Oils produced by pyrolysis of biomass present advantages in energy density and transport when compared to soild biomass. Nevertheless, serious drawbacks like high viscosity, corrosivity or unstability limit their utilization. Hydroprocessing of pyrolytic oils has been demonstrated as an adapted way to improve their quality due to a decrease of oxygen content. Partial hydrotreatment of pyrolytic oils conjugated to molecular analysis enables to identify the reactions occurring during pretreatment. Carbonyl, carboxylic groups and alcohols are eliminated at temperature lower than 300 C. Further hydroprocessing corresponds to phenols hydrodeoxygenation and hydrocracking of large molecules. Catalytic tests with model mixtures containing phenols permit a rapid evaluation of the influence of reaction parameters like the partial pressures of hydrogen sulphide, water and ammonia on catalyst efficiency.
BIO-FUELS PRODUCED BY PYROLYSIS OF BIOMASS CAN BE USED AS A COMPONENT OF COMBUSTIBLE MIXTURES CONSTITUTED BY BIO-OIL, ETHANOL,CHAR, WATER AND ADDITIVES AS PROPOSED IN THE LEBEN PROJECT. NEVERTHELESS, AS PRODUCED, THEY PRESENT A NUMBER OF DRAWBACKS AS A VERY HIGH VISCOSITY (RANGING BETWEEN 1000 AND 3000 CP AT 60 CELSIUS DEGREES), UNSTABILITY DURING STORAGE, CORROSIVITY AND A VERY UNPLEASANT SMELL. THE VERY HIGH LEVEL OF OXYGEN PRESENT IN THE OILS (CLOSE TO 20% WT) IS LARGELY RESPONSIBLE FOR THESE NEGATIVES CHARACTERISTICS.
FURTHERMORE THEY CONTAIN NITROGEN AND SULFUR IN CONCENTRATIONS HIGH ENOUGH TO LEAD TO AN ENVIRONMENTAL CONTAMINATION AFTER BURNING. THE WORK DONE UNDER THE PRESENT PROJECT WAS COORDINATED WITH COMPLEMENTARY WORKS OF ITALENERGIE AND CRITA. TREATMENTS UNDER HIGH PRESSURE OF HYDROGEN IN PRESENCE OF CATALYST HAVE BEEN MADE IN A BATCH REACTOR IN ORDER TO ELIMINATE OXYGEN, NITROGEN AND SULFUR. THE FIRST TEST HAVE SHOWN THAT THE PRESENCE OF A REACTION SOLVENT (A HYDROGEN DONOR) ALLOWS A HIGHER CONVERSION TO LIGHT PRODUCTS; 1, 2, 3, 4 TETRAHYDRONAPHTALENE IS HIGHLY EFFECTIVE. AMONG THE SULFIDED CATALYSTS USED COBALT-MOLYBDENUM SUPPORTED ON ALUMINA WAS MORE ACTIVE THAN NICKEL-MOLYBDENUM IN HDO AND REDUCING VISCOSITY. A REDUCED (NON-SULFIDED) NICKEL CATALYST PRESENTED A LOWER ACTIVITY. A VERY INTERESTING RESULT HAS BEEN OBTAINED WITH SNCL2 AS CATALYST, AS A MATTER OF FACT IT HAS SHOWN THE BEST HDO ACTIVITY. IN ALL CASES VISCOSITY HAS BEEN LARGELY IMPROVED AND IT CAN BE COMPARED WITH AN ASTM NUMBER 6 FUEL OIL.