Hydrothermal Gasification of Nannochloropsis sp. with Ru/C

Abstract

We determined the effects of different process variables on the gasification of Nannochloropsis sp., a marine microalga, in water with a Ru/C catalyst at 410 °C. About 45% gasification efficiency was achieved at 75 min with a catalyst loading (mass of Ru/C catalyst/mass of dry algal biomass) of 1 g/g, a water density of 0.096 g/cm 3 , and a 4.3 wt % loading of algae. Longer reaction times, higher catalyst loadings and water densities, and lower algae loadings provided higher gas yields. The level of catalyst loading had the most significant effect on both the yields and composition of the gaseous products. Complete gasification of the microalga was achieved with a catalyst loading of 2 g/g. The Ru/C catalyst recovered from an experiment and then reused in a new experiment was less active than fresh Ru/C. This loss of activity is, in large part, due to deactivation by sulfur, which is present in the microalga at about 0.5 wt %. A simple two-step catalytic gasification mechanism, along with a step for catalyst poisoning by sulfur, led to a rate equation that was consistent with the experimental results for gasification efficiency. The presence in algae of sulfur and perhaps other elements, such as Cl, that are not as prevalent in terrestrial biomass indicates that efficient and effective gasification of microalgae could present new challenges in engineering and catalyst design.

Catalytic supercritical water gasification of plastics with supported RuO2: A potential solution to hydrocarbons–water pollution problem

“…Moreover, Osada and co-workers [29][30] have demonstrated that ruthenium-based catalysts are stable in hydrothermal conditions after regeneration but may require slightly longer residence time to perform at the same level as the fresh catalyst. In addition, other authors [31][32] have reported that sulphur-poisoning was a major cause of deactivation of ruthenium catalyst; hence this was not expected in this work as the feedstock used contained no sulphur. The SEM micrographs in Figure 7 present the details of the surfaces of the fresh, used non-calcined and used calcined 20 wt% RuO2/ -Al2O3 catalyst.…”

Catalytic gasification of lignin with Ni/Al2O3–SiO2 in sub/supercritical water

“…The reactors had an internal volume of 4 cm 3 . The reactor had a Swagelok cap on one end and a HiP high-pressure valve assembly on the other, which were described in greater detail in our previous reports [14,15].…”

“…Previous work [15] indicates that Ru/C is easily poisoned by sulfur, and suffered from rapid activity decrease after reuse. sulfur linkage could be hydrolyzed to hydrogen sulfide during hydrolytic degradation of alkaline lignin [16].…”

Energetic analysis of gasification of biomass by partial oxidation in supercritical water

“…As the increase of biomass loading, the efficiency of gasification and gaseous yields decrease dramatically due to the lower steam reforming reactions [12,13]. It is found that as the concentration of glucose increases from 10 to 24%, the hydrogen yield decreases from 8.9 to 2 mol·kg − 1 and the CO yield decreases from 7.9 to 5.9 mol·kg −1 .…”

“…water provides a potential way to convert biomass to fuel-rich gas containing H 2 and/or CH 4 [12,13]. Commercial SCWG facility can be found for treatment of surplus active sludge for gaseous fuels in Japan, but Matsumura's evaluation indicates that SCWG requires a significant amount of energy to pre-heat and maintain a desired high temperature for the reactions [14].…”