Process optimization and kinetic modeling of biodiesel production using non-edible Madhuca indica oil

Highlights

• Non-edible mahua oil is utilized for biodiesel production.

• RSM was used to optimize the transesterification process variables.

• Catalyst, methanol and temperature had significant effect on mahua biodiesel yield.

• Biodiesel production follows first-order kinetics.

• Mahua biodiesel satisfied the ASTM standards.

Abstract

Optimization and kinetic modeling of biodiesel production from non-edible Madhuca indica oil were investigated in this study. Type of catalyst, catalyst concentration, methanol amount, and reaction temperature were optimized by the univariate method. KOH was found as a better catalyst for conversion of mahua oil to biodiesel. Response surface methodology (RSM) was employed to determine the optimal level of KOH (%), methanol amount (v/v), temperature (°C) and time (min). Maximum biodiesel yield of 91.76% was predicted at the optimal level of KOH as catalyst (1.5%), methanol amount (0.32% v/v), temperature (60 °C) and time (90 min). Biodiesel yield (88.71%) was obtained in the validation experiments and fitted 96.6% with the RSM predicted results. Kinetic studies were performed at different temperatures and observed that the conversion of mahua oil to biodiesel follows the first order reaction. The kinetic rate constants and activation energy were calculated. The physiochemical properties of mahua biodiesel were determined using standard methods and the mahua biodiesel properties are in accordance with the ASTM D6751 standards.

Introduction

An image on fuel consumption represents the oil demand in India. According to the Petroleum Planning and Analysis Cell, India is Asia’s third-largest country consumes about 15.48 million tons of fuel by the year 2015. On putting the country’s track on fuel demand, it requires 300,000 barrels per day and the need surpass the China in an incremental growth [1]. According to U.S. Energy Information Administration (EIA), India’s demand will be more than double to 8.2 million bbl/d by 2040 while domestic production will remain at 1 million bbl/d. The country mainly depends on imported crude oil to meet the petroleum demand. Due to these reasons, the need for an alternative to traditional petroleum arises. In search of an alternative source of energy which reduces the carbon emission to environment and dependency on fossil fuel is the major key factor which drives towards the production of biodiesel. Biodiesel is mono-alkyl esters of fatty acid derived from transesterification reaction between oil and alcohol in the presence of catalyst [2]. Biodiesel has similar properties with conventional petroleum fuel and has several advantages over it such as low CO₂ emission, safe and easy to handle, nontoxic, high fuel efficiency [3], [4]. Nowadays >95% of biodiesel produced from the edible oils by transesterification with alcohol and catalyst. It will be difficult for large scale production of biodiesel because it imbalances the global food demand and diminishes the line between the food and fuel as both if the fields strive to gain from the same oil resources. The use of low-cost feed stock will decrease the production cost, research on biodiesel production from non-edible oils such as jatropha [5], rapeseed [6], karanja [7], palm [8], mahua [9], Hodgsonia macrocarpa seed [10], Cerbera odollam [11], moringa [12] and rubber seed [13] are increasing nowadays.

Mahua oil is a non-edible vegetable oil obtained from seeds of Madhuca indica tree found in many parts of India. Mahua oil is an excellent source of fuel comparable with diesel. It possesses a high content of free fatty acids (FFA) and, therefore it makes as a good initiator for transesterification process and can be transesterified into methyl esters, ethyl esters and butyl esters based on treatment with methanol, ethanol and butanol respectively. It has been reported that the methyl esters of mahua oil is closer to the properties of diesel and also having less carbon emission [14]. Methanol is used rather than other alcohols due to its high efficiency, increased thermal efficiency; low stoichiometric air to fuel ratio (6.42:1), recovery of biodiesel from final product is easy. To construct an economically attainable bioprocess, the operating parameters must be optimized perfectly. Using an effective experimental design, the combined interaction of processing parameters can be optimized to produce the desired product. Response Surface Methodology (RSM) is a promising tool for designing the experiments, constructing models, analyzing the effects of factors and scrutinizing the optimum conditions [15]. Ghadge and Raheman employed RSM for optimizing the acid pre-treatment parameters for biodiesel production using mahua oil [16]. In this study, process variables for transesterification of mahua oil were optimized using RSM and kinetic modeling of transesterification was studied.

The present study reports an approach based on the use of mahua oil as low-cost feed stock and the influence of various operating parameters such as catalyst type, catalyst concentration, methanol to oil molar ratio, and temperature on the yield of fatty acid methyl esters (FAMEs). Kinetic constant, as well as activation energy for the transesterification reaction have also been determined at optimum operating conditions. The properties of synthesized biodiesel are analyzed in order to compare with ASTM standards.