Evaluating Regeneration Options of Solid Amine Sorbent for CO2 Removal.

Biogas is one of the most popular alternative energy resources to replace fossil fuels. The product of anaerobic fermentation in a digester contains several impurities such as H2S and especially CO2 that needs to be removed in order to upgrade the gas quality. Supported amine sorbents (SAS) might provide an attractive option to remove these impurities. However, little is known about the regeneration of the sorbent. This study evaluates experimentally and by modeling the options for regeneration of the SAS. Theoretically, pressure swing adsorption without purge flow is the most energy efficient method (1.7 MJ/kg CO2). It was found that when using a purge flow the desorption rate is strongly influenced by the equilibrium between the gas and adsorbed phase. With elevated temperature (>80 °C) both the working capacity and the productivity increase significantly. Finally, an energy evaluation for a typical biogas case study is carried out, showing the trade-offs between power consumption, heat demand, and sorbent inventory. Interestingly, at the expense of a somewhat higher power consumption, the use of inexpensive air as purge gas at 60 °C could be an attractive option, but case-specific costs are needed to identify the economic optimum.

A Multistage Fluidized Bed for the Deep Removal of Sour Gases: Proof of Concept and Tray Efficiencies.

Currently there are significant amounts of natural gas that cannot be produced and treated to meet pipeline specifications, because that would not be economically viable. This work investigates a bench scale multistage fluidized bed (MSFB) with shallow beds for sour gas removal from natural gas using a commercially available supported amine sorbent. A MSFB is regarded as a promising adsorber type for deep sour gas removal to parts per million concentrations. A series of experiments was conducted using carbon dioxide as sour gas and nitrogen to mimic natural gas. Removal below 3 mol ppm was successfully demonstrated. This indicates that gas bypassing is minor (that is, good gas-solid contacting) and that apparent adsorption kinetics are fast for the amine sorbent applied. Tray efficiencies for a chemisorption/adsorption system were reported for one of the first times. Current experiments performed at atmospheric pressure strongly indicate that deep removal is possible at higher pressures in a multistage fluidized bed.

Renewable Alkenes from the Hydrothermal Treatment of Polyhydroxyalkanoates-Containing Sludge.

Polyhydroxyalkanoates (PHA) are a key constituent of excess sludge produced by Aerobic Sewage Sludge Treatment plants. The accumulation of significant amount of PHA inside aerobic microbial cells occurs when a surplus of an easily degradable carbon source (e.g., volatile fatty acids, VFA) is found in combination with other nutrients limitation. Herein, hydrothermal treatment (HT) of PHA-containing sludge at 300 and 375 °C was demonstrated to be effective in converting most (>70% w/w) of the bacterial PHA stored inside microbial cells into alkene/CO2 gas mixtures. Simultaneously, most of non-PHA biomass was converted into water-soluble compounds (50% carbon yield) that were acidogenic fermented to produce volatile fatty acids, ideal substrate to feed aerobic bacteria and produce more PHA. According to results here presented, HT of excess sludge with moderate (13%) PHA content can produce about 50 kg of alkenes per tonne of suspended solids treated, with a significant reduction of sludge mass (80% reduction of wet sludge volume) and consequent disposal cost.

Maximizing Lipid Yield in Neochloris oleoabundans Algae Extraction by Stressing and Using Multiple Extraction Stages with N-Ethylbutylamine as Switchable Solvent.

The extraction yield of lipids from nonbroken Neochloris oleoabundans was maximized by using multiple extraction stages and using stressed algae. Experimental parameters that affect the extraction were investigated. The study showed that with wet algae (at least) 18 h extraction time was required for maximum yield at room temperature and a solvent/feed ratio of 1:1 (w/w). For fresh water (FW), nonstressed, nonbroken Neochloris oleoabundans, 13.1 wt % of lipid extraction yield (based on dry algae mass) was achieved, which could be improved to 61.3 wt % for FW stressed algae after four extractions, illustrating that a combination of stressing the algae and applying the solvent N-ethylbutylamine in multiple stages of extraction results in almost 5 times higher yield and is very promising for further development of energy-efficient lipid extraction technology targeting nonbroken wet microalgae.

Stability of a Benzyl Amine Based CO2 Capture Adsorbent in View of Regeneration Strategies.

In this work, the chemical and thermal stability of a primary amine-functionalized ion-exchange resin (Lewatit VP OC 1065) is studied in view of the potential options of regenerating this sorbent in a CO2 removal application. The adsorbent was treated continuously in the presence of air, different O2/CO2/N2 mixtures, concentrated CO2, and steam, and then the remaining CO2 adsorption capacity was measured. Elemental analysis, BET/BJH analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis were applied to characterize adsorbent properties. This material was found to be thermally and hydrothermally stable at high temperatures. However, significant oxidative degradation occurred already at moderate temperatures (above 70 °C). Temperatures above 120 °C lead to degradation in concentrated dry CO2. Adding moisture to the concentrated CO2 stream improves the CO2-induced stability. Adsorbent regeneration with nitrogen stripping is studied with various parameters, focusing on minimizing the moles of purge gas required per mole of CO2 desorbed.

Assessment of a dry and a wet route for the production of biofuels from microalgae: energy balance analysis.

In this study, the energy balance of two microalgae-to-biofuel concepts, one via a so called "dry route" (oil extraction from dried algae) and one via a "wet route" (oil extraction in the water phase), are assessed. Both routes are intended to convert the chemical energy contained in the microalgae into high-value biofuels with minimal fossil energy consumption. The analysis shows that the drying process in the dry route and the oil extraction process in the wet route consume a significant amount of energy. By coupling waste heat from a nearby power plant to the process, the energy balance can be improved and a potential fossil energy ratio (FER) up to 2.38 and 1.82 can be reached for the dry and wet route, respectively. The results indicate that based on current available technologies, the dry route has higher FER and the wet route has more potential in producing high valuable biofuels.