Acid-catalyzed Depolymerization Research Articles

Selective oxidative devulcanization of hydrosilylation-cured silicone elastomers: enhanced circularity

Oxidative bromination of hydrosilylation cured silicone elastomers occurs much more rapidly than acid-catalyzed depolymerization. The β-effect facilitates SiC cleavage permitting decrosslinking to oils that can be reprocessed into RTV elastomers.

Depolymerization of hemicelluloses utilizing hydrothermal and acid catalyzed processes proceed by ultrafiltration as fractionation media

Replacement of fossil-based polymers is a current challenge, which needs a broad feedstock of bio-based substitutes produced with a reasonable CO2-footprint. As indigestible biopolymers ß-1,4-hemicelluloses were extracted with an extraction process without usage of chemicals from plant-based industrial residues as a heterogeneous mixture. Requirements for industrial applications as binder in coatings or printing inks the hemicelluloses need to be tailored in size and distribution. Solving these issues hydrothermal (HTD) and acid catalyzed depolymerization (ACD) are used to improve suitability of our hemicelluloses for various applications. Desired degree of polymerization (DP) below 15 could be achieved at 190 °C in 50 min with HTD and at 90 °C in 120 min with 1.5 wt% H2SO4 with ACD, which have been characterized by SEC-MALS-dRI, ATR-IR and elemental analysis. For further improvement of monodispersity and purification ultrafiltration was introduced as fractionation media with 1 and 4 kDa multi-channel ceramic membranes. With this process, hemicelluloses from food processing industry residues will be harnessed as a substitute for fossil-based polymers after tailoring molar mass distribution and chemical modification.

Sustainable production of dopamine hydrochloride from softwood lignin.

Dopamine is not only a widely used commodity pharmaceutical for treating neurological diseases but also a highly attractive base for advanced carbon materials. Lignin, the waste from the lignocellulosic biomass industry, is the richest source of renewable aromatics on earth. Efficient production of dopamine direct from lignin is a highly desirable target but extremely challenging. Here, we report an innovative strategy for the sustainable production of dopamine hydrochloride from softwood lignin with a mass yield of 6.4 wt.%. Significantly, the solid dopamine hydrochloride is obtained by a simple filtration process in purity of 98.0%, which avoids the tedious separation and purification steps. The approach begins with the acid-catalyzed depolymerization, followed by deprotection, hydrogen-borrowing amination, and hydrolysis of methoxy group, transforming lignin into dopamine hydrochloride. The technical economic analysis predicts that this process is an economically competitive production process. This study fulfills the unexplored potential of dopamine hydrochloride synthesis from lignin.

A solid acid-catalyzed depolymerization of pine lignin to obtain guaiacol using a hydrogen-free strategy

Guaiacol is an important raw material to produce many value-added chemicals. Here, we report a strategy for directly cleaving the Car-Cα and Cβ-O bonds in pine lignin over a solid acid to generate guaiacol. The guaiacol yield in 90% methanol aqueous solution is up to 18.2 wt%, which is 5.6 wt% higher than that in methanol. The reaction pathway is proposed by combining controlled experiments with density functional theory. Different from previous views, the Car-Cα bond cleavage was found to be related to deacetylation, while the formation of Cα=O bond was found to change the intramolecular charge distribution and promote the Car-Cα bond cleavage through validation experiments. Adding water promotes methanol decomposition to produce more active hydrogen species and thereby promote the Car-Cα bond cleavage. This work provided a feasible pathway for obtaining guaiacol by directly cleaving the Car-Cα and Cβ-O bonds in lignin.

Coupling Hydrophilic Interaction Chromatography and Reverse-Phase Chromatography for Improved Direct Analysis of Grape Seed Proanthocyanidins.

Acid-catalyzed depolymerization is recognized as the most practical method for analyzing subunit composition and the polymerization degree of proanthocyanidins, involving purification by removing free flavan-3-ols, as well as acid-catalyzed cleavage and the identification of cleavage products. However, after the removal of proanthocyanidins with low molecular weights during purification, the formation of anthocyanidins from the extension subunits accompanying acid-catalyzed cleavage occurred. Thus, grape seed extract other than purified proanthocyanidins was applied to acid-catalyzed depolymerization. Hydrophilic interaction chromatography was developed to quantify free flavan-3-ols in grape seed extract to distinguish them from flavan-3-ols from terminal subunits of proanthocyanidins. Reverse-phase chromatography was used to analyze anthocyanidins and cleavage products at 550 and 280 nm, respectively. It is found that the defects of the recognized method did not influence the results of the subunit composition, but both altered the mean degree of polymerization. The established method was able to directly analyze proanthocyanidins in grape seed extract for higher accuracy and speed than the recognized method.

Understanding Acid-Catalysed Lignin Depolymerisation Process by Model Aromatic Compound Reaction Kinetics

Understanding Acid-Catalysed Lignin Depolymerisation Process by Model Aromatic Compound Reaction Kinetics

Effective Biomass Fractionation through Oxygen-Enhanced Alkaline–Oxidative Pretreatment

The high recalcitrance of plant cell walls is an obstacle for effective chemical or biological conversion into renewable chemicals and transportation fuels. Here, we investigated the utilization of both oxygen (O₂) and hydrogen peroxide (H₂O₂) as co-oxidants during alkaline–oxidative pretreatment to improve biomass fractionation and increase enzymatic digestibility. The oxidative pretreatment of hybrid poplar was studied over a variety of conditions. Employing O₂ in addition to H₂O₂ as a co-oxidant during the two-stage alkaline pre-extraction/copper-catalyzed alkaline hydrogen peroxide (Cu-AHP) pretreatment process resulted in a substantial improvement in delignification relative to using H₂O₂ alone during the second-stage Cu-AHP pretreatment, leading to high overall sugar yields even at H₂O₂ loadings as low as 2% (w/w of the original biomass). The presence of H₂O₂, however, was both critical and synergistic. Performing analogous reactions in the absence of H₂O₂ resulted in approximately 25% less delignification and 30% decrease in sugar yields. The lignin isolated from this dual oxidant second stage had high aliphatic hydroxyl group content and reactivity to isocyanate, indicating that it is a promising substrate for the production of polyurethanes. To test the suitability of the isolated lignin as a source of aromatic monomers, the lignin was subjected to a sequential Bobbitt’s salt oxidation followed by a formic acid-catalyzed depolymerization process. Monomer yields of approximately 17% (w/w) were obtained, and the difference in yields was not significant between lignin isolated from our Cu-AHP process with and without O₂ as a co-oxidant. Thus, the addition of O₂ did not lead to significant lignin crosslinking, a result consistent with the two-dimensional heteronuclear single-quantum coherence NMR spectra of the isolated lignin.

Intermittent recycle-integrated reactor-separator for production of well-defined non-digestible oligosaccharides from oat β-glucan

A recycle-integrated reactor-separator system was studied experimentally and based on simulations for the acid-catalyzed depolymerization of oat beta-glucan polysaccharide. The aim was to produce oligosaccharides with degree of polymerization in a narrow range (DP = 15–30). The reactor was operated intermittently at 80 °C. Batch chromatography with Sephadex G-25 size-exclusion gel was found suitable for the separation of product from reactants and impurities. Part of the reaction mixture was periodically withdrawn and fed to the separation column. Molar mass distributions in four chromatographic fractions (waste, recycle, product, impurities) were monitored with SEC-MALLS. Experiments with 4 h mean residence time showed that the reactor-separator achieved approximately 2.0 and 2.5 times higher yield and purity of target DP than a batch reactor. Dimensionless operating parameters and equipment design parameters were introduced for analyzing performance of intermittent reactor-separators. The simulations show that intermittent operation offers higher yield and product purity than continuous operation (CSTR and chromatographic separation) when mean residence time in the reactor is long. Continuous operation is better when productivity is maximized by using short mean residence time and low yield.

Kinetic investigations of sulfite addition to flavanols

Flavanols are an important class of natural products occurring in almost all plants, fruits and vegetables; they have a great influence on wine ageing potential, astringency, colour stability and biological activities. In wine, flavanols react with sulfur dioxide (hbox {SO}_2), the most widely used preservative in oenology, leading to sulfonated products. Here we report a kinetic investigation, through LC-MS quantitative measurements carried out at different pH (3 and 4) and temperature values (23, 30, 40, 50 and 60, ^circ hbox {C}), of the reaction products obtained by hbox {SO}_2 addition to both monomeric (epicatechin and catechin) and dimeric flavanols (procyanidin B2 and procyanidin B3). The results proved that: (a) the major sulfonation route that leads quickly and in good yields to monomeric 4beta-sulfonated derivatives passes through the acid-catalysed depolymerisation of proanthocyanidins; (b) monomeric flavanols lead to the same 4beta-sulfonated products, although in a considerably slower manner, and also to other sulfonated regioisomers; (c) the kinetic data in our hands, in particular the temperature dependence of the observed rates, suggest the involvement of two completely different reaction mechanisms for the hbox {SO}_2 addition to dimeric and monomeric flavanol substrates; (d) direct sulfonation of epicatechin is slightly faster than that of catechin.

Pyrolysis of Humins Obtained from Acid-catalyzed Depolymerization of Rice Husk Cellulose: Model-free Approach to Non-isothermal Kinetics

Pyrolysis of Humins Obtained from Acid-catalyzed Depolymerization of Rice Husk Cellulose: Model-free Approach to Non-isothermal Kinetics

Using Lignin Monomer As a Novel Capping Agent for Efficient Acid-Catalyzed Depolymerization of High Molecular Weight Lignin to Improve Its Antioxidant Activity

In this work, a mild and efficient process for acid-catalyzed depolymerization of lignin to improve its antioxidant activity was proposed using lignin monomer, p-hydroxybenzyl alcohol (HBA), as a n...

Factors Influencing Cellulosic Sugar Production during Acid-Catalyzed Solvent Liquefaction in 1,4-Dioxane

This work explores the use of 1,4-dioxane to depolymerize cellulose into solubilized carbohydrates. This low boiling point solvent offers inexpensive and simple separation as compared to higher boiling point solvents such as γ-valerolactone previously considered for acid-catalyzed depolymerization of cellulose. In the present study, several key reaction parameters, including reaction temperature, catalyst concentration, and water content, were studied as major factors influencing sugar production from cellulose. A maximum yield of 51% for levoglucosan, the major product of cellulose depolymerization, was achieved at higher temperature, shorter reaction time, and lower acid concentration in the ranges tested for these parameters. Addition of water as cosolvent enhanced solubilization of cellulose and increased solubilized carbohydrate production, which could potentially enable processing of cellulose at high feedstock loadings and milder operating conditions.

Comprehensive Monosaccharide Composition Analysis of Insoluble Polysaccharides by Permethylation To Produce Methyl Alditol Derivatives for Gas Chromatography/Mass Spectrometry.

Knowledge of the monosaccharide composition of plant and microbial cell wall polysaccharides is critical for the understanding of polysaccharide structure and function. Differences in the hydrolytic stability of the glycosidic bonds and in the susceptibility of monosaccharides to acid-catalyzed degradation cause inconsistency of signal response in the common glycosyl composition methods. In addition, many polysaccharides are insoluble, partially soluble, or form highly viscous gels in water, and this also hinders or even prevents detection by traditional methods. As a result, currently available methods for monosaccharide composition analysis lack accuracy and are limited to the soluble portions of biological samples or expose the polysaccharides to very harsh conditions, resulting in loss of less stable residues. Here we present a new approach to accomplish the monosaccharide composition analysis of polysaccharides, including those that are not or sparingly soluble, based on permethylation in DMSO as the initial derivatization step. Our key finding is that the permethylation solubilizes the polysaccharide before the hydrolysis step, so that differences in solubility are no longer a factor in the efficiency of the acid-catalyzed depolymerization. After the hydrolysis, the partially methylated monosaccharides are reduced to alditols and remethylated for GC/MS analysis. In addition to enabling composition analysis of insoluble polysaccharides, this method also has the advantages that it is comprehensive, allowing quantification of all types of sugars, including uronic acids, on the same column and gives consistent response factors for different monosaccharide classes.

Rapid determination of lignosulfonate depolymerization products by advanced polymer chromatography.

Depolymerized lignin products are very complex mixtures. Based on a depolymerization solution of commercially available sodium lignosulfonate under mild conditions, a fast and efficient method for the separation and direct characterization of the degree and efficiency of the acid-catalyzed depolymerization of lignin was developed in this study. Using an ultraviolet detector, the depolymerized lignosulfonate products were well separated and characterized according to the relative molar mass distribution on an advanced polymer chromatographic system with three ethylene-bridged hybrid columns having small pore sizes (45 Å) in series and tetrahydrofuran as the mobile phase. The developed advanced polymer chromatography method enabled the detection of low-molecular-weight lignin degradation products (Mn =260-1100Da) with high peak resolutions in less than 7.2min. Furthermore, preliminary advanced polymer chromatography studies to determine the influence of reaction temperature on the depolymerized products indicated that the depolymerized aromatics fell in several molecular weight ranges with an extremely low dispersity. This new approach can be used for the rapid analysis of lignin depolymerization products.

Katalin Barta

Katalin Barta

A rapid method based on advanced polymer chromatography for analyzing the products of the acid-catalyzed depolymerization of lignosulfonate

In this study, a fast and efficient method for the separation and analysis of the products in the acid-catalyzed depolymerization of commercially available sodium lignosulfonate has been developed. The depolymerized lignosulfonate products were well separated and characterized by advanced polymer chromatography (APC) employing four ACQUITY APC XT columns in series and a ultraviolet detector. The developed method enabled the detection of relative-low-molecular-mass lignin degradation products with peak molecular weights (Mp) of 720, 490, and 260 Da, and an extremely low polydispersity index (PDI) of 1, indicating almost complete conversion of lignosulfonate to smaller molecules. The effects of reaction temperature, time, and catalyst/lignin ratio on the reaction products were systematically investigated. High yields of depolymerization (>80%) could be obtained under the mild acid-catalyzed conditions at 130℃ for 60 min using a catalyst/lignin ratio of 2.334:1. Preliminary studies also indicated that the mild acid-catalytic mechanism is unaffected by the reaction time, temperature, or catalyst concentration, thus suggesting the specificity of the catalytic procedure employed.

Sorption-active transparent films based on chitosan

In this paper we describe the preparation of alkanoic acid-based aqueous chitosan solutions, which show no sign of acid-catalysed depolymerisation over time – something commonly accompanying other preparation methods. Longer chitosan chains have previously been shown to exhibit more advantageous biological activities, and constant viscosities are essential for consistent quality in biomedical applications. Avoiding acid-catalysed depolymerisation requires careful control of the stoichiometry between the free amino groups of chitosan and the appropriate solubilising acid. Acetic and butyric acid are both suitable solubilising agents, but chitosan butyrate exhibits lower solution viscosities due to a combined electric and steric shielding of the chains.These solutions dry into clear transparent films that remain fully water soluble and absorb up to 70 wt% of water from 90%-RH vapour phase at 25 °C. The absorption follows simple first-order kinetics and the rate constants increase with increasing humidity up to approx. 71%-RH, where a metastable chitosan trihydrate salt appears to be formed. Desorption is slightly faster, but more complex, as it exhibits two distinct first-order processes. In addition, films prepared in this way are thermally more stable than the usual chitosan hydrochloride.

Accelerated Thermal Depolymerization of Cyclic Polyphthalaldehyde with a Polymeric Thermoacid Generator.

Thermally triggerable polymer films that degrade at modest temperatures (≈85 °C) are created from a blend of cyclic polyphthalaldehyde (cPPA) and a polymeric thermoacid generator, poly(vinyl tert-butyl carbonate sulfone) (PVtBCS). PVtBCS depolymerizes when heated, generating acid which initiates the depolymerization of cPPA into volatile byproducts. The mass loss onset for 2 wt% PVtBCS/cPPA is 22 °C lower than the onset for neat cPPA alone in dynamic thermogravimetric analysis experiments. Increased concentrations of PVtBCS increase the rate of depolymerization of cPPA. Raman spectroscopy reveals that the monomer, o-phthalaldehyde, is the main depolymerization product of the acid-catalyzed depolymerization of cPPA. The PVtBCS/cPPA blend is a promising material for the design and manufacture of transient electronic packaging and polymers.

Catalytic Effects of Various Acids on Microwave-assisted Depolymerization of Organosolv Lignin

The catalytic effects of various acids (sulfuric acid, hydrochloric acid, phosphoric acid, and formic acid) on the depolymerization of organosolv lignin under mild microwave heating (approximately 100 W, 160 °C for 30 min) were investigated. The liquid product was separated from the solid residue and analyzed by gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The solid residue was analyzed with thermogravimetric analysis (TG-DTG) and observed by scanning electron microscopy (SEM). The experimental results showed that sulfuric acid exhibited a better catalytic effect than the other acids. The SEM and TG-DTG results showed that the solid residue from sulfuric acid-catalyzed depolymerization was not only remarkably smaller than that of the other groups, but also presented a faster thermal decomposition rate. The molecular weight (Mw, weight-average) of the liquid product (Mw = 1020) from sulfuric acid-catalyzed depolymerization was also lower than that of the other groups.

Furylated Flavonoids: Fully Biobased Building Blocks Produced by Condensed Tannins Depolymerization

An original method has been set up to produce fully biobased phenolic building blocks from condensed tannins, largely available from agroindustrial residues or wood industry coproducts. The acid-catalyzed depolymerization of condensed tannins in the presence of furan or sylvan in mild conditions (30–40 °C, 0.1 M HCl) gives the corresponding furylated flavonoids with high yields. The reaction was more efficient with sylvan than with the less nucleophilic furan. A key feature of the products is the high stability of the flavanyl to furyl C–C linkage compared to the thioether bond obtained by the classical thiolysis, which makes them promising platform molecules for further functionalization, including in alkaline conditions. The simplicity of the process makes it easy to scale-up, and the reaction can be carried out on raw plant materials directly. In accordance with green chemistry concepts, solvents and excess reagents can readily be recovered by distillation and recycled.