In situ Transesterification of Microalgal Oil to Produce Algal Biodiesel (Year 2)
Project Title
In situ Transesterification of Microalgal Oil to Produce Algal Biodiesel (Year 2)
University
University of Idaho
Principal Investigator
Brian He, Zheting Bi
U of I Biological Engineering
PI Contact Information
Funding Sources and Amounts Provided
US Department of Transportation — $69,922
University of Idaho — $69,922
Total Project Cost
$139,844
Agency ID or Contract Number
DTRT12-G-UTC17 UI-KLK902
Start Date
1/01/12
End Date
5/31/14
Description of Research Project
Lipid-bearing microalgae have been widely researched and proven to be a promising feedstock for biofuel production. Tremendous effort was focused on microalgal biology, strain screening, cultivation under different conditions, and harvesting as the initial stage. The post-harvest processing of microalgae, i.e., dewatering, oil extraction, and conversion to biofuels, is now the logical next step in microalgae-to-biofuel research. In this project, we will explore a novel process that will convert the algal oils in the microalgae directly by a thermochemical processing, without first extracting lipids. Methanol under sub-or supercritical condition is used as the solvent to extract the lipids out of algae; meanwhile, methanol as a reactant esterifies the free fatty acids and transesterifies the triglycerides in the microalgae into biodiesel in-situ. These two steps are performed simultaneously, which simplifies the processing and is therefore more economical. The process parameters will be investigated and the process efficiency will be evaluated. The expected outcome from this project will be an approval of feasible technology that converts lipids in microalgae into biodiesel in-situ without pre-extracting lipids out of microalgae.
Implementation of Research Outcomes
Microalgae are considered one of the most promising feedstocks for biofuel production for their environmental and social benefits. Challenges exist in converting microalgal lipids into algal biofuels due to the unique characteristics of microalgae and the technologies for processing them. In this study, we aimed at exploring an alternative technology that combines lipid extraction from whole microalgae and lipid esterification/ transesterification in a single step or in situ transesterification. Specifically, the effects of process parameters on the process efficiency were investigated using whole microalgae biomass as the feedstock to obtain microalgal methyl esters or algal biodiesel. The advantages of the proposed one-step, in situ transesterification include the simplified process for the conversion of microalgal lipids to algal biodiesel and the reduction of some technological challenges in traditional processes.
Microalga Schizochytrium limacinum, a well-known lipid-rich strain of green microalgae, was used as the model algae in this study for its high lipid content (50%). Experiments were performed on the lipid-to-methanol molar ratio (sRatio; 1:50, 1:75 and 1:100), operating temperature (170°C, 210°C, 250°C, and 290°C), reaction time (30, 60, 90, and 120 minutes), and initial pressure of CO2 (0 psig and 200 psig of CO2) based on a factorial design. All experiments were carried out in a batch reactor system with precise temperature control. The content of microalgal methyl esters, the targeted product in the mixture after reaction, was analyzed by a gas chromatography-mass spectrometry (GC-MS). The product yield and the product selectivity were used as the indicators for process efficiency.
Experimental findings indicated that the operating temperature and the reaction time are the most influential process parameters in the in situ transesterification of the microalga in sub-/super-critical methanol with no catalyst application. The effects on the process efficiency were collectively contributed by the combinations of these two parameters. A product yield of 68.7% was achieved after a 60 minute reaction time at 210°C with a corresponding product selectivity of 35%. A similar product yield of 68.6%, with a corresponding product selectivity of 46.8%, was obtained after 30 minutes when the operating temperature increased to 250°C. The lipid-to-methanol molar ratio (sRatio) is an important parameter for lipid extraction, but its effects on product yield were found insignificant between levels of sRatio due to the higher ratios tested in this study. The addition of carbon dioxide (CO2) as a co-solvent showed a noticeable influence on the processing in preliminary investigations; however, further investigation did not reveal significant effects on the overall in situ transesterification process. This is likely because not all operating conditions reached the supercritical pressure of CO2 (7.4 MPa or 1,073 psi), thus a lack of the supercritical fluid effect from the CO2.
The conditions for optimum product yield and/or product selectivity were inconclusive. Preliminary statistical analysis on the experimental data did not show an optimum point; instead, multiple points of higher yield and/or selectivity can be found under the interactive effect of the process parameters.
The project for this stage is complete. However, many questions remained unanswered. The overall research is still a work in progress. We will continue experimenting on the process and exploring further to gain better understanding. The recommended future work includes further investigation on the process parameters and statistical analyses on the data, thermodynamic and/or reaction kinetic analysis of the process, potential technologies for separating the targeted algal methyl esters from the product mixture, and a conceptual process design for performing the in situ transesterification of microalgae in a continuous-flow mode. An engineering economic analysis on the process is also under consideration to develop estimates on the energy and operating costs.
Impacts and Benefits of the Project
This study aimed to respond to the demand for advanced processing technologies for microalgae conversion to biofuels. Conduction of this research has enabled us to gain better knowledge and experience on microalgae processing from an engineering aspect. The findings discovered from this research have been disseminated to share with the microalgae research community, which would also greatly contribute to the technological advancement on microalgal conversion for biofuels.
Through participation in the project, two undergraduate and one graduate researchers have had the opportunity to integrate their education with research in the areas of biofuels. They have gained the first-hand experience in scientific research. Being part of the next generation researcher in biofuel research and utilization, these students are well prepared in a real-world problem-solving scenario with the fundamentals and skills for being future scientists and/or engineers. This is an equally important aspect of the higher education in this nation.
Paper
- Bi, Z., and B. He. 2013. Characterization of Microalgae for the Purpose of Biofuels Production. Trans. ASABE 56(4):1529-1539.
Presentation
- A technical presentation on preliminary study of in situ transesterification of microalgal oil to produce algal biodiesel was presented orally at the 2013 International Annual Conference of the ASABE held in Kansas City, KS on July 23, 2013.
Web Links
Final Report: UI_TranLIVE Final Report_Algal Biodiesel
Keywords
- biodiesel fuels
- microalgae
- fuel processing
- microalgal biofuels
- microalgal biodiesel, in-situ transesterification
- supercritical methanol