Case study on steam-assisted solvent-free microwave extraction of black pepper essential oil: Comparative performance, kinetics, and process intensification against microwave hydrodistillation

Abstract

Steam-assisted solvent-free microwave extraction (SFMES) has been proposed as an intensified alternative to microwave hydrodistillation (MHD) for essential oil recovery; however, comparative engineering evidence under harmonized operating conditions remains limited. This case study evaluates and compares the extraction performance, kinetics, and process intensification characteristics of SFMES and MHD for black pepper (Piper nigrum L.) essential oil production. Both extraction routes were investigated under identical microwave power (150–600 W), feed loading, and extraction time windows using a Taguchi L₃₂ experimental design. Extraction yield, recovery relative to Soxhlet reference, start-up dynamics, and physicochemical quality (ISO 3061:2008) were assessed, supported by GC–MS compositional analysis and kinetic modeling. The results demonstrate that SFMES consistently achieved higher oil yield and recovery, reaching up to 90.14 % Soxhlet-equivalent recovery, compared with 73.37 % for MHD at 600 W. Steam assistance significantly reduced first-drop time, stabilized thermal behavior at elevated microwave power, and enabled earlier attainment of extraction plateaus. Kinetic analysis revealed that SFMES followed Elovich-type behavior, indicating surface-controlled desorption, whereas MHD obeyed Power-Law kinetics characteristic of diffusion-limited liquid-phase transport. GC–MS analysis confirmed improved preservation of monoterpene-rich fractions under solvent-free steam-microwave conditions, while both methods produced oils compliant with ISO quality specifications. Hence, this case study demonstrates, using black pepper essential oil as a representative system, that steam-assisted solvent-free microwave extraction represents a practical and scalable process-intensification route for essential oil production, offering reduced processing time, improved recovery efficiency, and enhanced product quality relative to microwave hydrodistillation.