Kinetics and optimization studies using Response Surface Methodology in biodiesel production using heterogeneous catalyst

https://doi.org/10.1016/j.cherd.2018.05.022Get rights and content

Highlights

  • Production of biodiesel by transesterification of palm oil.

  • CaO as a heterogeneous catalyst yielded high %FAME.

  • Effect of operating parameters on %FAME yield estimated using Box–Behnken Design.

  • The optimum conditions determined using RSM to obtain highest %FAME yield.

  • Produced biodiesel characterized to determine the conversion and FAME selectivity.

Abstract

Biodiesel is an eco-friendly fuel is known to be an alternative source for fossil fuels. Many studies reported transesterification based reaction methods for biodiesel production from edible/non-edible oils. In this study, Calcium Oxide (CaO) has been used as a heterogeneous catalyst for transesterification of palm oil to biodiesel. Effect of process parameters such as temperature, reaction time and Methanol to oil molar ratio on biodiesel production is analyzed using Response Surface Methodology (RSM) based on Box–Behnken Design: (BBD) in statistica, with fixed catalyst concentration as an input parameter. In the present study, 3-level, 3-factor Box–Behnken statistical design was used to analyze and optimize the biodiesel production with respect to the percentage yield of Fatty Acid Methyl Esters (FAME). This has been done with 15 standard experimental runs. Kinetics of the reaction have been assumed to be of pseudo first order. Obtained biodiesel is found to be of high quality with a high FAME yield; and CaO is found to have high catalytic activity towards biodiesel production.

Introduction

Biodiesel (Mittelbach and Remschmidt, 2004) is an alternative source for fossil fuels such as petrol and diesel. Combustion of fossil fuels to extract their stored chemical energy is a major source of greenhouse gas emissions, mostly carbon dioxide (CO2), and thus contributes to global warming (Agarwal, 2007, Quaye, 1996, Zhou and Thomson, 2009). Increasing consumption of petroleum oil has a great impact on environmental pollution. This non renewable energy source is limited by its abundance and expense. In this study, eco friendly and low cost biodiesel can be used as a substituent for petro based oils. Nowadays usage of biodiesel has become more popular, because of its notable advantages like its biodegradability, non-toxicity, clean, renewable and economics. However, availability of the primary raw material for biodiesel production has always been a challenge. Biodiesel is a Fatty Acid Methyl Ester (FAME) of vegetable oils and animal fats, which can be obtained by transesterification (Demirbas, 2002) of these oils with methanol in the presence of a suitable catalyst.

The reactions of transesterification of oils can also be carried out using homogenous catalyst (such as KOH), which do offer high yields in a relatively less time; however, the produced biodiesel should be neutralized after the reaction and the catalyst cannot be reused (Semwal et al., 2011). In search of eco friendly quality of biodiesel the solid heterogeneous catalyst is found to be more suitable for biodiesel production (Feng et al., 2011) also considering the regenerative capacity of the heterogeneous catalyst and reduced downstream processing for any steps such as neutralization. Process for production of biodiesel using solid catalyst in a continuous fixed bed reactor to reduce the time and the process cost by reusing the catalyst, and to improve the purity (Ren et al., 2012, Lopez et al., 2005, McNeff et al., 2008).

The main reason behind the increased process efficiency by using heterogeneous catalyst is that the catalyst is a solid. Furthermore in homogenous catalyzed transesterification reactions removal of base after reaction is a major problem, since the presence of water and FFA in feed stock results in the formation of stable emulsions and saponification, thus making the methyl esters separation very difficult. A significant amount of water is required for rinsing the leftover catalyst thus resulting in loss of FAME yield (Kouzu et al., 2008), whereas this can be avoided by using solid base catalyst. Studies reveal that the heterogeneous catalyst gives higher yield when compared to homogenous catalyst, and further studies are needed to investigate effect of process parameters on reaction efficiency; temperature, reaction time and solvent to oil molar ratio (Borges and Diaz, 2012).

It has been reported previously that the transesterification reaction of soybean oil using a catalyst alumina supported potassium achieved 87.4% conversion in 7 h of reaction time (Xie et al., 2006). Georgogianni et al. (2009) reported, the production of biodiesel from soybean oil with the catalyst KNO3/mesoporous ZrO2 yielded 89% of biodiesel content in 24 h. Recent studies on biodiesel production using Calcium Oxide (CaO) as a heterogeneous catalyst is advantageous because of its low cost, high basicity and natural abundance (Kouzu and Hidaka, 2012, Veljkovic et al., 2009, Serio et al., 2008, Lopez Granados et al., 2007, Demirbas, 2007, Somnul et al., 2014, Chen et al., 2014). Kouzu et al. (2008) carried out a reaction using hydrated lime as catalyst that gave 62.28% yield of FAME after 4 h. It was reported that in transesterification reactions of biodiesel production, catalytic activity of CaO is more when compared to hydrated lime with the order of activity varying as CaO > Ca(OH)2 > CaCO3. Arpornchai et al. (2012) reported that using CaO–ZnO as heterogeneous catalyst for biodiesel production yielded 79.62% conversion at 60 °C, with 6 wt% catalyst and methanol to oil molar ratio 15:1 for a reaction time of 8 h. Liu et al. (2008) and Zhu et al. (2006) achieved 93% conversion with Jatropha oil (non-edible) using CaO with ammonia carbonate as a catalyst. Liu et al. (2007) achieved 95% conversion of the oil to the ester using a methanol to oil molar ratio of 12:1, with 3% of SrO as catalyst in 3 h of reaction time. Prasertsit et al. (2014) reported that the maximum FAME yield of 84.78% was obtained using 21:1 methanol to oil molar ratio, 7.35% wt of catalyst for more than 6 h of reaction time. Xie and Yang (2007) studied biodiesel through transesterification of soybean oil over zinc oxide modified with alkali earth metals yielded 89.23% for 9.72 h of reaction time, 12:1 of methanol/oil ratio, and 5.52 wt% of catalyst loading.

Response Surface Methodology (RSM) (Douglas, 1991) is a collection of mathematical and statistical techniques that are useful for modelling and analysis of problems in which response of interest is influenced by several variables to optimize the response. RSM is one of the standard statistical techniques, has been using in many research investigations to find and optimize the operating parameters. Ferella et al. (2010) investigated the optimization of transesterification reaction of rapeseed oil for biodiesel production using KOH as a catalyst using RSM tool. Silva et al. (2011) reported the optimization studies of biodiesel production by transesterification reaction of soybean oil with ethanol using NaOH as an alkaline catalyst using factorial design and Response Surface Methodology. Omar and Amin (2011) studied the optimization of biodiesel production from waste cooking palm oil using Sr/ZrO2 heterogeneous catalyst using Response Surface Methodology.

Considering all the reported studies, there is no comprehensive study detailing upon the effect of parameters, which is also feasible through mathematical modelling. With this as motivation, the present study has been carried out, with an aim to optimize the process parameters. The main objective of this study intended to develop an approach for better understanding of the relation between operating parameters such as reaction time, temperature and methanol to oil molar ratio and the %FAME yield response to obtain the optimum conditions using Box–Behnken Design (BBD) and Response Surface Methodology (RSM).

Section snippets

Experimentation and product analysis

Experiments were conducted in a batch reactor that is equipped with jacketed glass reactor with a mechanical stirrer and a condenser to reflux the methanol in a reaction. Heating is supplied for the reaction using heating liquid pumped with a circulator. Schematic shown in Fig. 1 represents transesterification reaction with experimental set-up of jacketed reactor with mechanical over head stirrer with a condenser setup and a separator for methanol, glycerol and biodiesel mixture followed by

Regression model validation

Regression model best gives out the relation between the dependent and independent variables typically. The feasibility of the testing of effect of parameters supported by the experimental data is well shown in Regression model. Experimental and the predicted values of % FAME yield are shown in Table 3. After several trails in fitting the experimental data into regression equations, developed mathematical models with linear–linear interaction of operating parameters resulted in poor adequacy

Conclusion

The present study on optimising the operating parameters using Response Surface Methodology and kinetics of reaction for the production of biodiesel by transesterification of palm oil using heterogeneous base catalyst Calcium Oxide (CaO) yielded high %FAME. The proposed model describes the feasibility of biodiesel production with a detailed understanding of the effect of parameters. Herein, it is noteworthy that commercial CaO as a catalyst for biodiesel production can be used even for larger

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