Novel Simulated moving bed technologies
Cellulose and hemicellulose from plants and other biomass can be hydrolyzed to produce sugars (i.e. glucose and xylose). Once these sugars are separated from other impurities, they can serve as feedstock in fermentation to produce ethanol (as fuels), lactic acid, or other valuable chemicals. The need for producing fuels and chemicals from renewable biomass has become abundantly clear over the last decade. However, the cost of producing fermentable sugars from biomass hydrolyzate using existing technology is relatively high and has been a major obstacle. The objective of this project is to develop an efficient and economical simulated moving bed (SMB) process to recover fermentable sugars from biomass hydrolyzate. Sulfuric acid can hydrolyze the cellulose and hemicellulose in biomass to sugars, but this process can generate byproducts such as acetic acid, and can lead to further degradation of the xylose to furfural and glucose to hydroxymethyl furfural (HMF). Also, lignin and other compounds in the biomass will degrade to various phenolic compounds. If the concentrations of these compounds exceed certain threshold levels, they will be toxic to the downstream fermentation, and will severely limit the usefulness of the derived sugars. Standard post-hydrolysis processing involves neutralization of sulfuric acid, usually with lime (calcium hydroxide). A study by Wooley et al.showed that the limed hydrolyzate gave a low ethanol yield in fermentation test (20% of theoretical yield compared to 77% of theoretical yield from fermentation of pure sugars). They showed that instead of adding lime, an ion exclusion chromatography process could be used to remove acids, as well as to isolate the sugars from the biomass hydrolyzate. In this project, we investigated the feasibility of developing an economical SMB process based on (1) a polymeric adsorbent, Dowex99, which was used by Wooley et al., (2) a second polymeric adsorbent, poly-4-vinyl pyridine (or PVP in short, Reilly Industries Inc., Indianapolis, IN), which has been used for organic acid separations, and (3) an activated carbon adsorbent. The adsorption isotherms and mass transfer parameters of the two polymeric adsorbents were estimated using single-component pulse tests and frontal tests. The parameters were then validated using batch elution chromatography test of a corn-stover hydrolyzate, which was provided gratis by NREL. The sugars recovered in batch chromatography were then fermented using yeast developed at Dr. Ho's LORRE laboratory. A standard mixture of pure sugars and an overlimed corn-stover hydrolyzate were fermented using the same procedure simultaneously. The fermentability of the overlimed hydrolyzate was the worst, and that of the sugars recovered using the PVP column was similar to that of the pure sugar mixture. The sugars recovered using the Dowex99 column had an intermediate fermentability. Since the sugars were the ''center cut'' in the Dowex99 column, a tandem SMB (two SMB's in series) design was needed to obtain sugars of high purity. By contrast, sugars were the fast-moving components in the PVP column, and only a single SMB was needed to recover sugars from the hydrolyzate. The impurities, such as sulfuric acid, acetic acid, HMF, and furfural, had higher affinities for PVP. Caustic regeneration was needed to efficiently remove these impurities from PVP. Therefore, a five-zone SMB, which includes a regeneration zone and a reequilibration zone, was developed. The isotherms and mass transfer parameters estimated from batch chromatography experiments were used in the design of SMB processes. A Standing Wave Design method was developed for the five-zone SMB and the tandem SMB. Cost analysis was carried out based on the resulting operating conditions. The analysis showed that the PVP five-zone SMB process was more economical than the Dowex99 tandem SMB process. The cost analysis also showed that elution and equipment costs are dominant for the Dowex99 SMB and the regeneration cost is dominant (60%) for the PVPSMB. Both the cost analysis and the fermentation tests of the sugars obtained from batch chromatography suggested that the PVP was a better choice than Dowex99. We thus focused on experimental testing of the PVP five-zone SMB. Three SMB experiments were conducted. The sugar yields were very high (> 99%), but the purities were from 93-95%.
- Research Organization:
- Golden Field Office, Golden, CO (US)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EE) (US)
- DOE Contract Number:
- /GO/11071
- OSTI ID:
- 828174
- Report Number(s):
- DE-FC36-01GO11071; TRN: US200430%%1053
- Resource Relation:
- Other Information: PBD: 30 Dec 2003
- Country of Publication:
- United States
- Language:
- English
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