Just as with direct co-liquefaction, in recent years significant attention to co-pyrolysis of a variety of mixed feedstock has been given. Some of these studies have been focused on low-severity (low residence time as with fast pyrolysis) conditions to produce more oil and these are summarized in Table 7.13. Although the studies have examined a wide range of feedstock and reaction conditions, the major conclusion that emerges is that the pyro­lytic reactivity of biomass and coal are different because biomass in general is more reactive than coal and requires a lower temperature to devolatilize

TABLE 7.13

Some Typical Studies of Co-Pyrolysis

Mixed Feedstock Author Comment

and depolymerize compared to coal. However, there seem to be no or very little reactions or interactions between species of biomass and coal. Hydrogen release from biomass does not appear to interact with the species from coal. Thus, in general there is no synergy between coal and biomass pyrolysis. The final results for co-pyrolysis are additives of individual pyrolysis. Each species within the mixture produces its own liquids and gases. The situation is, however, different for the mixtures of biomass and a variety of plastics. In these cases, there appears to be a significant synergy between pyrolysis of these two substances. Not many studies using catalyst and hydrogen (i. e., hydropyrolysis) for a mixed feedstock have been reported. It is possible that under those conditions more synergies between coal and biomass pyrolysis would be observed. More work in this area is needed.