| Microalgae are considered to be one of the biomass resources to replace fossil energy in the future due to the advantages of strong environmental adaptability,fast growth cycle,high photosynthesis efficiency,no land occupation,rich nutrients and ability to survive in sewage.Microalgae-based long carbon chain lipids are very suitable for biodiesel production.Fatty acid methyl esters and glycerin can be obtained through transesterification,which can alleviate the current shortage of diesel.With the development of microalgae-based biodiesel industry,there are more and more residues after microalgae oil extraction.The main components are protein,carbohydrates and a small amount of oil.At present,these algal residues are mostly used in animal feed,if It can be used for the production of biofuels and will have potential application prospects in the production of biodiesel.This article explores and compares microalgae cultured under two different conditions(CM medium and biogas slurry)as raw materials.The thermal degradation behavior and heat of microalgae residues CM-9 and BS-3 after oil extraction are respectively studied.Research on cracking products,and on this basis,carry out life cycle assessment of the thermal cracking process of the two algal residues,select energy efficiency analysis and potential environmental impact as the inspection indicators,and comprehensively evaluate the whole process of thermal cracking conversion of two microalgal residues.The results show that the thermal weight loss analysis(20? to 800?)of CM-9 and BS-3 at a heating rate of 20?/min.It was found that the pyrolysis process of CM-9 and BS-3 was the same,which was divided into three stages.The first stage was dehydration drying stage(20? to200?).The second stage was the rapid weight loss stage(200? to 700?)and the weight loss rate peaked at 320?.The third stage was the slow carbonization stage,the weight loss rate approaches zero,and the final residual carbon content of CM-9 and BS-3 were 36.72%and 17.61%,respectively.Using pyrolysis-gas chromatography-mass spectrometry on-line testing technology(Py-GC/MS),the thermal cracking products of CM-9 and BS-3 were measured at 350? to 750?(at intervals of 100?)to analyze the thermal,and the trend of pyrolysis products with temperature was analyzed.The thermal cracking products of CM-9and BS-3 mainly include alkanes,olefins,acids,phenols,aldehydes and ketones,alcohols,aromatic compounds,nitrogen-containing compounds,sulfur-containing compounds,furans and other substances.The maximum bio-oil yield of CM-9 was 33.72% at 750?,followed by 24.69% at 650?.However,the content of nitrogen compounds and pahs pollutants generated at 750? was 28.75%,12.42% more than that at 650?.Therefore,in order to reduce environmental pollution and increase the production rate of bio-oil,the optimum pyrolysis temperature of CM-9 was about 650?.BS-3 reached a maximum bio-oil yield of 29.7% at 750?,followed by 18.92% at 650?.The pollutant content generated at 750? was 27.3%,which was 13.84% more than that at 650?.Therefore,the optimal pyrolysis temperature of BS-3 was about 650?.In the whole life cycle stage,the energy consumption order of CM-9 and BS-3 was in the same order as that of pyrolysis stage,acquisition of microalgae,cultivation of microalgae,acquisition of microalgae residues.The energy conversion efficiency of CM-9 and BS-3 was 3.03 and 1.57,respectively,indicating that this process was advantageous,and the energy conversion efficiency of CM-9 was higher.The entire life cycle of CM-9 and BS-3 has an environmental impact of 411.956 m PE and 398.649 m PE,respectively.The main types of environmental impact of the two are the same,followed by global warming(68.63% and68.62%),acidification(28.01% and 28%),photochemical ozone synthesis(2.11% and2.14%),eutrophication(1.25% and 1.25%),indicating that the two algal residues have little environmental impact,but the influence of BS-3 is relatively small. |
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