Torrefaction has been shown to improve the chemical composition of bio-oils produced from fast pyrolysis by lowering its oxygen content and enhancing the aromatic yield.

Hydrothermal liquefaction (HTL) has been identified as an innovative technique to convert aquatic or wet biomass such as algae into biofuels. In this study, HTL was performed on three algae strains viz. Nannochloropsis, Pavlova and Isochrysis at three temperatures of 250, 300 and 350 o C, with and without using Na 2 CO 3 as catalyst and a holding time of 60 minutes. The effect of temperature on the HTL product yields and their properties were studied for both catalytic and non-catalytic HTL. Maximum bio-oil yield for non-catalytic (48.67 wt.%) and catalytic (47.05 wt.%) HTL was obtained at 350 o C from Nannochloropsis and Pavlova, respectively. Compared to non-catalytic HTL, Na 2 CO 3 increased the bio-oil yield for high carbohydrate containing algae (Pavlova and Isochrysis) at higher temperatures (300 and 350 o C) whereas for high protein containing algae (Nannochloropsis) the yield was higher only at lower temperature (250 o C). Total acid number, pH, density, higher heating value (HHV), ash, moisture and elemental composition were measured for bio-oils produced. The bio-oil obtained had the HHV in the range of 32 to 37 MJ/kg, which was comparable to heavy crude oil. Proximate and ultimate analyses were performed to characterize solid residue, and aqueous fraction was analyzed for acidity, total organic carbon and total nitrogen.

Pyrolysis and oxidation of triethyl phosphate (TEP) were performed in the reflected shock region at temperatures of 1462-1673 K and 1213-1508 K, respectively, and at pressures near 1.3 atm. CO concentration time histories during the experiments were measured using laser absorption spectroscopy at 4580.4 nm. Experimental CO yields were compared with model predictions using the detailed organophosphorus compounds (OPC) incineration mechanism from the Lawrence Livermore National Lab (LLNL). The mechanism significantly underpredicts CO yield in TEP pyrolysis. During TEP oxidation, predicted rate of CO formation was significantly slower than the experimental results. Therefore, a new improved kinetic model for TEP combustion was developed, which was built upon the AramcoMech2.0 mechanism for C-C chemistry and the existing LLNL submechanism for phosphorus chemistry. Thermochemical data of 40 phosphorus (P)-containing species were reevaluated, either using recently published group values for P-containing species or by quantum chemical calculations (CBS-QB3). The new improved model is in better agreement with the experimental CO time histories within the temperature and pressure conditions tested in this study. Sensitivity analysis was used to identify important reactions affecting CO formation, and future experimental/theoretical studies on kinetic parameters of these reactions were suggested to further improve the model. To the best of our knowledge, this is the first study of TEP kinetics in a shock tube under these conditions and the first time-resolved laser-based species time history data during its pyrolysis and oxidation.

In situ catalytic upgrading is a promising technique to improve the properties of bio-oil because the bio-oil produced from the conventional method has several negative attributes, such as low heating value and highly acidic nature, and is also unstable during storage. In this study, the catalytic effect of CaO, MgO, and ZSM-5 as in situ upgrading catalysts during biomass pyrolysis was studied in a fluidized-bed reactor. Southern pine sawdust was subjected to pyrolysis with inert bed material (quartz sand) and subsequently with the catalysts. The quality of bio-oil obtained was compared to the baseline values (i.e., with the use of sand as bed material without any catalyst) in terms of its chemical composition, heating value, viscosity, pH, total acid number (TAN), and oxygen and water contents. The use of CaO resulted in an improvement in pH (2.39−3.98) and TAN (88.9−46.6) of the bio-oil when compared to the results when using only sand. In comparison, MgO was a mild catalyst because it altered the bio-oil quality slightly, while ZSM-5 had no effect on the acid content in bio-oil, although it produced bio-oil with the least oxygen content at a significantly lower yield and higher water content (38.5%). In terms of chemical composition, the catalysts exhibited different behaviors to various groups of compounds. Anhydrosugars were reduced by all of the catalysts tested to different extents, but CaO significantly altered the quality of bio-oil by reducing organic acids, while CaO and ZSM-5 reduced the abundance of phenolic compounds with a higher oxygen content. An accelerated aging test was performed to compare the efficacy of these in situ catalysts on improving the stability of bio-oil, and it was observed that the bio-oil produced using CaO was the most stable when compared to the baseline and other catalytic bio-oils tested in this study.

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