conductivity method (Söhnel and Mullin 1978), turbidity method (Hennessy, Neville, and Roberts 2004; Marciniak 2002; Parsons, Black, and Colling 2003), ultrasonic technology (Gürbüz and Özdemir 2003), FBRM (focus beam reflectometer) (Barrett and Glennon 2002; Nasser et al. 2008; Qian et al. 2014), are commonly used to measure induction period. FBRM, with simplicity, high sensitivity, fast dynamic response, and wide application properties, is widely used to detect the formation of nuclei. The number and size of particles, as well as other important information in the crystallization process, can be directly measured online.
Mathematical modeling of the detonation wave structure in the silane-air mixture
Published in Combustion Science and Technology, 2018
A.V. Fedorov, D.A. Tropin, P.A. Fomin
Note that the value of β affects only the profiles of the wave parameters in the induction zone. The wave velocity, the flow parameters at the C.-J. point and the main heat release zone do not depend on β. Therefore, once the above conditions on the value of β are satisfied, the specific form of the equation for calculating it affects the profiles of the wave parameters in the induction zone only quantitatively and has no fundamental significance. As a rule, the chemical reaction rate increases at the end of the induction period. In this connection, the formula for calculating β should be chosen so as to satisfy the above boundary conditions and so that the rate of its decrease increases as the mixture moves in the induction zone. For example, the following formula can be used: