Reducing acid in dilute acid pretreatment and the impact on enzymatic saccharification

Abstract

Dilute acid pretreatment is a leading pretreatment technology for biomass to ethanol conversion due to the comparatively low chemical cost and effective hemicellulose solubilization. The conventional dilute acid pretreatment processes use relatively large quantities of sulfuric acid and require alkali for pH adjustment afterwards. Significant amounts of sulfate salts are generated as by-products, which have to be properly treated before disposal. Wastewater treatment is an expensive, yet indispensable part of commercial level biomass-to-ethanol plants. Therefore, reducing acid use to the lowest level possible would be of great interest to the emerging biomass-to-ethanol industry. In this study, a dilute acid pretreatment process was developed for the pretreatment of corn stover. The pretreatment was conducted at lower acid levels than the conventional process reported in the literature while using longer residence times. The study indicates that a 50% reduction in acid consumption can be achieved without compromising pretreatment efficiency when the pretreatment time was extended from 1-5 min to 15-20 min. To avoid undesirable sugar degradation and inhibitor generation, temperatures should be controlled below 170°C. When the sulfuric acid-to-lignocellulosic biomass ratio was kept at 0.025 g acid/g dry biomass, a cellulose-to-glucose conversion of 72.7% can be achieved at an enzyme loading of 0.016 g/g corn stover. It was also found that acid loading based on total solids (g acid/g dry biomass) governs the pretreatment efficiency rather than the acid concentration (g acid/g pretreatment liquid). While the acid loading on lignocellulosic biomass may be achieved through various combinations of solids loading and acid concentration in the pretreatment step, this work shows that it is unlikely to reduce acid use without undermining pretreatment efficiency simply by increasing the solid content in pretreatment reactors, therefore acid loading on biomass is indicated to be the key factor in effective dilute acid pretreatment.

Understanding of alkaline pretreatment parameters for corn stover enzymatic saccharification

“…To achieve this goal, extremely high chemical loading and enzyme dosages were frequently used. Relatively little attention has been paid to process waste management, including chemical recovery and recycle, which has proven to be an indispensable component of the biorefineries [16]. A literature survey also indicates that both alkali concentration in pretreatment solution (g alkali/g pretreatment liquor or g alkali/L pretreatment liquor) and alkali loading based on biomass solids (g alkali/g dry biomass) have been widely used as indicators of alkali strength.…”

Cellulose Degradation by Sulfolobus solfataricus Requires a Cell-Anchored Endo-β-1-4-Glucanase

“…The high energy demand and waste production (coming from the harsh process parameters), together with the production of degradation compounds that can be toxic for a further fermentation step, shaped the research in developing a more sustainable mixed chemical-physical/ biological process (3,23,40,49). Nowadays, a first pretreatment step usually uses dilute acids and/or steam to weaken the crystalline structure of cellulose, followed by an enzymatic hydrolysis step where a cellulolytic enzyme mixture is added to convert the cellulose chains to glucose (1,3,12,15,19,36). The use of enzymes enables a reduction in the utilization of harsh chemicals and/or heat needed to produce fermentable sugars, raising the environmental feasibility of the process.…”

Newly isolated Penicillium oxalicum A592-4B secretes enzymes that degrade milled rice straw with high efficiency

“…For example, conversion rates of 80-90% can be achieved by pretreatment with dilute sulfuric acid, 23) dilute NaOH, 24,25) and AFEX. 26) This is because chemical treatments decrease lignin and hemicellulose contents and cause a swelling effect of cellulose in addition to the effects of milling treatments such as increased surface area and reduced cellulose crystallinity.…”