Study On The Control Of Nitrogen/Oxygen And Reaction Mechanism Of Hydrocarbon-Rich Liquid Oil Preparation From Microalgae Pyrolysis

Pyrolysis is one of the most promising methods to prepare oil products from microalgae.But the low product selectivity and high O and N elements in oil limit the commercial utilization.Therefore,it is necessary to control the nitrogen and oxygen components to improve the quality of liquid oil.Catalytic pyrolysis and polymer co-feeding are effective methods to improve the quality of bio-oil.However,the influence of both methods on the distribution of microalgae pyrolysis products and the mechanism of the reaction process have not been clearly understood.This dissertation presented a study for the control of N and O and the production of hydrocarbon-rich oil during microalgae pyrolysis via catalytic pyrolysis and plastic co-feeding,and explored the reaction mechanism.The main contents are as follows:Firstly,thermogravimetric combined with infrared spectroscopy(TG-FTIR)was used to study the thermal characteristics and volatile release characteristics of microalgae and the model compounds(soybean protein(PT),sunflower oil(OL)and sucrose(SC)),and the pyrolysis kinetics was analyzed.The results indicated that the main pyrolysis stage of microalgae was 180～500℃.Proteins and carbohydrates mainly pyrolyzed at 180～400℃,and lipids pyrolysis at 400～500℃.Besides,NH3 was released earlier than carboxyl group and CO2 during PT pyrolysis.OL pyrolysis mainly produced chain C-H and carboxyl/carbonyl compounds.And C=O was generated earlier than CO2 releasing during SC pyrolysis process.Moreover,the protein-rich algae had higher average activation energy in comparison with that of lipid-rich algae.But the average activation energy of model compounds was OL>PT>SC.Secondly,in order to solve the problem of high N-and O-compounds in microalgae pyrolytic oil,the effects of catalytic temperature and catalyst species(zeolite(HZSM-5,Hβ,HY)and activated carbon(AC))on the pyrolysis characteristics of microalgae were studied in a fixed-bed reactor.The results indicated that with the increase of catalytic temperature,oil yields and the N yields of oil decreased gradually.And BTEX yields reached the maximum at 500～600 ~oC.And the ability of N and O control is HY>AC>HZSM-5>Hβ.But the lowest oil yield and the highest H2O yield were obtained with HY catalysis.Therefore,in view of the balance of quality and yield of oil,AC has stronger comprehensive advantage.Then,the product evolution mechanism of microalgae catalytic pyrolysis with activated carbon was further analyzed on a fixed-bed reactor.The results showed that AC promoted fatty acids decarbonylation and long-chain C-C rupture to form CO2 and C2+.And it also accelerated the dehydroxylation,ring-opening and decarbonylation of furfural compounds to generate ketones and CO.Moreover,AC catalysis promoted the oxidation of nitrogenous groups and the conversion of N into Nx Oy.Furthermore,AC significantly promoted aromatization and water-gas reaction to generate aromatics and CO,the aromatics yields were followed as:OL>PT>SC,while high value-added gas products with high LHV were obtained.In order to balance the quality and yield of microalgae pyrolysis oil,the influence of plastic co-feeding on the characteristic of products distribution from microalgae pyrolysis was studied on TG-FTIR and fixed-bed reactor.It was discovered that plastics co-feeding could inhibit the formation of long-chain acids and furans,as well as amide/amine and N-heterocyclics,while O mainly generated H2O,and N gradually released to gas.Therefore,PE co-feeding significantly increased aliphatic hydrocarbon,decreased O-and N-compounds,and increased gas yield and LHV.And carbohydrate promoted the formation of CH4 and C2+significantly.Finally,combined with the advantages of plastic co-feeding and AC catalysis,the co-pyrolysis of microalgae and plastics catalyzed by AC was studied,and the interaction mechanism was explored.The results indicated that compared with catalytic pyrolysis,catalytic co-pyrolysis further reduced the water yield,nitrogen and oxygen content in oil.The hydrocarbon content in liquid oil reached 96.86%when microalgae catalytic co-pyrolyzed with plastics.In addition,O-groups could effectively promote the long-chain C-C breaking,benzene ring de-branched chain reaction,and the cyclization of chain hydrocarbons during catalytic process.Besides,N-groups could significantly promote the aromatization of unsaturated hydrocarbons.Therefore,catalytic co-pyrolysis of microalgae with PE promoted the formation of BTEX observably,and the promotion reached optimization at 30%PE with the BTEX yield reaching 79.53 mg/g.