Hydrothermal co-liquefaction of sewage sludge and formic acid

The biocrude produced by non-catalytic hydrothermal liquefaction (HTL) has a too high heteroatomcontent to be used directly as a fuel [1-3]. Several studies found that different H2 initial pressuresduring HTL experiments were ineffective in improving the biocrude yield [4-6], nevertheless it wasobserved that higher initial pressures of H2 brought an improvement of the concentration of lightcompounds in the biocrude, decreasing the average molecular weight of biocrude oil. To date H2 ismainly generated from fossil sources and realization of a possible hydrogen economy fromalternative sources presents many challenges. The use of a liquid hydrogen storage media couldrepresent for the HTL process an alternative solution to avoid the mass transport resistanceassociated to gaseous H2, furthermore Biller and Ross [7] observed that the addition of selectedorganic acids had similar effects than the addition of molecular H2. According to these premises, westudied the influence of formic acid as hydrogen donor on the yield and quality of the biocrudeproduced by HTL of sewage sludge (SS). Formic acid was selected because it can decompose tohydrogen and carbon dioxide under mild conditions [8] and it can be produced by electrochemicalreduction of carbon dioxide, an appealing process to capture atmospheric carbon dioxide under theform of a useful chemical [9].