Experimental Study On Catalytic Pyrolysis Of Microalgae To Bio-oil

A microalgae has a wide development prospect. Due to the diminishing ofpetroleum reserves and the environmental eonsequences of exhaust gases frompetroleum-fuelled engines, the application of biomass energy can reduce ourdependence of petroleum and phase down environmental pollution. In addition, thedevelopment of biomass energy is also a energy strategy of China, which has attractedmuch attention in the world.The chlorella is studied from proximate and ultimate analysis. It is found thatchlorella has a low content of voltitle and high content of ash. Based on the elementaryanalysis, chlorella has lower oxygen content than terrestrial biomass. Thermal(TG/DTG) analysis was an important method to analyze the pyrolysis process. Theresults indicated that the non-isothermal mass loss process of samples is composed ofdehydration, rapid mass loss, and solid residue decomposition at which the secondphase of maximum rate of weight loss more than60%. The kinetic parameters werecalculated by using the Coats-Redfern method, indicating that the second ordermechanism function was suitable for the pyrolysis and catalytic pyrolysis of chlorella.Pyrolysis and catalytic pyrolysis experiments of chlorella were conducted in afixed bed reactor by using GC-MS analysis. A number of major components of bio-oilwere hydrocarbon, aldehydes, ketones, phenolic and alcohols compounds, as well aslarge molecular weight carboxylic acids and their derivatives, and includes a smallamount of heterocyclic compounds (derivatives of furan, pyridine, etc.). It improvedthe quality of the bio-oil using HZSM-5than using MCM-41in the catalytic pyrolysisof chlorella. Using HZSM-5as catalysts, the optimized operational conditions are asfollows, catalyst: chlorella=1:4, temperature600℃, heating rate30℃·min-1, N2flowrate100mL·min-1. Under the optimum pyrolysis conditions, bio-oil maximum yieldsis23.82%, the calorific value raised31.896MJ·kg-1, the moisture content is equal to7.001%.HZSM-5zeolites were modified using mesoporous molecular sieve MCM-41. NH3-TPD showed that the addition of10%MCM-41could significantly increase thenumber of acid sites on the catalyst surface. The catalytic pyrolysis of chlorella wascarried out in a bench-scale fixed bed reactor using HZSM-5/MCM-41mixingcatalysts. It indicated that the selectivity of3,7,11,15-tetramethyl-2-Hexadecene wasenhanced greatly by mixing catalysts of10%MCM-41and90%HZSM-5compared tothat by pure HZSM-5. Carboxylic acid and nitrogen reduced to12.85%and43.97%respectively. The yield of maximum aromatic and aliphatic hydrocarbons reached50.34%, while the Octadecaneamide and Oleanitrile disappeared in pyrolysis oil. Theelemental analysis of the bio-oil revealed that O/C atomic ratio was decreased greatlyto oxygen levels by23.52%, while H/C atomic ratio was increased with the calorificvalue reaching32.995MJ·kg-1using mixing catalysts of10%MCM-41and90%HZSM-5. It demonstrated that deactivation of molecular sieve catalyst was mainly dueto the production of coke, however HZSM-5/MCM-41exhibits good stability.The desilication of HZSM-5zeolite was carried out using aqueous solutions ofNaOH. The structure and acid property of HZSM-5before and after desilication werecharacterized by XRD, N2sorption and TPD of ammonia. Meanwhile, the catalyticpyrolysis of chlorella was also studied in a fixed-bed reactor. The proportion ofmesopores framework in the zeolite can be turned commodiously by controllingconcentration of NaOH at a given temperature with optimal time of desilication, andthe acidity also can be varied. The catalyst with higher surface acidity and lower acidstrength can favor the reaction over the HZSM-5treated in0.3mol·L-1of NaOH at80℃for2hours. Furthermore, the catalyst can remove most of the oxygen in the formof CO and CO2, thus it reduce the oxygen content in the biological oil effectively.Liquid yields of chlorella catalytic pyrolysis and bio-oil calorific value are46.83%and32.851MJ·kg-1, respectively. The hydrocarbons yield reached40.34%(mass fraction),while the carbonyl and alcohols compounds decrease significantly.