Transesterification of leather tanning waste to biodiesel at supercritical condition: Kinetics and thermodynamics studies

Efficient and Easily Recyclable Catalyst for the Alkylation Reaction of Phenol and tert-Butyl Alcohol

tert-Butylphenol is widely used as an intermediate in organic synthesis, and the catalyst for the alkylation reaction of phenol and tert-butyl alcohol is the key to synthesizing tert-butylphenol. In our work, a catalyst, 1H-imidazole-1-acetic acid tosilate ([HIMA]OTs), was synthesized and characterized, and an efficient and easily recyclable catalytic system of an ionic liquid was established. In addition, the kinetic and thermodynamic parameters were calculated; the positive value of ΔH* indicated the endothermic nature of the alkylation reaction, and the positive value of ΔS* and negative value of ΔG* implied that the process of alkylation of phenol and tert-butyl alcohol was spontaneous in the current reaction system. The recovery experiments of [HIMA]OTs were performed, and an excellent recycling performance was obtained. This method provides a potential way for the industrial synthesis of tert-butylphenol.

Biodiesel production from candlenut oil using a non-catalytic supercritical methanol transesterification process: optimization, kinetics, and thermodynamic studies

The present study was conducted to determine the feasibility of biodiesel production from candlenut oil using supercritical methanol (scMeOH) as a non-catalytic transesterification process. The influence of the scMeOH transesterification process was determined with varying pressure (85–145 bar), temperature (260–300 °C), methanol to oil (M : O) ratio (15 : 1–35 : 1), and reaction time (15–25 min). The experimental conditions of the scMeOH transesterification process were designed using central composite design (CCD) of experiments, and the process was optimized using response surface methodology (RSM). It was found that scMeOH temperature, pressure, M : O ratio, and reaction time substantially influenced the transesterification process. The maximum biodiesel yield of 96.35% was obtained at an optimized scMeOH transesterification process at the pressure of 115 bar, the temperature of 285 °C, M : O ratio of 30 : 1, and reaction time of 22 min. A second-order kinetics model and Eyring equations were utilized to determine the kinetics and thermodynamics of biodiesel production from candlenut oil. The activation energy value was determined to be 28.35 KJ mol⁻¹. Analyses of the thermodynamic properties of biodiesel revealed that the transesterification process was non-spontaneous and endothermic. The physicochemical properties of produced candlenut biodiesel via scMeOH complied with most of the biodiesel properties as per ASTM D6751 and EN14214, thereby referring to good quality biodiesel production. The findings of the present study reveal that the scMeOH is an effective non-catalytic transesterification process for biodiesel production from candlenut oil.

The present study was conducted to determine the feasibility of biodiesel production from candlenut oil using supercritical methanol (scMeOH) as a non-catalytic transesterification process.

Application of radio analytical tracer technique to study the performance of industrial grade ion exchange resin exposed to UV radiations

The thermodynamics and kinetics of bromide ion-isotopic exchange reactions performed by using fresh and UV radiation degraded industrial grade anion exchange resin Duolite A-638 resins were studied by application of radio analytical tracer technique. The reaction rate k in min−1 for the fresh resin decreases sharply with decrease in wavelength of UV radiations. Thus for 0.200 M labeled bromide ion solution maintained at a constant temperature of 30.0 °C, the k value for fresh resin (0.367 min−1), decreases to 0.335 min−1 for λ384 UV radiation degraded resin, which further decreases to 0.273 min−1 for λ284 UV radiation degraded resin. Under identical experimental conditions, the thermodynamic parameters like energy of activation (−1.65 kJ/mol), enthalpy of activation (−4.24 kJ/mol), free energy of activation (64.85 kJ/mol), and entropy of activation (−0.229 kJ/K/mol) calculated for the fresh resin increases to −1.61 kJ/mol, −4.19 kJ/mol, 64.92 kJ/mol, and −0.228 kJ/K/mol respectively for λ384 UV radiation degraded resin; which further increases to −1.60 kJ/mol, −4.18 kJ/mol, 65.17 kJ/mol, and −0.228 kJ/K/mol respectively for λ284 UV radiation degraded resin. Increase in thermodynamic parameters calculated here for the fresh and degraded resins suggests that decrease in wavelength of UV radiations has catastrophic effect on the resin making the bromide ion-isotopic exchange reactions thermodynamically less feasible. The impact of UV radiation on resin degradation was supported by their characterization study using Fourier-transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) techniques.

Development and validation of a simple and reliable alternative method for process monitoring and final product quality control during fatty acid ethyl esters production

As the production of biofuels increase, there is an urgent need to easily analytically control their production at the plant level as well as to assess the quality of the final products. Especially method capable of determining fatty acid ethyl ester content of 96.5% is crucial for utilization in praxis. In this work, a refractive index method with required sensitivity was developed and validated by means of a standard reference gas chromatography method. Validation with a considerable set of real unique samples obtained at pilot scale was performed for both purposes - process monitoring at high conversions and final product quality control. The results confirmed a favourable degree of accuracy with a relative deviation lower than 3.5% from the reference value given by the gas chromatography. Moreover, application of the method for quality control of fresh and long-term stored samples revealed that the deterioration of final products during storage can be detected. The developed refractive index method is thus suitable for the simple and rapid evaluation of the quality of produced fatty acid ethyl esters and for analytical monitoring of their production process.

Characterization of polystyrene and polyacrylic based polymeric materials exposed to oxidative degradation

The characterization of oxidative degraded polystyrene-based resin (R1) and polyacrylic based resin (R2) resins in H2O2 and HClO4 degradation medium were made based on the kinetics and thermodynamic data obtained for the ion-isotopic exchange reactions using such resins. For the reactions performed by using resins degraded in H2O2 medium, the reaction rate (k) values obtained for the fresh R1 (0.315 min–1) and R2 (0.187 min–1) resins decreases to 0.300 and 0.155 min–1 respectively for the resins degraded in 20% H2O2 medium, which further decreases to 0.289 and 0.142 min–1 respectively for the resins degraded in 30% H2O2 medium. A similar trend in the results were observed for the reactions performed by using the above resins degraded in HClO4 medium. The higher values of k (min–1) and low values of various thermodynamic parameters for the ion-isotopic exchange reactions performed by using fresh and degraded polystyrene-based resin R1 resins suggests superior degradation stability as compared to polyacrylic based R2 resin.

Experimental investigation of biodiesel production from Madhuca longifolia seed through in situ transesterification and its kinetics and thermodynamic studies

The present investigation aims to develop simultaneous extraction and conversion of inedible Madhuca longifolia seed oil into biodiesel by one-step acid-catalyzed in situ transesterification/reactive extraction process. Six different types of pretreatment were used to assess maximum yield of biodiesel. The maximum yield of 96% biodiesel was acquired with ultrasonic pretreatment at 1% moisture content, 0.61 mm seed grain size, 55 °C temperature, 400 rpm stirring speed, 15 wt% catalyst (H₂SO₄) concentration, and with 1:35 seed oil to methanol ratio in a time period of 180 min. This reaction kinetics precedes first order also the finest value of rate constant and activation energy were calculated as 0.003 min^-1 and 14.840 kJ mol^-1. The thermodynamic energy properties ΔG, ΔH, and ΔS are computed as 96457.172 J/mol, 12121.812 J/mol K, and - 257.12 J/mol K correspondingly. The enumerated outcome illustrates a heat absorb non-spontaneous/endergonic and endothermal reaction. The result of proposed work unveils ultrasonic pretreatment escalates the biodiesel efficiency and reactive extraction exemplifies the clean, cost-effective single-step approach for production of biodiesel from non-edible sources.

Structure elucidation and formation mechanistic study of a methylene-bridged pregabalin dimeric degradant in pregabalin extended-release tablets

During the pharmaceutical development of pregabalin extended-release tablets, an unknown degradant at a relative retention time (RRT) of 11.7 was observed and its nominal amount exceeded the ICH identification threshold in an accelerated stability study. The aim of this study is to identify the structure and investigate the formation mechanism of this impurity for the purpose of developing a chemically stable pharmaceutical product. By utilizing multi-stage LC-MS analysis in conjunction with mechanism-based stress study, the structure of the RRT 11.7 impurity was rapidly identified as a dimeric degradant that is caused by dimerization of two pregabalin molecules with a methylene bridging the two pregabalin moieties. The structure of the dimer was confirmed by 1D and 2D NMR measurement. The formation pathway of the dimeric degradant was also inferred from the mechanism-based stress study, which implicated that the bridging methylene could originate from formaldehyde which might be the culprit that triggers the dimerization in the first place. The subsequent API-excipients compatibility study indicated that the degradant was indeed formed in the compatibility experiments between pregabalin API and two polymeric excipients (PEO and PVPP) that are known to contain residual formaldehyde, but only in the co-presence of another excipient, colloidal silicon dioxide (SiO₂). The kinetic behavior of the degradant formation was also investigated and two kinetic models were utilized based on the Arrhenius and Eyring equations, respectively, to calculate the activation energy (E_a) as well as the enthalpy of activation (△H^‡), entropy of activation (△S^‡), and Gibbs free energy (△G^‡) of the degradation reaction. The results of this study would be useful for the understanding of similar dimeric degradant formation in finished products of drug substances containing primary or secondary amine moieties.

Ultrasound assisted two-stage biodiesel synthesis from non-edible Schleichera triguga oil using heterogeneous catalyst: Kinetics and thermodynamic analysis

Present work deals with the ultrasound-assisted biodiesel production from low cost, substantial acid value kusum (Schleichera triguga) oil using a two-step method of esterification in presence of acid (H2SO4) catalyst followed by transesterification using a basic heterogeneous barium hydroxide (Ba(OH)2) catalyst. The initial acid value of kusum oil was reduced from 21.65 to 0.84 mg of KOH/g of oil, by acid catalyzed esterification with 4:1 methanol to oil molar ratio, catalyst concentration 1% (v/v), ultrasonic irradiation time 20 min at 40 °C. Then, Ba(OH)2 concentration of 3% (w/w), methanol to oil molar ratio of 9:1, ultrasonic irradiation time of 80 min, and temperature of 50 °C was found to be the optimum conditions for transesterification step and triglyceride conversion of 96.8% (wt) was achieved. This paper also examined the kinetics as well as the evaluation of thermodynamic parameters for both esterification and transesterification reactions. The lower value of activation energy and higher values of kinetic constants indicated a fast rate of reaction, which could be attributed to the physical effect of emulsification, in which the microturbulence generated due to radial motion of bubbles, creates an intimate mixing of the immiscible reactants causing the increase in the interfacial area, giving faster reaction kinetics. The positive values of Gibbs-free energy (ΔG), enthalpy (ΔH) and negative value of entropy (ΔS) revealed that both the esterification and transesterification were non-spontaneous, endothermic and endergonic reactions. Therefore, the present work has not only established the escalation obtained due to ultrasonication but also exemplified the two-step approach for synthesis of biodiesel from non-edible kusum oil based on the use of heterogeneous catalyst for the transesterification step.

Pilot-scale production of biodiesel from waste fats and oils using tetramethylammonium hydroxide

Annually, a great amount of waste fats and oils not suitable for human consumption or which cannot be further treated are produced around the world. A potential way of utilizing this low-cost feedstock is its conversion into biodiesel. The majority of biodiesel production processes today are based on the utilization of inorganic alkali catalysts. However, it has been proved that an organic base - tetramethylammonium hydroxide - can be used as a very efficient transesterification catalyst. Furthermore, it can be employed for the esterification of free fatty acids - reducing even high free fatty acid contents to the required level in just one step. The work presented herein, is focused on biodiesel production from waste frying oils and animal fats using tetramethylammonium hydroxide at the pilot-plant level. The results showed that the process performance in the pilot unit - using methanol and TMAH as a catalyst, is comparable to the laboratory procedure, even when the biodiesel is produced from waste vegetable oils or animal fats with high free fatty acid content. The reaction conditions were set at: 1.5% w/w of TMAH, reaction temperature 65°C, the feedstock to methanol molar ratio to 1:6, and the reaction time to 120min. The conversion of triglycerides to FAME was approximately 98%. The cloud point of the biodiesel obtained from waste animal fat was also determined.

Synthesis of ethylene glycol monomethyl ether monolaurate catalysed by KF/NaAlO2as a novel and efficient solid base

NaAlO₂modified with KF (KF/NaAlO₂) was prepared using a simple wet-impregnation method and used for the transesterification of ethylene glycol monomethyl ether and methyl laurate. The catalyst showed excellent catalytic activity and good stability.

The mechanism of hydrothermal hydrolysis for glycyrrhizic acid into glycyrrhetinic acid and glycyrrhetinic acid 3-O-mono-β-D-glucuronide in subcritical water

To improve the bioactivity and sweetness properties of glycyrrhizic acid (GL), the hydrothermal hydrolysis of GL into glycyrrhetinic acid (GA) and glycyrrhetinic acid 3-O-mono-β-D-glucuronide (GAMG) in subcritical water was investigated. The effects of temperature, time and their interaction on the conversion ratios were analyzed and the reactions were elaborated with kinetics and thermodynamics. The results showed that GL hydrothermal hydrolysis was significantly (P < 0.05) affected by reaction time and temperature, as well as their interaction, and could be fitted into first-order kinetics. The thermodynamic analysis indicated that the hydrolysis of GL was endergonic and non-spontaneous. The hydrolytic pathways were composed of complex consecutive and parallel reactions. It was concluded that subcritical water may be a potential medium for producing GAMG and GA.

Biodiesel production via ethanolysis of jatropha oil using molybdenum impregnated calcium oxide as solid catalyst

Mo/CaO catalyst was employed for the ethanolysis of high free fatty acid containing (up to 18 wt%) vegetable oils to produce biodiesel.

Response surface optimization and artificial neural network modeling of biodiesel production from crude mahua (Madhuca indica) oil under supercritical ethanol conditions using CO2 as co-solvent

The present study describes the renewable, environment-friendly approach for the production of biodiesel from low cost, high acid value mahua oil under supercritical ethanol conditions using carbon dioxide (CO₂) as a co-solvent.

One-pot transesterification and esterification of waste cooking oil via ethanolysis using Sr:Zr mixed oxide as solid catalyst

Prepared 2Sr:Zr-650 catalyst possesses both acidic and basic sites, hence it was able to catalyze the simultaneous esterification and transesterification of free fatty acid containing vegetable oils.