Biomass Pyrolysis And Lipid Transesterification Of Some Biodiesel Promising Microalgae: Comparative Study For Bio-oil And Biodiesel Production

Recently,microalgal biomass is attracting a great attention in energy research as a third-generation biofuel feedstock.Microalgae possess exceptional advantages which distinguished them from other generation feedstocks,such as high photosynthetic rate,growth rate/biomass productivity,and the ability to grow on waste liquids or seawater.However,the commercial feasibility of microalgal biofuels on comparing with conventional fuel market is the prevailing challenge to overcome.The present research project focused on biomass pyrolysis and lipid transesterification of some biodiesel-promising microalgae including Micractinium reisseri,Scenedesmus obliquus SAG276-10 and Scenedesmus obliquus FACHB-276.Conversion of lipids to fatty acid methyl esters?FAMEs?,biomass pyrolysis using a fixed bed reactor,thermogravimetric analyzer,gas chromatography/mass spectrometry?GC/MS?analysis and Fourier Transform Infrared?FTIR?spectroscopy were used.In the first section,the study compared the bio-oil productivity of selected biodiesel promising microalgae using a fixed-bed reactor under different operating conditions for high yield of crude bio-oil.The main factors that were optimized in the present study are temperature and time.Pyrolysis experiments were performed at different temperatures?450,500,550 and 600?and different retention times?15 min,30 min,45 min and 60 min?.In addition,thermal behaviors,quality of products,and catalytic pyrolysis were investigated for the most productive strain.Moreover,ZSM-5 and MCM-41 were used as catalysts in order to increase the bio-oil yield and quality.For S.obliquus SAG276-10,the highest bio-oil yield of 54.37%was obtained at 600 for 60 min retention times.Moreover,GC/MS results of non-catalytic pyrolysis revealed slight higher relative contents of hydrocarbons in S.obliquus SAG276-10 bio-oil?20.84%?compared to the other two microalgae.FTIR analysis was in agreement with the results obtained from direct pyrolysis oils by GC-MS analysis.However,the maximum bio-oil yield in S.obliquus FACHB-276 of 56.36%was recorded by catalytic pyrolysis with MCM-41 catalyst.This section provides useful selection of catalyst and it would dictate the composition of the bio-oils as well as pyrolysis conditions optimization.The second section of the present study investigated the efficiency of S.obliquus SAG276-10 to grow at elevated CO₂ concentrations.Thus,the study examined the growth of S.obliquus SAG276-10 at different concentrations of CO₂?0%,2%,5%and 10%,v/v?.Although the maximum biomass productivity of 0.113 g L^-1 d^-11 was recorded at 5%CO₂,the yield of bio-oil was negatively affected?46.0%?compared to the control?54.4%?.Therefore,growth was performed in the further studies without additional CO₂ supply.In the last section,optimization of harvest method and energy recovery from S.obliquus SAG276-10 was studied.Centrifugation was used as a standard harvest method,while chemical flocculation was comparatively used as a cost-effective harvest method.Crude bio-oil and biodiesel production using the two harvest methods were compared and energy output as well as the estimated cost were calculated.Lipid recovery from the centrifuged cells was 17.4%,which significantly increased by flocculation to 20.7%.Although both harvest methods showed similar thermal decomposition patterns,flocculated biomass showed 15.7%higher bio-char formation than the centrifuged cells,which resulted in significant reduction in the bio-oil yield by 18.5%.The estimated energy output of bio-oil using centrifugation and flocculation were 0.87 and 0.68GJ per ton,respectively.For biodiesel production,the energy output using centrifugation and flocculation were 0.177 and 0.211 GJ per ton,respectively.Due to the higher biodiesel yield,better bio-oil quality and lower energy consumption,flocculation was suggested by the present study as a superior method over centrifugation for microalgae harvest from the economic point of view.