Enhancing oil extraction processes for flaxseed and microalgae

Ali, Mehmood (2015) Enhancing oil extraction processes for flaxseed and microalgae. PhD thesis, University of Glasgow.

Abstract

Sustainable biodiesel can be produced by processing vegetable oil seeds or microalgae. The processing includes numerous processes which impact the quality and cost of the final product. Oil extraction from the feedstock is one of the most energy intensive parts of the process in the production chain. Oil extraction methods are influenced by the operational physical parameters or chemical characteristics, and their selection greatly impacts the final oil yields. This thesis investigates and compares different oil extraction methods and tries to fill the research gaps in the oil extraction processing, for example, utilising new techniques such as ultrasonic or microwave assisted solvent extraction. A detailed energy analysis for the extraction processes was conducted for each method to investigate the process feasibility to produce biodiesel more economically. Two major feedstocks were considered, flax seed and microalgae.
Microwave treatment was found the most effective in terms of less time consumption and low energy requirement with higher oil yields as compared to other methods applied to flaxseed. The extracted oil fatty acid profile showed favourable properties to convert the oil into biodiesel. In-situ transesterification of flaxseed was conducted and 93 % was converted into biodiesel. The de-oiled cake and in-situ cake were torrefied (slow pyrolysis) to convert the residue into a high energy density solid bio-char, which can be used as a feedstock to produce heat energy.
Microalgae can be used as a source of biofuel and food supplements, however, their exploitation is lacking due to various bottlenecks including realistic processing options at scale. Microalgae species Nannochloropsis oculata, was cultivated and harvested in the School of Engineering, University of Glasgow. The lipids were extracted to investigate their potential to produce algal biodiesel. Different techniques of cell disruption were applied prior to lipid extraction with solvent to enhance lipid yield. To assess the cell disruption viability, treatments such as: microwave, ultrasonic, water bath, blender, laser and hydraulic pressing were investigated. The microwave treatment was found the most energy efficient method with a higher percentage of cell disruption as compared the other treatments.
The microwave treatment, was chosen to enhance the lipid extraction with an organic solvent extraction from dry powdered and wet algal paste. The microalgae biomass was applied with 1-5 min treatment at 50% and 100% power settings and lipids were extracted. Thermal analysis with Differential Scanning Calorimetry (DSC) was conducted to investigate the thermal behaviour of algal biomass with microwave treatment. The hydraulic pressing (10-100 bars) with and without LN2 treatment was also found with promising results with more than 90 % cell disruption. The extracted algal lipids physical and chemical properties were found in an agreement with previous workers.
Powdered Chlorella vulgaris biomass was treated with hydrothermal treatment (Hydrothermal Liquefaction, HTL) in a reactor between 40-350 oC at holding times of 30 and 60 min. The vapour pressure developed in the reactor were calculated with the Clausics-Clapeyron equation and with some realistic assumptions. The bio-oil content yield was found higher at 350 oC with 30 as compared to 60 min holding times and the GC-MS analysis showed the presence of fatty acids (C14-C18). The aqueous phase contained TOC, TN and TP, which are useful nutrients for microalgae cultivation. The solid bio-char had HHV values between 17-20 MJ/kg for 30 and 60 min holding times.
The protein and carbohydrates content present in the aqueous phase, after hydrothermal treatment, at 40, 60, 80 and 100 oC were measured at both holding times. Aqueous phase reforming (APR) of powdered Chlorella vulgaris biomass was done at the University of Zaragoza, Spain to produce hydrogen with or without Ni catalyst with two pressure 30 or 35 bars at 227 oC. The maximum H2 yield was 0.427 x 10-3 and 0.542 x 10-3 moles of H2 per 3 g of dry algal biomass, with Ni as catalyst at both pressure conditions.
From this work, there is clearly significant benefit to using advanced processes for oil extraction such as HTL or microwave enhanced processing. Compared to other parts of the extraction process, such as energy used for drying, the use of a microwave has been shown to be economically viable. These advantages should scale with production volumes. HTL and APR offer similar advantages for processing wet feedstock’s, eliminating drying requirements altogether.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Due to copyright issues this thesis is not available for consultation. Access to the print version is available.
• Keywords: Oil extraction, biodiesel, flaxseed, microalgae, torrefaction, energy analysis
• Subjects: T Technology > TJ Mechanical engineering and machinery
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Watson, Dr. Ian
• Date of Award: 2015
• Depositing User: Mr. Mehmood Ali
• Unique ID: glathesis:2015-6970
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 24 Dec 2015 09:06
• Last Modified: 03 Jan 2019 09:19
• URI: https://theses.gla.ac.uk/id/eprint/6970