Conclusions and future trends

This work sets out a comprehensive review of catalytic pyrolysis centred on the production of fuel oils for use in transportation and energy production. An overview of pyrolysis economics is given and the environmental requirement to generate fuels that are environmentally benign. It should be stressed that catalytic pyrolysis should be viewed as a ‘refinement’ of thermal pyrolysis. The products of conventional thermal pyrolysis are a bio-oil that can be combusted in turbines and boilers but has less value for transportation because of its stability and quality. Catalytic pyrolysis can be viewed as a technique to upgrade the pyrolysis products to transportation fuel quality. This is important because transport accounts for around 70% of all fossil fuel use. Pyrolysis is a sustainable technology using waste materials, fast-growing low value crops and other organic materials such as polymers that can only be recycled at considerable cost. It can be almost carbon neutral and through combustion of waste pyrolysis products such as char and gas the process costs can be reduced to effectively zero (since pyrolysis is an endothermic process). Methods and techniques in the general area of pyrolysis are reviewed in order to introduce the technology and science of catalysed pyrolysis. A thorough review of the science of catalytic pyrolysis, the process methodology and the catalyst and feedstocks are provided.

The development of catalytic pyrolysis into a common and widespread commercial technology is reliant on a number of factors. The construction of pyrolysis plants is capital intensive and profitability requires the products to be competitive against fossil fuel prices or to be preferentially marketed with proactive government subsidies. However, it is clear that the increasing cost and shortages of crude oil will necessitate the development of new fuels akin to petrol/gasoline and diesel. It seems likely that the depletion of fossil fuel sources coupled to increased energy demand will ensure the uptake of new and emerging technologies such as pyrolysis. Whilst it is generally accepted that bio-fuels will become an increasingly important component of global energy strategy, there are a number of parallel and competitive technologies for generation of biofuels. Pyrolysis has considerable advantages over some of these competitive techniques such as fermentation and bio-degradation because it is closer to market and is based on well-established and large scale methods used in the petroleum industry. Pyrolysis also offers considerable advantage in that it does not place further pressures on food security as it does not require sugar-rich crops. It should also be noted that catalytic pyrolysis products are a direct replacement for current energy/transportation fuels and do not necessitate any costly technological development of turbines, boilers or internal combustion engines. In many cases and in properly controlled processes, the catalytic pyrolysis products are indistinguishable from conventional petroleum products and can be distributed through existing infrastructure and retailers. This is a major cost advantage over alternative energy sources such as hydrogen. The choice of biofuel technology will also be partly dependent on the local environment and it is likely that pyrolysis will not be a universal solution. For example in a country that has no facilities for cost-effective recycling of waste polymers, pyrolysis may be a very attractive possibility reducing land-fill, transportation and energy costs. Pyrolysis may also be a preferred option if there are large areas of non-arable land where low-value, fast-growing, sustainable energy crops such as miscanthus and switch grass can be readily grown and harvested. Further, areas highly dependent on forestry and agriculture where significant amounts of waste are generated may find pyrolysis a useful technology. One further advantage of pyrolysis is that it is highly scalable and plants can be designed and constructed to process tonnes to thousands of tonnes of feedstock per day.

It should not be thought that catalytic pyrolysis is unproven on the commercial scale; it is at an advanced stage of development and, in all likelihood, will become ever more important. Commercial scale plants operate in China due to a shortage of crude oil and the poor quality of China’s oil stocks. The uptake of pyrolysis technology in China has been reviewed.141 Progress in pyrolysis has been rapid, Envergent Technologies now offers commercial technology to prospective partners.230 Envergent Technologies is a Honeywell company that combines pyrolysis expertise (Ensyn Corp.) with petroleum refining and process technology from UOP which have been leaders in refining and catalyst technologies for over 100 years. Evergent offers a fast pyrolysis process for biomass (forestry, paper manufacture and agricultural waste materials) via a circulating transported FBR system similar to the one used in conventional petroleum cracking technologies. The production of transportation grade fuels is via a secondary upgrading process using hydroprocessing technology. This technology is expected to be available for licensing of large scale production (2000 tonnes per day) from 2012. In November 2009, Envergent Technologies announced a partnership with the Italian power company Industria e Innovazione for the development of a facility to convert biomass (pine forest residue and waste wood from construction) into pyrolysis oil for renewable power generation. Whilst the planned plant is only of the scale 150 tonnes per day, it represents a major step in commercialising pyrolysis. It thus seems that pyrolysis and catalytic pyrolysis will truly be an emerging technology. Further research and development are required to maximise yields from many sources and provide catalysts of improved efficacy but the technique and methods have been established for both commercial and environmental exploitation.