Optimization of esterification of palm fatty acid distillate using conventional approach and its comparison with ultrasonic and microwave irradiation

Abstract

The current work deals with the process intensification of esterification reaction via ultrasonic (US) and microwave (MW) irradiations using the cheapest feedstock, such as Palm Fatty Acid Distillate (PFAD). Systematic studies have been done by conventional methods to find the optimum parameters, such as molar ratio of PFAD to methanol, temperature, type of catalyst, and catalyst loading. In order to enhance the rate of reaction, experiments were carried out using approaches based on ultrasound and microwave irradiations at optimal parameters obtained from the conventional approach. Significant enhancement in extent of equilibrium conversion and rate of reaction is observed in the presence of microwave irradiation than any other method used in the current study. The maximum reduction in acid value obtained using MW irradiation, US irradiation, and conventional approaches was 98.8% (for 25 min of reaction time), 97.8% (for 150 min of reaction time), and 97.6% (for 180 min of reaction time), respectively. The kinetic rate constants (activation energy) for the reaction using MW irradiation, US irradiation, and conventional approach were 0.7089 (9.6 × 10⁴ kJ/mg), 0.2063 (1.7 × 10⁵ kJ/mg), and 0.1629 (2.1 × 10⁵ kJ/mg) l/mol/min, respectively.

Appendix 1

• (I) Determination of energy requirement for esterification using conventional approach

  $$\begin{aligned} {\text{Total}}\;{\text{energy}} & = \left( {{\text{Power}}\;{\text{used}}\;{\text{for}}\;{\text{one}}\;{\text{stirrer}} \times {\text{stirring}}\;{\text{times}}\;{\text{in sec}}} \right) + \left( {mcp\Delta T} \right) \\ & \quad + \;{\text{energy}}\;{\text{required}}\;{\text{to}}\;{\text{maintain}}\;{\text{the}}\;{\text{temperature}} \\ & = \left( {1 \, \times \, 120 \, \times \, 180 \times \, 60} \right) \, + \, \left( {0.1 \, \times \, 4.18 \, \times \, 10^{3} \times \, \left( {60 - 40} \right)} \right) \, + \, \left( {120 \, \times \, 150 \, \times \, 60} \right) \\ & = 12, \, 96,000 \, + 8360 + \, 10, \, 80,000 \\ & = 2.3 \, \times \, 10^{6} \;{\text{J}} \\ \end{aligned}$$

  For 1 g of oil, the observed reduction in the acid value = 11.2 mg.

  Energy required for unit reduction = total energy required/net reduction.

   = 2.1 × 10⁵ kJ/mg.

• (II) Determination of energy requirement using ultrasonic irradiation (for the same conversion)

  $$\begin{aligned} {\text{Total}}\;{\text{energy}} & = \left( {mcp\Delta T} \right) + {\text{power}}\;{\text{used}}\;{\text{by}}\;{\text{ultrasonic}}\;{\text{horn}} \\ & = \left( {0.1 \, \times \, 4.18 \, \times \, 10^{3} \times \, \left( {60 - 40} \right)} \right) \, + \, \left( {100 \times \, 150 \times \, 60} \right) \\ & = 8360 \, + \, 10, \, 80,000 \\ & = 1.08 \times \, 10^{6} J \\ \end{aligned}$$

  For 1 g of oil, the observed reduction in the acid value = 6.06 mg.

  Energy required for unit reduction = total energy required/net reduction.

   = 1.7 × 10⁵ kJ/mg.

• (III) Determination of energy requirement for microwave irradiation

  $$\begin{aligned} {\text{Total}}\;{\text{energy}} & = \left( {{\text{Power}}\;{\text{for}}\;{\text{one}}\;{\text{stirrer}} \times {\text{stirring}}\;{\text{times}}\;{\text{in}}\;{\text{sec}}} \right) + \left( {mcp\Delta T} \right) \\ & \quad + {\text{power}}\;{\text{forMW}} \\ & = \left( {1 \, \times \, 120 \, \times \, 25 \times \, 60} \right) \, + \, \left( {0.1 \, \times \, 4.18 \, \times 10^{3} \times \, \left( {60 - 40} \right)} \right) \, + \, \left( {100 \, \times \, 25 \, \times \, 60} \right) \\ & = 1, \, 80,000 \, + \, 8360 \, + \, 1, \, 50,000 \\ & = 3.38 \times \, 10^{5} \;{\text{J}} \\ \end{aligned}$$

For 1 g of oil, the observed reduction in the acid value = 3.5 mg.

Energy required for unit reduction = total energy required/net reduction.

 = 9.6 × 10⁴ kJ/mg.