Five-factor response surface optimization of the enzymatic synthesis of citronellyl butyrate by lipase IM77 from Mucor miehei

Response surface methodology (RSM) and a five-level-five-factor central composite rotatable design (CCRD) were used to evaluate the effects of synthetic variables, such as reaction time (3 to 27 h), temperature (25 to 65 °C), enzyme amount (10 to 50%), substrate molar ratio of citronellol to butyric acid (1∶1 to 1∶3), and added water amount (0 to 20%) on molar percent yield of citronellyl butyrate by direct esterification, using lipase IM77 from Mucor miehei. Reaction time and temperature were the most important variables. Substrate molar ratio had no effect on percent molar conversion. Based on contour plots, optimal synthetic conditions were these: reaction time 24 h, temperature 60°C, enzyme amount 20%, substrate molar ratio 1∶1.5, and added water 0%. The predicted molar conversion value was 100%. An actual experimental value of 98% molar conversion was obtained.     

Optimized synthesis of lipase‐catalyzed biodiesel by Novozym 435

The ability of immobilized lipase from Candida antarctica (Novozym 435) to catalyze the alcoholysis of canola oil and methanol was investigated. Response surface methodology (RSM) and five–level–five–factor central composite rotatable design (CCRD) were employed to evaluate the effects of synthesis parameters, such as reaction time, temperature, enzyme concentration, substrate molar ratio of methanol to canola oil, and added water content on percentage weight conversion of canola oil methyl ester by alcoholysis. Reaction temperature and enzyme concentration were the most important variables. High temperature and superabundant methanol inhibited the ability of Novozym 435 to catalyze the synthesis of biodiesel. Based on the analysis of ridge max, the optimum synthesis conditions were as follows: reaction time 12.4 h, temperature 38.0 °C, enzyme concentration 42.3%, substrate molar ratio 3.5:1, and added water 7.2%. The predicted value was 99.4% weight conversion, and the actual experimental value was 97.9% weight conversion. Copyright © 2004 Society of Chemical Industry     

Synthesis of monoterpene esters by alcoholysis reaction with Mucor miehei lipase in a solvent-free system

The syntheses of geranyl acetate and citronellyl acetate by alcoholysis reaction catalyzed by immobilized lipase from Mucor miehei was studied for the first time in a solvent-free system. Reactions were carried out at a terpene alcohol/acyl donor molar ratio of 1:5 with Lipozyme at 10% of the total weight of the reactants in a solvent-free system. Incubations were carried out at 55 to 60°C for ethyl and butyl acetates as acyl donors, whereas for methyl acetate the incubation temperature was 40 to 45°C. Excess concentration of acyl donor increases the percentage of geranyl acetate and citronellyl acetate, while excess of terpene alcohol concentration decreases the same. Yields from 75 to 77% molar conversion (90 to 98% conversion, w/w) were obtained after 8 to 28 h of reaction time.     

Highly efficient reversible addition–fragmentation chain‐transfer polymerization in ethanol/water via flow chemistry

Utilization of a flow reactor under high pressure allows highly efficient polymer synthesis via reversible addition–fragmentation chain‐transfer (RAFT ) polymerization in an aqueous system. Compared with the batch reaction, the flow reactor allows the RAFT polymerization to be performed in a high‐efficiency manner at the same temperature. The adjustable pressure of the system allows further elevation of the reaction temperature and hence faster polymerization. Other reaction parameters, such as flow rate and initiator concentration, were also well studied to tune the monomer conversion and the molar mass dispersity (?) of the obtained polymers. Gel permeation chromatography, nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopies (FTIR) were utilized to monitor the polymerization process. With the initiator concentration of 0.15 mmol L^?1, polymerization of poly(ethylene glycol) methyl ether methacrylate with monomer conversion of 52% at 100 °C under 73 bar can be achieved within 40 min with narrow molar mass dispersity (D) ? (<1.25). The strategy developed here provides a method to produce well‐defined polymers via RAFT polymerization with high efficiency in a continuous manner. © 2017 Society of Chemical Industry     

Optimization of Lipase-Catalyzed Synthesis of Cetyl Octanoate in Supercritical Carbon Dioxide

Cetyl octanoate, a wax ester of 24 carbons, is widely used in the cosmetic industry as a base oil. The current work focuses on lipase-catalyzed synthesis of cetyl octanoate in supercritical carbon dioxide (SC-CO₂) by esterification of cetyl alcohol and octanoic acid. Three immobilized lipases were screened, and 15 reaction conditions were tested in order to find the combination for maximal yield. The results showed that Novozym^® 435 was the best catalyst for the synthesis, and a reaction time of 20 min was adequate for a maximal yield. Response surface methodology (RSM) with a 3-factor-3-level Box-Behnken design was employed to evaluate the effects of synthesis parameters, including reaction temperature (35–75 °C), pressure (8.27–12.41 MPa), and enzyme amount (5–15% wt of cetyl alcohol). A model for the synthesis was developed and the optimum conditions could be predicted to be reaction pressure of 10.22 MPa, reaction temperature of 63.70 °C, and enzyme amount of 11.20%. An experiment was performed under this optimum condition and a yield of 99.5% was obtained. This experimental yield correlated well with the predicted value of yield (97.6%). We concluded that, in a SC-CO₂ system, nearly 100% molar conversion of cetyl octanoate could be obtained by immobilized Novozym^® 435 in a short reaction time (20 min) under the predicted optimal conditions.     

Lipase‐catalyzed ethanolysis of soybean oil in a solvent‐free system using central composite design and response surface methodology

BACKGROUND: In this work we describe the synthesis of ethyl esters, commonly known as biodiesel, using refined soybean oil and ethanol in a solvent‐free system catalyzed by lipase from Thermomyces lanuginosus. Central composite design and response surface methodology (RSM) were employed to optimize the biodiesel synthesis parameters, which were: reaction time, temperature, substrate molar ratio, enzyme content, and added water, measured as percentage of yield conversion. RESULTS: The optimal conditions obtained were: temperature, 31.5 °C; reaction time, 7 h; substrate molar ratio, 7.5:1 ethanol:soybean oil; enzyme content, 15% (g enzyme g⁻¹ oil); added water, 4% (g water g⁻¹ oil). The experimental yield conversion obtained under these conditions was 96%, which is very close to the maximum predicted value of 94.4%. The reaction time‐course at the optimal values indicated that 5 h was necessary to obtain high yield conversions. CONCLUSION: A high yield conversion was obtained under the optimized conditions, with relative low enzyme content and short time. Comparison of predicted and experimental values showed good correspondence, implying that the empirical model derived from RSM can be used to adequately describe the relationship between the reaction parameters and the response (yield conversion) in lipase‐catalyzed biodiesel synthesis. Copyright © 2008 Society of Chemical Industry     

Biodiesel Production from Soybean Oil Catalyzed by Li<Subscript>2</Subscript>CO<Subscript>3</Subscript>

In the present study, we synthesized biodiesel from soybean oil through a transesterification reaction catalyzed by lithium carbonate. Under the optimal reaction conditions of methanol/oil molar ratio 32:1, 12 % (wt/wt oil) catalyst amount, and a reaction temperature of 65 °C for 2 h, there was a 97.2 % conversion to biodiesel from soybean oil. The present study also evaluated the effects of methanol/oil ratio, catalyst amount, and reaction time on conversion. The catalytic activity of solid base catalysts was insensitive to exposure to air prior to use in the transesterification reaction. Results from ICP-OES exhibited non-significant leaching of the Li₂CO₃ active species into the reaction medium, and reusability of the catalyst was tested successfully in ten subsequent cycles. Free fatty acid in the feedstock for biodiesel production should not be higher than 0.12 % to afford a product that passes the EN biodiesel standard. Product quality, ester content, free glycerol, total glycerol, density, flash point, sulfur content, kinematic viscosity, copper corrosion, cetane number, iodine value, and acid value fulfilled ASTM and EN standards. Commercially available Li₂CO₃ is suitable for direct use in biodiesel production without further drying or thermal pretreatment, avoiding the usual solid catalyst need for activation at high temperature.     

OPTIMIZATION OF LIPASE-CATALYZED SYNTHESIS OF N-trans-FERULOYLTYRAMINE USING RESPONSE SURFACE METHODOLOGY (RSM)

Enzymatic synthesis of N-trans-feruloyltyramine amide was optimized by response surface methodology (RSM) using 4-hydroxy-3-methoxycinnamic acid and tyramine hydrochloride in a one-step lipase catalyzed reaction using Lipozyme TL IM. Response surface methodology (RSM) based on five-level, four-variable central composite rotatable design (CCRD) was used to evaluate the interaction of synthesis, reaction time (24–96 h), temperature (30°–50°C), amount of enzyme (50–500 mg, 12.5–125.0 IUN), and substrate molar ratio (cinnamic acid:tyramine HCl) 1:1–8:1 mmol on the percentage yield of N-trans-feruloyltyramine amide. The optimum conditions derived via RSM were: reaction time 52 h, temperature 43°C, amount of enzyme 260 mg (65.0 IUN), and substrate molar ratio (cinnamic acid:tyramine HCl) 6.2:1. The actual experimental yield was 96.3% under optimum conditions, which compared well to the maximum predicted value of 97.2%.     

A continuous ultrasound‐assisted packed‐bed bioreactor for the lipase‐catalyzed synthesis of caffeic acid phenethyl ester

BACKGROUND: The focus of this paper is the ultrasound‐assisted synthesis of caffeic acid phenethyl ester (CAPE) from caffeic acid and phenyl ethanol in a continuous packed‐bed bioreactor. Immobilized Novozym^® 435 (from Candida antarctica) is used as the catalyst. A three‐level–three‐factor Box–Behnken design and a response surface methodology (RSM) are employed to evaluate the effects of temperature, flow rate, and ultrasonic power on the percentage molar conversion of CAPE. RESULTS: Based on ridge max analysis, it is concluded that the optimum condition for synthesis is reaction temperature 72.66 °C, flow rate 0.046 mL min^?1, and ultrasonic power 1.64 W cm^?2. The expected molar conversion value is 97.84%. An experiment performed under these optimal conditions resulted in a molar conversion of 92.11 ± 0.75%. The enzyme in the bioreactor was found to be stable for at least 6 days. CONCLUSIONS: The lipase‐catalyzed synthesis of CAPE by an ultrasound‐assisted packed‐bed bioreactor uses mild reaction conditions. Enzymatic synthesis of CAPE is suitable for use in the nutraceutical and food production industries. Copyright © 2011 Society of Chemical Industry     

Synthesis of Trimethylolpropane Esters of Oleic Acid Using a Multi-SO<Subscript>3</Subscript>H-Functionalized Ionic Liquid as an Efficient Catalyst

Biodegradable trimethylolpropane triesters of oleic acid were synthesized by esterification of trimethylolpropane and oleic acid over a multi-SO₃H-functionalized strong Brønsted acidic ionic liquid as the catalyst. The results showed that the esterification can proceed satisfactorily over the catalyst at an ambient pressure even without simultaneous removal of water. Under the optimal reaction conditions (temperature: 100 °C, reaction time: 3 h, reactant molar ratio: 3.6:1, and catalyst amount, high conversion rate of trimethylolpropane (99.0%) and selectivity of trimethylolpropane triester (92.1%) were obtained. The ionic liquid was reused six times after the removal of water and no obvious change in catalytic activity was detected. Operational simplicity, high yields along with good reusability makes the multi-SO₃H-functionalized ionic liquid a promising catalyst for the esterification of trimethylolpropane with oleic acid.     

Effect of carbon deposition over carbonaceous catalysts on CH<Subscript>4</Subscript> decomposition and CH<Subscript>4</Subscript>-CO<Subscript>2</Subscript> reforming

An investigation was made using a continuous fixed bed reactor to understand the influence of carbon deposition obtained under different conditions on CH₄-CO₂ reforming. Thermogravimetry (TG) and X-ray diffraction (XRD) were employed to study the characteristics of carbon deposition. It was found that the carbonaceous catalyst is an efficient catalyst in methane decomposition and CH₄-CO₂ reforming. The trend of methane decomposition at lower temperatures is similar to that at higher temperatures. The methane conversion is high during the initial of stage of the reaction, and then decays to a relatively fixed value after about 30 min. With temperature increase, the methane decomposition rate increases quickly. The reaction temperature has significant influence on methane decomposition, whereas the carbon deposition does not affect methane decomposition significantly. Different types of carbon deposition were formed at different methane decomposition reaction temperatures. The carbon deposition Type I generated at 900°C has a minor effect on CH₄-CO₂ reforming and it easily reacts with carbon dioxide, but the carbon deposition Type II generated at 1000°C and 1100°C clearly inhibits CH₄-CO₂ reforming and it is difficult to react with carbon dioxide. The results of XRD showed that some graphite structures were found in carbon deposition Type II.     

Preparation of CuO-CeO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst with mesopore structure for water gas shift reaction

The water gas shift (WGS) reaction has been investigated widely in fuel cell technologies due to the potential for high fuel efficiency and lower emissions during the production of pure hydrogen. Industrially, the WGS reaction occurs in one of the following two ways: (a) high-temperature in the range of 310–450°C with Fe-Cr catalyst, (b) low-temperature in the range of 210–250°C with Cu-ZnO-Al₂O₃. In this study, a mesoporous catalyst was prepared, with a large surface area and uniformity in both pore size and distribution, by using a one-pot synthesis method. The prepared CuO-CeO₂-Al₂O₃ brought high CO conversion (82%), and was suitable for WGS reaction at low temperature (250 °C). This article is dedicated to Professor Chang Kyun Choi for celebrating his retirement from the School of Chemical and Biological Engineering, Seoul National University.     

High yields of ascorbyl palmitate by thermostable lipase-mediated esterification

High yields of ascorbyl palmitate (6-O-palmitoyl-l-ascorbic acid) were obtained by lipase-mediated esterification using Bacillus stearothermophilus SB 1 lipase. The final yield was greatly influenced by the initial water content of the system, quantity of enzyme, and molar ratio of palmitic acid to l-ascorbic acid. Reaction rates increased directly with temperature from 40 to 100°C. Maximum conversion (97%) was achieved after 30 min at 100°C (solvent-free), 1 h at 80°C (solvent-free), and 2 h at 60°C (solvent/hexane). The synthesis was scaled up to 1-l volume with 95% conversion using 50 mmoles of ascorbic acid and 250 mmoles of palmitic acid in hexane. Similar yields of ester were obtained in five repetitive cycles using 5 g enzyme immobilized on Accurel. The present B. stearothermophilus SB 1 lipase was a more efficient catalyst for the synthesis of ascorbyl palmitate than other commercial lipases.     

Production of geranyl propionate by enzymatic esterification of geraniol and propionic acid in solvent‐free system

Background: This work reports the optimization of geranyl propionate production by esterification of geraniol and propionic acid in a solvent‐free system using a commercial lipase as catalyst. For this purpose, a sequential strategy was performed applying two experimental designs. Results: The operating conditions that optimized geranyl propionate production were determined to be 40 °C, geraniol to propionic acid molar ratio of 3:1, 150 rpm and 10 wt% of enzyme, with a resulting reaction conversion of about 93%. After determining the optimum reaction parameters, a kinetic study was carried out evaluating the influence of substrates molar ratio, enzyme concentration and temperature on reaction conversion. Results obtained in this step allow one to conclude that an excess of alcohol (acid to alcohol molar ratio of 1:6), relatively low enzyme concentration (5 wt%), temperature of 40 °C and substrates molar ratio of 1:1 afforded nearly complete reaction conversion after 30 min of reaction. Conclusion: New experimental data on enzymatic esterification of geraniol and propionic acid for geranyl propionate production are reported in this work, showing a promising perspective of the technique to overcome the well‐known drawbacks of the chemical‐catalyzed route. Copyright © 2010 Society of Chemical Industry     

Synthesis of alkenyl succinic anhydrides from methyl esters of high oleic sunflower oil

Alkenyl succinic anhydrides (ASA) have been prepared by ene‐reaction of high‐oleic sunflower oil methyl esters with maleic anhydride in a 50% xylene medium. Response surface methodology (RSM) was used to investigate the influence of two factors: reaction temperature and molar ratio between maleic anhydride (MA) and methyl esters (SME). The studied parameters in 8‐h reactions were the methyl oleate conversion, the distillation yield in ASA, and responses allowing the indirect estimation of side reaction products: clarity index and dynamic viscosity. The highest yield in ASA (>70%; clarity index ≈10) was reached for a temperature of 240–250 °C with a molar ratio of 1.5–1.7. But for an industrial application requiring minimized side products (clarity index >40), the optimal synthesis conditions were: temperature between 220 and 235 °C and molar ratio of 1.2–1.35 (yield ≈55%). Such conditions did not provide a medium free of side products, even if xylene decreased their formation. Compared to solvent‐free synthesis, conversion was lower with xylene. With solvent, higher temperatures were needed to reach the same yields. Supplementary heating compensated the reagent dissolution effect that slows down the kinetics of the ene‐reaction. The influence of reaction time at 220 °C with a MA/SME ratio of 1.2 in a 50% xylene medium was studied. A reaction time of 8–10 h provided a good compromise between ASA yield and side products.     

Influence of Operating Parameters on Biomass Conversion under Sub‐ and Supercritical Water Conditions

The influence of reaction pressure, reaction time, reaction temperature, and biomass‐to‐water mass ratio R on the conversion of miscanthus biomass to biofuels under sub‐ and supercritical water (SCW) conditions was investigated. The highest total conversion was obtained under SCW conditions and the heating value increased under subcritical and SCW conditions. The findings herein show that near‐supercritical and supercritical water at 400 °C and high pressure can be an effective reaction medium for converting biomass to oils with relatively low oxygen contents in high yields.     

Optimization of the coordination–insertion ring‐opening polymerization of poly(p‐dioxanone) by programmed decreasing reaction temperatures

The optimization of the synthesis of poly(p‐dioxanone), by ring‐opening polymerization with tin II bis(2‐ethylhexanoic acid) as the catalyst, was conducted by a new method in which programmed decreasing reaction temperatures were employed. The results were compared with those obtained for polymerization reactions performed at constant temperatures in the 80–180°C range. In the novel method, the temperature was gradually reduced, as the reaction proceeded, to maintain a maximum polymerization rate and monomer conversion as the monomer was consumed. The experiments performed at constant temperatures confirmed previous reports that the bulk polymerization of 1,4‐dioxan‐2‐one is an equilibrium polymerization reaction. With increasing polymerization temperature, the initial rate of polymerization increased, but the monomer conversion, reaching equilibrium, decreased. High conversions were obtained at low temperatures and long reaction times. Therefore, reducing the reaction temperature, to ensure working conditions that guaranteed the maximum polymerization rate and monomer conversion, could optimize the polymerization process. These conditions were calculated under the assumption of equilibrium polymerization reaction kinetics. With our proposed method, a 71% conversion was achieved in half the time needed when the polymerization was performed at a constant temperature of 120°C. Similarly, a 78% conversion was obtained with our proposed method in only a third of the time employed when the reaction was carried out at a constant temperature of 80°C. Our method guarantees high conversions in shorter times and a gradual reduction of the polymerization temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 659–665, 2005     

Upgrading of pyrolysis bio-oil using WO<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript> and Amberlyst catalysts: Evaluation of acid number and viscosity

Tungstated zirconia (WO₃/ZrO₂ with WO₃ loadings of 9.9 (WZ9.9), 15.5 (WZ15.5), and 15.7 wt% (WZ15.7)) and Amberlyst (15, 35, 36, 39 and 45) catalysts were employed to upgrade pyrolysis bio-oil of acacia sawdust through an esterification reaction using methanol at atmospheric pressure and room temperature or 80 °C. The upgrading efficiency was evaluated by measuring the total acid number (TAN) and viscosity. The viscosity and TAN of the resulting upgraded bio-oil were found to be dependent on the calcination temperature of the WO₃/ZrO₂ catalysts. At room temperature, the largest decrease in viscosity and TAN of the bio-oil and methanol mixture was obtained using WZ9.9 tungstated zirconia calcined at 900 °C. An increase in reaction temperature to 80 °C improved the flowability and TAN of the methanol-added bio-oil using WZ9.9 activated at 900 °C. The product distribution of the bio-oil upgraded using methanol revealed esterification to be the dominant reaction pathway under the reaction conditions of this study. When the ether extracted bio-oil was upgraded at 80 °C using methanol over catalysts, the Amberlyst catalysts were found more effective than tungstated zirconia catalysts in enhancing the esterification reaction and reducing TAN.     

Noncatalytic Hydrolysis of Iminodiacetonitrile in Near‐Critical Water – A Green Process for the Manufacture of Iminodiacetic Acid

The hydrolysis of iminodiacetonitrile (IDAN) in near‐critical water, without added catalysts, has been successfully conducted with temperature and residence time ranges of 200–260 °C and 10–60 min, respectively. The effects of temperature, pressure, and initial reactant/water ratio on the reaction rate and yield have been investigated. The final reaction products primarily included iminodiacetic acid (IDA) and ammonia associated with other by‐products; gas formation was negligible. The maximum yield of IDA was 92.3 mol.‐% at 210 °C and 10 MPa, with a conversion of almost 100 %.The apparent activation energy and ln A of IDAN hydrolysis were evaluated as 45.77 ± 5.26 kJ/mol and 8.6 ± 0.1 min^–1, respectively, based on the assumption of first‐order reaction. The reaction mechanism and scheme were similar to those of base‐catalyzed reactions of nitriles examined in less severe conditions.     

Fourier transform infrared and wide‐angle X‐ray diffraction studies of the thermal cyclization reactions of high‐molar‐mass poly(acrylonitrile‐co‐itaconic acid)

The stabilization reactions of a high‐molar‐mass poly(acrylonitrile‐co‐itaconic acid) precursor in air at 200, 220, and 240°C were studied with Fourier transform infrared. Principally, the cyclization of nitrile groups leading to the ladder structures of tetrahydropyridine occurred. Evidence for oxidative reactions causing the conversion of the C? C structure to C?C and generating groups such as ? OH and C?O was also obtained. As the temperature of stabilization was increased, the rate of the reaction increased without causing great changes in the Fourier transform infrared spectral patterns. The maximum nitrile conversion achievable was limited by the temperature of stabilization. Although the reaction stagnated at 40 and 80% at 200 and 220°C, it was practically complete in about an hour at 240°C. Higher temperatures also favored the formation of extended conjugated structures. Wide‐angle X‐ray diffraction studies of the polymer stabilized at 300 and 400°C in argon confirmed that the aromatization index value and the crystallinity of the polymer increased proportionally to the temperature of pyrolysis. An analysis of the wide‐angle X‐ray diffraction pattern and the elemental composition of the stabilized polymer implied the formation of the tetrahydropyridine structure at 400°C. The higher pyrolysis temperature favored the formation of the lattice constituted by this group. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3055–3062, 2006