Chemical Engineering & Processing: Process Intensification 126 (2018) 62–73 Contents lists available at ScienceDirect Chemical Engineering & Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep Process intensification using corning® advanced-flow™ reactor for continuous flow synthesis of biodiesel from fresh oil and used cooking oil Srinath Suranania, , Yadagiri Marallaa, Shekhar M. Gaikwadb, Shirish H. Sonawanea, ⁎ a b T ⁎ Department of Chemical Engineering, National Institute of Technology, Warangal, Telangana State, India Department of Research and Development, Application Engineer, Corning Technologies India Pvt Ltd, Pune, Maharashtra, India A R T I C L E I N F O A B S T R A C T Keywords: Corning® advanced flow™ reactor Biodiesel synthesis Olive oil Cooking oil Homogenous catalyst FAME (Fatty Acid Methyl Ester) Modelling The corning® Advanced Flow™ Reactor (AFR) was used for continuous synthesis of biodiesel from fresh oil and used cooking oil. All Experiments were carried out in AFR at different parameters such as feed flow rates, temperature and concentration of catalyst to study the optimum operating conditions for synthesis of biodiesel. Two different oils (fresh oil (FO) and used cooking Oil (CO)) were used for continuous flow synthesis of biodiesel. The maximum oil conversion of 99 and 93% were achieved in presence of 2 wt.% of catalyst (sulfuric acid) at 80 °C and feed flow rate of 30 mL/h in AFR™ for FO and CO respectively. The composition of fatty acid methyl esters (FAMEs) in finished biodiesel product was found to be 0.2788 mol/L and 0.2742 mol/L for FO and CO respectively. A mathematical model was developed, assuming that the AFR™ module behave as a PFR. The model consists of ordinary differential equations, which were solved by Euler’s method in MATLAB to study the change of concentration of oils against time at different parameters. The simulation results shown good agreement with the experimental results. 1. Introduction Process intensification (PI) in the chemical process industry is one of recent area of research in the field of chemical engineering. The concept of PI is hardly a decade old. It is a highly innovative concept in the design of chemical process plants. The aim of process intensification is to optimize capital, energy, environmental and safety benefits by radical reduction in the physical size of the plant. Thus, the concept is intimately connected with the physical nature of the plant, which will take a long time to move from theory to final commercial application using existing and available hardware [1,2]. Process intensification consists of the development of novel equipments and techniques, as compared to the present state-of-art, to bring remarkable improvements in manufacturing and processing. As compared to conventional batch reactors, the scale up (numbering up) is easy for microstructured reactors. The corning® Advanced Flow™ Reactor (AFR) is very emerging invention and technology that helps to reduce the complications of equipment and give better yield which substantially decreases the equipment size, energy consumption, reduction in waste. The main advantages of AFR are, it reduces the reaction time drastically, it gives improved selectivity and yield of product due to the better mixing inside the heart shape. It may not possible to have direct quantitative comparison of batch and microreactor in ⁎ terms of energy efficiency. However, it is clear that the microreactors have higher surface area and hence, improved heat transfer (h – heat transfer coefficient is 1000 times higher than the conventional batch reactor). Hence, it will improve overall energy efficiency [3,6]. Perhaps a simpler definition could be any chemical engineering development that leads to a substantially smaller, cleaner, and more energy-efficient technology is called as “process intensification”[2,4,5]. The AFR is a continuous flow reactor in which many of the batch chemical reactions can be effectively carried out and substantially optimized. It offers broad capability from feasibility to production and the batch reactions are made continuous process to control the production as per demand. Small-scale channel reactors have emerged as a technology offering advantages over classical approaches due to miniaturization, such as faster mixing, better heat and mass transfer [1,6]. The large surface-to-volume ratio of the small channels improves heat transfer for exothermic reactions, thus preventing thermal degradation or explosive evolution. It allows the control of reactions that need very short residence time and/or fast mixing and enables performing greener, more economical and safer processes [2,7,8]. The AFR is used to intensify the synthesis of biodiesel reactions at various parameters, which can affect the conversion and yield of products [8,9]. Biodiesel, also named as fatty acid methyl ester (FAME), is an alternative fuel obtained from renewable biological sources by the Corresponding authors. E-mail addresses: srinath@nitw.ac.in (S. Suranani), shirish@nitw.ac.in (S.H. Sonawane). https://doi.org/10.1016/j.cep.2018.02.013 Received 27 November 2017; Received in revised form 11 February 2018; Accepted 11 February 2018 Available online 13 February 2018 0255-2701/ © 2018 Elsevier B.V. All rights reserved. Chemical Engineering & Processing: Process Intensification 126 (2018) 62–73 S. Suranani et al. transesterification of triglycerides (TGs) or the esterification of free fatty acids (FFAs) with methanol/ethanol [10,11]. A variety of oils (both vegetable oils and animal oils) can be used to produce biodiesel such as sunflower oil, palm oil and pork lard [12–19]. Feedstock from vegetable oils and animal oils causes the production of biodiesel to be very expensive. Exploring new methods to produce the biodiesel from low-cost raw materials such as nonedible crude oils, by-products of the refining vegetable oils and used vegetable oil (UVO) are the main interests in recent biodiesel research. Biofuels, which are fuels derived from biomass such as cottonseed oil, corn, soybeans, sunflowers, algae, wood chips, palm oil, rapeseed oil etc., are ideally suited for meeting the future energy challenges because they do not add to global climate changes [20–22]. This is attributed to the fact that plants use CO2 to grow during the photosynthesis process; consequently, the CO2 formed during combustion of biofuels is balanced by that absorbed during the annual growth of plants used as the biomass feedstock. Another key advantage of biofuels over other alternative energy sources is that they can be burned (either alone or mixed with petroleum-derived gasoline) in existing internal combustion engines [11,13,14,23–25]. Biodiesel can be used most effectively as a supplement to other energy liquid fuels such as diesel fuel. It is made from renewable biological sources such as vegetable oils and animal fats. It is biodegradable and non-toxic has low pollutant emission and is therefore environmentally beneficial. Biodiesel has been produced in different way such as through microemulsions, pyrolysis (Thermal Cracking), transesterification and more recently developed methods such as reaction with supercritical methanol. An overview of the catalytic transesterification method is presented as follows. Catalytic transesterification (also called alcoholysis) is the reaction of a fat or oil with an alcohol to form esters and glycerol [25–27]. Methanol/or ethanol is used most frequently. Methanol is mostly used because of its low cost and its physical and chemical advantages (polar and shortest chain alcohol). Transesterification can occur at different temperatures, depending on the oil. However, a higher temperature clearly influences the reaction rate and yield of esters. The product stream of the transesterification reaction consists mainly of esters, glycerol, traces of alcohol, catalyst and tri-, di-, and mono-glycerides [28–33]. Biodiesel can be used most effectively as a supplement to other energy liquid fuels such as diesel. A number of research works have been carried out in the field of biodiesel production in batch and continuous mode. The same transesterification reaction was performed in AFR. The objective of the work aims at intensification of the existing chemical reaction of biodiesel and to study the performance of AFR for the synthesis of biodiesel from fresh oil (FO) (i.e., olive oil) and used cooking oil (CO) without and with catalyst as sulfuric acid (H2SO4) at various parameter such as flow rate, temperature, catalyst concentration to establish the optimum conditions in a continuous flow process. Hence, modeling and simulation of biodiesel synthesis process from CO and to compare with experimental results [21,33–42]. Further, continuous flow synthesis of biodiesel from waste cooking oil in the AFR was reported by the same authors Gaikwad et al. However, the comparision of biodiesel from the fresh oil with cooking oil is reported in this article [43]. Table 1 Initial acid values of oils (FO and CO) without and with catalyst. Oil \ Catalyst acid value at 0% Catalyst acid value at 1% Catalyst acid value at 2% Catalyst FO, mg KOH/g of oil CO, mg KOH/g of oil 0.60 20 78 0.2 15 44 CO) without and with acid catalyst are given in Table 1. Collected CO was filtered through a filter cloth and used derectly as a reactant for the synthesis of biodiesel. No specific pretreatment was carried out because authors would like to check the conversion of cooking oil at original conditions. 2.2. Reaction 2.2.1. Synthesis of biodiesel Production of biodiesel in AFR has been carried out by transesterification process. Oil is reacted with the methanol in presence of homogeneous catalyst such as sulfuric acid. The chemical reactions for the synthesis of biodiesel are shown in Schemes 1to 4. Synthesis of biodiesel by transesterification reaction of oil (olive oil as FO and CO) with methanol (MeOH) consists of a several consecutive, reversible reactions, as shown below. The first step is the conversion of oil (tri-glycerides (TG)) to di-glycerides (DG), which is followed by the conversion of di-glycerides to mono-glycerides (MG) and finally by the conversion of mono-glycerides to glycerol (GL). After the conversions, three moles of methyl esters (ME) are obtained for each triglyceride reacted. RCOOH + CH3OH ↔ RCOOCH3 + H2O (1) Tri-glyceride + ROH ↔ Di-glyceride + R'COOR (2) Di-glyceride + ROH ↔ Mono-glyceride + R″COOR (3) Mono-glyceride + ROH ↔ Glycerol + R‴COOR (4) 2.3. Experimental set-up The experiments were conducted in Corning® AFR™. The experimental set-up for the synthesis of biodiesel is shown in Fig. 1. It consists of Corning® AFR™, syringes, syringe pumps, peristaltic pump and a cooling unit. The AFR contains the heart shaped plates made up of glass with the volume of 0.45 mL each. For this experiment, we had used two plates, to maintain suitable residence time. Two syringe pumps were used to feed the reactants into the AFR system. Feed flow rates were maintained in the range of 10 to 50 mL/h. Teflon tubes were used for connecting syringes with the AFR. Peristaltic pump was used for maintaining the utility requirements. Utility flow rate was maintained at 200 mL/h. Before starting the experiments, the system was calibrated. In this experimental set up, the AFR consist of two modules and the plate arrangement shown in Fig. 1. From Fig. 2, it was observed that there were four plates; they were arranged in the manner such that a chemical reaction was carried out inside the reaction layer. Both reactants were fed to the reactor simultaneously and the outer layer called heat exchanger plate used for the utility. These layers maintain the temperature of reactor by passing the water, hot or cold water as per the reaction requirements. It was observed that there was no settling of glycerol inside the AFR. In all the experiments, oil to methanol ratio was maintained at 1:3 (volume ratio). The reactants were fed to AFR at the bottom of the AFR module as shown in Figs. 1 and 2. 2. Materials and methods 2.1. Materials Olive oil (Fresh oil) procured from local market, used cooking oil (CO) collected from local hotels. Methanol (MeOH, 99%), sulfuric acid (SA, 98%), Potassium hydroxide (KOH, 99%) and n-hexane (NH, 95%) obtained from S D fine-chem Ltd, Mumbai, India. FO, CO, MeOH and SA were used to carry out the experiments. KOH and NH were used for the analysis of biodiesel sample. All chemicals were used as they received without any further purification. Distilled water was used for preparing of the required stock solutions. The initial acid values of oils (FO and 63 Chemical Engineering & Processing: Process Intensification 126 (2018) 62–73 S. Suranani et al. Fig. 1. Experimental set-up of AFR of two modules. the biodiesel production, the conversion of oil increases as the temperature, concentration of catalyst increases and residence time decreases. The reactants, from both syringes, were pumped into AFR, where they reacted and formed two layers of biodiesel and glycerol with different thicknesses that can be seen in Fig. 3. The volumes of both phases were recorded and then parts of both phases were stored separately and analyzed. Biodiesel contains the different types of FAMEs (fatty acid methyl esters) depending on the type of oil used. The conversion of oil into the biodiesel was analyzed by titration method and the identification of type of methyl esters was carried out using gas chromatography (GC) (FS CAP OMEGAWAX 320). The composition of the methyl esters was analyzed by the GC–MS (7890 Agilent) equipped with a flame ionization detector (FID). The GC–MS was configured according to the requirements of method. This configuration is shown in Table 2. The sample mixture of oil was dissolved in n-hexane. The composition of sample was analysed by GC–MS, which was performed on a gas chromatograph equipped with a mass spectrometer (7890 Agilent). Oxygen-free nitrogen was used as carrier gas at a flow rate of 1.0 mL/ min. 2.4. Experimental procedure for the synthesis of biodiesel from FO and CO The laboratory experiments were carried out using AFR. The experimental set-up consists of two feed streams to inject into the AFR by using syringe pumps as shown in Fig. 1. All experiments were performed at atmospheric pressure. In this work, FO (olive oil) and CO used as a raw material for production of biodiesel. One feed was oil (FO and/or CO) and other was methanol. Both the feeds were fed in equal molar ratios. Initial experiments were carried out without catalyst and then with sulfuric acid as a homogeneous catalyst at same operating conditions. It was found that use of catalyst in a reaction, accelerates the reaction rate and alters the yield of FAME (biodiesel). The number of experiments was carried out in the AFR in order to optimize the reaction and operating conditions to synthesize the biodiesel. The experiments were carried out at different flow rates of feeds, concentration of catalytic and temperatures for biodiesel production through AFR. As the flow rate increase, the residence time decreases which results in high mixing among the reactants in the heart shape of AFR which leads to improved conversion of reactants, beyond the certain flow rate the conversion of oil decreases due to small residence time. In Fig. 2. (A). Front view of AFR, (B). Rear view of AFR, (C). Side view of AFR. 64 Chemical Engineering & Processing: Process Intensification 126 (2018) 62–73 S. Suranani et al. Table 3 Fatty acids presents in FO and CO (wt %). Sr. No Components FO CO 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Myristic acid Palmitic acid Palmitoleic acid Stearic acid Oleic acid Linoleic acid Linolenic acid Arachidic acid Eicosenoic acid Behenic acid Total 0.31 10.19 0.56 3.71 62.1 20.1 1.08 0.90 0.76 0.19 99.90 – 11.32 – 3.61 24.50 52.92 6.87 0.18 0.09 0.51 100.00 (AV2). [29,44,45] Fig. 3. Two layers formation of fatty acid methyl esters and glycerol in product. Acid value (AV) = Table 2 Instrument condition for GC–MS method. (5) where V is the volume of the alcoholic KOH solution of the titration (mL)C is the concentration of the alcoholic KOH solution (mol/L)Mol. Wt. is molecular weight of KOHm is the weight of the sample (g) The oil conversion can be calculated from the following formula Column oven conditions Initial oven temperature Oven ramp 1 Oven ramp 2 Oven ramp 3 Inlet and sampling conditions Column V× C× Mol. Wt. m 70 °C for 1 min 15 °C/min to 160 °C 7 °C/min to 260 °C 5 °C/min to 380 °C AV2 ⎞ X(%) = ⎛1 − x100 AV1 ⎠ ⎝ ⎜ ⎟ (6) Where, X is the oil conversion, AV1 is the initial acid value of the mixture and AV2 is the acid value of mixture after reaction. Fused Silica Capillary OMEGAWAX 320 (L = 30 m, ID = 0.32 mm, df = 0.25 μm) Column flow flow Hydrogen at 1 mL/min constant flow Inlet temperature 220 °C Inlet mode Split flow 50 mL/min Injection volume 1 μL Flame ionization detector (FID) condition Detector temperature 380 °C 3. Results and discussion 3.1. Effect of feed flow rate with and without catalyst on the conversion of oils The experiments have been carried out to study the effect of flow rate on the conversion of oils. The reactions were performed without and with a homogeneous catalyst such as sulfuric acid. To study the effect of catalyst on the conversion of oils, initially the reaction was carried out at different flow rate, in the volume ratio of oil and methanol of 1:3, varied from 10 to 50 mL/h with increment of 10 mL/h without using the catalyst and temperature was maintained at 60 °C throughout the experiments. Each sample was collected and analyzed. After that, same set of reactions were carried out at varied flow rate from 10 to 50 mL/h in presence of 1 wt.% catalyst and then 2 wt.% catalyst and each sample was analyzed. Generally, for any catalyzed reaction, as the concentration of catalyst increases the reaction rate increases up to some extent and beyond that limit no further changes takes place. In this case, it may be generation of insufficient amount of H+ ions for the case of 1 wt.% catalyst as when compared to 2 wt.% catalyst. Further increase in catalyst concentration, there was no significant improvement is observed in the conversion of oils [5]. For the determination of oil conversion in the transesterification reaction is calculated by formula given by Eqs. (5) and (6). Fig. 4 shows the variation in the conversion in the oils with respect to flow rates. It was found that at 30 mL/h and in presence of 2 wt.% catalyst, higher conversion of oils (FO and CO) was achieved. 2.5. Analysis procedure for biodiesel The Oil is mainly composed of triglycerides or fats and contains small amounts of free fatty acids (FFA), glycerol, sterols etc. CO is also composed of fatty acids but the concentrations found to be slightly less. FFA percentage is usually used to describe the FFA content of oils, while acid number or acid value is commonly used to describe the FFA content of finished biodiesel. Generally, free acids are not present in the lubricants unless refined in a faulty manner. Free organic acid bodies are always found in oils, they may be pure mineral oils or oils compounded with fatty oils. In unused refined petroleum oils, the quantity is invariably negligible. When fatty acids present or in case of used oil, the acid content should be determined, because it may cause the corrosion of the equipment. To avoid autoxidation by air, in oil, the acid value should be very low (< 0.1). Increase in acid value should be taken as an indicator of oxidation of the oil, which may lead to gum and sludge formation besides corrosion. It affects result in the formation of odor and destruction of essential fatty acids, generating of glycerol, free fatty acids and toxic products. The acid value was determined based on ASTM D664 and EN 14104 methods. Composition of the fatty acids present in the oils analyzed by Gas chromatography-mass spectrometry (GC–MS) are shown in Table 3. 2.6. Calculation of acid value and conversion of oil to biodiesel 3.2. Effect of feed flow rate with respect to the temperature on the conversion of oils Free Fatty Acids (FFA) are the result of the breakdown of oil or biodiesel. The percentage of FFA is usually used to describe the FFA content of oils, while acid number (AN)/acid value (AV) is commonly used to describe the FFA content of finished biodiesel. The oil conversion can be identified by the acid value calculation of sample before chemical reaction (AV1) and after chemical reaction Transesterification reaction is an endothermic reaction. Therefore, it requires high temperature to get higher conversion and yield. The reactions were carried at a temperature of 60 °C. From the above discussion it is known that the higher conversion can be achieved by maintaining at the flow rate of 30 mL/h in presence of 2 wt.% catalyst. Furthermore, confirmation of the optimum flow rate and temperature, 65 Chemical Engineering & Processing: Process Intensification 126 (2018) 62–73 S. Suranani et al. Fig. 4. Effect of feed flow rate and catalyst concentration on oil conversion. Fig. 6. Effect of different feed flow rates on the conversions of oils with respect to time. the reactions were carried out at different temperatures with different flow rates ranging from 10 to 50 mL/h at catalytic concentration of 2 wt.%. The chemical reactions at different flow rates carried out at temperature ranging from 40 °C to 80 °C with increment of 20 °C. Each sample was collected and analyzed immediately. From Fig. 5, it was confirmed that the optimum feed flow rate was 30 mL/h. In addition, it shows that the reaction gives 99% conversion of FO and 93% conversion of CO at a temperature of 80 °C. As the temperature goes on increasing from 40 °C to 80 °C the conversion of oils and the reaction rate also increases. The reaction rate increases with increase in temperature, the same is observed for this reaction. So, the conversion of oils was high at 80 °C when compared to 40 °C. However, the effect of temperature was explained in section 3.4. The time required to obtain 99% and 93% conversion of FO and CO respectively was 120 s (2 min). [46]. For the production of biodiesel from oils (FO and CO), the optimum conditions of total volumetric flow rate and operating temperature were studied. The comparison between flow rates was studied experimentally. The reactions were carried out with 2 wt.% of H2SO4 as catalyst and at 60 °C with different flow rates. The flow rates were varied from 10 to 50 mL/h with the increment of 10 mL/h. Fig. 6 shows the variation in the conversion of oils with respect to time at different flow rates. It could be observed that the conversion of oil is significantly invariable with the time at all the flow rates studied. It shows that once the reaction completes, there is no appreciable change in further conversion. 3.4. Effect of different temperatures on the conversions of oils with respect to time The effects of temperatures on the conversion and on the reaction rate were studied experimentally. The reactions were carried out with 2 wt.% of catalyst and flow rate of 30 mL/h with different operating temperatures from 40 °C to 80 °C with the increment of 20 °C. The temperature 80 °C is higher than the boiling point of methanol (∼65 °C). However, at this temperature (80 °C) methanol existed as gas which results in popping out of bubbles in the AFR. Consequently, transformation of a flow pattern in the AFR was observed i.e. conversion of slug flow into number of gas bubbles in oil phase. Due to the formation of bubbles, the interfacial area drastically increases, which leads to increase in the mass transfer. Furthermore, temperature at 80 °C led to a speed-up of the conversion of oil to biodiesel. The silmilar observation has been reported by Leung and Guo [47]. From Fig. 7, it was observed that at 80 °C, the maximum FO and CO conversion was achieved (XFO = 99% and XCO = 93%). Biodiesel 3.3. Effect of different feed flow rates on the conversions of oils with respect to time The properties of CO (used oil) can alter depending on the cooking conditions, such as cooking time and temperature. In fact, a vegetable oil subjected to thermal stress such as during cooking can completely changes its original physical and chemical properties. The cooking/ frying process may convert the vegetable oil to triglyceride and further to diglycerides, monoglycerides and free fatty acids (FFAs). Furthermore, as a consequence of oxidation and polymerization reactions, there is increase in the viscosity and the saponification number of the CO when compared with the fresh oil. During the transesterification reaction, the presence of water in the CO samples often leads to hydrolysis, whereas high FFA content and high saponification number can lead to saponification reactions. Both hydrolysis and saponification reactions may cause low biodiesel yield and high catalyst consumption Fig. 5. Effect of operating temperatures at different feed rates on oil conversion. Fig. 7. Effect of different temperatures on the conversions of oils with respect to time. 66 Chemical Engineering & Processing: Process Intensification 126 (2018) 62–73 S. Suranani et al. 60 °C, the optimum catalytic loading (i.e., 2 wt.%) was observed at 80 °C (see Fig. 7). Furthermore, addition of catalyst above 2 wt.% did not show noticeable changes in conversion of oils. From Fig. 8, it was clear that the conversion of oil remains almost the same after the complete reaction occurs. High temperature favors the biodiesel production. Synthesis of biodiesel was carried out by some researcher by using batch reactors and microreactors but effective conversion of oil and yield of biodiesel was not achieved. Transesterification of sunflower oil to biodiesel was carried out in a microtube reactor with a micromixer and achieved the maximum conversion of sunflower oil was 90% [21]. The maximum Soybean oil conversion achieved in microtube reactor was 92% [29–31,48] but in AFR™, the high conversion of oils were noticed. Fig. 8. Effect of catalyst loading on the conversions of oils with respect to time. 3.6. FTIR analysis method reaction is an endothermic reaction so that the temperature required to carry out the reaction is quite high. Therefore, is difficult to maintain the temperature above 60 °C constantly during the experiments. Hence, the rest of the experiments were carried out at 60 °C, it was observed that after certain residence time there was no appreciable change in the conversion of oil. It can be conclude that with increase in temperature the oil conversion increases. Fourier transform infrared spectrometry (FTIR) was used to evaluate the possible functional groups present in biodiesel. It is an easy way to identify the presence of functional groups in the sample and its structure based on the energies associated with the molecular vibration when irradiated. Biodiesel can be used in any mixture with petro-diesel fuel, as it has very similar characteristics (e.g. cetane number, viscosity, heating value, etc.) and also in any diesel engine without modification. The FTIR technique is used to identify the frequency peaks are formed with respect to the percentage transmittance. The FTIR spectrum is used to ensure the reaction progress and triglyceride conversion to biodiesel (methyl ester) by using a 3000 Hyperion Microscope with Vertex 80 FTIR System. Fig. 9 shows the FTIR spectrum of biodiesel derived from FO. The biodiesel impurities include FFA, alcohol, water, mono-glyceride, and di-glyceride. All of them have OH functional group which displayed a peak at 3200–3500 cm−1. Peak at 1747 cm−1 is related to C]O functional group in methyl esters. Peaks at 1150–1350 cm−1 are related to the torsional vibrations of CH2 groups which show the reaction progress in kinetics point of view [50]. Fig. 10 shows the FTIR spectrum of biodiesel derived from CO. The spectrum was characterized with asymmetric and symmetric strong stretching vibrations of carboxyl group at 2675.6 cm−1, along with the OeH stretching of the hydroxyl bonded with alcohol at 2947.40 cm−1 and Aldehyde, Ketones(C]O) group along with carboxylic group at 1739.50 cm−1. CeO group combined with carboxylic group at 1436.84, 3.5. Effect of catalyst loading on the conversions of oils with respect to time Reactions were performed using homogeneous catalyst (sulfuric acid). The advantages of homogenous catalysts are (i) ability to catalyze reaction at lower reaction temperature and atmospheric pressure; (ii) high conversion can be achieved in less time. Fig. 8 shows the study of conversion of FO and CO against time at different catalyst concentration at 60 °C. The transesterification reaction is slow chemical reaction. The addition of homogenous catalyst in the reaction helps to accelerate the transesterification reaction by making the H+ ions available. Therefore, the different amount of catalyst was loaded in the reactions and the results were studied. The effect of catalyst loading was studied from 1 to 2 wt.%, it was observed that 2 wt.% catalysts (i.e., H2SO4) generates sufficient amount of H+ ions which helps in attaining maximum conversion of oil (FO and CO) [5]. Though the difference in conversion for different amount of catalyst loading is very small at Fig. 9. FTIR spectrum of biodiesel prepared from FO. 67 Chemical Engineering & Processing: Process Intensification 126 (2018) 62–73 S. Suranani et al. Fig. 10. FTIR spectrum of biodiesel prepared from CO. values were converted into concentrations of methyl esters at different mean replication timing (MRT). To determine the methyl ester moles at the biodiesel phase in a typical analysis, 5 μL of the biodiesel phase experimental sample was diluted with a solvent (hexane).The amount of solvent (5000 μL) used depended on the biodiesel concentration in the sample. 1 μL of the diluted sample was injected into the GC to obtain the chromatographic record. The identification of standard methyl esters peak can be seen in following Figs. 11 and 12. The standard methyl esters present in the biodiesel sample prepared from FO and CO can be identified by the peaks shown Figs. 11 and 12. To identify the methyl esters present in the biodiesel product from CO, the samples were analyzed by GC. Fatty acid methyl esters of biodiesel product were successfully synthesized. The method employed was proved to be an excellent method for the conversion of high free fatty acid value oil to biodiesel. The synthesis of biodiesel was confirmed by the FTIR analysis. The chemical composition of methyl esters was determined by using GC–MS analysis. The fatty acid methyl esters (FAMEs) presents in the finished biodiesel sample from fresh vegetable oil and used vegetable oil were given in Table 4. 1175.4 cm−1 [50]. 3.7. GC analysis method Biodiesel contains the different types of fatty acid methyl esters (FAMEs) depending on types of oil one used in the reaction. The biodiesel product was analyzed by titration for oil conversion and its methyl esters contents were analyzed by gas chromatography (GC). The composition of the methyl esters was analyzed by the gas chromatography–mass spectrometry (GC–MS) equipped with a flame ionization detector (FID). GC was configured according to the requirements of method. To determine the methyl esters in the biodiesel, 5 μL of the biodiesel phase experimental sample was diluted with a solvent (hexane).The amount of solvent (5000 μL) used depended on the biodiesel concentration in the sample. From the diluted sample, 1 μL of the diluted sample was injected into the GC to obtain the chromatographic record. 3.8. GC–MS analysis of FO/CO 4. Modeling and simulation Table. 3 summarizes the fatty acid composition of oils. The type and amounts of fatty acids in oils were measured by gas chromatography. The fatty acids which were commonly found in vegetable oils were Myristic acid (C14:0), Palmitic acid (C16:0), Palmitoleic acid (C16:1), Stearic acid (C18:0), Oleic acid (C18:1), Linoleic acid (C18:2), Linolenic acid (C18:3), Arachidic acid (C20:0), Eicosenoic acid (C20:1) and Behenic acid (C22:0). The fatty acids of FO (olive oil) are classified into saturated acids (palmitiz, stearic, etc.) and unsaturated acids (oleic, linoleic, linolenic). The unsaturated acids are again classified into monounsaturated and polyunsaturated acids. 4.1. Mathematical modeling The AFR, continuous flow reactor, is used for the synthesis of biodiesel. From Figs. 1 and 2, it can be easily identified that it is similar to plug flow reactor (PFR) in which the key part is the heart shaped design in such way that there will be high mixing of reactants inside the reaction layer. The experiments were carried out at different flow rates, temperatures, and different catalyst and the data was collected and studied. The AFR is modeled by assuming it as PFR because of high mixing properties. In general, chemical reaction describes the chemical conversion under certain conditions of inflow of substances to a product. To simplify the problem the following assumptions were made. 3.9. GC–MS analysis of fatty acids product sample (biodiesel) from FO and CO Oleic acid and Linoleic acid are major fatty acids found in the FO and CO respectively. The reaction products obtained from the AFR in two phases, a biodiesel phase and a glycerol phase. Both phases were collected in a single bottle. Part of the biodiesel phase was diluted and injected into the GC to obtain the peak records of the methyl esters. With help of methyl esters standards, the recorded chromatographic 1) The liquid in the reactor is ideally mixed. 2) The density and the physical properties are constant. 3) The liquid flow rates in and out of the module are constant which implies that the input and the output flows are equal. 4) The reaction is second order with a temperature relation according 68 Chemical Engineering & Processing: Process Intensification 126 (2018) 62–73 S. Suranani et al. Fig. 11. Chromatograms of FAMEs in biodiesel sample of FO. 4.2. Model formulation to the Arrhenius law. Model formulation is used as a common tool for constructing the mathematical model. It includes reaction kinetics, reaction rates, concentration of reactants and equations which represent property changes [29–31,33,41]. The overall mass balance equation is given as follows It suffices to know that within a module two reactants are mixed at concentrations of CA (t), CB (t) and reacted to produce a product at certain parameters like temperature of the mixture T (t).The CA is the inlet feed concentration, F is the process flow rate and T is the inlet feed temperature. All of which are assumed constant at nominal values. The reacting mixture properties can be approximated to be that of the solvent. It can be considered that the inlet concentration can change with time. However, the volume of reactor and the inlet volumetric flow rate to the reactor can be considered as constant. Input = output + accumulation within the system The material balance for individual components is given as follows Input = output + disappearance within the system by the reaction + accumulation To develop a realistic module for AFR the change of individual Fig. 12. Chromatograms of FAMEs in biodiesel sample of CO. 69 Chemical Engineering & Processing: Process Intensification 126 (2018) 62–73 S. Suranani et al. Table 4 GC results of FAMEs of finished biodiesels from FO and CO were compared with reported data. Components of FAMEs present in Biodiesel. Biodiesel from FO Biodiesel from CO Biodiesel from olive oil [34] Biodiesel from sunflower oil [34] Biodiesel from burned oil. [44] Methyl Methyl Methyl Methyl Methyl Methyl Methyl Methyl Methyl Methyl Methyl others Total 0.20 8.90 0.49 3.10 58.84 20.0 0.94 0.83 0.66 0.10 – 5.94 100.00 – 10.70 – 2.87 22.72 50.53 4.16 0.10 0.01 0.31 – 8.60 100.00 0.10 6.90 0.43 2.20 57.93 19.25 6.84 0.42 – 0.58 4.14 0.32 6.67 0.17 3.65 28.64 57.63 0.48 0.23 – – – 98.79 97.79 0.41 8.22 0.89 5.61 48.83 10.94 2.68 0.56 0.97 – – 20.89 100.00 myristate palmitate palmitoleate stearate oleate linoleate linolenate arachidate 11-eicosenoate behenate tricosanoate The reaction kinetics of transesterification reaction can be written in the form of rate of disappearance (−rA) for a batch reactor species (or components) with respect to reaction time is considered. This is because individual components appear and disappear during the reaction and the overall mass of reactants and products will always stay the same. A component balance could be written for each species. Assume that the general reaction described as follows − rCTG = dCTG = −K1CTG CROH + K2CDG CME dt (7) − rCDG = That is component A reacts with B to form component C and D. Furthermore, assumed that the reaction rate is second order and reversible. Therefore, the rate of reaction with respect to CA is written as, dCDG = K1CTG CROH − K2CDG CME − K3CDG CROH + K 4 CMG CME dt (12) − rCMG = dCMG = K3CDG CROH − K 4 CMG CME − K5CMG CROH + K 6CGL CME dt (13) − rCGL = dCGL = K5CMG CROH − K 6CGL CME dt − rCME = dCME = K1CTG CROH − K2CDG CME + K3CDG CROH − K 4 CMG CME dt A+B↔C+D − rA = − dCA = K1CA CB − K2CC CD dt (8) The negative sign implies that CA disappears because of reaction. A mathematical model was developed and derived ODEs for simulation for continuous reactor module. Thus, the expression for the mass balance for continuous module is given by the following equation. + K5CMG CROH − K 6CGL CME Input = Output + Disappearance FJ0 CJ0 = FJ CJ + −rJ V − rCROH = (9) Eq. (9) is which accounts for A in the differential section of reactor of volume dV. In addition, here, FA0, feed rate, is constant. However, −rA is definitely dependent on the reactants’ concentration and the reaction temperature. Grouping the terms Eqs. (8) and (9) consequently, obtained the following equation τ= V VCJ0 = = CJ0 v0 FJ0 ∫ XJ 0 dCJ dXJ or = rJ dτ −rJ dCROH dC = − ME dt dt (11) (14) (15) (16) By substituting Eqs (11)–(16) in mass balance Eq. (10), it gives mathematical model equations for continuous flow reactor system as follows (10) 4.3. Synthesis of biodiesel from CO A mathematical model was simulated for AFR module. The Kinetic model [31,33,36,40,41] was obtained through laboratory experiment on which ester was produced using alcohol to oil molar ratios of 3:1 at isothermal reaction temperature of 60 °C. In the simulation, AFR modeled as ideal PFR. The equations system for the transesterification of oil in AFR were constructed and solved at various residence times, various operating temperatures. The simulated model equations were able to show the concentration of methyl esters with respect to time at different specified parameters. A mass balance is taken for entering and leaving species together with interfacial area between phases describe the reactor performance. The mass balance also accounts for the chemical reaction and reaction rates taking place in the reactor. Thus, the expression for the mass balance for module is given by Eq. (9). Production of biodiesel by transesterification reactions of CO with methanol consists of a several consecutive reversible reactions shown by the Eqs. (1)–(4). dCTG = −K1CTG CROH + K2CDG CME dτ (17) dCDG = K1CTG CROH − K2CDG CME − K3CDG CROH + K 4 CMG CME dτ (18) dCMG = K3CDG CROH − K 4 CMG CME − K5CMG CROH + K 6CGL CME dτ (19) dCGL = K5CMG CROH − K 6CGL CME dτ (20) dCME = K1CTG CROH − K2CDG CME + K3CDG CROH − K 4 CMG CME dτ + K5CMG CROH − K 6CGL CME dCROH dC = − ME dτ dτ (21) (22) Eqs. (17)–(22) are the mathematical model equations. The model equations were solved with MATLAB programming technique. The results obtained for continuous reactor module were compared with experimental results to validate the model used. The fixed parameters of the reactor are the initial concentration of reactants and the volume of reactor (the module volume is taken as same as AFR). The reactants mainly contains the number of free fatty acids which were analysed by GC–MS, the weight percentage of free 70 Chemical Engineering & Processing: Process Intensification 126 (2018) 62–73 S. Suranani et al. Fig. 13. A plot of concentrations against time: (a) 40 °C, (b) 60 °C and (c) 80 °C. where CTG = concentration of TG, CMeOH = concentration of MeOH, CDG = concentration of DG, CMG = concentration of MG, CGL = concentration of GL and CME = concentration of ME. developed by using the reaction kinetics are simulated in MATLAB. The CO used as it contains mainly tri-glycerides (TG), di-glycerides (DG) and mono-glycerides (MG). The initial concentration of these free fatty acids, the volume of reactor and the equilibrium constants are initialized in the program. The simulation was carried out with different volumetric flow rates to study effect of reaction time on the formation of biodiesel. According to the mechanism of transesterification reaction the TG is the major fatty acid which converts into DG and MG as intermediate product and immediately reacts with methyl alcohol to produce biodiesel i.e. methyl esters and byproduct of glycerol. In the experimentation, the ultimate goal was to produce the biodiesel of high concentration. Fig. 13 shows that TG and methyl alcohol (MeOH) concentration gets reduced and increases the FAMEs and glycerol concentration. The simulations for different volumetric flow rates were fatty acids converted into molar concentration (mol/L). CTG0 = 3.156; CTG = 0; CROH0 = 9.27; CROH=0; CDG0 = 4.74*10 ; CDG = 0.0; CMG0 = 0.014; CMG = 0.0; CGL0 = 0; CGL = 0; CME0 = 0; CME = 0; V = 1 mL −3 Equilibrium constants for all consecutive reactions were taken from reported literature [49]. The Initial value (Euler’s method) method is used for numerical solution for the set of ODEs. 4.4. Change of concentration with respect to time at different flow rates and temperatures Mathematical model equations for the transesterification reaction 71 Chemical Engineering & Processing: Process Intensification 126 (2018) 62–73 S. Suranani et al. temperature as 80 °C, total feed flow rate as 30 mL/h, concentration of catalyst as 2 w% catalyst to give the maximum oil (FO and CO) conversion and composition of fatty acid methyl esters. The synthesis of biodiesel in AFR was modelled assuming that it behaves as PFR. The resultant model equations were solved using the Euler’s method in MATLAB software. The simulation results were compared with experimental values and found that they presented worthy agreement with the experimental results. Acknowledgments The authors are grateful to Corning Technologies Pvt Ltd, Haryana, India for providing Corning® Advanced-Flow™ Reactors and their support for carrying out the experiments at the Department of chemical Engineering, National Institute of Technology, Warangal, Telangana state-506004, India. Fig. 14. Comparison of Methyl esters concentration against time between experimentation and simulation results for flow rate of 30 mL/h at 60 °C. 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Comparison of experimental and simulation results The quality of the biodiesel depends upon its alkyl esters composition, to identify the concentration of methyl esters in biodiesel obtained from CO; each sample was analyzed in GC–MS. The finished biodiesel sample produced at a flow rate of 30 mL/h and at temperature of 60 °C was analysed by GC–MS, the concentration of biodiesel at these conditions was 0.2742 mol/L. Fig. 14 shows that the comparison between the experimental and simulation results obtained at a flow rate of 30 mL/h and 60 °C. The achieved concentration of methyl esters in simulation was 0.270 mol/L whereas the experimental value is 0.2742 mol/L with a maximum deviation of about 12%. The esterification reaction in AFR was simulated assuming it as Plug flow reactor (PFR). The rate constants for the simulation were adopted from reported literature [49]. The flow behaviour, geometry are different in AFR when compared to PFR. The deviation from experimental values may be due to the different geometry, flow behaviour and hydrodynamic, which were not considered for simulation. 5. Conclusion The AFR is the efficient technology to convert a batch process into continuous process in fulfilling the major aspects of process intensification. The heart shaped structure in the AFR provides better mixing with short residence time (moderate flow rate) to achieve maximum conversion and yield. The structure of the each heart shape in the AFR module is such that when two stremas are coming together at the entrance they split and again remix together. The area to volume ratio is quite high for each heart shape. Both of the above hydrodynamic conditions leads to better mixing as compared with conventional batch reactor. The AFR technology offers the possibility to conduct chemical reactions in a more sustainable way due to miniaturization and increased safety. 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