8 Search Results

Towards the goal of integrating CO₂ capture using aqueous ammonia with its utilization for algae cultivation, Scenedesmus acutus (UTEX B72) was grown in 1100 L open raceway ponds using CO₂ and NH₃ supplied from gas cylinders. CO₂/NH₃ mole ratios of 7 and 10 were employed, the gas mixture acting as a surrogate for the output from a CO₂ scrubbing system using aqueous ammonia. Compared to Scenedesmus acutus grown in open ponds using gaseous CO₂ and NaNO₃ as the N-source, the ponds supplied with gaseous CO₂ and NH₃ displayed higher productivity at both CO₂/NH₃ ratios, with the higher ratio providing themore » best growth. Depending on the culturing conditions and CO₂/NH₃ ratio, CO₂ utilization ranged up to 15.8% and NH₃ utilization to 23.0%. These rather low values reflect the fact the high CO₂/NH₃ feed rate used, resulting in a substantial release of NH₃ from the ORPs (~45%). Finally, these findings demonstrate the suitability of gaseous NH₃ as a N-source for microalgae cultivation, while highlighting the need for a control strategy that closely balances the CO₂/NH₃ supply with the algae growth rate. The produced algae biomass possessed a high protein and low ash content, rendering it particularly suitable for use as a bioplastic feedstock.« less

The use of γ-Al₂O₃-supported Ni catalysts promoted with either Cu or Fe was investigated for the reductive catalytic fractionation (RCF) of hybrid poplar in methanol at 200 and 250 °C. The effectiveness of lignin depolymerization was quantified in terms of the lignin oil production, the quantity and distribution of identifiable monomers present in the lignin oil, and the yield of residual solids. All of the Ni-based catalysts tested provided improved yields of lignin oil and monomers, along with reduced char formation, relative to blank (sans catalyst) runs. The highest monomer yield of 51 % was obtained at 250 °C overmore » a 20 wt.% Ni-5 wt.% Cu/Al₂O₃ catalyst, the improved performance obtained through Cu promotion being attributed to the ability of Cu to facilitate NiO reduction, resulting in an increased amount of Ni⁰ on the catalyst surface and, consequently, improved hydrogenation activity. Finally, the main monomers formed were propanol-, propyl- and propenyl-substituted guaiacol and syringol, the S/G ratio of the products corresponding closely to that in the native lignin.« less

Integrating CO₂ scrubbing from flue gas with its utilization in algae cultivation represents a potential means of lowering the cost of CO₂ capture. Towards this goal, this study sought to assess the feasibility of using gaseous a CO₂/NH₃ stream, derived from CO₂ capture using aqueous ammonia, as a C- and N-source for algae cultivation. Scenedesmus acutus was cultured in 800 mL photobioreactors using gaseous CO₂/NH₃ in mole ratios varying from 7 to 18. Excellent growth of Scenedesmus acutus was observed, the average growth rate for CO₂/NH₃ = 10 of 0.171 ± 0.015 g/L·day exceeding that obtained using 1% CO₂/N₂ andmore » urea as the N-source (0.099 ± 0.28 g/L·day). Under optimal growth conditions (CO₂/NH₃ mole ratio of 10), CO₂ utilization ranged from 57% to 72%, while the NH₃ utilization was >90%. The CO₂/NH₃ feed rate was also found to exert a significant effect on algae productivity, excessive feed rates leading to accumulation of NH₃ in the culture at concentrations that were toxic to the algae. Consequently, to avoid the toxic effects of high NH₃ concentrations (>2.0 mM), it proved necessary to balance the NH₃ supply with the algae growth rate so that excessive NH₃ accumulation was prevented. This indicates that for practical applications, a CO₂/NH₃ feed control strategy would be required that takes into account the ammonium ion concentration in solution and the pH so as to avoid significant concentrations of free NH₃. Furthermore, analysis of the harvested biomass revealed a high protein (≥ 47 wt%) and a low ash content (< 3.6 wt%), suggesting it would be well suited for use as animal feed or as a feedstock for the production of bioplastics.« less

This contribution describes an algal fractionation scheme based on cell lysing and carbohydrate hydrolysis under acidic conditions, coupled with solvent extraction, that produces algal lipids, carbohydrates, and proteinaceous solid from partially dewatered algal biomass. Here, a design of experiments analysis was employed to identify the effect of fractionation conditions on the yields of the three product streams. By selection of appropriate conditions, the process can be steered from simple lipid extraction to near complete fractionation of the biomass. Lipid purification and upgrading were respectively achieved with a low-cost adsorbent and an inexpensive Ni-based catalyst that deoxygenated the lipids via decarboxylation/decarbonylation,more » an approach offering several advantages over the hydrodeoxygenation-based processes typically employed to convert lipids to hydrocarbons. The proteinaceous solids obtained were found to have much lower ash content as well as higher protein content relative to the untreated algae, enhancing the suitability of this material as a feedstock for the production of bioplastics.« less

DDQ oxidized lignins were used as substrates to assess the effectiveness of secondary depolymerization methods for the production of aromatics.

Microalgae are a potential means of recycling CO2 from industrial point sources. With this in mind, a novel photobioreactor (PBR) was designed and deployed at a coal-fired power plant. To ascertain the feasibility of using waste heat from the power plant to heat algae cultures during cold periods, two heat transfer models were constructed to quantify PBR cooling times. The first, which was based on tabulated data, material properties and the physical orientation of the PBR tubes, yielded a range of heat transfer coefficients of 19–64 W m−2 K−1 for the PBR at wind speeds of 1–10 m s−1. Themore » second model was based on data collected from the PBR and gave an overall heat transfer coefficient of 24.8 W m−2 K−1. Energy penalties associated with waste heat utilization were found to incur an 18%–103% increase in energy consumption, resulting in a 22%–70% reduction in CO2 capture for the scenarios considered. A techno-economic analysis showed that the cost of heat integration equipment increased capital expenditures (CAPEX) by a factor of nine and increased biomass production costs by a factor of three. Although the scenario is thermodynamically feasible, the increase in CAPEX incurs an increase in biomass production cost that is economically untenable.« less

A heterogeneous catalyst system, employing Au nanoparticles (NPs) and Li–Al (1:2) layered double hydroxide (LDH) as support, showed excellent activity in aerobic oxidation of the benzylic alcohol group in β-O-4 linked lignin model dimers to the corresponding carbonyl products using molecular oxygen under atmospheric pressure. The synergistic effect between Au NPs and the basic Li–Al LDH support induces further reaction of the oxidized model compounds, facilitating facile cleavage of the β-O-4 linkage. Extension to oxidation of γ-valerolactone (GVL) extracted lignin and kraft lignin using Au/Li–Al LDH under similar conditions produced a range of aromatic monomers in high yield. Hydrolysis ofmore » the Au/Li–Al LDH oxidized lignin was found to increase the degree of lignin depolymerization, with monomer yields reaching 40% for GVL extracted lignin. According to these results, the Au/Li–Al LDH + O₂ catalyst system shows potential to be an environmentally friendly means of depolymerizing lignin to low molecular weight aromatics under mild conditions.« less