Synthesis of a green biosolvent: Isopropyl esters: A statistical approach
Introduction
In recent years, concern over the potential impact of petroleum-based solvents on the environment has created an opportunity to promote environmentally acceptable alternatives. Biosolvents have been developed as one type of environment-friendly product.
Sustainable development has become the ideal key of the 21st century in the search for green engineering process. Considerable importance is attached for the use of renewable raw materials like vegetables oils.
Fatty acids alkyl esters such as isopropyl esters show an increasingly growing demand in Europe and the USA due to their numerous applications in cosmetic, pharmaceutical, and food industries [1], [2], as bio-lubricants for high precision machinery [3], and as biosolvents. Some of these esters can be extracted from natural sources (usually plant seeds or animals), but the cost of the production process is high due to the limited availability of vegetable and animal sources and the associated environmental and sustainable development problems.
Nowadays, new synthesis methods are being developed to produce esters in large quantities and low cost. Most synthesis processes are based on an esterification reaction where the ester is formed from the corresponding acid and alcohol in the presence of a catalyst [4]. Traditionally, strong mineral acids have been used as catalysts for esterification reactions, but the quality of the products is low due to side reactions [5].
Alcoholysis of fats and oils is simpler than direct esterification and the starting material is cheaper [6]. This process has been shown to be of interest for the production of wax esters of high commercial value whose applications vary from lubricants to cosmetics. Among the vegetable oils, high oleic sunflower oil is a very interesting substrate for the synthesis of esters. New hybrid varieties produce oil that can contain about 80% of oleic acid.
The potential industrial-scale application of enzymes as catalysts is being studied for a number of reactions [7]. Lipases have been successfully applied to the production of esters [8], [9]; hydrolysis of oils [10], interesterification of fats [11], polymers [12] and additives has also been suggested [13]. This is understandable since the trend towards ecologically acceptable processes is steadily growing.
For transesterification reactions immobilized lipases show many advantages over traditional catalysts: they allow working under mild operating conditions, show high selectivity and no significant side reactions, and lead to products of high purity. In addition they are easily recoverable and there is no contamination of the final product, saving time and cost in the purification stage.
Chemical processes which takes into account environmental considerations in the selection of reactants and reactions conditions is growing in importance as both industrial and academic researchers become aware of the environmentally benign or “green” approach. The principles of green chemistry [15] focus on reducing, recycling, or eliminating the use of toxic chemicals in chemistry by finding creative ways to minimize the human and environmental impact without stifling scientific progress.
In the present work, an immobilized lipase has been used as selective catalyst for the transesterification of high oleic sunflower oil and isopropanol to produce a biosolvent, isopropyl esters, based upon the principles of “green chemistry”, using techniques and methodologies that reduce or eliminate the use or generation of feed-stocks, products, by-products, solvents, reagents, etc., that are hazardous to human health or the environment.
Optimization is one of the most important problems when it comes to developing any chemical process. Trying to achieve the maximum conversion in the most adequate catalyst concentration, temperature, and the initial alcohol/oil molar ratio can be an exhausting task when changing each of the separate operating variables at a time, and most of the time only an apparent optimum is obtained, where the interactions among the variables involved frequently are ignored. To achieve this goal, the process has been developed and optimized following the response surface methodology [14]. This technique is a powerful tool to determine the optimum operating conditions (catalyst concentration, temperature, and the initial alcohol/oil molar ratio) necessary for the scale-up of the process, minimising the consumption of water and energy, and using moderate operations conditions: temperature, low organic solvent, and short reaction time.
Section snippets
Equipment
Experiments were carried out in a stirred tank reactor of 1000 cm3 volume provided with a reflux condenser and immersed in a thermostatic bath (HETO-HOLTEN A/S, Allerod, Denmark), capable of maintaining the reaction temperature at a constant value. The impeller speed was set at 0.02PN (700 rpm) to avoid mass transfer limitations.
Materials
Sunflower oil with a high content of oleic acid (75%) was supplied by Capicua (Coreysa) (Spain). Isopropanol of 99.8% C-plus from Alcoholes de Aroca S.A. (Spain). The
Linear stage
The experimental design applied in this study was a full 23 factorial design. Table 1 shows the standard experimentation matrix for the design, the results, and yield of ester, after 60 and 120 min of reaction. A statistical analysis was performed on these experimental values and the main effects and interaction effects for two and three variables were calculated. The analysis of the main effects and interaction for the chosen response, yield of ester together with the test of statistical
Discussion
The influence of variables, reaction temperature, catalyst concentration, and alcohol/oil molar ratio on the ester yield will now be discussed. The influence of the main factors and interactions will be discussed from statistical models.
Conclusions
In the present work, design of experiments has been applied to optimize the enzymatic synthesis process of isopropyl ester. A full three-factorial design has proved effective in the study of the influence of the variables on the process. Central Composite Design procedure has been followed to optimize the variables that determine the yield of ester. A response equation has been obtained for the yield of ester. From this equation, it is possible to predict adequately the operating conditions
Acknowledgment
Financial support from the Comunidad Autónoma de Madrid, Spain, Spanish project CAM 07M/0045/98 is gratefully acknowledged.
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2023, Food and Bioproducts ProcessingEnzymatic production of isopropyl and 2-ethylhexyl esters using γ-linolenic acid rich fungal oil produced from spent sulphite liquor
2021, Biochemical Engineering JournalCitation Excerpt :The Eastman Company reported that enzymatic production of 2-ethylhexyl palmitate has significant environmental benefits, such as reduced CO2 emissions, waste generation and energy consumption [26]. The enzymatic production of isopropyl and 2-ethylhexyl esters for cosmetic applications have been studied using either purified C16 and C18 fatty acids [24,27,28] or vegetable oils such as high-oleic sunflower oil [29], crambe and camelina oil [30], camellia oil [23] and rapeseed oil [31]. Microbial oil produced by oleaginous yeasts has been employed for the enzymatic production of fatty acid esters, such as biolubricants and wax esters [32,33].
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2020, Green Sustainable Process for Chemical and Environmental Engineering and Science: Solvents for the Pharmaceutical IndustryBiocatalytic behavior of a new Aspergillus Niger whole-cell biocatalyst with high operational stability during the synthesis of green biosolvent isopropyl esters
2016, Journal of Molecular Catalysis B: EnzymaticCitation Excerpt :Fatty acid isopropyl esters (IPEs) have been in increasing demand because of their numerous applications in the cosmetic, pharmaceutical, food, and other industries [1–4].