M. A. MORRIS, University College Cork, Ireland

Abstract: This chapter provides a review of catalytic pyrolysis summarising the potential of the methodology. Catalytic pyrolysis is centred on the use of catalysts in the production of bio-oils and related oils by pyrolysis of biomass and various waste materials. The subject is detailed against growing requirements for development of sustainable energy and fuel sources as pressures on fossil fuels increase as well as increasing fears on climate change and potential fuel shortages. The economics of pyrolysis derived bio-oil production against competing established and emerging technologies is provided. The review summarises the current state-of-the-art with particular reference to the challenges of catalysing reactions in the harsh environments of pyrolysis reactors. The types of active solid materials that can be used to generate oil are detailed so as to indicate the flexibility of the methodology. The outlook for commercialising of the technology is also summarised. A brief review of the potential use of pyrolysis products is given and barriers to uptake of this emerging technology are explained.

Key words: pyrolysis, catalytic pyrolysis, zeolites, mesoporous silicates, transition metal catalysts, bio-oil, pyrolysis-oil.

14.1 Introduction

There is little doubt that the world is facing an uncertain future around the continued use of fossil fuels as has been outlined previously in this book and elsewhere.1 Fossil fuel related climate change due to anthropogenic emissions of carbon dioxide is well known with 98% of carbon emissions arising from fossil fuel combustion.2 Further, depletion of fossil fuel reserves is expected within a few generations3 and energy security has become a major issue.4 Whilst the major uses of fossil fuels are in domestic energy production5 and transportation,6 petroleum, gas and coal have very significant other uses. For example, oil is used to prepare in excess of 70 million tonnes of polyolefins per year.7 Perhaps most importantly, very significant amounts of gas and oil are used in the production of fertilisers.8 Fertiliser is wholly necessary for maintaining food supplies and feeding the growing world population. Fertiliser is prepared via the fixation of nitrogen by reaction of atmospheric nitrogen with hydrogen over transition metal catalysts, usually using iron based catalysts as were originally developed by Haber and Bosch.11 The product of the reaction, ammonia, can be subsequently oxidised to nitric acid and the direct reaction of further ammonia yielding ammonia nitrate and this has been the basis of the modern fertiliser industry for almost 100 years.12 The hydrogen needed in ammonia synthesis is derived from nickel catalysed reactions of gas or oil with water (steam reforming13) followed by a copper-zinc oxide catalysed reaction of carbon monoxide with water (water gas shift14). These reactions are outlined further below. Because of the hydrogen sources used, the fertiliser price is closely related to the oil price.9 It should be noted that alternatives to steam reforming exist and hydrogen can also be obtained from methane by decomposition15 and aromatisation.16 Because hydrogen is essentially derived from fossil fuels (either directly, as detailed here, or indirectly via electrolysis of water using convention fossil fuel energy sources), it seems appropriate that, for the purposes of this review, hydrogen is considered as a petroleum product.

The over-reliance on fossil fuels derives from the convenience of these energy sources as a means of transporting and delivering energy.17 Alternative sources of energy (wind, solar, nuclear, etc.) are unlikely to provide a convenient source of energy consistent with industry requirements and not precipitate large-scale industry changes and the capital required to replace current large scale chemical technologies based on oil processing that supply polymers, fertiliser, fine chemicals, etc. An alternative strategy to drastic modification of the chemical economy and the use of oil as a form of transporting energy is to find an effective means to generate petroleum-like products from renewable or waste material sources. The potential of pyrolysis is one means to affect the delivery of both petroleum and hydrogen allowing maintenance of current technologies.