Depolymerization Products Research Articles

Abundance and characteristics of lignin liquid intermediates in wood (Pinus ponderosa Dougl. ex Laws.) during hot water extraction

The objective of this research was to investigate the effects of the conditions of hot water extraction (HWE) on abundance, properties, and structure of lignin depolymerization products. HWE of extracted softwood (ponderosa pine) was conducted using temperatures from 140 to 320 °C for 90 min. HWE materials were then subjected to a soxhlet extraction process using dichloromethane (DCM). The composition and molecular weight of this DCM-soluble material was conducted using semi-quantitative Py-GC/MS and ESI/MS, which showed that this material is rich in lignin with low molecular weight (<1200 g mol−1) and low polydispersity (∼1.4). The highest yield of this material (∼4.2%) was obtained in material processed at 260 °C. Py-GC/MS of the solid fraction after the DCM process showed a progressive reduction of products of the pyrolysis of lignin as the HWE temperature increased. This finding suggests that the lignin content in the solid decreased due in part to migration from the cell walls and middle lamella to the particles surfaces, particularly the inner surface of the cells. SEM and AFM techniques helped to visualize the ability of this DCM-soluble extract to adhere to cellulosic fibers. Therefore, this lignin-rich material presents properties that depend on the conditions of the operation. Results indicate that during HWE it is possible to control the process parameters to limit or increase the amount of DCM-soluble lignin and its properties as required for downstream processes.

Elucidation of the different devolatilisation zones of tyre rubber pyrolysis using TGA-MS

The presented derivative thermogravimetric and mass spectral data, obtained simultaneously for the pyrolysis of three different tyre rubbers, corroborate the assumption that the devolatilisation of a tyre rubber proceeds via two consecutive zones of weight loss and that these zones are characterised by different products and thus different reactions. The spectral data of the depolymerisation products moreover confirm that depolymerisation occurs exclusively (in case of polyisoprene rubber) or predominantly (in case of the polybutadiene rubbers) during primary devolatilisation.

Lewis-acid catalyzed depolymerization of Protobind lignin in supercritical water and ethanol

The use of metal acetates, metal chlorides and metal triflates as Lewis acid catalysts for the depolymerization of soda lignin under supercritical conditions was investigated. The reactions were carried out at 400°C in water and ethanol. Lignin conversion in supercritical water led to formation of insoluble char and resulted in low yields of monomeric products. When the reaction was performed in supercritical ethanol, char formation was inhibited and higher yields of low molecular-weight organic products were obtained. The ethanol solvent was also converted in two ways. Firstly, the lignin depolymerization products were alkylated by ethanol. Secondly, ethanol was converted into a range of higher hydrocarbons including paraffins and olefins. Possible mechanisms of the lignin and ethanol conversion reactions are discussed.

Obtaining Carbon Dendrites from the Products of Conversion of Polymer Materials

In the work we give the results of an experiment during which carbon dendrite structures were formed in the plasma of an atmospheric-pressure gas discharge by using depolymerization products of polymer materials.

Efficient valorization of lignin depolymerization products in the present of NixMg1−xO

Efficient conversion of lignin depolymerization products to more stable chemicals has attracted increasing attention during last few years. Here, we reported a novel and efficient method for lignin depolymerization products valorization on the simple and economic catalyst NixMg1−xO. In which, the unsaturated ingredients were converted to thermal and chemical stable products, resulting in the obvious decreasing of the unsaturated degree of the products and the repolymerization of the phenolic oligomer. The results showed that more than 98% of phenol, a model chemical of lignin depolymerization products, could be converted to cyclohexanol with 100% selectivity. Further investigation demonstrated that it was also efficient for the real lignin depolymerization products, where a significant decrease on the oxygen content and the average molecular weight were shown. Moreover, the NixMg1−xO catalyst was recyclable, and no significant loss of the catalytic activity was exhibited even after 5 runs.

Defective structure and reactivity of mechanoactivated magnesium/fluoroplastic energy-generating composites

Mechanical activation has been employed to produce highly reactive energy-saturated Mg/(-C2F4-)n composites, chemical transformations in which are initiated by either heating or shock-wave loading. The structure and reactivity of these composites have been analyzed with the use of X-ray diffraction, microscopy, thermogravimetry, calorimetry, and the measurement of combustion and detonation velocities. Mechanical activation is accompanied by the formation of a magnesium/fluoroplastic composite structure with the intercomponent contact area as large as 6 m2/g and accumulation of chaotically arranged dislocations to concentrations as high as 6 × 1010 cm−2, basal and prismatic deformation stacking faults (the maximum probabilities of their formation are 2.1 and 1.4%, respectively), and boundaries of coherent-scattering regions in magnesium. In fluoroplastic, disordering and partial amorphization of the structure take place. Mechanical activation leads to a dramatic increase in the propagation velocity of Mg + (-C2F4-)n → MgF2 + C chemical reaction in the explosive combustion regime (to 400 m/s) and the development of knocking combustion, in which the reaction propagates at a velocity as high as 1100 m/s. The optimal dose of mechanical activation (7–8 kJ/g), at which the maximum velocity of reaction propagation is reached, has been determined. The use of a “slow” heating in the cell of a calorimeter in combination with the mass-spectral analysis of evolved gases has made it possible to distinguish processes of three types in the thermally activated interaction between magnesium and fluoroplastic. The formation of MgF2 at temperatures below 300°C seems to be due to the interaction between defects in magnesium (dislocations and stacking faults) and macromolecules. The reaction occurring at 300–420°C with a slight thermal effect is caused by the solid-phase interaction between magnesium and fluoroplastic brought in contact with one another. The main contribution to the conversion is made by the processes that take place at temperatures above 420°C and are relevant to the thermal depolymerization of fluoroplastic. The layered structure of the composite and the large area of the intercomponent contact ensure the penetration of gaseous products of depolymerization into the bulk of magnesium particles and the completeness of the interaction.

Natural aluminosilicates for catalytic depolymerization of polyethylene to produce liquid fuel-grade hydrocarbons and low olefins

Different chemical modifications were performed to the natural aluminosilicate Montanit300® in order to improve its catalytic activity in PE depolymerization. Performance of such prepared catalysts was compared to established solid acid catalysts, such as HZSM-5, sulfonated and fluorinated γ-Al2O3 and amorphous silica–alumina. Pyridine TG and DRIFTS characterization revealed mild acid treatment and aluminum grafting as successful in increasing acid site density through impurity removal and specific surface area increase. Mesoporous catalyst structure that allows facile diffusion through its pore network, together with high-density Brønsted acid sites, was found to be crucial to obtain high catalytic activity. The T50 value for PE depolymerization was lowered by 162°C with sulfonated γ-Al2O3 solid, compared to non-catalyzed reaction, whereas with aluminum-grafted Montanit300® catalyst this value was lowered by 65°C. PE depolymerization products present in the condensed liquid phase using aluminum-grafted Montanit300® catalyst were exclusively alkanes with chain length up to 21 carbon atoms. Liquid, coke and gas yields were found to be 53, 0.4 and 46.6%, respectively, the latter consisting of linear and branched C2–C4 alkenes and alkanes.

Iron‐catalyzed depolymerizations of silicones with hexanoic anhydride provide a potential recycling method for end‐of‐life polymers

One of the great impacts of polymeric materials is the matter of the accumulation of huge amounts of end‐of‐life polymers. At the present date, waste management is based primarily on landfills, thermal recycling, and down‐cycling, while only a small part of the waste is subjected to feedstock recycling. In more detail, polymers are converted to low‐molecular weight synthons by depolymerization and a subsequent polymerization process creates new high‐quality polymers. Widely‐used polymers in modern society are polysiloxanes (silicones) and recycling is still an issue. In this regard, we present herein the depolymerization of polysiloxanes, applying a fatty acid anhydride as the depolymerization reagent. In the presence of catalytic amounts of iron salts, low‐molecular weight products with the motif RC(O)(OSiMe2)mOC(O)R (R = n‐pentyl, m = 1–4) were observed. Notably, the reaction of RC(O)(OSiMe2)mOC(O)R with water revealed the formation of octamethylcyclotetra‐ and decamethylcyclopentasiloxanes and the corresponding fatty acid as side product, which can potentially be reconverted to the fatty acid anhydride. Interestingly, a recycling of the polymer and the depolymerization reagent is feasible.Practical applications: Huge amounts of end‐of‐life polymers are produced by our society and several methodologies for waste treatment have been established so far. One interesting recycling approach can be the conversion of end‐of‐life polymers, via depolymerization, into useful commodities, which can be applied as feedstock for new materials. Taking these aspects into account we studied the depolymerization of end‐of‐life polysiloxanes, applying cheap and abundant iron salts as a precatalyst and a fatty acid anhydride as a depolymerization reagent, which can be easily accessed from renewable resources, hence avoiding the use of fossil fuels‐based chemicals. As major products RC(O)(OSiMe2)mOC(O)R were obtained, these can be utilized as starting material for new polysiloxanes. Moreover, the simple operation of the reaction (e.g., no protection atmosphere, solvent free) makes this recycling method attractive for large scale applications.In the present work, the straightforward iron‐catalyzed depolymerization of end‐of‐life polysiloxanes with a fatty acid anhydride has been studied. Depolymerization products RC(O)O(SiMe2)mOC(O)R have been produced, which can be appropriate starting materials for new polymers.

Cu–Mo doped zeolite ZSM-5 catalyzed conversion of lignin to alkyl phenols with high selectivity

Challenging issues of lignin conversion processes including char formation, lower degree of depolymerization and lower product yield with no selectivity are worked out in this study.

Production of Hydrocarbons via Hydrodeoxygenation of Lignin-Derived Phenolic Compounds

Lignin is the component with the highest carbon content in biomass. The transformation of lignin to high-grade liquid fuels can be achieved via hydrodeoxygenation(HDO) of phenolic intermediates derived from the products of lignin depolymerization. The octane numbers of the hydrodeoxygenation products of phenolic intermediates are quite high. They have vapor pressures and carbon atom number (C6 similar to C10) within the range of gasoline. Thus, these hydrodeoxygenation products would be the most desirable components for a fungible liquid transportation fuel. This is very meaningful to application of lignin. Recently, researches about the hydrodeoxygenation of phenolic compounds develop rapidly. In this paper, the HDO reactions of phenolic compounds using sulfided Mo-based catalyst, noble metal catalyst and inexpensive non-sulfided catalyst are reviewed in detail. It is found that most of the investigated catalysts are bifunctional catalysts, combining the hydrogenation function of active metal with hydrolysis and dehydration of support. The catalytic mechanism for the HDO of phenolic compounds is sketched, and the effects of catalyst supporter on the catalytic activity are also discussed. Furthermore, the current technique challenges are summarized, and future technologic explorations for the efficient hydrodeoxygenation of lignin-derived phenolic compounds are proposed.

Kinetics and Thermodynamic Studies of Depolymerization of Nylon Waste by Hydrolysis Reaction

Depolymerization reaction of nylon waste was carried out by hydrolysis reaction. Yield of depolymerization products was up to 72.20% for a two-hour reaction time. The products obtained were characterized by melting point and FTIR spectra. The values obtained for dibenzoyl derivative of hexamethylenediamine (DBHMD) agreed with those of the pure substance. Chemical kinetics of this reaction shows that it is a first-order reaction with respect to hexamethylenediamine (HMD) concentration with velocity constant 7.32×10-3 min−1. The energy of activation and Arrhenius constant obtained by Arrhenius plot were 87.22 KJg−1 and 0.129, respectively. The other thermodynamic parameters such as enthalpy of activation (ΔH‡) and entropy of activation (ΔS‡) and free energy of activation were 5975.85 J and −270.86 J·K−1·mol−1 and 101.59 KJ·mol−1, respectively.

Solvent effect on HZSM-5 catalyzed solvolytic depolymerization of industrial waste lignin to phenols: superiority of the water–methanol system over methanol

Kraft lignin from industrial black liquor was subjected to one-pot solvolytic depolymerization and hydrodeoxygenation over zeolite HZSM-5 as catalyst and NaOH as co-catalyst at 220 °C. The effect of methanol and a water–methanol (1:1) mixture as solvent on the lignin depolymerization products was studied. The products were characterized by infrared spectroscopy and numerical indices based on IR spectra of the product mixture were defined to study the functional group transformations occurring in the reaction. Compared to NaOH in pure methanol, NaOH in water–methanol was found to be efficient in suppressing char formation and enhancing product quality and quantity. Alkyl substituted phenols were found to be the major product (14.1 wt%). Other than phenols, formation of long chain aliphatic compounds was also observed.

Recent Developments in the Chemical Recycling of Postconsumer Poly(ethylene terephthalate) Waste

Global production and consumption of poly(ethylene terephthalate) (PET) products has increased dramatically over the past few decades. World consumption of PET has exceeded 13 million tonnes, of which about 1.5 million tonnes is exclusively consumed by the packaging sector itself. However, this tremendous increase in PET consumption has resulted in the accumulation of an enormous quantity of waste, the disposal of which is complex day by day. Among different PET recycling methods, chemical recycling (chemolysis) is the most successful method to convert PET into its monomers/oligomers. This review presents in detail recent developments in the chemical recycling (glycolysis and aminolysis) of PET. The wide spectrum of depolymerizing agents used, the reaction conditions, catalysts, products of depolymerization, and their potential applications are described.

Disassembly and reassembly of polyhydroxyalkanoates: Recycling through abiotic depolymerization and biotic repolymerization

An abiotic–biotic strategy for recycling of polyhydroxyalkanoates (PHAs) is evaluated. Base-catalyzed PHA depolymerization yields hydroxyacids, such as 3-hydroxybutyrate (3HB), and alkenoates, such as crotonate; catalytic thermal depolymerization yields alkenoates. Cyclic pulse addition of 3HB to triplicate bioreactors selected for an enrichment of Comamonas, Brachymonas and Acinetobacter. After each pulse, poly(3-hydroxybutyrate) (P3HB) transiently appeared: accumulation of P3HB correlated with hydrolysis of polyphosphate; consumption of P3HB correlated with polyphosphate synthesis. Cells removed from the cyclic regime and incubated with 3HB under nitrogen-limited conditions produced P3HB (molecular weight>1,000,000Da) at 50% of the cell dry weight (<8h). P3HB also resulted from incubation with acetate, crotonate, or a mixture of hydrolytic depolymerization products. Poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) resulted from incubation with valerate or 2-pentenoate. A recycling strategy where abiotic depolymerization of waste PHAs yields feedstock for customized PHA re-synthesis appears feasible, without the need for energy-intensive feedstock purification.

The optimization of the conversion of agricultural waste into volatile fatty acids under anaerobic conditions

The selection of a biocatalyst was performed and the first optimal microbial association was obtained. This association was capable of converting products of depolymerization of sawdust, straw, and lignin into volatile fatty acids with an acid-producing activity that was greater by 1.3 times than the initial methane activity. The largest percentages of butyric acid (40%) and ethanol (14%) were obtained from biomass out of straw in concentrations of soluble organic substances from 2.5 to 6.3 gCOD/L. Using biomass from sawdust and lignin at concentrations of organic substances from 4.0 to 8.0 gCOD/L and a duration of the conversion process of up to 18 days we obtained an output of butyric acid that was two times smaller than that on a biomass from straw.

Rapid Qualitative and Quantitative Analyses of Proanthocyanidin Oligomers and Polymers by UPLC-MS/MS

This paper presents the development of a rapid method with ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for the qualitative and quantitative analyses of plant proanthocyanidins directly from crude plant extracts. The method utilizes a range of cone voltages to achieve the depolymerization step in the ion source of both smaller oligomers and larger polymers. The formed depolymerization products are further fragmented in the collision cell to enable their selective detection. This UPLC-MS/MS method is able to separately quantitate the terminal and extension units of the most common proanthocyanidin subclasses, that is, procyanidins and prodelphinidins. The resulting data enable (1) quantitation of the total proanthocyanidin content, (2) quantitation of total procyanidins and prodelphinidins including the procyanidin/prodelphinidin ratio, (3) estimation of the mean degree of polymerization for the oligomers and polymers, and (4) estimation of how the different procyanidin and prodelphinidin types are distributed along the chromatographic hump typically produced by large proanthocyanidins. All of this is achieved within the 10 min period of analysis, which makes the presented method a significant addition to the chemistry tools currently available for the qualitative and quantitative analyses of complex proanthocyanidin mixtures from plant extracts.

Quality control of poly(methylphenyl)siloxanes by liquid chromatography and NMR spectroscopy

A procedure based on liquid chromatography and NMR spectroscopy was developed for controlling the quality of poly(methylphenyl)siloxanes prepared in industry by chemical ring opening of cyclosiloxanes with three (A3) and four (A4) units. The suggested procedure allows rapid analysis of poly(methylphenyl)siloxanes with determination of the following parameters: residual content of A3 and A4, overall molecular-weight distribution, fractional composition, and molecular characteristics. The results obtained also allow estimating the rheological characteristics of the polymers and the total content of depolymerization products in them.

Supported Pd Catalysts for the C—O Cleavage of the Lignin Derived Model Dimers through Intramolecular Hydrogenolysis Reaction

The selective depolymerization of the C—O ether bonds in lignin has attracted considerable attentions which would facilitate the valorization of lignin. The model compounds with β-O-4 type ether bonds were the most frequently stud- ied molecules. In this study, we used 2-(2-methoxyphenyl)oxy-1-phenethanol (1a) as model compound for the C—O cleav- age through intramolecular hydrogenolysis reaction. The hydroxymethyl group acted as the hydrogen source by dehydroge- nating over Pd catalysts. Then, the cleavage of C—O bond takes place on the supported Pd catalyst with Pd-H active species. All the catalysts were prepared and characterized by XRD, TEM and BET. Among different metal catalysts, Pd catalysts gave best results toward the C—O bond cleavage reaction. After that, the influences of solvent were studied and the best solvent was cyclohexane. Different additives such as acids and bases were also tested in the model reaction. The strong base (i.e. KOH) showed negative effect on the product yield, but a weak base (i.e. Na2HPO4) gave a promotion effect on the reaction. The result indicated that the modification of the Pd catalysts' supports would be a good option for the C—O bond cleavage reaction. Thus, different Pd catalysts with different supporting materials were prepared and tested, and found that MgO, a weak basic support, gave promoted performance on this reaction. Finally, to figure out the reaction pathway, the reaction mixtures with different reaction time were analyzed by GC-MS which showed that the ketone was the main intermediate of the reaction. The result indicated that the main route for the intramolecular hydrogenolysis reaction was (1) the dehydrogena- tion of -CCHOH to ketone to form Pd-H species and then (2) the C—O bond was cleavage by the Pd-H species to form the depolymerization products. Keywords lignin; depolymerization; Pd-catalyzed reaction; C—O bond cleavage; catalytic transfer hydrogenation

The use of aminolysis, aminoglycolysis, and simultaneous aminolysis–hydrolysis products of waste PET for production of paint binder

This work is concerned with the use of aminolysis, aminoglycolysis, and simultaneous aminolysis–hydrolysis products of waste PET for production of paint binder based on alkyd resin. For this purpose, first, aminolysis, aminoglycolysis, and simultaneous hydrolysis–aminolysis reactions of waste PET were carried out in the presence of different chemical agents in xylene medium at high pressures. Reactions of waste PET flakes obtained from grinding postconsumer water bottles were carried out in an autoclave at higher temperatures. Then, four alkyd resins, formulated to have oil content 40–50%, were prepared using these depolymerization products. One of resins is “reference alkyd resin” which was prepared by using soybean oil fatty acid, phthalic anhydride, glycerine, and ethylene glycol for comparison. Other three alkyds are “depolymerization product‐based alkyd resins” in which depolymerization products is used instead of ethylene glycol. Then, the physical and chemical surface coating properties and thermal behaviors of alkyd resins films were investigated comparatively. As a result, we concluded that aminolysis, aminoglycolysis, and simultaneous aminolysis‐hydrolysis products of waste PET are suitable for manufacturing both air drying and oven curing paint binder based on alkyd resins. The film prepared from alkyd resin based on simultaneous aminolysis‐hydrolysis product showed extremely good surface coating properties and thermal stability. POLYM. ENG. SCI., 54:2272–2281, 2014. © 2013 Society of Plastics Engineers

Arabinoxylan Oligosaccharide Hydrolysis by Family 43 and 51 Glycosidases from Lactobacillus brevis DSM 20054

Due to their potential prebiotic properties, arabinoxylan-derived oligosaccharides [(A)XOS] are of great interest as functional food and feed ingredients. While the (A)XOS metabolism of Bifidobacteriaceae has been extensively studied, information regarding lactic acid bacteria (LAB) is still limited in this context. The aim of the present study was to fill this important gap by characterizing candidate (A)XOS hydrolyzing glycoside hydrolases (GHs) identified in the genome of Lactobacillus brevis DSM 20054. Two putative GH family 43 xylosidases (XynB1 and XynB2) and a GH family 43 arabinofuranosidase (Abf3) were heterologously expressed and characterized. While the function of XynB1 remains unclear, XynB2 could efficiently hydrolyze xylooligosaccharides. Abf3 displayed high specific activity for arabinobiose but could not release arabinose from an (A)XOS preparation. However, two previously reported GH 51 arabinofuranosidases from Lb. brevis were able to specifically remove α-1,3-linked arabinofuranosyl residues from arabino-xylooligosaccharides (AXHm3 specificity). These results imply that Lb. brevis is at least genetically equipped with functional enzymes in order to hydrolyze the depolymerization products of (arabino)xylans and arabinans. The distribution of related genes in Lactobacillales genomes indicates that GH 43 and, especially, GH 51 glycosidase genes are rare among LAB and mainly occur in obligately heterofermentative Lactobacillus spp., Pediococcus spp., members of the Leuconostoc/Weissella branch, and Enterococcus spp. Apart from the prebiotic viewpoint, this information also adds new perspectives on the carbohydrate (i.e., pentose-oligomer) metabolism of LAB species involved in the fermentation of hemicellulose-containing substrates.