|Biocrude compounds, product gas and reaction pathways from APR of wastepaper at 250 °C in presence of 5 wt % Ni(NO3)2 catalyst. Credit: ACS, Tungal and Shende. Click to enlarge.|
A pair of researchers at the South Dakota School of Mines & Technology have demonstrated homogeneously catalyzed subcritical aqueous phase reforming (APR) of wastepaper to produce biocrude and hydrogen. A paper on their work is published in the ACS journal Energy & Fuels.
Wastepaper can be a combination of newspaper—a lignocellulosic biomass containing cellulose (62%), hemicellulose (16%), and lignin (16%)—and used office printing papers which consist of mainly cellulose (85−99%) and negligible (0.4%) lignin. Using a homogeneous Ni(NO3)2 catalyst, they produced about 44 wt % biocrude from wastepaper slurry at 250 °C after 120 minutes of reaction time. The biocrude contained ∼1 wt % HMF/furfural, 7.5 wt % sugars, 49.1 wt % acids, and 42.4 wt % oxygenated hydrocarbons.
The product gas showed a maximum of about 0.2 mol % and 3.75 mol % H2 (17.7 mol % N2 free basis) after 120 min of reaction time at 225 and 250 °C, respectively, along with CO, CH4, and CO2. At a higher reforming temperature of 275 °C, 10.2 mol % H2 was observed with 51.9 wt % biocrude production.
Production of paper products is expected to increase to 4.6 × 108 tonnes by 2015, a 28% increased from 2005 levels, the authors noted. The current preferred way of managing wastepaper disposal is via landfilling and/or incineration; one hindrance to recycling activity is the difficulty in manufacturing high quality paper products because of higher pulp fiber content. The researchers decided to explore the potential for converting wastepaper to fuels.
Biocrude and H2 can be produced from thermochemical processing of biomass using gasification, pyrolysis, fast pyrolysis, and aqueous phase reforming under subcritical and supercritical conditions. Among these processes, aqueous phase reforming or hydrothermal treatment has several advantages, which include lower energy consumption, direct utilization of biomass without any pretreatment or drying and lower tar and char formation, as compared with other thermochemical processes where significant biochar and tar are generally produced by polymerization of dehydrated products.
The biocrude generated from different biomass feedstocks under hydrothermal conditions has shown lower oxygen content (10−20%) and higher heating value (30−36 MJ/kg) as compared with a biomass, which has higher oxygen content and lower heating value. In addition to biocrude, aqueous phase biomass reforming is also capable of generating high energy density fuel, H2 (143 MJ/kg).
It is to be noted that under subcritical conditions, the dielectric constant of water is significantly lower, which allows solubilization of organic compounds whereas ionization constant is approximately 3 orders of magnitude higher than at ambient conditions providing acidic medium for the hydrolysis of biomass compounds. Consequently, subcritical water not only serves as a reaction medium but also acts as reactant leading to liquefaction of a biomass that proceeds through a series of chemical modifications involving depolymerization, solvolysis, and chemical and thermal decomposition of monomers into smaller molecules.
This aspect of subcritical water processing of biomass is attractive as it encompasses several competing reaction pathways converting biomass to liquefied biocrude and gaseous fuels such as H2 and/hydrocarbons. The use of a catalyst further influences the production of biocrude and gaseous fuels. Among different feedstocks investigated so far, the information on homogeneously catalyzed subcritical aqueous phase reforming of wastepaper for biocrude and H2 generation is missing in the literature.—Tungal and Shende
In their experiments, the team prepared slurries of 15 g wastepaper in 150 mL of distilled water using 5 wt % catalyst for loading in the reactor. The reactor was pressurized to 40 psi at room temperature with N2; temperature was varied between 200−275 °C. The reforming reaction was continued for 120 min and while the reaction was in progress, gas and liquid samples were withdrawn periodically and analyzed using gas chromatography (GC), gas chromatography mass spectrometry (GC-MS), high-performance liquid chromatography (HPLC), and total organic carbon (TOC) analyzer.
HPLC analysis of the resulting biocrude revealed presence of sugars such as cellobiose, xylobiose, glucose, and mannose and organic acids, which include formic, acetic, propionic, and lactic. GC-MS analysis of the biocrude identified 46 oxygenated hydrocarbons with >85% confidence level, which mainly include cyclic ketones and substituted cyclic ketones, quinone derivatives, phenols and substituted phenols, and aromatic alcohols.
Richa Tungal and Rajesh Shende (2013) Subcritical Aqueous Phase Reforming of Wastepaper for Biocrude and H2 Generation. Energy & Fuels doi: 10.1021/ef302171q