Hydrodeoxygenation (HDO) upgrading of pyrolysis bio-oils: developing novel carbon-supported catalysts and addressing process corrosion challenges
Abstract
Fast pyrolysis has been regarded as one of the most promising thermochemical conversion technologies for liquid bio-fuels production. However, the poor quality of generated crude bio-oils, such as high oxygen and water content, low thermal stability, and high corrosivity, make them difficult as alternative transportation fuels.
Catalytic hydrodeoxygenation (HDO) is one of the most promising processes to reduce oxygen content in pyrolysis oil, which normally operates at moderate temperatures from 200 to 400 °C, with high pressure (4-20 MPa) hydrogen gas. However, high-pressure hydrogen gas is not an ideal hydrogen source due to safety issues associated with transportation, storage, and operation. Supercritical fluid treatment is another bio-oil upgrading process which could enhance the energy content of the bio-oil while substantially reducing the acid number, heteroatoms content, and viscosity of the oil. Supercritical ethanol (Tc: 241 °C, Pc: 6.3 MPa) can be applied as an effective hydrogen-donor solvent for bio-oil upgrading, because of its liquid-like solubility and heat transfer rate, gas-like diffusivity and high miscibility to both liquid and gas. Large-scale commercial implementation of catalytic HDO of pyrolysis oil has not been achieved yet due to limited materials performance knowledge specific to reactor construction. For example, there is limited research about the corrosion effects of catalytic HDO of bio-oil in supercritical ethanol.
In this thesis, a comparative investigation on different hydrogen sources (i.e., hydrogen gas as an ex-situ hydrogen source and formic acid as an in-situ hydrogen source) was conducted on upgrading pyrolysis oil by catalytic HDO in supercritical ethanol. Moreover, different catalysts, such as inexpensive NiMoW catalysts on alumina and carbon supports were studied, where carbon supported catalysts showed superior performance in terms of activity. Studies on CoMoP and CoMoW on different carbon supports were carried out to further improve catalyst activity. Co-processing pyrolysis oil with vacuum gas oil (VGO) has also been successfully demonstrated as a promising method to incorporate biocarbon into petroleum refining to reduce greenhouse gas (GHG) emissions from the petrochemical industry. Lastly, this thesis examined the corrosion resistance of candidate alloy (SS304) for reactor construction during the catalytic HDO of bio-oil in supercritical ethanol.