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Two-stage continuous flow synthesis of epoxidized fatty acid methyl esters in a micro-flow system
Accepted Manuscript Title: Two-stage continuous flow synthesis of epoxidized fatty acid methyl esters in a micro-flow system Author: Wei He Zheng Fang Qitao Tian Dong Ji Kai Zhang Kai Guo PII: DOI: Reference:
S0255-2701(15)30079-9 http://dx.doi.org/doi:10.1016/j.cep.2015.07.028 CEP 6649
To appear in:
Chemical Engineering and Processing
Received date: Revised date: Accepted date:
20-6-2015 30-7-2015 31-7-2015
Please cite this article as: Wei He, Zheng Fang, Qitao Tian, Dong Ji, Kai Zhang, Kai Guo, Two-stage continuous flow synthesis of epoxidized fatty acid methyl esters in a micro-flow system, Chemical Engineering and Processing http://dx.doi.org/10.1016/j.cep.2015.07.028 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Two-stage continuous flow synthesis of epoxidized fatty acid methyl esters in a micro-flow system Wei Hea, Zheng Fangb, Qitao Tiana,Dong Jia, Kai Zhanga, Kai Guoa,c,*
a
College of Biotechnology and Pharmaceutical Engineering, Nanjing Technology
University, Nanjing 210009, Jiangsu, P.R. China b
School of Pharmaceutical, Nanjing Technology University , Nanjing 210009,
Jiangsu, P.R. China c
State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech
University,30 Puzhu Rd S., Nanjing 211816, PR China
Corresponding author: Kai Guo
[email protected]
Highlights
► 1. A new protocol combining transesterification with epoxidation was reported. ► 2.
Continuous synthesis and consumption of FAMEs without purification was realized. ► 3. Online separation promoted by a novel oil-water separating device was conducted. ► 4. Epoxide number can reach up to 5.52 within 12 minutes. Abstract
A new protocol combining transesterification reaction with epoxidation process was reported. Besides, a novel continuous extraction device was employed in the integrated process to realize the automatic continuous flow synthesis of epoxidized fatty acid methyl esters (FAMEs). Furthermore, a capillary column containing desiccants was used in the post-processing, leading to dry product.
Keywords: epoxidized fatty acid methyl esters; micro-flow system; continuous flow synthesis
Introduction Renewable energy has been developed rapidly recently due to the depletion of fossil fuel. As one of the main fossil fuel alternatives, biodiesel shows several unique advantages, such as biodegradable and non-toxic.1 In the past several years, many new efficient and environmentally friendly synthetic methods have been applied in the preparation of biodiesel.2-4 On the industrial level, one of the most extensively applied reactions on the unsaturation is epoxidation due to the high reactivity of oxirane ring.5-6 Epoxidation of olechemicals has been extensively investigated over the past several years since epoxidized products are good substitutes for phthalates which are banned by the EU and FDA.7 Besides, epoxidized olechemicals have been widely used as lubricants,8 plasticizers,9 stabilizers,10 cosmetics and biofuel additives.11-12 Compared with epoxidized vegetable oil, epoxidized FAMEs show the unique plasticizing property in the synthesis of cellulosic resin and synthetic rubber. Furthermore, higher flexibility
and longer ageing time were acquired by adding FAMEs into the products. During the past decade, studies of epoxidized FAMEs have been reported by several groups. A novel catalyst, Ti/SiO2, had been employed as a solid catalyst for the epoxidation of FAMEs. 13 A high epoxide yield was obtained at room temperature. Meanwhile, epoxidation of FAMEs in the presence of SO3H-functional Bronsted acidic ionic liquid was also reported. 14 The conversion reached a maximum in 60 min at 343.15K. Typically, commercially available epoxidized FAMEs are synthesized through the epoxidation reaction between FAMEs and the peracids. However, adding rate and temperature must be strictly controlled in order to make the process safe. In addition, side reactions, especially ring-opening reaction, are always present in the process.15 Most of all, high quality epoxidized FAMEs are obtained provided that purified FAMEs are supplied (Scheme 1). To date, there is no report of direct synthesis of epoxidized FAMEs in a micro-flow system with soybean oil as a raw material. As a common problem for most cases of micro-flow system, separation of the biphasic mixture was still carried out on a rhythmic mode. Thus, investigations concerning integration of purification in micro-flow system have been widely reported.4 N-arylpyrazoles were synthesized continuously in a micro-flow system which was composed of separation units based on gravity and microreactor.16 In this study, we developed a new method for the direct continuous synthesis of epoxidized FAMEs with soybean oil as a raw material in a micro-flow system
consisting of microstructed reactors and separation units.
Experimental section General methods The quantitative analysis of FAMEs was performed on a gas chromatograph system(Agilent 7890A) employing a 30m×0.32mm, 0.25µm film thickness DB-WAX capillary column. Epoxide number was analyzed by acetone-hydrochloride method.17 All organic reagents were commercially available. Standard analytical reagents were obtained from Fluka. All micro-flow experiments were performed using commercially available Sandwich microreactor (Ehrfeld Mikrotechnik BTS GmbH).
S0255-2701(15)30079-9 http://dx.doi.org/doi:10.1016/j.cep.2015.07.028 CEP 6649
To appear in:
Chemical Engineering and Processing
Received date: Revised date: Accepted date:
20-6-2015 30-7-2015 31-7-2015
Please cite this article as: Wei He, Zheng Fang, Qitao Tian, Dong Ji, Kai Zhang, Kai Guo, Two-stage continuous flow synthesis of epoxidized fatty acid methyl esters in a micro-flow system, Chemical Engineering and Processing http://dx.doi.org/10.1016/j.cep.2015.07.028 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Two-stage continuous flow synthesis of epoxidized fatty acid methyl esters in a micro-flow system Wei Hea, Zheng Fangb, Qitao Tiana,Dong Jia, Kai Zhanga, Kai Guoa,c,*
a
College of Biotechnology and Pharmaceutical Engineering, Nanjing Technology
University, Nanjing 210009, Jiangsu, P.R. China b
School of Pharmaceutical, Nanjing Technology University , Nanjing 210009,
Jiangsu, P.R. China c
State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech
University,30 Puzhu Rd S., Nanjing 211816, PR China
Corresponding author: Kai Guo
[email protected]
Highlights
► 1. A new protocol combining transesterification with epoxidation was reported. ► 2.
Continuous synthesis and consumption of FAMEs without purification was realized. ► 3. Online separation promoted by a novel oil-water separating device was conducted. ► 4. Epoxide number can reach up to 5.52 within 12 minutes. Abstract
A new protocol combining transesterification reaction with epoxidation process was reported. Besides, a novel continuous extraction device was employed in the integrated process to realize the automatic continuous flow synthesis of epoxidized fatty acid methyl esters (FAMEs). Furthermore, a capillary column containing desiccants was used in the post-processing, leading to dry product.
Keywords: epoxidized fatty acid methyl esters; micro-flow system; continuous flow synthesis
Introduction Renewable energy has been developed rapidly recently due to the depletion of fossil fuel. As one of the main fossil fuel alternatives, biodiesel shows several unique advantages, such as biodegradable and non-toxic.1 In the past several years, many new efficient and environmentally friendly synthetic methods have been applied in the preparation of biodiesel.2-4 On the industrial level, one of the most extensively applied reactions on the unsaturation is epoxidation due to the high reactivity of oxirane ring.5-6 Epoxidation of olechemicals has been extensively investigated over the past several years since epoxidized products are good substitutes for phthalates which are banned by the EU and FDA.7 Besides, epoxidized olechemicals have been widely used as lubricants,8 plasticizers,9 stabilizers,10 cosmetics and biofuel additives.11-12 Compared with epoxidized vegetable oil, epoxidized FAMEs show the unique plasticizing property in the synthesis of cellulosic resin and synthetic rubber. Furthermore, higher flexibility
and longer ageing time were acquired by adding FAMEs into the products. During the past decade, studies of epoxidized FAMEs have been reported by several groups. A novel catalyst, Ti/SiO2, had been employed as a solid catalyst for the epoxidation of FAMEs. 13 A high epoxide yield was obtained at room temperature. Meanwhile, epoxidation of FAMEs in the presence of SO3H-functional Bronsted acidic ionic liquid was also reported. 14 The conversion reached a maximum in 60 min at 343.15K. Typically, commercially available epoxidized FAMEs are synthesized through the epoxidation reaction between FAMEs and the peracids. However, adding rate and temperature must be strictly controlled in order to make the process safe. In addition, side reactions, especially ring-opening reaction, are always present in the process.15 Most of all, high quality epoxidized FAMEs are obtained provided that purified FAMEs are supplied (Scheme 1). To date, there is no report of direct synthesis of epoxidized FAMEs in a micro-flow system with soybean oil as a raw material. As a common problem for most cases of micro-flow system, separation of the biphasic mixture was still carried out on a rhythmic mode. Thus, investigations concerning integration of purification in micro-flow system have been widely reported.4 N-arylpyrazoles were synthesized continuously in a micro-flow system which was composed of separation units based on gravity and microreactor.16
consisting of microstructed reactors and separation units.
Experimental section General methods The quantitative analysis of FAMEs was performed on a gas chromatograph system(Agilent 7890A) employing a 30m×0.32mm, 0.25µm film thickness DB-WAX capillary column. Epoxide number was analyzed by acetone-hydrochloride method.17 All organic reagents were commercially available. Standard analytical reagents were obtained from Fluka. All micro-flow experiments were performed using commercially available Sandwich microreactor (Ehrfeld Mikrotechnik BTS GmbH).
As a fluid-temperature residence reactor, Sandwich microreactor (Figure 1) is designed for several reactions under defined conditions in a continuous mode. Intensive cross-mixing of the process medium results in narrow residence time distribution. Besides, better heat exchange with the heat medium flowing through the process channel is obtained through the establishment of a heat exchange setup. The slit-plate micromixer LH25 works (Figure 2) according to the multilamination principle. When the fluids are fed into two concentric annular feed channels, streams of two different fluids are fanned out in a large number of small streams which are arranged alternately in an interdigital configuration.
The oil-water separator (Figure 3) used in the study was made based on different adhesion forces towards equipment surfaces. The organic layer was obtained from the
upper outlet, while, the aqueous solution was acquired from the bottom outlet.
upper outlet, while, the aqueous solution was acquired from the bottom outlet.
General procedure for the continuous synthesis of epoxidized FAMEs FAMEs were prepared by the transesterification of oil with methanol in the presence of basic catalysts. The mixture of methanol and sodium methoxide was merged with soybean oil using two medium pressure constant flow pumps (Shanghai Tauto Biotech Co., Ltd.). Then the reaction solution was introduced into the first microreactor. When the reaction was conducted for given time in a flow mode, the effluent went into a specific oil-water separator to separate the FAMEs from glycerol. A stream of acidic solution containing hydrogen peroxide (30 wt %), formic acid (98 wt %), catalyst and stabilizer was then mixed with the FAMEs and flowed into the second Sandwich microreactor (Figure 4). Temperature inside the two Sandwich microreactors was adjusted by external heating cycle. The corresponding reaction mixture went into the same oil-water separator. Additionally, the process for obtaining neutral product was also realized in a continuous mode by using oil-water separators. Subsequently, drying process was conducted in a capillary column containing anhydrous sodium sulfate. Analytical Method for epoxide number In terms of its physical meaning, epoxide number was equivalent number of epoxy groups in 100 grams of epoxy resin. And it was calculated in accordance with the standards.
EN =
[V − (V 1 −
V2 × W )]N × 0.016 G × 100% W
Where V is the volume of sodium hydroxide used to titrate blank sample. [ml] V1 is the total volume of sodium hydroxide used to titrate pilot sample. [ml] V2 is the volume of sodium hydroxide used to titrate pilot sample for acid value. [ml] N is the concentration of sodium hydroxide solution. [mol/l] W is the mass of pilot sample. [g] G is the mass of pilot sample for determining acid value. [g]
Results and discussion We set out to investigate the automatic synthesis of epoxidized FAMEs in a micro-flow system depicted in Figure 4.
EN =
[V − (V 1 −
V2 × W )]N × 0.016 G × 100% W
Where V is the volume of sodium hydroxide used to titrate blank sample. [ml] V1 is the total volume of sodium hydroxide used to titrate pilot sample. [ml] V2 is the volume of sodium hydroxide used to titrate pilot sample for acid value. [ml] N is the concentration of sodium hydroxide solution. [mol/l] W is the mass of pilot sample. [g] G is the mass of pilot sample for determining acid value. [g]
Results and discussion We set out to investigate the automatic synthesis of epoxidized FAMEs in a micro-flow system depicted in Figure 4.
Focusing initially on the flow synthesis of FAMEs, we screened a variety of solid base catalysts and different aperture plates related to mixing efficiency using a single Sandwich microreactor. The use of sodium methoxide was profitable to obtain a higher yield compared to other catalysts (Table 1), likely due to saponification caused by other base catalysts. 17 As a typical two-phase reaction, mixing efficiency is crucial for high yield. In this study, different mixing efficiencies were obtained by adjusting the width and length of the circular slit in the plate. Thus, different aperture plates inside the slit-plate micromixer LH25 (Figure 2) were evaluated. As shown in Table 1,
a decrease in the size of aperture plate resulted in lower yield, which was not in agreement with the fact that better mixing was easily acquired in microreactor with smaller size. In this study, the aperture plate was replaced, which meant that different a-values were obtained (Figure 2). The contact surface became narrower when a lower a-value was acquired, leading to worse mass-transfer efficiency. Based on Fick’s law of diffusion, better mixing was achieved at given time when the contact areas increased .18 With the aim to a complete conversion, the optimization of reaction conditions was further investigated. Research results monitorin.g by GC analysis showed that the conversion of soybean oil to FAMEs reached 96.9% within 7 min in a Sandwich microreactor at 75°C in the presence of 3 wt% sodium methoxide (Table 1, entry 3). The optimal temperature (75°C) above the normal boiling point of methanol led to intensified mass transfer.19 Generally, vaporization of methanol is observed when the temperature is above its boiling point. However, higher boiling point was obtained when methanol is mixed with soybean oil. In addition, the boiling point is related to methanol content. Higher methanol-to-oil molar ratios resulted in a discontinuous flow of the mixture that shifted between liquid-liquid and liquid-gas22, while, a continuous flow was observed when the molar ratio was less than 15:1 in the study. Furthermore, moderate residence time is important for higher yield. More or less residence time went against the synthesis of FAMEs. The hydrolysis of esters was enhanced with extended residence time, leading to a slight loss of esters. Besides,
a decrease in the size of aperture plate resulted in lower yield, which was not in agreement with the fact that better mixing was easily acquired in microreactor with smaller size. In this study, the aperture plate was replaced, which meant that different a-values were obtained (Figure 2). The contact surface became narrower when a lower a-value was acquired, leading to worse mass-transfer efficiency. Based on Fick’s law of diffusion, better mixing was achieved at given time when the contact areas increased .18