Published October 2018
Recent commercial developments in the cellulosic ethanol space demonstrate significant economic challenges facing the industry. Many demonstration and commercial plants have either been put on hold or the companies have been sold to other entities. For example, on 3 November 2017, DuPont announced that it had halted operations at its two-year-old cellulosic ethanol plant in Nevada, Iowa, and plans to sell it. Similarly, on 30 October 2017, M&G Group filed for bankruptcy, forcing Beta Renewables to shut down its cellulosic ethanol plant in Crescentino, Italy. IHS Markit PEP Report 263A, Cellulosic Bioethanol (November 2017) examined the production economics of cellulosic ethanol production. In that report, and in the wake of the aforementioned DuPont and Beta Renewables plant closures and the technology feasibility questions thus raised, it is evident that cellulosic ethanol production is not attractive from a cost perspective, and that many challenges need addressing. Biomass pretreatment is one of those challenges, as it alone accounts for a significant percentage of overall cellulosic ethanol plant cost. As such, in this report, we look very closely at different biomass pretreatment processes, addressing such questions as where the opportunities to reduce cost are and how we can improve the biomass pretreatment process.
Lignocellulosic biomass is an abundant, nonfood-based, sustainable, and low-cost resource to produce renewable fuels and chemicals. However, its inherent recalcitrance to biological conversion hinders its application for commercial production of biofuels. Therefore, a pretreatment step is applied to overcome that biomass recalcitrance prior to biological conversion. Worldwide research is being carried out to improve the pretreatment efficiencies by understanding the biomass recalcitrant structure and changes made by pretreatment to the biomass structure. In general, it is thought that the cell wall components, their distribution, and the inter- and intra-linkages between components influence biomass recalcitrance.
This report discusses different biomass pretreatment technologies in detail, including their reaction mechanisms, chemistry, operating conditions and efficiencies, different approaches to biomass pretreatment, and the advantages and disadvantages thereof. This report also highlights pretreatment effectiveness, severity, and selectivity. These technologies include steam explosion with dilute sulfuric acid (H2SO4), ammonia fiber expansion (AFEX), aqueous ammonia treatment, wet oxidation, treatment with liquid hot water, ionic liquid treatment, alkali treatment, and treatment with organic solvents (referred to as organosolv), among others. Almost all different biomass pretreatment techniques have been tested at lab or at demo scale for all different types of biomass. We have included comprehensive tables in this regard to help our readers categorize technology status, the type of biomass, and the type of pretreatment implemented in the plant. The main target product to date is ethanol for all of the techniques being considered herein.
For this report, we used Intelligen’s SuperPro Designer software to evaluate commercially implemented biomass pretreatment technologies including steam explosion with dilute H2SO4, ammonia fiber explosion (AFEX), and organosolv. For these cases, we provide design basis, process flow diagrams, material balances, equipment details, utility summaries, total capital investments, and production and variable costs.