UPGRADE OF FLASH PYROLYSIS CONDENSATE BY ESTERIFICATION WITH HIGHER ALCOHOLS

摘要

The utilization of condensates from flash pyrolysis is hindered by unwanted properties like corrosivity, high viscosity and the tendency to polymerization during prolonged storage. These characteristics result from the high content of organic acids and multiple functional groups and C-C double bonds in its constituents. As an alternative to severe hydroprocessing for the mitigation of these challenges, the addition of butanol and subsequent esterification of acids and acetalisation of ketones is investigated. Ablative flash pyrolysis of different biomasses is performed in a laboratory plant designed for a capacity of 10 kg/h input. The cylindrical biomass with a diameter of 50 mm is pressed by hydraulic piston against an electrically heated, rotating plate. The pyrolysis vapors are cleaned from fine dust by means of a cyclone and condensed in a double-effect cooler followed by an electrostatic precipitator. Samples of pyrolysis condensates are mixed with butanol and an acidic catalyst is added. This mixture is heated and kept under reflux in a dean-stark-apparatus to continuously boil off the water, which is solved in the organic liquid and additionally produced by the esterification and acetalisation reactions. The process is stopped, when no more water evaporates from the reactor. As reference homogeneous acids like sulfuric acid and p-toluenesulfonic acid are used and compared to solid acid catalysts like ZnO or zeolithes. Figure 1 gives an overview about the results for the reduction of total acid number for the catalyst screening. The advantage of the heterogeneous, solid catalysts is the possibility to remove the solids after reaction and use them again for another batch in contrast to the homogeneous acids, which remain in the solution and need to be neutralized at the end. The most promising catalyst candidates from the screening are then used in experiments with varying process parameters like ratio of pyrolysis liquid to butanol, catalyst amount and biomass input to the pyrolysis plant (beech wood as reference and barley straw as example for agricultural residues). All products are analyzed for total acid number, water content, dynamic viscosity and higher heating value. The total acid number can be reduced by 90 % (from above 110 to below 10 mg/g), the water content by 90 % (from above 25 % to below 2 %), the viscosity by 70 % (from above 18 to 5 cSt) and the higher heating value can be increased by 45 % (from 16.6 to 31 MJ/kg). These improvements should allow the utilization of upgraded pyrolysis liquids in standard boilers and as fuel in CHP plants.