Abstract
In Asia, rice straw residue left in fields after harvest is often burned which causes air pollution or anaerobically digested in the rice patty moist soil to yield methane a greenhouse gas. Effective and efficient process strategies are needed to convert straw into fuels and feedstock’s which do not harm the environment. As a result, this study was undertaken to liquefy Japanese rice straw (RS) an abundant agricultural residue into a liquid after pre-treatment by ball-milling at various temperatures and develop a bioprocess model. Specifically, RS was ball milled into 75-100 μm size particles at temperatures of 60°C, 25°C, and -196°C (cryogenically) and dissolved by heating in 1-ethyl-3- methylimidazolium acetate [Emim][OAc] at different temperatures between 120° 140° and 160°C to understand the interactions between the process parameters. The milled RS powder particles were characterized by FTIR, XRD, BET analyzer and dissolution follow using optical microscopy. The particle dissolution was analyzed by measuring the particle light intensity ratio and particle cross-sectional area as a function of heating time. Higher milling temperature leads to amorphization of the RS cellulose accelerating dissolution. Measurement of the particle light intensity ratio was used to estimate the rice straw particles dissolution endpoint. A particle dissolution model indicated that ball milling temperature and [Emim][OAc] heating temperature strongly interacts influencing the dissolution time. To dissolve RS in [Emim][OAc] quickly, it important to reduce the crystallinity of the cellulose and increase the particle surface area by milling at higher temperature. It is believed this model would have applications to other biomass dissolution processes.
Highlights
Lignocellulosic agricultural crop residues i.e., rice straw, are an abundant underused raw material with potential for conversion to valuable chemical feedstock’s and liquid fuels
As a result in this study, we propose a rice straw particle dissolution process time-based model investigating the relationship between ball milling temperature and by heat treatment in [Emim][OAc] at various temperatures while following the dissolution using optical microscopy
These Fourier transform infrared spectroscopy (FTIR) results confirm the chemical transformation such as hydrogen bonds breakage of cellulose, less water in rice straw (RS) powder resulting from processing at different ball milling temperatures
Summary
Lignocellulosic agricultural crop residues i.e., rice straw, are an abundant underused raw material with potential for conversion to valuable chemical feedstock’s and liquid fuels. Developing effective and economical pretreatment processes for liquefaction and dissolution process models are extremely important for greater utilization of lignocellulosic biomass. Biomass pretreatment research and development has focused on amorphization of the cellulose crystalline component and particle size reduction by milling to improve the dissolution rate. Ogura et al revealed that ball milling converts rice straw containing cellulose from crystalline to amorphous material and results in physical changes [3]. Prolonged ball milling technique induces cellulose amphorization and enhances the reactivity of cellulose during subsequent processing [4]
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