Date of Award

19-2-2024

Document Type

Thesis

School

School of Chemical & Biotechnology

Programme

Ph.D.-Doctoral of Philosophy

First Advisor

Dr.R.Senthilkumar

Keywords

Engineering, Engineering and Technology, Engineering Chemical, Separation Thermodynamics, Pressure Extraction

Abstract

Over recent decades, the usage of nutraceuticals has been exponentially increasing as alternates to pharmaceutical drugs. However, extraction of these therapeutically significant compounds from their corresponding sources requires the use of volatile organic solvents like hexane, ethanol and chloroform which increases the global warming potential. This problem has been overcome in recent decades by the use of supercritical carbon dioxide (SCO2) as the extraction solvent. Since SCO2 is non-polar in nature, the extraction of polar compounds with better efficiency is questionable.

On the other hand, modernization in solvent engineering has created generations of green solvents like ionic liquids (ILs), deep eutectic solvents (DESs) and supramolecular solvents (SMSs) which are non-toxic, renewable, biodegradable and non-volatile in nature. Beyond being green in nature, deep eutectic solvents can be tailor-made based on the requirement and application. Thus, these two platforms, pressure liquid extraction using CO2 and deep eutectic solvents have been merged in this investigation.

The first phase of the work includes preparing five types of DESs (Ampiphilic, Protic, Natural, Surfactant based, Aminoacid based) with six individual mixtures in each type. Then it determined the density viscosity and conductivity of these DES. Further, the thermophysical properties of these DES were also measured (Cohesive energy density and Excess molar volume). It was observed that Protic, Ampiphilic and Aminoacid DES perform better on all the above aspects guaranteeing facile application in solid liquid extraction systems.

The second phase of work involves the measurement of carbon dioxide (CO2) solubility in these DES. As CO2 is the major extraction solvent, its solubility in DES is critical. Upon investigation, it was found that acid gas solubility is higher in amino acid-based DES than in other types investigated. Further, the selectivity of these amino acid-based eutectics towards three specific nutraceuticals (Rutin, Quercetin and Lutein) was measured. It was observed that A:DA (Alanine and Decanoic acid) acts selectively to Rutin, L:DA (Lysine and Decanoic Acid) acts selectively to quercetin and L:DOA (Lysine and Dodecanoic acid) acts selective to lutein.

Subsequently, to validate the process, the plant biomass rich in these corresponding nutraceuticals (Bael shell for rutin, peanut husk for quercetin and Dunaliella salina for lutein) were chosen for DES-assisted pressure liquid extraction with CO2 in an in-house fabricated extraction system. Finally, response surface methodology-based optimization is carried out to determine optimal extraction conditions which aids in a facile scale-up of the process.

The third phase consists of the validation of the DES-assisted PLE process. Initially, the kinetic data obtained for extraction of the three different nutraceuticals were fitted in a suitable second-order model equation. Further, mass transfer coefficienct (resistance on mass transfer) and thermodynamics of the system were determined. It was observed that the introduction of DES has reduced mass transfer coefficient increasing the spontaneity of the endothermic extraction process.

Finally, the surface morphology and particle texture of the biomass were analyzed by SEM and BET, respectively and it was found the extraction process has introduced uneven cracks on the surface of biomass and the pore volume has increased with the occurrence of micropores in the substrate.

It could be learned from this investigation that DES-assisted PLE has a significant effect on the extraction process and has tuned DES-CO2 mixture in to a tailor made solvent system which can be modified according to the physical properties of the target nutraceutical. Further, the developed optimal conditions can be scaled up further to establish industrially effective nutraceutical fractionation process in pressure liquid extraction system.

Download

Share

COinS