Esterification Of Isoamyl Alcohol Research Articles

How Two‐Dimensional Heterocovariance Spectroscopy and Data Fusion Level out the Inadequacies of Compact Spectrometers

ABSTRACTOver the past decade, sensors and compact spectrometers have emerged as a powerful means for real‐time monitoring of chemical and biochemical processes in the field of process analytical technologies (PATs). This is largely attributed to cost‐efficiency and their robustness in near‐line applications. In comparison to more sophisticated laboratory instruments, these devices exhibit limited sensitivity and resolution. In this study, a combination of near‐infrared, low‐field 1H nuclear magnetic resonance and compact Raman spectrometers were employed for the process monitoring of the acid‐catalyzed esterification of isoamyl alcohol and acetic acid to isoamyl acetate. The resulting real‐time data were transformed and visualized for interpretation using two‐dimensional heterocovariance spectroscopy. The data were also subjected to pretreatment, concatenation, and multivariate analysis in accordance with low‐ and mid‐level data fusion. The spectral interpretation derived from heterocovariance spectroscopy provided support for the data pretreatment during data fusion. By applying these computational techniques, the inherent limitations of sensitivity and resolution associated with compact spectroscopic instruments could be overcome, thereby facilitating the interpretation of data and yielding further insights into the process under study. A comparison of the process parameters resulting from the applied methods indicated that consistent data could be obtained. This study demonstrates that heterocovariance spectroscopy and data fusion allow to enhance compact, less expensive analytical instruments for process monitoring and to acquire process knowledge. This, in turn, enables material, financial, and energy resources to be conserved.

Process optimization for enzymatic production of a valuable biomass-based ester from levulinic acid.

The enzymatic production of isoamyl levulinate via esterification of isoamyl alcohol (IA) and levulinic acid (LA), a biomass-based platform chemical with attractive properties, in a solvent system has been performed in this study. For such a purpose, a low-cost liquid lipase (Eversa® Transform 2.0) immobilized by physical adsorption via hydrophobic interactions (mechanism of interfacial activation) on mesoporous poly(styrenene-divinylbenzene) (PSty-DVB) beads was used as heterogeneous biocatalyst. It was prepared at low ionic strength (5mmol.L-1 buffer sodium acetate pH 5.0) and 25℃ using an initial protein loading of 40mg.g-1 of support. Maximum protein loading of 31.2 ± 2.8mg.g-1 of support and an immobilization yield of 83% was achieved. The influence of relevant factors (biocatalyst concentration and reaction temperature) on ester production was investigated using a central composite rotatable design (CCRD). Maximum acid conversion percentage of 65% was achieved after 12h of reaction at 40°C, 20% of mass of heterogeneous biocatalyst per mass of reaction mixture (20% m.m-1), and LA:IA molar ratio of 1:1.5 in a methyl isobutyl ketone (MIBK) medium. The biocatalyst retained around of 30% of its initial activity after five consecutive esterification batches under optimal experimental conditions. The proposed experimental procedure can be considered as an acceptable green process (EcoScale score of 66.5), in addition to the fact that a new strategy is proposed to sustainably produce a valuable industrial ester (isoamyl levulinate) from biomass-based materials using an immobilized and low-cost commercial lipase as catalyst.

Production of isoamyl acetate by enzymatic reactions in batch and packed bed reactors with supercritical CO2

Batch reactors (BRs) are probably the most widely used reactor designs for biocatalysis in supercritical fluids, but for industrial scale applications packed bed reactors (PBRs) are frequently preferred. The objective of this work was to investigate and compare BR and PBR in the synthesis of isoamyl acetate through enzymatic reactions in SCCO2 media. Experiments were performed to determine the kinetic parameters and to evaluate the internal and external mass transfer effects. The results indicate that the reaction is kinetically controlled, independently of particle diameter and agitation, therefore intra-particle diffusion and external mass transfer resistance are unimportant. The kinetic Ping-Pong Bi–Bi model described well the esterification of isoamyl alcohol with acetic anhydride at the evaluated conditions, indicating that the affinity of the enzyme to acetic anhydride is larger than to isoamyl alcohol. The PBR achieved the highest productivity of isoamyl acetate, although its conversion was lower than that obtained by the BR. In summary, PBR is the best option to synthesize isoamyl acetate in SC-CO2 media.

Optimization of catalytic activity of sulfated titania for efficient synthesis of isoamyl acetate by response surface methodology

TiO2 nanoparticles were synthesized by sol–gel method using titanium tetraisopropoxide. Sulfate ions were introduced on the titania by impregnation method using sulfuric acid as precursor of sulfate ions. Fourier transform infrared and energy-dispersive X-ray spectroscopy, X-ray fluorescence as well as X-ray diffraction, scanning electron microscopy, and BET methods were used for the characterization of the obtained nanoparticles. The esterification of isoamyl alcohol with acetic acid was investigated to prove the catalytic activity of the TiO2 nanoparticles under solvent-free conditions. Response surface methodology was applied to optimize the effect of some parameters such as the molar ratio of acetic acid to alcohol, catalyst loading, reaction temperature, and reaction time on the yield of the isoamyl acetate. The TiO2 nanoparticles were proved to be an excellent heterogeneous catalyst for isoamyl acetate synthesis under solvent-free conditions affording a high yield of 94 % under the following optimal conditions: molar ratio of acetic acid to alcohol (1:7), catalyst loading (3.2 wt% with respect to the acetic acid), the reaction temperature (130 °C), and the reaction time (300 min).

Microwave assisted lipase catalyzed synthesis of isoamyl myristate in solvent-free system

► Lipase catalyzed solvent-free synthesis of isoamyl myristate. ► Novozyme 435 was found to be the best catalyst. ► Synergism of microwave irradiation with enzyme catalysis. ► Equimolar reactants, 0.38% (w/v) Novozym 435, 400 rpm, 60 °C, 1 h: 96% conversion. Isoamyl myristate finds many applications in food, cosmetic and pharmaceutical industries as a flavor and fragrance compound. The current work focuses on solvent-free lipase catalyzed microwave assisted synthesis of isoamyl myristate from isoamyl alcohol and myristic acid. The activities of a number of commercially available lipases such as Novozym 435, Lipozyme RM IM and Lipozyme TL IM were evaluated, amongst which Novozym 435 was found to be the most active. Effect of solvent, agitation speed, type of enzyme, enzyme concentration, reactant concentrations and temperature was systematically studied on the esterification of isoamyl alcohol with myristic acid under microwave irradiation. Equimolar quantities of the reactants with 0.38% (w/v) Novozym 435 catalyst loading and agitation speed of 400 rpm leads to 96% conversion at 60 °C in 1 h. Based on the initial rates and concentration profiles, the reaction was found to obey the ping-pong bi-bi mechanism with inhibition by isoamyl alcohol and the kinetic parameters were evaluated by using non-linear regression analysis.

Modelling and experimental studies on lipase-catalyzed isoamyl acetate synthesis in a microreactor

A lipase-catalyzed synthesis of isoamyl acetate was studied in a continuously operated pressure-driven microreactor. The esterification of isoamyl alcohol and acetic acid occurred at the interface between n-hexane and an aqueous phase with dissolved lipase B from Candida antarctica. By adjusting flow rates of both phases, a parallel laminar flow with liquid–liquid boundary in the middle of the microchannel could be reestablished and a separation of phases was achieved at the y-shaped exit of the microreactor. Since product remained in the organic phase, this also enabled its continuous separation from the aqueous phase with the enzyme. A three-dimensional mathematical model was developed, considering the velocity profile developed for steady-state conditions between two immiscible fluids. The model contained convection, diffusion, and enzyme reaction terms, where esterification rate was described with a Ping-Pong Bi-Bi mechanism and inhibition by both substrates. Experimental data, which were in good agreement with model simulations, have demonstrated 35% conversion at residence time 36.5 s at 45 °C and at 0.5 M acetic acid and isoamyl alcohol inlet concentrations, which is much faster as in any literature reported so far. According to model simulations, obtained by non-equidistant finite differences numerical solutions of complex non-linear equations system, further microreactor design and process optimization are feasible.

Silicotungstic acid/zirconia immobilized on SBA-15 for esterifications

A simple wet-impregnation method and controlled calcination process was used for preparing nano-sized silicotungstic acid (STA) supported on zirconia embedded inside the various mesoporous silicas such as SBA-15, MCM-41 and MCM-48. Catalysts with different (%) STA loadings were also synthesized and characterized by XRD, N 2 adsorption–desorption, TEM, 29Si-MAS NMR, FT-Raman spectroscopic techniques. The acidic behavior of the catalysts was studied by TPD of ammonia and FT-IR pyridine adsorption technique. The effect of calcination temperature on the textural parameters of the catalysts and the integrity of STA on the surface of the catalyst were also examined. Moreover, the performance of these catalysts was investigated in the esterification of isoamyl alcohol (IAA) with acetic acid (AA). Catalytic activities were correlated with the acidity of the catalysts. Effects of reaction parameters such as mole ratio of reactants, reaction temperature, catalyst concentration and reusability of the catalyst were studied to get higher substrate conversions and product selectivities. Among the catalysts, 15 wt.% STA/22.4 wt.% ZrO 2/SBA-15 calcined at 1123 K was found to be the most active and acidic catalyst, showing higher conversion and selectivity than neat 15 wt.% STA/ZrO 2 in esterification of IAA by AA. The reaction was found to be heterogeneously catalyzed and no contribution from homogeneous (leached) STA into the medium under the reaction conditions was observed.

Stability and activity of enzyme aggregates of Calb in supercritical CO 2

The activity and stability of a cross-linked enzyme aggregate of Candida antarctica lipase B (CLEA-Calb) in supercritical carbon dioxide (SC-CO 2) have been studied. The model reaction used is the esterification of isoamyl alcohol with acetic acid. The catalytic performance of CLEA-Calb is evaluated both in batch and in continuous experiments, with a focus on the effect of water production upon reaction. The results of the batch experiments show a decreasing initial activity of the CLEA-Calb with an increase in pressure. Moreover, CLEAs appear to be highly stable in supercritical carbon dioxide and also remain active during continuous reactions. Suggestions for improved process designs are given for which the optimal design depends on the specific reaction requirements.

Supported Keggin type heteropolycompounds for ecofriendly reactions

New supported Keggin heteropolyacid (HPA) catalysts were prepared in order to make a contribution to the field of catalyzed acid reactions by means of ecofriendly technologies. The esterification of isoamyl alcohol and acetic acid in gaseous phase was studied using tungstophosphoric acid (TPA) supported on different carriers, silica materials, carbon and alumina. These catalysts were characterized by FT-IR, DRS, TPR and their acidity was evaluated through the isopropanol dehydration test reaction. The higher acidic catalysts prepared with silica materials led to the greatest activities due to the higher proton availability which, in turn, was related to the lower interaction and dispersion of the active species. In order to perform this acid reaction in heterogeneous liquid phase and to avoid the tungstophosphoric or molybdophosphoric acid (MPA) solubilization during reaction, functionalized silica and SiMCM-41, and polyvinyl alcohol hydrogel–polyethylenglycol (PVA-PVG) beads were used as new supports. The physical–chemical characterization of the supported catalysts by FT-IR, XRD, 31P MAS NMR and TG-DTA showed mainly undegraded primary Keggin structure. The solids exhibited low or negligible solubilization and their acidity, measured by potentiometric titration with n-butylamine, was high. The SiMCM-41 and polymeric bead-supported catalysts lead to obtain attractive activity in the isoamyl acetate synthesis through esterification reaction.

Optimising the synthesis of isoamyl butyrate using Rhizopus sp. lipase with a central composite rotatable design

Microbial lipases (E.C. 3.1.1.3) produced by Geotrichum sp. and Rhizopus sp. were prepared and tested as catalysts in the esterification of isoamyl alcohol and butyric acid in a solvent-free system. Response surface methodology (RSM) based on a five-level, two-variable central composite rotatable design (CCRD) was used to optimise this process, with respect to important reaction variables-substrate molar ratio (RM), temperature and lipase concentration (L). The variables RM and L were the most significant in the process. An increase in alcohol concentration from 1:2 to 4:1 caused a decrease in yield to 18.45%, after 48 h of reaction time, and a variation of L from 1 to 10% caused an increase in yield to 32.2%. The optimum conditions found to achieve maximum ester yield (75%) are: RM=1.5:1; L=5.5% (w/w), 40 °C, after 48 h of reaction time.

Optimization of the enzymatic production of isoamyl acetate with novozym 435 from candida antarctica

In this study the production of isoamyl acetate by esterification of isoamyl alcohol and acetic acid was carried out using immobilized C . antarctica lipase (Novozym 435) as a catalyst without any organic solvent. The esterification yield was optimized with response surface methodology. This method was used with four parameters to evaluate the effects of important variables on the esterification yield. The parameters are acid/alcohol mole ratio (0.2-0.8), enzyme amount (4-12%, w/w), temperature (30-50 °C), and reaction time (4-8 hr). It was found that the most effective parameter was acid/alcohol mole ratio. As acid/alcohol mole ratio increased at any given reaction time and amount of enzyme, ester concentration, C p (mmol ester/g mixture), increased up to an acid/alcohol mole ratio of 0.7 and thereafter decreased. The model indicated the optimum conditions for maximum esterification (3.45 mmol ester/g mixture) in the acid/alcohol mole ratio of 0.52 for 8.15% enzyme at 43.2 °C and after 5.27 hr, which were in good agreement with the experimental value (3.5 mmol ester/g mixture).

Enzymatic synthesis of isoamyl butyrate using immobilized Rhizomucor miehei lipase in non-aqueous media

Isoamyl butyrate, an important fruity flavor ester, was synthesized using Rhizomucor miehei lipase immobilized on a weak anion exchange resin (Lipozyme IM-20) by the esterification of isoamyl alcohol and butyric acid. The effects of various reaction parameters such as substrate and enzyme concentrations, substrate molar ratio, temperature and incubation time have been investigated. Yields above 90% were obtained with substrate concentrations as high as 2.0 M. No evidence of enzyme inhibition by butyric acid was present up to 1.0 M concentration. Acid inhibition and, to a small extent, alcohol inhibition were evident above 1.0 M substrate concentration. Conversions reached a saturation value by the end of 24–48 h of incubation due to the accumulation of the water of reaction. The equilibrium was successfully pushed forward towards esterification by removing the accumulated water using a molecular sieve.Journal of Industrial Microbiology & Biotechnology (2000) 25, 147–154.

The efficacy of zotepine in both long term and short term treatment of schizophrenia

Batch reactors (BRs) are probably the most widely used reactor designs for biocatalysis in supercritical fluids, but for industrial scale applications packed bed reactors (PBRs) are frequently preferred. The objective of this work was to investigate and compare BR and PBR in the synthesis of isoamyl acetate through enzymatic reactions in SCCO2 media. Experiments were performed to determine the kinetic parameters and to evaluate the internal and external mass transfer effects. The results indicate that the reaction is kinetically controlled, independently of particle diameter and agitation, therefore intra-particle diffusion and external mass transfer resistance are unimportant. The kinetic Ping-Pong Bi–Bi model described well the esterification of isoamyl alcohol with acetic anhydride at the evaluated conditions, indicating that the affinity of the enzyme to acetic anhydride is larger than to isoamyl alcohol. The PBR achieved the highest productivity of isoamyl acetate, although its conversion was lower than that obtained by the BR. In summary, PBR is the best option to synthesize isoamyl acetate in SC-CO2 media.

Adsorptive control of water in esterification with immobilized enzymes. Continuous operation in a periodic counter-current reactor

A periodic counter-current adsorptive-reactor system is developed to carry out continuous esterifications in organic solvents with immobilized enzymes. The system comprises a number of fixed-beds distributed between a reaction-adsorption zone and a regeneration zone and operated in a "merry-go-round" sequence. Water formed in the reaction is adsorbed preventing the formation of a free-water phase and deactivation of the biocatalyst. The adsorbed water is, in turn, recovered by desorption in the regeneration zone. The concept is tested experimentally on a laboratory-scale using, as a model, the esterification of isoamyl alcohol and propionic acid in hexane catalyzed by an immobilized lipase. Pure isoamyl alcohol is used as a regenerant to remove excess water from the biocatalyst. In the periodic steady-state, improvements in ester productivity greater than 50% over that achievable with a conventional fixed-bed reactor are demonstrated experimentally with just two beds in a series arrangement. Use of a water-selective adsorbent in conjunction with the biocatalyst provides further improvements by reducing accumulation of water on the enzyme. A mathematical model is also developed to predict the thermodynamic activity of water along the reactor and describe the dynamic behavior of the system. The model, based on independently developed rate and equilibrium parameters, successfully predicts the experimental behavior and provides an effective tool for scale-up and optimization.

Adsorptive control of water in esterification with immobilized enzymes. Continuous operation in a periodic counter‐current reactor

A periodic counter-current adsorptive-reactor system is developed to carry out continuous esterifications in organic solvents with immobilized enzymes. The system comprises a number of fixed-beds distributed between a reaction–adsorption zone and a regeneration zone and operated in a “merry-go-round” sequence. Water formed in the reaction is adsorbed preventing the formation of a free-water phase and deactivation of the biocatalyst. The adsorbed water is, in turn, recovered by desorption in the regeneration zone. The concept is tested experimentally on a laboratory-scale using, as a model, the esterification of isoamyl alcohol and propionic acid in hexane catalyzed by an immobilized lipase. Pure isoamyl alcohol is used as a regenerant to remove excess water from the biocatalyst. In the periodic steady-state, improvements in ester productivity greater than 50% over that achievable with a conventional fixed-bed reactor are demonstrated experimentally with just two beds in a series arrangement. Use of a water-selective adsorbent in conjunction with the biocatalyst provides further improvements by reducing accumulation of water on the enzyme. A mathematical model is also developed to predict the thermodynamic activity of water along the reactor and describe the dynamic behavior of the system. The model, based on independently developed rate and equilibrium parameters, successfully predicts the experimental behavior and provides an effective tool for scale-up and optimization. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 66: 137–146, 1999.

Esterification by the Nitronium Ion in Aqueous Perchloric Acid

THE nitronium ion, NO2 +, has been shown to be the active nitrating entity in the O-nitration of certain alcohols in organic solvents1 in which nitric acid is present in large excess. Kinetic studies in progress on the esterification of isoamyl alcohol with nitric acid in 55–62 per cent aqueous perchloric acid have now indicated that here also O-nitration proceeds through the nitronium ion, although only a very small fraction of the nitric acid can be present in this cationic form in media of such high water-content. Rate measurements at 25° C. made by ultra-violet spectrometric analysis of the unchanged nitric acid after dilution of aliquots with water and extraction of the isoamayl nitrate product show that the rate equation (1) is obeyed: