Document Type

Dissertation - Open Access

Award Date

2019

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

First Advisor

Douglas E. Raynie

Keywords

Accelerated solvent extraction, Extraction, Green analytical chemistry, Green solvents, Soybean oil

Abstract

Of all analytical techniques, extraction is a huge solvent-consuming process that could adversely impact the environment. Use of petroleum-based solvents for extraction of oilseeds is still a common practice, despite the potential fire hazard and the toxic water pollution. The rising awareness of chemical activities created immense need for sustainable development schemes and strategies that should address the environmental impact without compromising the yield. In the course of developing green extraction techniques, automation, alternative solvents, and selective extractions are the growing trend. This dissertation aligns with that progress by surveying green solvents, comparing their performance during oil extraction, examining a prototype automated extraction system, and studying the efficiency of selective adsorbents. Green solvents are of great interest as they are sourced from renewable feedstock and pose little or no danger to the environment. But their application in analytical chemistry is not widely appreciated. This dissertation aimed to study the extraction efficiency of green solvents during accelerated solvent extraction of soybean oil. Five green solvents, 2-methyltetrahydrofuran (2-MeTHF), alpha-pinene, cyclopentyl methyl ether (CPME), ethyl lactate, and t-butyl methyl ether (TBME), were chosen based on the literature, solubility, and viscosity. Using the GSK solvent-scoring system obtained from literature, the ecological and economic impact of these solvents were roughly identified with respect to n-hexane. As the solubility of analytes can influence the initial part of the extraction, relative solubility of triglycerides (of the major soybean fatty acids such as linoleic acid, oleic acid, palmitic acid, and stearic acid) in the green solvents was theoretically predicted using a computer program. Also, the viscosities of the green solvents at different temperatures was investigated prior to the extraction study. Soybean, the most dominant oilseed in the market with rich protein and oil content, was used as the sample for the extraction study. As the initial analysis indicated that the lower size particles give greater oil recovery, soybean particles of average diameter 513 μm were chosen for the elaborate extraction evaluation. For a small-scale fast extraction of analytes from solid and semisolid samples, accelerated solvent extraction (ASE) is a powerful and sophisticated device. This fully automated extraction system uses very little solvent at elevated temperature and pressure and is able to run several queued experiments at programmed conditions. To rely on the results from ASE of soybean oil using green solvents, the hot-ball model was used as a validating tool. The hot-ball model gives a theoretical extraction profile for an ideal spherical matrix that can be used to evaluate and validate any experimental extraction results. As diffusion plays a major role in the kinetics of extraction, comparing the diffusion coefficient of green solvents was the key approach. Upon assessing the performance of green solvents with respect to percent oil recovery, CPME demonstrated the highest diffusion coefficient and highest % recovery for soybean oil. A remarkable 99% recovery was attained within 30 min, which is 17 times faster than n-hexane. These results suggest CPME as a promising green alternative solvent for soybean oil extraction. The second part of this dissertation examines a new green extraction system. A prototype automated extractor from CEM was investigated in terms of its extraction efficiency. The knowledge obtained from previous ASE extraction studies were used to gauge the capabilities of this instrument, and the hot-ball model was used to validate the results. Adsorbents are a significant part of the post-extraction cleanup process and studying their efficiency could reveal their ability to green the analytical techniques. The mechanism of adsorption is complex, and it varies with each adsorbate-solvent-adsorbent system. The last part of the dissertation aimed to investigate the oil adsorption efficiency of five adsorbents – silica, florisil, activated carbon, alumina and diatomaceous earth – during ASE extractions at different temperatures and concentration. Results showed that activated carbon has remarkable tendency to retain oil, at low temperatures and high adsorbent concentrations.

Library of Congress Subject Headings

Solvent extraction -- Environmental aspects.
Green chemistry.
Solvents.
Soy oil.
Oilseeds.

Format

application/pdf

Number of Pages

185

Publisher

South Dakota State University

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Rights Statement

In Copyright