NOVELTY - Pyrolysis of biomass involves providing biomass to a pyrolysis reactor (3) to produce a vapor product; condensing the vapor product to produce a condensed product; and adding a phase separation suppression agent during the process to promote the formation of a single phase condensed product.    USE - For pyrolysis of biomass e.g. lignin containing biomass (claimed) for producing resins which is useful as glue binders in the production of man-made wood products, such as plywood and fibre board.    ADVANTAGE - The phase separation suppression agent suppresses the separation of phases in the condensed product; it reduces the rate of phase separation in the condensed single phase condensed product; and it produces a condensed product that does not separate for at least one week (preferably one month, especially one year); and it remains unseparated indefinitely. The process reduces the quantity of odorous compounds in the bio-oil and also reduces the acidity of the bio-oil. The formation of a single-phase bio-oil by addition of a phase separation suppression agent has the effect of reducing the concentration of reactive compounds compared to the concentration of these compounds within the organic phase of a bi-phasic or multi-phase bio-oil product. Reducing the rate of reaction reduces the amount of water produced over time, thus reducing the likelihood of phase separation during later processing and storage stages. The phase separation suppressing agent reduces the viscosity of the bio-oil; and yields a product that is less likely to foul the pyrolysis system. The recovery of single phase pyrolysis product is easier compared to a bi-phasic or tri-phasic pyrolysis product. When the coolant is used to extract components from the bio-oil that contribute to phase separation, the combined organic yield (the yield of organic material in the bio-oil and recovered from the coolant), is not reduced by the use of a phase separation suppression agent.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of the pyrolysis system for use in performing the process.    Sealable feed container (1)    Screw feeder (2)    Reactor (3)    Heater (4)    Collectors (5, 6)    Condensing column. (9)