The Scope For Generating Bio-oils With Relatively Low Oxygen Contents Via Hydropyrolysis

The primary oils obtained in high yields from fast (fluidised-bed) pyrolysis of biomass generally have high oxygen contents (ca. 40% w/w). The scope for using pyrolysis under hydrogen pressure (hydropyrolysis), to give oils with much lower oxygen contents compared to normal pyrolysis has been investigated. Fixed-bed hydropyrolysis tests have been conducted on cellulose, sugar cane bagasse and eucalyptus wood using hydrogen pressures up to 10 MPa, with heating rates of 5 and 300 °C min-1. A colloidal FeS catalyst was used in some tests (Fe loading of 5%, w/w) to increase overall conversions. Further, the attractive option of using a two-stage reactor in Which the primary oil vapors are passed though a bed of hydrotreating catalyst is also described. Raising the hydrogen pressure from atmospheric to 10 MPa reduced the oxygen content of the primary oil by over 10% to below 20% w/w. The addition of a dispersed iron sulphide catalyst gave conversions close to 100% for all three biomass samples investigated at 10 MPa under conditions in the fixed-bed reactor where significant diffusional resistance existed and reduced the oxygen content of the bio-oil by a further 10%. Although NMR indicated that the oils became increasingly aromatic as more oxygen was removed, the increase in hydrogen pressure decreased the extent of overall aromatisation that occurs primarily due to the lower char yields obtained. In two-stage tests for cellulose, using a commercial sulphided Ni/Mo γ-Al2O3 catalyst at 400 °C, increasing the hydrogen pressure from 2.5 to 10 MPa decreased the oxygen content of the oil by over 20% to 10% w/w. The H/C ratios were higher and O/C ratios smaller for the two-stage bio-oils compared to their single stage counterparts. However, the differences in the O/C ratios between the single and two-stage bio-oils increase with pressure.The primary oils obtained in high yields from fast (fluidized-bed) pyrolysis of biomass generally have high oxygen contents (ca. 40% w/w). The scope for using pyrolysis under hydrogen pressure (hydropyrolysis), to give oils with much lower oxygen contents compared to normal pyrolysis has been investigated. Fixed-bed hydropyrolysis tests have been conducted on cellulose, sugar cane bagasse and eucalyptus wood using hydrogen pressures up to 10 MPa, with heating rates of 5 and 300 °C min-1. A colloidal FeS catalyst was used in some tests (Fe loading of 5%, w/w) to increase overall conversions. Further, the attractive option of using a two-stage reactor in which the primary oil vapors are passed though a bed of hydrotreating catalyst is also described. Raising the hydrogen pressure from atmospheric to 10 MPa reduced the oxygen content of the primary oil by over 10% to below 20% w/w. The addition of a dispersed iron sulphide catalyst gave conversions close to 100% for all three biomass samples investigated at 10 MPa under conditions in the fixed-bed reactor where significant diffusional resistances existed and reduced the oxygen content of the bio-oil by a further 10%. Although NMR indicated that the oils became increasingly aromatic as more oxygen was removed, the increase in hydrogen pressure decreased the extent of overall aromatization that occurs primarily due to the lower char yields obtained. In two-stage tests for cellulose, using a commercial sulphided Ni/Mo γ-Al2O3 catalyst at 400 °C, increasing the hydrogen pressure from 2.5 to 10 MPa decreased the oxygen content of the oil by over 20% to 10% w/w. The H/C ratios were higher and O/C ratios smaller for the two-stage bio-oils compared to their single stage counterparts. However, the differences in the O/C ratios between the single and two-stage bio-oils increase with pressure.301215271534Antal, J.R., Biomass pyrolysis: A review of the literature. Part 1-carbohydrate pyrolysis (1983) Advances in Solar Energy, p. 2. , In: Boer, K.W., Duffie, J.A. (Eds.) vol. 61-111Bolton, C., Snape, C.E., Stephens, H.P., Hydrocracking of hydropyrolysis tar with hydrous titanium oxide catalysis (1989) Fuel, 68, pp. 161-167Brito, J.O., Fuelwood utilization in Brazil (1997) Biomass and Bioenergy, 12, pp. 69-74Brown, S.D., Sirkecioglu, O., Snape, C.E., Eglinton, T.I., Speciation of the organic sulphur forms in a recent sediment and type I and II-S kerogens by high pressure temperature programmed reduction (1997) Energy and Fuels, 11, pp. 532-538Churin, E., Maggi, R., Grange, P., Delmon, B., Characterisation and upgrading of a bio-oil produced by pyrolysis of biomass (1988) Research in Thermochemical Biomass Conversion, pp. 896-909. , In Bridgewater, A.V., Kuester, J.L. (Eds.)De Freitas, M.A.V., Moreira, J.R., The Brazilian renewable energy program. The biomass national plan (1997) Proceedings of the 3rd Biomass Conference of the Americas, pp. 1263-1271. , In Overend, R.P., Chornet, E. (Eds)Diebold, J., Phillips, S., Tyndall, D., Scahill, J., Feik, C., Czernik, S., Catalytic upgrading of biocrude oil vapors to produce hydrocarbons for oil refining applications (1994) Preprints American Chemical, Society Division of Fuel Chemistry, 39 (4), pp. 1043-1047Gergel, F., Citiroglu, M., Snape, C.E., Putun, E., Ekinci, E., Beneficial effects of hydrogen pressure in the pyrolysis of biomass: A study of Euphorbia rigida (1993) Fuel Processing Technology, 36, pp. 299-305Goudriaan, F., Pefereon, D.G.R., Liquid fuels from biomass via a hydrothermal process (1990) Chemical Engineering Science, 45, pp. 2729-2734La Rovere, E.L., Biomass in developing countries (1995) 8th European Biomass Conference, 1, pp. 83-86. , In Chartier, P., Beenackers, A.A.C.M., Grassi., G. (Eds.) Pergamon, OxfordLove, G.D., Snape, C.E., Carr, A.D., Houghton, R.C., Release of covalently-bound alkane biomarkers in high yields from kerogen via catalytic hydropyrolysis (1995) Organic Geochemistry, 23, pp. 981-986Love, G.D., McAulay, A.D., Snape, C.E., Bishop, A.N., Effect of process variables in catalytic hydropyrolysis on the release of covalently-bound aliphatic hydrocarbons from sedimentary organic matter (1997) Energy and Fuels, 1997, pp. 522-531Mastral, A.M., Mayoral, M.C., Izquierdo, M.T., Rubio, B., Role of iron in dry hydroconversion (1995) Energy and Fuels, 9, pp. 953-959Meier, D., Berns, J., Faix, O., High liquid yields from lignin via catalytic hydropyrolysis (1994) Advances in Thermochemical Biomass Conversion, pp. 1016-1031. , In: Bridgwater, A.V. (Ed.) BlackiePindoria, R.V., Lim, J.-Y., Hawkes, J.E., Lazaro, M.-J., Herod, A.A., Kandiyoti, R., Structural characterisation of biomass pyrolysis tars/oils from eucalyptus wood waste: Effect of H2 pressure and sample configuration (1997) Fuel, 76, pp. 1013-1023Pindoria, R.V., Megaritis, A., Herod, A.A., Kandiyoti, R., A two-stage fixed-bed reactor for direct hydrotreatment of volatiles from the hydropyrolysis of biomass: Effect of pressure and catalyst ageing time on product characteristics (1998) Fuel, 77, pp. 1715-1726Roberts, M.J., Snape, C.E., Mitchell, S.C., Hydropyrolysis: Fundamentals, two-stage processing and PDU operation (1995) Geochemistry, Characterisation and Conversion of Oil Shales. NATO ASI Series C, 455, pp. 277-295. , In: Snape C.E. (Ed.) Kluwer, DordrechtRocha, J.D., Luengo, C.A., Snape, C.E., Hydrodeoxygenation of oils from cellulose in single and two-stage hydropyrolysis (1996) Proceedings World Renewable Energy Congress IV, 2, pp. 950-953Rocha, J.D., Brown, S.D., Love, G.D., Snape, C.E., Hydropyrolysis: A versatile technique for solid fuel liquefaction, sulphur speciation and biomarker release (1997) Journal of Analytical and Applied Pyrolysis, 4041, pp. 91-103Rocha, J.D., Luengo, C.A., Snape, C.E., Bio-oil obtained from Eucalyptus wood and sugar cane bagasse via fixed-bed hydropyrolysis (1998) Proceedings 10th European Biomass Conference, pp. 606-609. , Wurzburg, GermanySamolada, M.C., Baldauf, W., Vasalos, I.A., Production of a bio-gasoline by upgrading biomass flash pyrolysis liquids via hydrogen processing and catalytic cracking (1998) Fuel, 77, pp. 1667-1675Sharma, R.K., Bakhshi, N.N., Catalytic upgrading of pyrolysis oil (1993) Energy and Fuels, 7, pp. 306-314Snape, C.E., Putun, E., Lafferty, C.J., Donald, F.J., Ekinci, E., High oil yields from Euphorbia rigida via hydropyrolysis (1994) Advances in Thermochemical Biomass Conversion, pp. 1047-1052. , In Bridgwater, A.V. (Ed.) BlackieSnape, C.E., Lafferty, C.J., Eglinton, G., Robinson, N., Collier, R., The potential of hydropyrolysis as a route for coal liquefaction (1994) International Journal of Energy Research, 18, pp. 233-242Sofer, S.S., Zaborsky, O.R., (1981) Biomass Energy Conversion Processes for Energy and Fuels, , London: Elsevier Applied ScienceSoltes, J.E., Hydrocarbons from lignocellulosic residues. Journal of Applied Polymer Science, Applied Polymer (1983) Symposium, 37, pp. 775-786Vitolo, S., Seggiani, M., Frediani, P., Ambrosini, G., Politi, L., Catalytic upgrading of pyrolytic oils to fuel over different zeolites (1999) Fuel, 78, pp. 1147-115