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Advanced Risk-Based Biodegradation Study Using Environmental Information System and the Holistic Macroengineering Approach
Published in Donald L. Wise, Debra J. Trantolo, Edward J. Cichon, Hilary I. Inyang, Ulrich Stottmeister, Remediation Engineering of Contaminated Soils, 2000
Stergios Dendrou, Basile Dendrou, Mehmet Tumay
Abiotic reactions are typically not complete and often result in the formation of intermediate by-products that may be at least as toxic as the original contaminant. The most common reactions are hydrolysis (a substitution reaction) and dehydrohalogenation (an elimination reaction). Other possible reactions include oxidation and reduction. However, no abiotic oxidation reactions involving typical halogenated solvents have been reported. Also, reduction reactions (which include hydrogenolysis and dihaloelimination) are commonly mediated microbially, although some abiotic reduction reactions have been observed. In general, attributing changes in either the presence or absence of halogenated solvents or the concentrations of halogenated solvents to abiotic processes is usually difficult. Often, chlorinated solvents may be undergoing both biotic and abiotic degradation, and discerning the relative contribution of each mechanism on the field scale is very difficult, if possible at all. As another example, to substantiate that hydrolysis is occurring, the presence of nonhalogenated breakdown products such as acids and alcohols should be established. In general, these products are more easily biodegraded than their parent compounds and can be difficult to detect.
Elimination Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
When a highly ionizing medium such as water is present and substitution is slow, elimination can occur via a carbocation intermediate. Typically, E2 reactions are faster in protic solvents, but a first-order elimination reaction, termed E1, can occur under certain conditions. When 2-bromo-2-methylpropane reacts with KOH in dry ethanol, is carbocation formation possible?
Theoretical investigation of N (2D) + HOX (Cl, Br) reaction
Published in Molecular Physics, 2019
Jagannath Pal, Ranga Subramanian
Once the trans-HNOX is formed, new possibilities open up. The trans-HNOX undergoes elimination reaction in which either halogen or hydrogen atom is the leaving group. From a thermodynamic point of view, elimination of X atom is favoured over the elimination of H atom, because N-H bond is stronger than the O-X bond. The only process leading to the product formation, which plays a relatively important role in this dissociation process is the formation of HNO + X from trans-HNOX. The O-Cl bond of TS3a is elongated to 1.99 Å from the equilibrium geometries 1.73 Å of trans-HNOCl (I2a) and the O-Br bond of TS3b is elongated to 1.99 Å from the equilibrium geometries 1.86 Å of trans-HNOBr (I2b). The elimination of Cl from the trans-HNOCl results in the formation of products HNO + Cl. The products are stable by 100.1 kcal mol−1 relative to the reactants. The products HNO + Cl can also be formed directly to from cis-HNOCl by the breaking of the O-Cl bond. The elimination of Br from trans-HNOBr yields HNO + Br, which are stable by 102.9 kcal mol−1 relative to the reactants. The breaking of O-Br bond in cis-HNOBr can also be given directly to the products HNO + Br. Moreover, HNO + Br lies 2.72 kcal mol−1 lower than the HNO + Cl. The trans-HNOCl decomposes to form HNO + Cl with a transition state, TS3a. The transition state, TS3a, is calculated to be 5.3 kcal mol−1 higher in energy relative to the reactant, trans-HNOCl. The IRC analysis indicates that TS3a is located at the first-order saddle point of this decomposition pathway. The TS3b was obtained as the transition state along the reaction pathway for trans-HNOBr → HNO + Br. The barrier height for this bond dissociation was predicted to be 4.3 kcal mol−1. The IRC analyses confirmed that TS3b is the transition state of this decomposition pathway.
Effect of substitution on dissociation kinetics of C2H5X, (X = F, Cl, Br and I): A theoretical study
Published in Molecular Physics, 2021
Nitin R. Gulvi, Priyanka Patel, Parimal J. Maliekal, Purav M. Badani
The pyrolysis of mono-halogen derivatives of ethane, i.e. C2H5X (X = F, Cl, Br, and I), were studied in detail using density functional theory (DFT), in conjunction with 6-311G** basis set and default spin option. This basis set was applied from EMSL basis set library [35]. It is worth mentioning here that the several research groups had utilised the 6-311G** basis set for halogen containing species in their theoretical work [36–39]. Their results suggested that the aforesaid basis set compute the energies that are in close agreement with experimental finding. Hence, the same basis set was utilised in the present study for quantum mechanical calculation. Furthermore, BMK [40], B3LYP [41], and MPW1PW91 [42] were chosen as a functional for electronic structure calculations. These DFT functionals are known to predict more accurately thermodynamic and kinetic parameters of main-group elements [40,41,42]. Geometry optimisation and frequency analysis for all the reactants, transition states (TS), and intermediates were performed at aforesaid level of theory. Moreover, the single point energy corrections were exploited using the ab initio level of theory, i.e. quadratic configuration interaction method, including single, double and triple substitutions [QCISD(T)] [43]. The reaction coordinates on the potential energy surface revealed zero imaginary frequency for all minima; whereas TS were characterised by the presence of one imaginary frequency [44,45]. TS structures of molecular elimination channels were further confirmed by intrinsic reaction coordinate (IRC) calculations, which showed that all transition state structures connect smoothly to the reactant and the product [46,47]. All the above-mentioned quantum mechanical calculations were executed with the Gaussian 09 program package [48]. Furthermore, the suitable kinetic model was used to exploit the kinetic behaviour of the decomposition reaction of alkyl halide. For instance, the canonical formulation of the transition state theory (CTST) [49,50], and statistical adiabatic channel model (SACM) [51–53] were employed to estimate the rate constant in the high-pressure region for molecular (HX) elimination reaction and C–X bond dissociation reactions respectively. Furthermore, the low-pressure limiting rate constant, for both the type of reactions was calculated by using Troe’s formalism [54–56]. Finally, Troe’s reduced model had been utilised to explore the falloff behaviour for pyrolysis of C2H5X (X = F, Cl, Br, and I) [57–59].
Thermal characterisation of dairy washed scum methyl ester and its b-20 blend for combustion applications
Published in International Journal of Ambient Energy, 2022
Vinay Atgur, G. Manavendra, G.P. Desai, B. Nageswara Rao
Biodiesel can be used directly in engines. It can be used by blending with diesel. Oxygen in fuel structures leads to clean combustion with increasing thermal efficiency (Rajasekar and Selvi 2014; Ramkumar and Kirubakaran 2016). Structural effects of ethyl esters’ combustion phenomena differ from methyl esters’. Due to uni-molecular decomposition reaction in the methyl esters, C–O bond breaks to form CH3 or CH3O radicals. Ethyl esters decompose and produce C2H4 through a six-member peri-cyclic transition state and uni-molecular elimination reaction. Fatty acids contain a long chain of 8–24 carbon atoms with different degrees of unsaturation influencing oil physical properties and its derived biodiesel. Generally, vegetable oils contain 95% of triglycerides, 0.2% of diglycerides and 2–3% of monoglycerides. Fatty acids are linked to the glycerine molecules. Those not linked to the glycerine molecules are termed free fatty acids. Free fatty acids in vegetable oils vary from 0.4 to –3% causing acidity. Annual milk production in India is 147 million tons (Sivakumar, Anbarasu, and Renganathan 2011; Srikanth et al. 2019a). Thousands of milk dairies refine milk daily and produce scum waste. Huge quantity of water is being used in the process for housekeeping and sterilising. The residual butter and related fats are washed and deposited in effluent treatment plants as scum waste (as shown in Figure 1). Dairies with a processing capacity of five lakhs produce 200–300 kg of scum waste. Biodiesel production by treating the scum waste enhances the economic growth of milk dairies, solves the waste disposal and serves as fuels in energy production (Kök 2002; Krishnamurthy, Sridhara, and Ananda Kumar 2018). Thermal analysis techniques are being used to analyse the thermal stability, oxidative reaction, volatisation, decomposition and combustion (Dwivedi and Sharma 2016). Complexity in thermal decomposition and kinetics of vegetable oils are due to complex series and parallel reactions (Punithkumar, Khaiser, and Mahesh 2018). Table 1 presents the properties of diesel, dairy scum oil (DSO), dairy washed scum methyl ester (DWSME) and its B-20 blend (Channappagoudra, Ramesh, and Manavendra 2019). Table 2 gives the fatty acid composition of DWMS oil and its derived biodiesel. 91.31% of saturated fatty acid content in scum oil (DWSO) leads to high a cetane number of 63. The transesterification reaction of the biodiesel makes the triglycerides more ignitable. Oil is composed of triglycerides. Biodiesels are composed of fatty acids possessing a high calorific value. Carbon chain length of DWSME is more when compared to that of DWMS oil. Hence, the biodiesel will have higher calorific value than oil.