The first step to higher yields.
Pretreatment is often the second most expensive unit cost in the conversion of biomass to bio-products. The pretreatment process breaks down lignin and increases the accessibility of pre-treated biomass to saccharification.
We take a holistic approach to all unit operations, starting with pretreatment. Our focus is on final yield and product cost. We monitor important factors that could reduce fermentation or chemical conversion yields.
Getting the Most Value
In developing an optimum pretreatment process, we place importance on:
- The most effective pretreatment catalyst for a given feedstock
- The compatibility of the feedstock-pretreatment catalyst combination
- The possibility of generating co-products, primarily from lignin
- Opex and capex investments
- Energy requirements for solid-liquid handling, separation, etc.
- Co-product value and residue disposal costs at scale
An Optimum Pretreatment Process
Our capabilities help us design the best process for your specifications:
- A broad range of aqueous phase thermochemical pretreatment processes that are suitable for the widest range of biomass and feedstock
- The ability to combine two or more pretreatment processes to achieve the best results across downstream unit operations
- Careful analysis of factors that will achieve the best process economics
- Meticulous assessment of the feasibility of integrating with downstream technologies and deploying the technology at a commercial scale
Pretreatment Process Options
Mechanical Biomass Size Reduction
Reduction of particle size is often needed to make material handling easier and to increase the surface/volume ratio. Depending on the feedstock and the process, we can perform size reduction through knife milling or ball milling.
Dilute acid pretreatment primarily breaks the lignin-hemicellulose matrix, hydrolyzes and removes hemicellulose as xylose into the aqueous phase, and increases the porosity of the cell walls. This, in turn, increases the enzymes’ access to the surface of cellulose available in the residual biomass. This treatment is ideally suited for herbaceous biomass and agricultural residues, such as corn stover. However, risk of corrosion issues mandates the use of expensive corrosion resistant reactors. Rapid heating and cooling is also required to minimize the production of inhibitory products such as furfural and hydroxymethylfurfural.
In hydrothermal pretreatment the lignin-hemicellulose matrix is broken and hemicellulose is released into the aqueous phase, but mostly in the oligomeric form. To improve conversion yields, it is necessary to enzymatically or chemically hydrolyze the oligomers further. Herbaceous biomass and agricultural residues, such as corn stover, are suitable for this type of pretreatment. However, due to lack of corrosion issues, this pretreatment can be carried out in a stainless steel pressure vessel. Also, fast—but not necessarily rapid—heating and cooling processes are required to minimize the production of inhibitory products.
Alkali pretreatment provides the most effective method for breaking the ester bonds between lignin, hemicellulose, and cellulose and avoids fragmentation of the hemicellulose polymers. The reaction temperatures for this process are usually much lower, at 120C, but reaction times are much longer, in the order of several hours. Corrosion-resistant metal and rapid heating and cooling are not required for this process.
Certain ionic liquids are considered efficient and “green” biomass solvents. They can dissolve large amounts of biomass components in extremely mild conditions, with the possibility of recovering nearly 100% of the ionic liquids used at their initial degree of purity. The dissolution mechanism of ionic liquids results in cellulose that has decreased degree of crystallinity, enabling extremely fast enzymatic hydrolysis. Most ionic liquid pretreatments are feedstock agnostic and can be used for a wide range of feedstock ranging from herbaceous and woody biomass to agricultural residues and municipal solid waste.
Organosolv processes use an organic solvent or mixtures of organic solvents with water, sometimes with a dilute acid, for removal of lignin before enzymatic hydrolysis of the cellulose fraction. In addition to lignin removal, hemicellulose hydrolysis occurs when acid is included in the process, leading to improved enzymatic digestibility of the cellulose fraction. The benefits of Organosolv pretreatment include the production of high-quality lignin and the potential to reduce enzyme cost.
To avoid material loss, depending on the biomass and the type of pretreatment, solids are separated from the liquids before they go to saccharification. Inhibitors may stay in the liquid portion, which may or may not be added back to the downstream conversion process based on the sugar concentration in the aqueous phase.