Reaction Equilibrium Research Articles

Расчет равновесного состава сложных термодинамических систем с использованием языка Julia и библиотеки Ipopt

The article considers the possibility of using the Ipopt optimization package for the calculating the phase and equilibrium compositions of a multicomponent heterogeneous thermodynamic system. Two functions are presented for calculating the equilibrium composition and properties of complex thermodynamic systems, written in the Julia programming language. These functions are the key ones in the program integrated with the IVTANTERMO database on thermodynamic properties of individual substances and used for conducting test calculations. The test calculations showed that Ipopt package allows determining the phase and chemical compositions of simple and complex thermodynamic systems with a fairly high speed. Using the JuMP modeling language significantly simplifies the preparation of the initial data for the Ipopt package, therefore the functions presented in this article are very compact. It is shown how the Ipopt package can be used when the temperature of the thermodynamic system is unknown. The approach proposed in this work is applicable both for analyzing the equilibrium of individual chemical reactions and for calculating the equilibrium composition of complex chemically reacting systems. The simplicity of the proposed functions allows their easy integrating into application programs, embedding them into more complex applications, using them in combination with more complex models (real gas, nonideal solutions, constrained equilibria), and, if necessary, modifying them. It should be noted that the versatility of the JuMP modeling language makes it possible to replace the Ipopt package with another one without significant modification of the program text

Research progress on antioxidant therapy and prevention in noise- induced hearing loss

Noise- induced hearing loss usually refers to auditory impairment which is caused by long-term exposure to noise. The occupational noise problem is serious and urgently needs to be addressed, along with the lack of effective treatments. Recent studies have shown that the imbalance between oxidation and antioxidation is the source of the disease. To correct the redox reaction imbalance and to maintain an equilibrium of the redox reaction have always been the research focus of the prevention and treatment in noise induced hearing loss. This article reviews antioxidant therapy and prevention in noise induced hearing loss, including antioxidants, antioxidant enzymes and herbal medicine.

Study on Simulation Technology in Chemical Equilibrium Experimental Teaching

Chemical simulation technology is a new experimental method that utilizes computer programs and applications to simulate and calculate objective substances, chemical reaction processes and status. In this paper, chemical equilibrium simulation technology is applied to the experimental teaching of liquid phase reaction equilibrium in chemical basic experiments. Taking the chemical equilibrium experimental teaching of iron ions and thiocyanate ions as an example, the distribution coefficient diagram, ion activity diagram, component solubility diagram and component stable equilibrium phase diagram under double influence factors are simulated dynamically, which provides great help for students to further understand the chemical equilibrium visually. At the same time, it is helpful to determine the optimal experimental concentration of reactants and has certain practical guiding significance for the optimization of an experimental scheme in a teaching experiment.

The Catalysis Effect of Na and Point Defect on NO Heterogeneous Adsorption on Carbon during High-Sodium Zhundong Coal Reburning: Structures, Interactions and Thermodynamic Characteristics

The reburning process in a furnace, a key way to reduce NOx emissions, is a heterogeneous reaction during coal combustion, in which the heterogeneous adsorption is dominant. Zhundong coal with a high content of alkali metal can enhance the reburning process. In this paper, the influence of sodium and a defect on NO heterogeneous adsorption was studied by the density functional theory, and the thermodynamic characteristic was also analyzed. The results indicate that the binding energy for NO adsorption on the pristine graphene surface (graphene-NO), Na-decorated pristine graphene surface (graphene-Na-NO), defect graphene surface (gsv-NO) and Na-decorated defect graphene (gsv-Na-NO) is −5.86, −137.12, −48.94 and −74.85 kJ/mol, respectively, and that the heterogeneous adsorption is an exothermic reaction. Furthermore, except for covalent bonds of C and N, C and O for gsv-NO, other interactions are a closed-shell one, based on the analysis of AIM, ELF and IGM. The area of electron localization for NO is graphene-Na-NO > gsv-Na-NO > gsv-NO > graphene-NO. The dispersion interaction is the main interaction force between NO and the pristine graphene surface. The δg index for the atom pairs about N–C and O–C on the pristine graphene surface is also the smallest. The density of spikes at graphene-Na-NO is bigger than that at gsv-Na-NO. Moreover, the thermodynamics characteristic showed that the reaction equilibrium constant of graphene-NO is less than those on the other surfaces under the same temperature. Thus, NO on the pristine graphene surface is the most difficult to adsorb, but the presence of sodium and a defect structure can promote its adsorption.

Removal of heavy metal ion cobalt (II) from wastewater via adsorption method using microcrystalline cellulose–magnesium hydroxide

Microcrystalline cellulose (MCC), magnesium sulfate hexahydrate, and trisodium citrate were reacted in ammonia bath in an aqueous solution to prepare a MCC–magnesium hydroxide (MH) composite adsorbent, which was used to adsorb heavy metal Co(II) ion. The method of using MCC–MH to adsorb and remove Co(II) was studied under different pH values, adsorbent dosages, contact times, initial Co(II) ion concentrations, and temperatures. The optimal process parameters include an MCC–MH dosage of 2.5 mg/mL, a contact reaction equilibrium time of 50 min, a Co(II) solution pH of 6.0–8.0, an initial Co(II) concentration of 300 mg/L, and a temperature of 303 K. The removal rate of Co(II) solution by MCC–MH was as high as 97.67%, and the maximum adsorption capacity of MCC–MH reached 153.84 mg/g under these optimal conditions. The adsorption isotherm of Co(II) conformed to the Langmuir model, the kinetic data of Co(II) conformed to the pseudo-second-order kinetic model, and the adsorption of Co(II) by MCC–MH was a spontaneous endothermic reaction under the optimized conditions. Analytical studies showed that Co(II) adsorption on MCC–MH composites is affected by chemical adsorption and involves the influence of intraparticle diffusion to a certain extent.

Simply closing the reactor improves the electron efficiency of zerovalent iron toward various metal(loid)s removal.

The controlled corrosion of zerovalent iron (ZVI) is crucial for the favorable performance of ZVI toward metal(loid)s removal, and dissolved oxygen (DO) plays an important role in the process of ZVI corrosion. However, few efforts have been made to control the concentration of DO in real practice. In this study, we found that the electron efficiency and the specific removal capacity of ZVI toward the removal of four metal(loid)s were increased by 1.2-9.1 times and 1.2-3.6 times, respectively, by simply closing the reactor, while the removal kinetics of metal(loid)s was slightly influenced. The rate constants obtained under open condition were always greater than those obtained under closed condition, and the removal amounts of metal(loid)s by ZVI at the reaction equilibrium under closed condition were nearly equivalent to those under open condition. Compared with the case under open condition, the consumption-redissolution process of DO was decelerated under closed condition, and the rapid corrosion of ZVI was alleviated subsequently. Although closing the reactor is simple, it does contribute much to the favorable electron efficiency of ZVI toward metal(loid)s sequestration and can be easily adopted in real practice. © 2021 Water Environment Federation PRACTITIONER POINTS: Closing the reactor promoted the selectivity of ZVI towards four metal(loid)s removal. The consumption-redissolution process of DO and corrosion of ZVI were decelerated by closing the reactor. Metal(loid)s were reduced to lower valence by ZVI under closed condition. Effect of DO was different when ZVI was applied to remove different metal(loid)s.

Influence of Chemical Kinetics Models on Plasma Generation in Hypersonic Flight

The accuracy and sensitivity of plasma generation predicted by several different chemical kinetics models is investigated in the context of weakly ionized hypersonic flowfields around the Radio Attenuation Measurement (RAM-C) vehicle. A computational fluid dynamics analysis is used to examine 13 independent trajectory points along the RAM-C II flight, and an assessment of the chemistry models is made by comparing results to available flight measurements. The limitations of making such comparisons with the raw flight data are established in detail, including the inherent shortcomings associated with interpolating the flight data to assess a single trajectory point. Two separate geometries are evaluated in this study, as the initial RAM-C geometry was altered during flight after its nose cap was pyrotechnically ejected. The blunter post-ejection geometry generates more electrons in the stagnation region. In general, good agreement is found between each chemistry model and flight data from both the electrostatic probe and reflectometer stations above 56 km. An expected sizable gap exists between the simulations and reflectometer data at lower altitudes. The impact of forward reaction rates, equilibrium constants, and number of species varies considerably based on altitude, velocity, and position along the body.

Separation of lithium and cobalt with N-salicylideneaniline from sulfate solution by hollow fiber membrane contactors

The study of the equilibrium concentrations for the extraction separation of cobalt from mixed sulfate solution with N-salicylideneaniline in membrane contactors is investigated. The reaction equilibrium constant (Kex) of 4.7 L2mol−2 was obtained from the modeling of the equilibrium distribution curves, which is carried out from the mass action law. A separation factor of 30,74 of cobalt was obtained. The calculation of the distribution coefficient (D) in the membrane contactors is carried out from global mass balances (operating line) and linear extraction isotherms in membrane contactors. The extraction kinetics of cobalt in the aqueous and organic phases in hollow fiber membrane contactors became slow and steady state is quickly reached. The steady state experimental concentration in aqueous and organic phase does not correspond to the concentration predicted by the calculation this deviation between the steady state concentration and calculated data could be explained that the diffusion of metal complex in the microporous is the main limiting step of mass transfer..

Experimental determination of the hydrogenation/dehydrogenation - Equilibrium of the LOHC system H0/H18-dibenzyltoluene

Liquid organic hydrogen carrier (LOHC) systems store hydrogen through a catalyst-promoted exothermal hydrogenation reaction and release hydrogen through an endothermal catalytic dehydrogenation reaction. At a given pressure and temperature the amount of releasable hydrogen depends on the reaction equilibrium of the hydrogenation/dehydrogenation reaction. Thus, the equilibrium composition of a given LOHC system is one of the key parameters for the reactor and process design of hydrogen storage and release units. Currently, LOHC equilibrium data are calculated on the basis of calorimetric data of selected, pure hydrogen-lean and hydrogen-rich LOHC compounds. Yet, real reaction systems comprise a variety of isomers, their respective partially hydrogenated species as well as by-products formed during multiple hydrogenation/dehydrogenation cycles. Therefore, our study focuses on an empirical approach to describe the temperature and pressure dependency of the hydrogenation equilibrium of the LOHC system H0/H18-DBT under real life experimental conditions. Because reliable measurements of the degree of hydrogenation (DoH) play a vital role in this context, we describe in this contribution two novel methods of DoH determination for LOHC systems based on 13C NMR and GC-FID measurements.

The Influence of the Furan and Maleimide Stoichiometry on the Thermoreversible Diels–Alder Network Polymerization

In recent work, the thermoreversible Diels–Alder reaction between furan and maleimide functional groups has been studied extensively in the context of self-healing elastomers and thermosets. To elaborate the influence of the stoichiometric ratio between the maleimide and furan reactive groups on the thermomechanical properties and viscoelastic behavior of formed reversible covalent polymer networks, a series of Diels–Alder-based networks with different stoichiometric ratios was synthesized. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and dynamic rheology measurements were performed on the reversible polymer networks, to relate the reversible network structure to the material properties and reactivity. Such knowledge allows the design and optimization of the thermomechanical behavior of the reversible networks for intended applications. Lowering the maleimide-to-furan ratio creates a deficit of maleimide functional groups, resulting in a decrease in the crosslink density of the system, and a consequent decrease in the glass transition temperature, Young’s modulus, and gel transition temperature. The excess of unreacted furan in the system results in faster reaction and healing kinetics and a shift of the reaction equilibrium.

CO2 absorption in amino acid-based ionic liquids: Experimental and theoretical studies

In this study, eight amino acid-based ionic liquids (AAILs) with 1-butyl-4-methyl pyridinium cation ([B4MPyr][AA]s) were synthesized and characterized. The CO2 absorption capacity of AAILs was studied using quartz crystal microbalance (QCM) at pressures up to 6 bars and at temperature 298.15 K. Based on the “deactivated model”, the reaction equilibrium constant and Henry's law constant were calculated to evaluate the efficiency of AAILs for CO2 absorption. The results indicate that CO2 absorption capacities are in the order of [Arg] > [Lys] > [His] > [Tyr] > [Gly] > [Val] > [Ala] > [Pro]. The accessibility of more available amine groups in AAIL with arginate anion is the main factor for the high CO2 absorption capacity. Also, the chemical absorption of CO2 through carbamate formation was corroborated by spectroscopy of FT-IR. Beside, the density functional theory (DFT) method was also employed to confirm the adsorption energy of CO2 onto AAILs with various anions.

Task-specific deep eutectic solvents for the highly efficient and selective separation of H2S

Developing environmental benign and efficient solvents for the natural gas sweetening is of great significance to the development of green chemistry. However, there is no task-specific deep eutectic solvents (DESs) for H2S absorption so far. Herein, we have for the first time developed a series of task-specific DESs for the selective separation of H2S, in which quaternary ammonium salts with free tertiary amine groups are designed as hydrogen bond acceptors (HBAs) and azoles as hydrogen bond donors (HBDs). Density, viscosity, and thermal decomposition temperature, as well as the solubility of H2S (0–1.0 bar), CO2 (0–1.0 bar), and CH4 (0–5.0 bar) were systematically determined. NMR paired with theoretical calculations are applied to characterize the interaction mechanism of H2S and DESs. A reaction equilibrium thermodynamic model (RETM) with a 1:2 stoichiometric reaction mechanism was screened to correlate H2S solubility data. It is found that [C4-TMHDA][Cl]-Im could achieve up to 0.996 mol H2S per mol DES at 303.2 K and 1.0 bar. Moreover, the captured H2S can be easily stripped out at elevated temperature and reduced pressure, with negligible loss in H2S capacities during four absorption–desorption cycles. The results obtained in this work indicate that these DESs are promising candidates for efficient and selective separation of H2S and CO2 from natural gas. This work provides novel insights into the future design of high-performance task-specific DESs for the capture of H2S.

Kinetics and catalytic distillation simulation for the heterogeneously catalytic synthesis of imine

Abstract(2‐methyl‐6‐ethylphenyl)‐1‐methoxypropyl‐2‐imine (MEMI) is an important intermediate for the synthesis of commercial pesticide S‐metolachlor. However, the research on heterogeneously catalytic kinetics of MEMI, and further the catalytic distillation simulation aiming at continuous operation, have never been reported. Herein, the catalytic kinetics for the synthesis of MEMI by HPW/Al‐MCM‐41 have been systematically investigated, and further fitted by using a pseudo‐homogeneous kinetic model, based on which, the reaction equilibrium constant, activation energy, and rate constant are obtained. Furthermore, simulation of the continuous process of MEMI synthesis was carried out using the software Aspen Plus V10. Sensitivity analysis of operating parameters such as feed stage, distillation rate, number of reactive theoretical stages, and the best operating conditions were also obtained. An excellent product purity (>98.9%) of MEMI could be achieved when operated at the optimum conditions. Compared with the batch method, catalytic distillation provided continuous synthesis of MEMI, and the reaction was more thorough, achieving process integration and optimization. Our results provide substantial theoretical and empirical supports for the industrial synthesis of MEMI.

Influence of the Diameter of Sections on Electrochemical Thermodynamics of Nanorod Electrodes: Theoretical and Experimental Research Studies

Nanorods have been widely applied in the electrochemistry field due to their excellent electrochemical properties. However, thermodynamic theory of nanorod electrodes still remains a blank, and the effect of the section diameter on the electrochemical thermodynamics of nanorod electrodes has not been clear. In this paper, theoretically, according to the thermodynamic definition of chemical potential, the expression of the surface chemical potential of nanorods was derived; then, the thermodynamic relations of the electrode potential, its temperature coefficient, reaction Gibbs energy, equilibrium constant, reaction enthalpy, reaction entropy, and reversible reaction heat of nanorod electrodes with the section diameter were derived based on the second law of thermodynamics; finally, the influencing regularities and mechanisms of the section diameter on these electrochemical quantities were discussed. Experimentally, the electrode reaction of rod-like nano-SnO2 was taken as an example, the solvothermal method was applied to prepare SnO2 nanorods with different section diameters, and a potentiometer was used to determine the electrode potentials of the nanorod electrodes. On this basis, we further obtained the standard electrode potentials and their temperature coefficients, reaction Gibbs energies, equilibrium constants, reaction enthalpies, reaction entropies, and reversible reaction heats of nanorod electrodes with different section diameters and discussed the influencing regularities of the section diameter on these electrochemical quantities. The experimental results are in agreement with the above theoretical relations. Both theoretical and experimental results show that the section diameter has a remarkable influence on electrochemical thermodynamics of nanorod electrodes. When the nanorods act as a reactant of an electrode reaction, with the decrease in section diameter, the standard electrode potential and the equilibrium constant of the electrode reaction increase, while the temperature coefficient of the standard electrode potential, the reaction Gibbs energy, the reaction entropy, the reaction enthalpy, and the reversible reaction heat decrease. When the nanorods act as a product of an electrode reaction, the effects of the section diameter on the electrochemical quantities are just reverse. Furthermore, when the section diameter exceeds 20 nm, the logarithm of the equilibrium constant and other electrochemical quantities are linearly related to the reciprocal of the section diameter. Besides, we also found that the additional electrode potential (i.e., surface electrode potential) of a nanorod electrode is exactly half that of the corresponding spherical nanoparticle electrode if the diameters are the same. The theory proposed in this paper can quantitatively describe the influencing regularities and mechanisms of the section diameter on electrochemical quantities of nanorod electrodes and can provide a foundation and guidance for the design, preparation, research, and applications of nanorod electrodes.

Multistimuli Responsive Solid-State Emission of a Zinc(II) Complex with Multicolour Switching.

The development of smart luminescent materials, especially those stimulus-responsive fluorescent materials that can switch between different colors repeatedly under external stimulation based on a single molecule, is of great significance but a challenge. In this work, a novel zinc(II)-Schiff base complex (ZnL2) was obtained and characterized. Upon exposure to the HCl and NH3 vapors, it displayed remarkable tricolor acidochromic behavior with high contrast and rapid response under the ambient light as well as UV light (365 nm). The XPS analyses of ZnL2 crystals before and after HCl/NH3 fuming show that the acidochromism originates principally from the adsorption of vapor and the gas-solid reaction equilibrium on the crystal surface. The reddish-brown color of the HCl-fumigated ZnL2 crystals could be attributed to the generation of HL at the surface of ZnL2, and red-shifted emission could be ascribed to the self-absorption effect. The single crystal X-ray diffraction data indicate that these processes cause slight changes in the molecular conformation and crystal packing. ZnL2 shows reversible mechanochromic luminescence behavior between yellow and orange emission during the grinding-fuming/heating cycles due to the modulation between amorphous and crystalline states. Moreover, ZnL2 was successfully made into test paper for the rapid detection of HCl/NH3 vapors and mechanical stimuli.

Efficient biosynthesis of D-allulose in Bacillus subtilis through D-psicose 3-epimerase translation modification

The combined catalysis of glucose isomerase (GI) and D-psicose 3-epimerase (DPEase) provided a convenient route for the direct synthesis of D-allulose from d-glucose, whose cost is lower than d-fructose. In the present research, the weak activity of DPEase was the key rate-limiting step and resulted in the accumulation of d-fructose in engineered Bacillus subtilis. Then, the 5′-untranslated region (5′-UTR) structure of the mRNA translational initiation region was optimized for the precise control of DPEase expression. The manipulation of the 5′-UTR region promoted the accessibility to ribosome binding and the stability of mRNA, resulting in a maximum of 1.73- and 1.98-fold increase in DPEase activity and intracellular mRNA amount, respectively. Under the optimal catalytic conditions of 75 °C, pH 6.5, 110 g/L d-glucose, and 1 mmol/L Co2+, the reaction equilibrium time was reduced from 7.6 h to 6.1 h. We hope that our results could provide a facilitated strategy for large-scale production of D-allulose at low-cost.

Highly efficient and reversible H2S capture by mercapto carboxylic anion functionalized ionic liquids

Four mercapto carboxylic anion functionalized ionic liquids (MCA-ILs) were designed and applied in H2S uptake. The solubility of H2S in MCA-ILs aqueous solution was measured from 303.2 to 333.2 K and pressure up to 1.0 bar. The reaction equilibrium thermodynamic model (RETM) was applied to fit the experimental data. Impressively, it was found that mercapto carboxylic anion captured H2S through 1:1 and 2:1 M ratio manner, which was supported by the results of RETM and quantum chemistry calculations. Furthermore, the solubility of H2S in 95% [P4444][MSA] could reach up to 0.9 mol/mol ILs and the enthalpy of the reaction was low (–22.21 kJ/mol). Considering the high H2S absorption capacity and low energy consumption of desorption, we believe that MCA-ILs solutions could provide an attractive alternative to be used as absorbent in H2S uptake.

Competition between reduction reaction and carbon deposition for CaSO4 oxygen carrier in chemical-looping combustion: A first-principle study and reaction equilibrium analysis

To understand the reaction mechanism of chemical looping combustion with calcium-based oxygen carrier, the competition mechanisms between reduction reaction and carbon deposition for CaSO4 oxygen carrier were calculated by density functional theory and simulated by chemical reaction equilibrium analysis. In this paper, the reaction paths of reduction reaction and carbon deposition at different CaSO4(010) surface outer oxygen content (100%, 75%, 50%, 25%) were studied, and the reversibility of the reaction was fully considered. Furthermore, based on the kinetic analysis of the transition state theory, the kinetic parameters of the elementary reaction were obtained. Moreover, the reaction equilibrium simulation revealed the competition of reactions under different conditions. The results show that the energy barriers of forward and reverse reactions decrease with the oxygen content decreasing on the CaSO4 (010) outer layer surface in the reduction reaction. Besides, the forward energy barriers at each stage are lower than the reverse energy. In the carbon deposition reaction, the energy barriers of the forward reaction are higher than the reverse reaction, and the energy barriers of the reverse reaction gradually increase with oxygen content decreasing. The kinetic analysis results show the rate-limiting steps of forward and reverse reaction in reduction reaction are 75% and 25% oxygen content stage. According to the reaction equilibrium, the conversion rate of CO oxidation to CO2 decreases with temperature increasing, and the conversion rate of carbon deposition increases. The rate of CO oxidation to CO2 increase and the occurrence of carbon deposition reaction decrease with oxygen carrier ratio increasing. Thus, when the oxygen carrier is insufficient or most of CaSO4 is reduced, the carbon deposition reaction occurs easily.

BIOSORPTION OF Pb(II) AND Cu(II) IONS FROM AQUEOUS SOLUTION USING COFFEE SENNA (Senna occidentalis) LEAVES AS BIOMASS

Conventional reagents for the remediation of heavy metals from wastewaters are expensive. Plant materials are being investigated to serve as alternative. The potential of Senna occidentalis leaves in removing Pb (II) and Cu (II) ions from aqueous solution was investigated using Batch adsorption method. The process was subjected to different experimental conditions such as initial metal concentration, solution pH, contact time, biosorbent dose, temperature and shaking speed. Atomic absorption spectroscopy (AAS) was employed in the determination of metal ion concentrations in solution after agitation, and characterization of plant biomass was done using infrared (IR) and scanning electron microscopy (SEM) analytical techniques. The adsorption process vary with the pH of the reaction medium. The optimum adsorption of Pb (II) and Cu (II) ions was achieved at pH 6 and 4 with percent uptake recorded at 97.70% and 82.32% respectively. At optimum temperatures of 40oC & 60oC for Pb (II) and Cu (II) ions, reaction equilibrium was attained after 120 min and 90 min of contact with 20 mg and 40 mg doses of the biomass respectively. The adsorption data for Pb (II) ion fitted well to Langmuir, Freundlich, Temkin and Dubbinin-Radushkevich isotherms. However, Cu (II) ion adsorption mechanism showed exception to Langmuir adsorption isotherm. The plant material was found to be effective in removing Pb (II) and Cu (II) ions and thus, can serve as a substitute for costly adsorbents in the remediation of Pb (II) and Cu (II) ions from wastewaters.

Methyl Esterification of Oleic Acid in Supercritical Methanol with Methyl Formate

Fatty acid methyl esters, which are used as biodiesel, can be produced by methyl esterification of fatty acids in supercritical methanol. However, in a reverse reaction, methyl esters are hydrolyzed to regenerate fatty acids due to the presence of water, which is produced by the esterification reaction, making it difficult to reduce the fatty acid content sufficiently. In this study, oleic acid was treated in supercritical methanol at 310 °C/20 MPa with a flow-type reactor by adding methyl formate to improve the yield of methyl ester. As a result, adding methyl formate improved the methyl ester yield approximately from 90 to 95 wt% compared with the treatment using methanol only. Methyl formate was hydrolyzed instead of fatty acid methyl esters, producing formic acid and methanol. Formic acid can be decomposed into gases such as H2 and CO2 by thermal decomposition in supercritical methanol. As these reactions consume water, removing it from the reaction system, the reaction equilibrium was considered to be shifted in the direction to improve the methyl ester yield.