Effect of Initial Particle Size and Densification on AFEX-Pretreated Biomass for Ethanol Production

Multifaced application of AFEX-pretreated biomass in producing second-generation biofuels, ruminant animal feed, and value-added bioproducts

Lignocellulosic biomass holds a crucial position in the prospective bio-based economy, serving as a sustainable and renewable source for a variety of bio-based products. These products play a vital role in displacing fossil fuels and contributing to environmental well-being. However, the inherent recalcitrance of biomass poses a significant obstacle to the efficient access of sugar polymers. Consequently, the bioconversion of lignocellulosic biomass into fermentable sugars remains a prominent challenge in biorefinery processes to produce biofuels and biochemicals. In addressing these challenges, extensive efforts have been dedicated to mitigating biomass recalcitrance through diverse pretreatment methods. One noteworthy process is Ammonia Fiber Expansion (AFEX) pretreatment, characterized by its dry-to-dry nature and minimal water usage. The volatile ammonia, acting as a catalyst in the process, is recyclable. AFEX contributes to cleaning biomass ester linkages and facilitating the opening of cell wall structures, enhancing enzyme accessibility and leading to a fivefold increase in sugar conversion compared to untreated biomass. Over the last decade, AFEX has demonstrated substantial success in augmenting the efficiency of biomass conversion processes. This success has unlocked the potential for sustainable and economically viable biorefineries. This paper offers a comprehensive review of studies focusing on the utilization of AFEX-pretreated biomass in the production of second-generation biofuels, ruminant feed, and additional value-added bioproducts like enzymes, lipids, proteins, and mushrooms. It delves into the details of the AFEX pretreatment process at both laboratory and pilot scales, elucidates the mechanism of action, and underscores the role of AFEX in the biorefinery for developing biofuels and bioproducts, and nutritious ruminant animal feed production. While highlighting the strides made, the paper also addresses current challenges in the commercialization of AFEX pretreatment within biorefineries. Furthermore, it outlines critical considerations that must be addressed to overcome these challenges, ensuring the continued progress and widespread adoption of AFEX in advancing sustainable and economically viable bio-based industries.

Sustainable valorization of sugarcane residues: Efficient deconstruction strategies for fuels and chemicals production

The global climate crisis and the ongoing increase in fossil-based fuels have led to an alternative solution of using biomass for fuel production. Sugarcane bagasse (SCB) is an agricultural residue with a global production of more than 100 million metric tons and it has various applications in a biorefinery concept. This review brings forth the composition, life cycle assessment, and various pretreatments for the deconstruction techniques of SCB for the production of valuable products. The ongoing research in the production of biofuels, biogas, and electricity utilizing the bagasse was elucidated. SCB is used in the production of carboxymethyl cellulose, pigment, lactic acid, levulinic acid, and xylooligosaccharides and it has prospective in meeting the demand for global energy and environmental sustainability.

Recent Advances in Biomass Pretreatment Technologies for Biohydrogen Production

Hydrogen is an economical source of clean energy that has been utilized by industry for decades. In recent years, demand for hydrogen has risen significantly. Hydrogen sources include water electrolysis, hydrocarbon steam reforming, and fossil fuels, which emit hazardous greenhouse gases and therefore have a negative impact on global warming. The increasing worldwide population has created much pressure on natural fuels, with a growing gap between demand for renewable energy and its insufficient supply. As a result, the environment has suffered from alarming increases in pollution levels. Biohydrogen is a sustainable energy form and a preferable substitute for fossil fuel. Anaerobic fermentation, photo fermentation, microbial and enzymatic photolysis or combinations of such techniques are new approaches for producing biohydrogen. For cost-effective biohydrogen production, the substrate should be cheap and renewable. Substrates including algal biomass, agriculture residue, and wastewaters are readily available. Moreover, substrates rich in starch and cellulose such as plant stalks or agricultural waste, or food industry waste such as cheese whey are reported to support dark- and photo-fermentation. However, their direct utilization as a substrate is not recommended due to their complex nature. Therefore, they must be pretreated before use to release fermentable sugars. Various pretreatment technologies have been established and are still being developed. This article focuses on pretreatment techniques for biohydrogen production and discusses their efficiency and suitability, including hybrid-treatment technology.

Urea-pretreated corn stover: Physicochemical characteristics, delignification kinetics, and methane production

Solids loading is a key factor in aqueous or gaseous ammonia production from urea. Methane production from urea-pretreated corn stover, as well as the physicochemical characteristics and delignification kinetics of the corn stover, were investigated with four solids loading values (10%-70%) and five ratios of urea to corn stover (1:100-7:10) at 35 °C for 6 weeks. A 1:20 ratio of urea to corn stover was optimal for achieving high lignin removal with ≤50% solids loading, and 7:10 was optimal with 70% solids loading. Under the two optimal conditions, 85.56% and 82.35% of cellulose and 85.76% and 85.49% of hemicellulose were retained. The maximum lignin removal rates of 69.67% and 68.27% and methane production of 294.70 and 292.56 L/kg volatile solids (VS) were achieved, respectively. The delignification kinetics of the urea-pretreated corn stover conformed to three first-order reactions. Most of the lignin was degraded within the first 3 weeks.

Recent advances on ammonia-based pretreatments of lignocellulosic biomass

Ammonia-based pretreatments have been extensively studied in the last decade as one of the leading pretreatment technologies for lignocellulose biorefining. Here, we discuss the key features and compare performances of several leading ammonia-based pretreatments (e.g., soaking in aqueous ammonia or SAA, ammonia recycled percolation or ARP, ammonia fiber expansion or AFEX, and extractive ammonia or EA). We provide detailed insight into the distinct physicochemical mechanisms employed during ammonia-based pretreatments and its impact on downstream bioprocesses (e.g., enzymatic saccharification); such as modification of cellulose crystallinity, lignin/hemicellulose structure, and other ultrastructural changes such as cell wall porosity. Lastly, a brief overview of process technoeconomics and environmental impacts are discussed, along with recommendations for future areas of research on ammonia-based pretreatments.

Understanding the Impacts of AFEX™ Pretreatment and Densification on the Fast Pyrolysis of Corn Stover, Prairie Cord Grass, and Switchgrass

Lignocellulosic feedstocks corn stover, prairie cord grass, and switchgrass were subjected to ammonia fiber expansion (AFEX™) pretreatment and densified using extrusion pelleting and ComPAKco densification technique. The effects of AFEX™ pretreatment and densification were studied on the fast pyrolysis product yields. Feedstocks were milled in a hammer mill using three different screen sizes (2, 4, and 8 mm) and were subjected to AFEX™ pretreatment. The untreated and AFEX™-pretreated feedstocks were moisture adjusted at three levels (5, 10, and 15 % wb) and were extruded using a lab-scale single screw extruder. The barrel temperature of the extruder was maintained at 75, 100, and 125 °C. Durability of the extruded pellets made from AFEX™-pretreated corn stover, prairie cord grass, and switchgrass varied from 94.5 to 99.2, 94.3 to 98.7, and 90.1 to 97.5 %, respectively. Results of the thermogravimetric analysis showed the decrease in the decomposition temperature of the all the feedstocks after AFEX™ pretreatment indicating the increase in thermal stability. Loose and densified feedstocks were subjected to fast pyrolysis in a lab-scale reactor, and the yields (bio-oil and bio-char) were measured. Bio-char obtained from the AFEX™-pretreated feedstocks exhibited increased bulk and particle density compared to the untreated feedstocks. The properties of the bio-oil were statistically similar for the untreated, AFEX™-pretreated, and AFEX™-pretreated densified feedstocks. Based on the bio-char and bio-oil yields, the AFEX™-pretreated feedstocks and the densified AFEX™-pretreated feedstocks (pellets and PAKs) exhibited similar behavior. Hence, it can be concluded that densifying the AFEX™-pretreated feedstocks could be a viable option in the biomass-processing depots to reduce the transportation costs and the logistical impediments without affecting the product yields.