Abstract
Catalytic hydrotreatment is recognized as an efficient method to improve the properties of pyrolysis liquids (PO) to allow co-feeding with fossil fuels in conventional refinery units. The promising catalyst recipes identified so far are catalysts with high nickel contents (38 to 57 wt.%), promoted by Cu, Pd, Mo and/or a combination, and supported by SiO2, SiO2-ZrO2, SiO2-ZrO2-La2O3 or SiO2-Al2O3. To gain insights into the reactivity of the pyrolytic sugar (PS) and pyrolytic lignin (PL) fraction of PO, hydrotreatment studies (350 °C, 120 bar H2 pressure (RT) for 4 h) were performed in a batch autoclave. Catalyst performance was evaluated by considering the product properties (H/C ratio, the charring tendency (TGA) and molecular weight distribution (GPC)) and the results were compared with a benchmark Ru/C catalyst. All Ni based catalysts gave products oils with a higher H/C compared to Ru/C. The Mo promoted catalyst performed best, giving a product with the highest H/C ratio (1.54) and the lowest TG residue (0.8 wt.% compared to 12 wt.% for the fresh PS). The results further revealed that the PS fraction is highly reactive and full conversion was achieved at 350 °C. In contrast, the PL fraction was rather inert, and only part of the PL fraction was converted. The fresh and spent catalysts after the hydrotreatment of the PS and PL fractions were characterized by elemental analysis, powder X-Ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM-EDX). The results revealed that the use of PS as the feed leads to higher amounts of coke deposits on the catalysts, and higher levels of Ni agglomeration when compared to experiments with PL and pure PO. This proofs that proper catalyst selection for the PS fraction is of higher importance than for the PL fraction. The Mo promoted Ni catalysts showed the lowest amount of coke and the lowest tendency for Ni nanoparticle agglomeration compared to the monometallic Ni and bimetallic Ni-Cu catalysts.
Highlights
Climate change due to emission of CO2 from fossil resources, together with a possible shortage of fossil reserves, has stimulated research on the production of renewable resources for fuels and chemicals
Other abundant components detected by HPLC and GC-MS
We here report on the catalytic hydrotreatment of the two main fractions of pyrolysis oils or bio-crude (PO) (PS and pyrolytic lignin (PL))
Summary
Climate change due to emission of CO2 from fossil resources, together with a possible shortage of fossil reserves, has stimulated research on the production of renewable resources for fuels and chemicals. Lignocellulosic biomass, such as wheat straw, forestry residues and grass, is considered as a sustainable resource as it contains renewable carbon, which can be recycled by green plants on earth. Full utilization of such materials can at least partially replace fossil based crude oil and derivatives [1]. The vapor phase is quickly quenched (1–2 s) to suppress secondary reactions, which reduce the liquid product yields [4]
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