In-situ catalytic fast pyrolysis (CFP) is considered to be a promising pathway to produce aromatic hydrocarbons from lignocellulosic biomass. However, the presence of variable amounts of inorganic ash in biomass in the form of alkali and alkaline earth metals (AAEMs) is a concern while using in situ catalysts because AAEMs could influence product distribution from CFP while also being a major reason for catalyst deactivation. In this study, the effect of four alkali and alkaline earth metals (K, Na, Mg, and Ca) commonly found in biomass was investigated to understand their individual influence on the fate of primary pyrolysis products as well as their effect on the selectivity of products from in situ CFP using ZSM-5 catalyst. Experiments were performed in a microreactor (Py-GC/MS) with ZSM-5 catalyst using AAEM-impregnated biomass. It was found that the type of AAEM as well as the concentration were significant, with Mg appearing to be relatively inert when compared to the stronger catalytic activity of K, Na, and Ca. The influence of AAEMs on the formation of pyrolysis products from cellulose, hemicellulose, lignin, and its subsequent influence on CFP is discussed. From noncatalytic pyrolysis experiments, even the lowest concentration of AAEMs (0.1 wt %) was observed to have a significant influence on the thermal decomposition behavior of biomass, promoting the formation of lower molecular weight cellulose and lignin-derived products. AAEMs were found to be influencing CFP product distribution by reducing the carbon yield of desired aromatic hydrocarbons and olefins, while it accelerated pathways resulting in increased yields of thermally derived char and noncondensable gases. The effect of AAEMs on CFP followed the order: Na > K > Ca > Mg.

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.

Hydrothermal liquefaction (HTL) of nine algae species were performed at two reaction temperatures (280 and 320°C) to compare the effect of their biomass composition on product yields and properties. Results obtained after HTL indicate large variations in terms of bio-oil yields and its properties. The maximum bio-oil yield (66wt%) was obtained at 320°C with a high lipid containing algae Nannochloropsis. The higher heating value of bio-oils ranged from 31 to 36MJ/kg and around 50% of the bio-oils was in the vacuum gas oil range while high lipid containing algae Nannochloropsis contained a significant portion (33-42%) in the diesel range. A predictive relationship between bio-oil yields and biochemical compositions was developed and showed a broad agreement between predictive and experimental yields. The aqueous phases obtained had high amount of TOC (12-43g/L), COD (35-160g/L), TN (1-18g/L), ammonium (0.34-12g/L) and phosphate (0.7-12g/L).

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