Algal FAME Production With A NOVEL Surfactant Based Catalyst In A Reactive Extraction

ALGAL FAME PRODUCTION WITH A NOVEL SURFACTANT BASED CATALYST IN

A REACTIVE EXTRACTION

*Kamoru A. Salam, **Sharon B. Velasquez-Orta, ***Adam P. Harvey

*Kamoru.salam@ncl.ac.uk, **Sharon.velasquez-orta@ncl.ac.uk, ***adam.harvey@ncl.ac.uk

School of Chemical Engineering and Advanced Materials (CEAM), Newcastle University,

NE1 7RU, United Kingdom.

ABSTRACT

One major challenge in conventional algal biodiesel production is the high energy requirement of the drying and solvent extraction steps. The high solvent requirement, (usually hexane) for the oil extraction in this process also has a significant environmental impact. Alternatively, biodiesel production could take place via in situ transesterification (“reactive extraction”). In this process fatty acid methyl ester (FAME) is produced directly from micro-algal biomass using methanol containing a catalyst. This approach is simpler and potentially more cost-effective, because of its elimination of the solvent extraction. The current study involved development of a novel surfactant catalyst (zirconium dodecyl sulphate) for usage in the “reactive extraction” of FAME from Chlorella vulgaris and Nannochloropsis occulata. Additionally, the FAME yield produced when using sodium dodecyl sulphate and H₂SO₄ catalyst was investigated. Microalgae was also characterised before and after the reactive extraction in terms of carbohydrate and protein content. For Chlorella strains a maximum 67wt% FAME yield was reached at 24 hours by the sodium dodecyl sulphate and H₂SO₄ catalyst; 54wt%  FAME yield by the H₂SO₄ catalyst. For the Nannochloropsis a maximum 75wt% FAME yield was reached at 12 hours by the sodium dodecyl sulphate and H₂SO₄ catalyst; 44wt%  FAME yield by the H₂SO₄ catalyst. At 12 hours the FAME yields produced by the zirconium dodecyl sulphate were 67wt% for Nannochloropsis and 8wt% for the Chlorella. In conclusion this finding shows that:

·         The inclusion of sodium dodecyl sulphate in H₂SO₄ significantly improved the FAME yields obtained from Nannochloropsis and Chlorella.

·         A zirconium dodecyl sulphate catalyst performed better with Nannochloropsis than in Chlorella.

·         The micro-algae maintains almost all the protein content and some of the

Carbohydrate after the in situ transesterification

·         The reaction time and yields were significant function of algae strain and catalyst.

Key words: reactive extraction, microalgae, catalyst, FAME, H₂SO₄, surfactant

INTRODUCTION

During plant photosynthesis, bio-oils are produced as triglycerides which have a high combustion heat.. One way of utilising this energy is trans esterification. The use of refined oil for trans esterification is however not economical as ~ 88% of total production cost of this conventional two steps biodiesel production is ascribed to refined oil feedstock (Haas, 2006). Similarly biodiesel production from non-food oil crops is not sustainable. Microalgae are one of the sustainable biofuel feed stocks because of their compelling advantages. They are non-food biofuel feed stocks. They can be cultivated on non-arable land. Algae can be grown on the sea or wastewater. They can also be used for capture highly concentrated CO_{2 .}

Production of FAME from micro-algae via in situ trans esterification is simple and potentially more economical since ~90% of the process energy is accounted for by the solvent extraction and drying steps in the conventional trans esterification (Lardon et al., 2009). Previous studies have demonstrated the feasibility of obtaining greater FAME conversion from such in situ trans esterification than from a conventional two-step approach (Lewis et al., 2000; Vicente et al., 2009. The major drawback of this method is the requirement of a large amount of methanol. This is necessary since methanol plays a dual role: it acts as an oil extractor and as a reactant. Moreover, the need to recover methanol from the products streams may add additional cost to the process.

This present research may render the process more economical by producing co-associating value products such as carbohydrate, protein and other components in the micro-algal residue after in situ trans esterification.

MATERIALS AND METHOD

Procedure for in situ trans esterification

This is a modification of Velasquez-Orta et al. (2012). The following process conditions were maintained in the in situ trans esterification: 100 milligram of microalgae, temperature: 60^oC, mixing rate: 450 rpm, mole ratio of catalyst to oil: 8.5:1, mole ratio of methanol to oil: 600:1 (Either the surfactant catalyst, Sodium dodecyl sulphate and H₂SO₄ or H₂SO₄  catalyst) and methanol was added to each tube consecutively and it was transferred to a shaking incubator (IKA KS 4000i control). The in situ trans esterification was run for time ranged from 30minutes - 36hours. After each completed reaction the tube was kept in a freezer for at least 6 hours to stop the reaction. The algae residues were separated from the bulk liquid by centrifugation. The bulk liquid mixture of methanol, FAME and by-products was transferred in pre-weighed tubes. The final weight of the bulk liquid was recorded for each tube and the FAME concentration was measured by gas chromatography.

 

RESULTS AND DISCUSSION

FAME yield profiles obtained in an in situ trans esterification of freeze dried cells of Nannochloropsis occulata is shown figure 1. It was observed that the FAME profiles for the three catalysts used general increased with reaction time. This is the general trend of a normal reaction. However, a drop in the FAME yield after 12 hours was observed with the SDS and H₂SO₄ catalyst. This could be due to conversion of FAME to free fatty acid by a side reaction. It was also observed that ~70% increase in FAME yield was produced by SDS and H₂SO₄  more than that of H₂SO₄  at 12 hour. FAME yield produced by the Zirconium dodecyl sulphate catalyst was also more than that of H₂SO₄ catalyst at 24 hours.

Fig.1: Reactive Extracted FAME Yield Profiles of the Nannochloropsis

Molar ratio of methanol to oil = 600; molar ratio of catalyst to oil = 8.4; Agitation rate = 450 rpm; Temperature = 60^oC; SDS: Sodium dodecyl sulphate; ZDS: Zirconium dodecyl sulphate

                                                                                                             

FAME yield profiles obtained in an in situ trans esterification of spray dried cells of Chlorella vulgaris is shown figure 2. It was observed that the FAME profiles for the three catalysts used general increased with reaction time. However, after 4 hours the FAME yield produced by the ZDS decreased with reaction time. Similarly, a relatively low performance of the ZDS catalyst was observed in this strain. This could be due to the difference in the cell wall Chemistry between the two strains. The inclusion of SDS with H₂SO₄ enhanced the FAME yield obtained from this species. At 24 hours ~24% increase in FAME yield was obtained by Sodium dodecyl sulphate and H₂SO₄ than that of H₂SO₄ catalyst.

Fig2. : Reactive Extracted FAME Yield Profiles of the Chlorella vulgaris

Molar ratio of methanol to oil = 600; molar ratio of catalyst to oil = 8.4; Agitation rate = 450 rpm; Temperature = 60^oC; SDS: Sodium dodecyl sulphate; ZDS: Zirconium dodecyl sulphate

The protein and carbohydrate content of the Nannochloropsis residue was measured after the reactive extraction. The results of the quantification are shown in Figure 3 and 4 respectively. It can be seen from the figure 3 that the biomass maintains almost all the protein content after the reactive extraction. The residual carbohydrate in contrast was lower than their original values before the reactive extraction. This shows that some of the carbohydrates have been hydrolysed during the reaction to simple sugars and other co-associated products.

Fig.3: Protein content of the Nannochloropsis before and after the reactive extraction

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Fig. 4: Carbohydrate content of the Nannochloropsis before and after the reactive extraction

The protein and carbohydrate content of the Chlorella residue was also measured after the reactive extraction. The results of the quantification are shown in Figure 5 and 6 respectively. It can be seen from the figure 5 that the biomass maintains almost all the protein content after the reactive extraction. The residual carbohydrate however was lower than their original values before the reactive extraction. This also shows that some of the carbohydrate has been hydrolysed during the reaction to simple sugars and other co associated products.

Fig.5: Protein content of the Chlorella  before and after the reactive extraction

Fig.6: Carbohydrate content of the Chlorella  before and after reactive extraction

Table 1: Initial Biochemical Content of the microalgae strains

Component (wt %)	Chlorella	Nannochloropsis
Carbohydratea	35	26
Proteinb	46	30

^aMeasured using acid digest by Gerhardt et al. [1]

^bMeasured using Nitrogen protein conversion factor for microalgae by Lourenc et al. [2]

REFERENCES

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[2] Sergio o. Lourenc, Elisabete Barbarino, Paris L. Lavixn, Ursula M. Lanfer Marquez and Elizabeth Aidar (2004) “Distribution of intracellular nitrogen in marine microalgae: Calculation of new nitrogen-to-protein conversion factors” Eur. J. Phycol., 39 (1): 17 – 32.

[3]  Velasquez-Orta, S. B., Lee, J. G. M. and Harvey, A. (2012). "Alkaline in situ transesterification of Chlorella vulgaris." Fuel, 94, 544-550.

[4] Haas, M. J., McAloon, A. J., Yee, W. C. and Foglia, T. A. (2006). “A process model to estimate biodiesel production costs.” Bioresource Technology, 97, 671-678.

[5] Lardon L., Sialve B., Steyer J. and Bernard O. (2009). “Life-Cycle Assessment of Biodiesel Production from Microalgae.” Environmental Science and Technology, 17, 6475-6481.