An official website of the United States government
Zeolites (ZSM-5 and Beta) with different SiO2/Al2O3 ratios were synthesized as solid acids for hydrolyzing cellulose in an inorganic ionic liquid system (lithium bromide trihydrate solution, LBTH) under mild conditions. The results indicated that the texture properties of zeolite had little effect on catalytic activity, while acidity of zeolite was crucial to the cellulose hydrolysis. In the LBTH system, H-form zeolites released H+ into the solution from their acid sites via ion-exchange with Li+, which hydrolyzed the cellulose already dissolved. This unique homogeneous hydrolysis mechanism was the primary reason for the excellent performance of the zeolites in catalyzing cellulose hydrolysis in the LBTH system. It was found cellulose could be completely hydrolyzed to glucose and oligoglucan by 2% (w/w on cellulose) zeolite at 140 °C within 3 h with a single-pass glucose yield 61%. The zeolites could be recovered with 50% initial catalytic activity after regeneration and reused with stable catalytic activity.
more »
« less
Reaction engineering implications of cellulose crystallinity and water-promoted recrystallization
Mechanical decrystallization and water-promoted recrystallization of cellulose were studied to understand the effects of cellulose crystallinity on reaction engineering models of its acid-catalyzed hydrolysis. Microcrystalline cellulose was ball-milled for different periods of time, which decreased its crystallinity and increased the glucose yield obtained from acid hydrolysis treatment. Crystallinity increased after acid hydrolysis treatment, which has previously been explained in terms of rapid hydrolysis of amorphous cellulose, despite conflicting evidence of solvent promoted recrystallization. To elucidate the mechanism, decrystallized samples were subjected to various non-hydrolyzing treatments involving water exposure. Interestingly, all non-hydrolyzing hydrothermal treatments resulted in recovery of crystallinity, including a treatment consisting of heat-up and quenching that was selected as a way to estimate the crystallinity at the onset of hydrolysis. Therefore, the proposed mechanism involving rapid hydrolysis of amorphous cellulose must be incomplete, since the recrystallization rate of amorphous cellulose is greater than the hydrolysis rate. Several techniques (solid-state nuclear magnetic resonance, X-ray diffraction, and Raman spectroscopy) were used to establish that water contact promotes conversion of amorphous cellulose to a mixture of crystalline cellulose I and cellulose II. Crystallite size may also be reduced by the decrystallization-recrystallization treatment. Ethanolysis was used to confirm that the reactivity of the cellulose I/cellulose II mixture is distinct from that of truly amorphous cellulose. These results strongly point to a revised, more realistic model of hydrolysis of mechanically decrystallized cellulose, involving recrystallization and hydrolysis of the cellulose I/cellulose II mixture.
more »
« less
- Award ID(s):
- 1726346
- PAR ID:
- 10188525
- Date Published:
- Journal Name:
- Green Chemistry
- Volume:
- 21
- Issue:
- 20
- ISSN:
- 1463-9262
- Page Range / eLocation ID:
- 5541 to 5555
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Solid acids as heterogeneous catalysts for cellulose hydrolysis have drawn increasing attention; however, current solid acids face challenges such as high catalyst loading (low catalytic activity), poor catalyst-substrate interaction, deficient hydrothermal stability, and unsatisfactory recyclability. This review critically discussed the recent efforts and progress in overcoming the issues of solid acids and developing high-performance solid acids for hydrolyzing cellulose. The key structural features of solid acids and their effects on the interactions with cellulose and cellulose hydrolysis were addressed in detail. Strategies and perspectives to enhance performance, hydrothermal stability and recyclability of solid acids were provided.more » « less
-
This study focuses on the development of environmentally sustainable polypropylene (PP)-based composites with the potential for biodegradability by incorporating cellulose and the oligomeric siloxane ES-40. Targeting industrial applications such as fused deposition modeling (FDM) 3D printing, ES-40 was employed as a precursor for the in situ formation of silica particles via hydrolytic polycondensation (HPC). Two HPC approaches were investigated: a preliminary reaction in a mixture of cellulose, ethanol, and water, and a direct reaction within the molten PP matrix. The composites were thoroughly characterized using rotational rheometry, optical microscopy, differential scanning calorimetry, and dynamic mechanical analysis. Both methods resulted in composites with markedly reduced crystallinity and shrinkage compared to neat PP, with the lowest shrinkage observed in blends prepared directly in the extruder. The inclusion of cellulose not only enhances the environmental profile of these composites but also paves the way for the development of PP materials with improved biodegradability, highlighting the potential of this technique for fabricating more amorphous composites from crystalline or semi-crystalline polymers for enhancing the quality and dimensional stability of FDM-printed materials.more » « less
-
Polyvinyl chloride (PVC) containing municipal solid waste (MSW) streams are difficult to recycle and mostly landfilled due to various detrimental effects PVC causes to waste recycling. In this work, a single-step upcycling of PVC-containing commingled wastes in tetrahydrofuran was investigated using cellulose, PVC, polyethylene (PE), polypropylene (PP), and polystyrene (PS) to model the wastes. During the co-conversion, in-situ produced HCl derived from PVC decomposition acted as an acid catalyst to selectively decompose cellulose into liquid mainly containing levoglucosan (LGA) and furfural. It was also found that the presence of PE, PP, and PS in the mixture synergistically enhanced the cellulose-derived monomer productions and increased the reaction rate for producing the monomers by suppressing secondary reactions of HCl in the solvent. The maximum LGA yield from co-conversion of cellulose, PVC, and PS was 35.4% after a 5 min reaction compared to the 31.7% obtained without PS in the mixture. In addition to converting cellulose to chemicals, PVC-derived polyaromatics and partly decomposed PE, PP, and PS were recovered as solids. The dechlorinated solids had higher heating values up to 46.11 MJ/kg, achieved by co-converting cellulose, PVC, and PP. When used as oil absorbents in water, the solid recovered from converting cellulose, PVC, and PE mixture showed the highest absorption capability. Overall, the presented approach offers a promising way for upcycling PVC-containing wastes in which PVC properties and its molecular structure are leveraged to enhance the conversion.more » « less
-
Abstract Metal‐containing polymers represent an ever‐expanding frontier of material science. Of the numerous biocompatible ligands used to create a metallopolymer, piperazine‐containing polymers are still in their early development, even though piperazine is a common functional group in drug design and bioengineering scaffolding elements. We report the first synthesis and characterization (with NMR, IR, GPC, UV–vis spectroscopy, and thermal analysis) of two thermoplastic poly(alkyl piperazine succinate) diols with either propyl or hexyl alkane chains bridging the piperazines. These polyester diols were then chain extended with hexamethylene diisocyanate to create highly amorphous polyester urethane thermoplastic polymers. Ru(III) or Fe(III) was then successfully coordinated with these polymers, with approximately 30% of the bulk metallopolymer product becoming 250x the molecular weight of the non‐metal containing polymers. However, coordination of Fe(III), and to a lesser extent Ru(III), to these polypiperazines accelerated the hydrolysis of the polyester linkage in water over 15 days. Thus, these novel polymers are highly biodegradable with Fe(III) metallopolymers hydrolyzing faster than Ru(III) metallopolymers and poly(propyl piperazine succinate) polymers hydrolyzing faster than poly(hexyl piperazine succinate) polymers.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9GC02466B
