Influence of Red Mud Catalyst and Reaction Atmosphere on Hydrothermal Liquefaction of Algae

Abstract

Algae are a diverse group of aquatic organisms and have a potential to produce renewable biofuel via hydrothermal liquefaction (HTL). This study investigated the effects of reaction environments on biocrude production from “Tetraselmis sp.” algae strain by HTL process using red mud (RM) based catalyst. The inert (N2), ethylene (C2H4), reducing (10% H2/90% N2), and oxidizing (10% O2/90% N2) environments were applied to the non-catalytic as well as catalytic HTL treatments with two forms of RM catalysts: RM reduced at 500 °C (RRM) and nickel-supported RM (Ni/RM). Under nitrogen, ethylene and reducing environments, the biocrude yield increased by the following trend: No Catalyst < RRM < Ni/RM. The Ni/RM catalyst produced the highest biocrude yield (37 wt.%) in an ethylene environment, generated the lowest total acid number (14 mg KOH/g) under inert atmosphere, and lowered sulfur (33–66%) and oxygen (18–30%) from biocrude products irrespective of environments. The RRM catalyst maximized the biocrude carbon content (61 wt.%) under a reducing environment and minimized the heavy metal and phosphorus transfer from the feedstock to biocrude in studied ambiences. The reducing environment facilitated mild hydrotreatment during HTL reaction in the presence of RRM catalyst. Among the non-catalytic experiments, the reducing atmosphere optimized carbon content (54.3 wt.%) and calorific value (28 MJ/kg) with minimum oxygen amount (27.2 wt.%) in biocrudes.

Depolymerization of Household Plastic Waste via Catalytic Hydrothermal Liquefaction

“…13 Acidity The acidity of HTL plastic crudes was significantly less than that reported in our previous HTL studies of municipal sewage sludge and algae. 20,34 However, the TAN values of plastic crudes were almost two times higher than those of the commercial diesel fuel. 52 In single plastic noncatalytic HTL conversion, the maximum TAN value was observed in the crude from HDPE and the minimum was found in LDPE one.…”

“…According to the literature, feedstock to water ratio of 1:1.75 was maintained by adding 50 g of shredded and sieved single plastic or plastic mixture with 87.5 g of deionized water inside the reactor . For all catalytic experiments, a 5 g catalyst was used for every 50 g of plastic feedstock . Once the plastic, water, and catalyst (if applicable) were loaded into the reactor, the reactor was sealed.…”

“…The high iron content of the RM catalyst (Table S4, Supporting Information) was mostly responsible for iron migration to crudes. 34 The catalytic PP and PS crudes contained significantly higher Co and Fe metals than noncatalytic products. However, the heavy metal migration to crude was negligible in comparison to that of the solid residue, as shown by the distribution of heavy metals in catalytic PM HTL products (Figure S4, Supporting Information).…”

“…15 For all catalytic experiments, a 5 g catalyst was used for every 50 g of plastic feedstock. 34 Once the plastic, water, and catalyst (if applicable) were loaded into the reactor, the reactor was sealed. To ensure an inert environment, the reactor was purged three times with nitrogen before being pressurized to a starting pressure of 90 psi (0.62 MPa) of the same gas.…”

“…The elemental composition of the feedstock, crude, and solid residue; total organic carbon (TOC) of the aqueous phase; and the mole fraction of CO, CO 2 , and CH 4 gases were employed to determine carbon recovery. 34 The carbon transfer to "Others (gases not quantified) " and losses during the HTL reaction was termed "Balance". Irrespective of catalyst and feedstock, the majority of carbon shifted toward crude products.…”