Utilizing hydrolysis residue from bioethanol production as an additive for solid fuel pellets

Abstract

Cellulosic bioethanol is produced from the structural carbohydrates (cellulose and hemicellulose) in non-food biomass feedstocks via biochemical conversion. A great amount of non-hydrolyzed material, mainly lignin, is left out as a residual byproduct in this process. For the overall process economy, a possible value added use of this hydrolysis residue is to produce solid fuel pellets to power the bioethanol production itself or residential combustion because lignin has a high net energy value and a low fuel-ash content. Moreover, lignin with its self-bonding behavior can serve as a natural binder if used as an additive to make stronger and more durable pellets for energy and other biorefinery applications. In this study, solid fuel pellets fully or partially made from corn stover hydrolysis residue were evaluated from physical, thermochemical, and hygroscopic perspectives. With 10% hydrolysis residue additive, pellet durability increased from 80.7% to 90.1% and reached 92.8% with further hydrolysis residue addition. Enhancements on pellet mechanical properties were also observed by adding 50% or more hydrolysis residue. Energy density increased from 13.7 GJ/m3 to as high as 17.6 GJ/m3 with the amount of additive increasing from none to 100%. Thermal gravimetric and differential scanning calorimetry results revealed that hydrolysis residue strengthened pellet thermal properties (heating value, thermal stability, and exothermal performance). FTIR and NMR spectra were studied to identify inner-unit linkages in aromatic and side-chain regions of lignin to understand its self-bonding behavior. Pellets also showed increased hydrophobicity and better water resistance when a higher percentage of hydrolysis residue additive was used.