Most biomass contains natural salts that will influence the decomposition products. However, since the salts cannot readily be removed without affecting the organic substrate, any catalytic effects become part of the simple thermal degradation process. Much of the early work on fundamentals such as Shafizadeh (11) recognised the effect but did not take advantage of the phenomena. A particular example is pyrolysis of sewage sludge, initially investigated at the University of Tubingen (12) and later applied to development of a commercial plant to recover oil (13, 14, 15). Bayer claimed that the inorganic constituents of sewage acted as a "natural catalyst" (12) and this work was extended to recovery of fatty acids (16). The University of Waterloo has clearly demonstrated the effects of natural catalysts on chemicals production, and details are given in Table 6.3 and beyond.

6.3.1 Chemicals production

The extraction and recovery of chemicals from biomass pyrolysis liquids is rapidly growing in interest as the natural catalysts in most biomass forms are enhanced or removed to emphasise production of specific chemicals or families of chemicals. In addition, specific chemicals are recovered by physical and/or chemical processing and may be subjected to catalytic processing to improve the product quality or yield or derive higher value chemicals. Since the primary formation of organics is significantly influenced by the presence or absence of natural or added catalysts, it is not practicable to differentiate between catalytic and non-catalytic processes, so all chemical extraction and recovery work is included. Secondary upgrading of the recovered compounds or fractions is also included here, but catalytic conversion of the primary vapours and whole product oil is-discussed separately below.

Table 6.3 lists the organisations currently and recently involved in chemicals extraction/recovery and derivation, while Table 6.4 lists the chemicals and where they are being investigated.