Microwave-assisted Degradation Research Articles

From plastics to jet fuel range alkanes via combined catalytic conversions

High carbon yields of jet fuel range alkanes were observed from plastics through a novel route. The integral processes were mainly performed via the catalytic microwave-assisted degradation of low-density polyethylene (a model compound of plastics waste) followed by hydrogenation process. The catalytic microwave degradation was carried out at 375°C with catalyst to feed mass ratio of 0.1 or 0.2 to manufacture distinct proportions of aliphatic and cyclic hydrocarbons. It was observed that the carbon yields of the raw organics from the catalytic microwave degradation were 66.18 and 56.32%, respectively. Several variables were employed to estimate the optimal conditions for the production of alternative jet fuels in the hydrogenation process. With the presence of 10 or 20wt% well-promoted ZSM-5 catalyst, the overall carbon yields of hydrogenated organics regarding raw plastics were approximately 54 or 63%. The alterations of reaction conditions did not have a remarkable effect on the overall carbon yield of hydrogenated organics. The raw organics (with the higher yield) could be hydrogenated to fit JP-5 navy fuel at 200°C for 2h using the 10wt% Raney Ni catalyst; while the raw organics (with the lower yield) could be hydrogenated to match high energy-density jet fuels (e.g. RJ-5 and JP-10) under very low-severity conditions. During the hydrogenation process, home-made Raney Ni catalyst showed more notable catalytic performance than that of as-purchased Raney Ni 4200 catalyst. In this regard, the catalytic conversions of plastics can be regarded as a clear breakthrough to produce various grades of jet fuels.

Synthesis of high-density jet fuel from plastics via catalytically integral processes

Synthesis of high density jet fuel from plastics via catalytic microwave-assisted degradation and a hydrotreating process.

Effect of pH on the microwave-assisted degradation of methyl orange using poly(1-naphthylamine) nanotubes in the absence of UV–visible radiation

Microwave-assisted degradation of dyes is being extensively investigated for wastewater remediation. The present work reports, for the first time, degradation of methyl orange (MeO) in neutral, acidic, and basic media under microwave irradiation using semiconducting polymer [poly(1-naphthylamine) (PNA)] nanotubes as catalyst in the absence of any light source. Degradation of the dye was followed spectrophotometrically and by total organic content (TOC) analysis. In the presence of poly(1-naphthylamine), microwave irradiation in 15 min caused 70, 84, and 64 % degradation at 280 nm, while at 460 nm the degradation values were 80, 96 and 78 % of MO in neutral, acidic, and basic media, respectively. The degradation of the dye in the absence and presence of PNA catalyst and in acidic, basic, and neutral media followed first-order rate kinetics. Rate constant, k, values were found to be slightly dependent on the pH of the dye solutions. Liquid chromatography–mass spectroscopy analysis confirmed that dye degrades into smaller fragments of low molar masses.

A Closed-Loop Process from Microwave-Assisted Hydrothermal Degradation of Starch to Utilization of the Obtained Degradation Products as Starch Plasticizers

A green closed-loop water-based process for chemical recycling of starch was demonstrated. The process starts from microwave-assisted controllable starch degradation to functional chemicals and continues to utilization of the formed degradation products, glucose and levulinic acid (LA), as starch plasticizers. The degradation process and the effect of process parameters on the formed degradation products and residues were carefully fingerprinted by multiple techniques, e.g., NMR, ESI-MS, FTIR imaging, UV–vis, and SEM. The degradation process took place in three steps, proceeding from rupture of starch granules and oligosaccharide formation to further hydrolysis to glucose. Finally, at well-defined time point rapid degradation of glucose to LA and formic acid (FA) was initiated through a 5-hydroxymethyl furfural (5-HMF) intermediate. 5-HMF also participated in carbonization reactions leading to formation of solid carbon spheres. Through selection of processing parameters, LA could be produced in high yield with 95% selectivity. The results demonstrated that microwave-assisted degradation of starch leads to well-defined controllable degradation products. These products are directly reusable as plasticizers for new starch products, which suggest great opportunities for biomass and starch recycling, opening the door toward potential industrial applications.

Microwave-Assisted Reaction in Green Solvents Recycles PHB to Functional Chemicals

An efficient microwave-assisted process for chemical recycling of poly(3-hydroxybutyrate) (PHB) in green solvents was demonstrated. Previously, PHB has been thermally recycled to crotonic acid and unsaturated oligomers. Our aim was to utilize green solvents (water, methanol, and ethanol) under alkaline conditions to achieve fast hydrolysis and monomeric or oligomeric degradation products with carboxyl and hydroxyl or methoxy or ethoxy end groups. Preliminary screening confirmed that the most efficient degradation process was obtained in alkaline methanol. In addition, sample amount, sodium hydroxide concentration, and degradation time all influenced the degradation process and final degree of degradation. Comparison with pure thermal degradation clearly demonstrated the effectiveness of the microwave-assisted process as the time and temperature needed for complete degradation was significantly reduced. Several characterization techniques were utilized for mapping the degradation processes and resulting degradation products. After optimization of the process, complete degradation of PHB to monomeric degradation products (3-hydroxybutanoic acid, 3-methoxybutanoic acid, and crotonic acid) was reached after only 20 min of microwave heating at 110 °C. Functional chemicals for synthesis or modification of biopolymers are thus obtainable from microwave-assisted degradation of PHB in green solvents. This offers new possibilities for retaining the material value of PHB via chemical recycling.

Mechanism on microwave-assisted acidic solvolysis of black-liquor lignin.

Microwave-assisted degradation of black-liquor lignin with formic acid was studied, concerning the product yield and distribution of phenolic compounds against reaction temperature (110-180°C) and reaction time (5-90 min). The liquid product consisting of bio-oil 1 and bio-oil 2, achieved the maxima yield of 64.08% at 160°C and 30 min (bio-oil 1: 9.69% and bio-oil 2: 54.39%). The chemical information of bio-oil 1 and bio-oil 2 were respectively identified by means of Gas Chromatography-Mass Spectrometer (GC-MS) and Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), while the solid residue was analyzed by Gel Permeation Chromatography (GPC) and Fourier Transform Infrared Spectroscopy (FTIR). A possible mechanism was proposed for the microwave-assisted acidic solvolysis of lignin, specifying the kinetic relationship among the primary cracking of lignin, repolymerization of the oligomers and formation of solid residue.

Microwave-Assisted Degradation of Lignin Model Compounds in Imidazolium-Based Ionic Liquids

A systematic study of microwave-assisted degradation of lignin model compounds such as benzyl phenyl ether (BPE) and guaiacol, in imidazolium-based ionic liquids, was performed by evaluating the catalytic activity of 29 types of ionic liquids as both solvent and catalyst. After measuring and comparing the acidity of each ionic liquid solution for BPE and guaiacol degradation under the microwave irradiation and conventional heating conditions, it was found that the ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4) was the most effective for decomposing the lignin model compounds. The experimental results indicate that ionic liquid acidity is in favor of the catalytic activity for BPE and guaiacol degradation, microwave irradiation could accelerate the degradation rate by 650% for BPE and 1120% for guaiacol and significantly increase the reaction selectivity. It was also found in experiments that the ionic liquid [BMIM]HSO4 could be used for 5 times without any loss of catalytic activity. The possible mechanisms for BPE and guaiacol degradation are proposed based on the product distributions.

A carbon nanodot modified Cu–Mn–Ce/ZSM catalyst for the enhanced microwave-assisted degradation of gaseous toluene

Toluene waste gas was treated with a carbon nanodot (CND) modified Cu–Mn–Ce/ZSM catalyst (CND–CMCZ) and a Cu–Mn–Ce/ZSM catalyst (CMCZ) respectively by a fixed bed under microwave irradiation. 75% of the gaseous toluene was degraded by the CND–CMCZ catalyst within 80 min at 150 °C, which was almost 1.9 times that of the CMCZ catalyst.

Microwave-assisted Degradation of Polyvinyl Chloride Induced by Complexes of Transition Elements

In this work, the presence of variable metals complex of [N,N-Bis(Salicylidene)1,2-[diaminoethane] Nickel(II), (Ni-BSEDA). And the PVC film were studied under the microwave radiation. The samples and complex metals salt were prepared using a hand molding casting with percentage ( 0.0 ,0.025 , 0.03, 0.04, 0.05, 0.1 ) % . Degradation studies were carried out using commercial microwave oven at constant power of 400W for all experimental. The specimens were exposed to microwave radiation with multiple time( 0.0 ,15, 30, 60) minutes , A degradation were followed via the decreace in average of molecular weights ( Mw-,Mn- ) and increase of the growth of absorbency the carbonyl index ICO and polyene index IPO at the total time of 60 minutes.

Microwave-assisted degradation of acid orange using a conjugated polymer, polyaniline, as catalyst

Microwave-assisted photocatalytic degradation of dyes is one of the emerging technologies for waste water remediation. Microwave effectively accelerates photocatalytic degradation, when microwave electrodeless lamp (MEL) substitutes traditional UV lamp as light source. This setup can be extremely simplified if MEL and photocatalyst can be replaced by a catalyst which can work under microwave irradiation in the absence of any light source. The present work reports for the first time degradation of acid orange 7 (AO) under microwave irradiation using polyaniline (PANI) as catalyst in the absence of any UV lamp as light source. The degradation/decolourization was carried out in neutral acidic and basic media and was monitored spectrophotometrically to evaluate the ability of microwave irradiation to degrade AO. Microwave irradiation showed excellent performance as it completely decolourizes AO dye solution in 10min. With the advantages of low cost and rapid processing, this novel catalyst is expected to gain promising application in the treatment of various dyestuff wastewaters on a large scale.

Quantitative Analysis of Oligosaccharides Derived from Sulfated Glycosaminoglycans by Nanodiamond-Based Affinity Purification and Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

Degraded fragments of sulfated glycosaminoglycans (GAGs) are key reporters for profiling the burden of mucopolysaccharidosis (MPS) disease at baseline and during therapy. Here, we present a high-throughput assay, which combines microwave-assisted degradation, solid-phase affinity purification, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS), for quantitative analysis of sulfated oligosaccharides in biological samples. First, sulfated oligosaccharides such as chondroitin-4-sulfate (CS) were efficiently isolated from highly diluted solutions or spiked artificial cerebrospinal fluid (aCSF) using polyarginine-coated nanodiamonds (PA-coated NDs) as affinity sorbents. Next, they were degraded to disaccharides through microwave-assisted methanolysis or enzymatic digestion for subsequent MALDI-TOF MS analysis. The reaction times for GAG depolymerization were significantly reduced from a few hours to less than 7 min under the microwave irradiation. Deuterium-labeled internal standards were then mixed with the CS-derived disaccharides for quantitative analysis by MALDI-TOF MS using the N-(1-naphthyl) ethylenediamine dihydrochloride (NEDC) matrix. The new assay is facile, specific (with distinct chlorine-isotope trait markers), sensitive (with a detection limit of ~70 pg), and potentially useful for clinical diagnosis of MPS.

Microwave-assisted Degradation of Polystyrene Induced by 8-hydroxy quinoline Nickel (II) complex.

The most serious problems encountered in polystyrene (PS) processing is due to a poisoning and pollution of environment because of the PS structure containing aromatic ring. This study suggests a clean and ecofriendly of (PS) degradation. To the PS film prepared [8-hydroxyquinoline nickel(II) complex added as inducing agent for degradation (PS) film exposed to the microwave radiation . A hand molding casting has been used for preparing specimens of the (PS) in percentages ( 0.0, 0.025, 0.05, 0.1, 0.2, 0.4 % ) of the complex. The Degradation were carried out using commercial microwave oven at constant power of 400 W for all experiments. Specimens were exposed to microwave radiation with multiple time ( 0.0, 15, 30, 60 minute), A degradation were followed via of the decrease in molecular weights averages ( Mw-, Mn-) and the increase of absorbancy of the carbonyl index ICO and hydroxyl index IOH at the total time of 60 minutes with microwave radiation .

Microwave-assisted degradation of chitosan for a possible use in inhibiting crop pathogenic fungi

Degradation of chitosan by H2O2 under microwave irradiation was investigated. The oxidative degradation of chitosan was highly accelerated by microwave irradiation under the condition of low temperature and low concentration of H2O2. The degraded chitosans with low molecular weight (Mw) were characterized by gel permeation chromatography, Fourier-transform infrared spectroscopy, ultraviolet–visible spectroscopy, X-ray diffraction and elemental analysis. The decrease of Mw led to transformation of crystal structure and increase of water solubility, whereas no significant chemical structure change in the backbone of chitosan was observed. Antifungal activities of chitosans with different Mw against crop pathogenic fungi Phomopsis asparagi, Fusarium oxysoporum f. sp. Vasinfectum and Stemphylium solani were investigated at the concentrations of 100, 200 and 400mg/L. All degraded chitosans with low Mw exhibited enhanced antifungal activity compared with original chitosan and the chitosan of 41.2kDa showed the highest activity. At 400mg/L, the chitosan of 41.2kDa inhibited growth of P. asparagi at 89.3%, stronger than polyoxin and triadimefon, the inhibitory effects of which were found to be 55.5% and 68.5%. All the results indicated that oxidative degradation under microwave irradiation was a promising technique for large-scale production of low Mw chitosan for use in crop protection.

Toward the controlled production of oligoesters by microwave-assisted degradation of poly(3-hydroxyalkanoate)s

The degradation of poly(3-hydroxyalkanoate)s (PHAs) could be performed in a rapid, inexpensive and straightforward way via microwave irradiation with good potential for further scale-up. One such degradation was compared to that induced by conventional heating at 190 °C. The experimental results showed that PHA oligomers with varying molar masses, characterized by a terminal crotonic double bond and a carboxyl group on the other chain end, could be effectively obtained from native PHAs in the bulk by both degradation approaches. The kinetics of PHA oligomer production was monitored by size exclusion chromatography and 1H NMR. The influence of temperature as well as microwave irradiation time and power was investigated, and the optimal conditions of degradation are described. It turned out that this treatment was much more efficient than a conventional thermally-induced degradation, as oligomers with similar molar masses were formed with an about 100 times faster rate corresponding to very short irradiation times (maximum 15 min). Two microwave-assisted procedures could be advantageously used: an irradiation with constant temperature was appropriate to afford PHA oligomers with molar masses lower than 1000 g.mol−1 and high yields, while irradiation under constant power was more convenient to provide oligoesters with higher molar masses.

The Effect of Microwave-Assisted for Photo-Catalytic Reaction in Aqueous Nano TiO<SUB>2</SUB> Particles Dispersions

In this study, the photo-catalytic degradation of methylene blue in TiO2 particles-dispersed aqueous solution was carried out by irradiating microwave and UV light simultaneously. The results of photocatalytic degradation of methylene blue showed that the decomposition rate increased with the microwave intensity, UV intensity, TiO2 particle dosages and the circulating fluid velocity. From the result of microwave-assisted photo-catalytic degradation of methylene blue, decomposition rate were shown gradually increased according to the increase of pH. The photo-catalytic degradation rate constant obtained under simultaneous irradiation of microwave and UV light case was about 1.5 times higher than irradiation of UV light only case. This result suggests that there is a synergy effect when the constituent techniques are applied together and that the additional irradiation of microwave can play a very important role in photo-catalysis of organic water pollutants.

Environmental remediation by an integrated microwave/UV-illumination technique: IV. Non-thermal effects in the microwave-assisted degradation of 2,4-dichlorophenoxyacetic acid in UV-irradiated TiO2/H2O dispersions

After establishing proof of concept in the first three articles of this series, in which we used the rhodamine-B dye to test the methodology, we herein report a study on the photocatalyzed degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous TiO2 dispersions that were subjected to simultaneous irradiation by UV light and microwave (MW) radiation. The characteristics of the process were monitored for the effect of microwave radiation by examining the fate of each substituent group, viz. the carboxylic acid group, the chlorine substituents and the benzene ring of the 2,4-D structure. The degradation dynamics of the microwave-assisted process were examined by decrease of UV absorption, loss of total organic carbon (TOC), formation of Cl− ions (dechlorination), and identification of intermediates by electrospray mass spectral techniques. The thermal effect of the microwave radiation to the system was considered by comparing results from MW-generated heat versus externally applied heat. The effect of dissolved oxygen or absence of oxygen on the degradative process was also investigated. The greater efficiency of the MW-assisted process is ascribed to a non-thermal effect of microwave radiation on the break-up of the aromatic ring of 2,4-D (oxidation) but evidently not on the dechlorination process (reduction) for which MW radiation seems to have a negligible influence, if any. Factors involved in this non-thermal component and a mechanism are proposed for the initial stages of the degradation.

Environmental Remediation by an Integrated Microwave/UV-Illumination Method. 1. Microwave-Assisted Degradation of Rhodamine-B Dye in Aqueous TiO2 Dispersions

The photocatalytic decomposition of the cationic rhodamine-B (RhB) dye was examined in aqueous TiO2 dispersions using an integrated microwave/UV-illumination (PD/MW) method. This procedure proved to be superior in the degradation of the dye than the TiO2 photocatalytic degradative method alone. With few exceptions, the integrated PD/MW method also proved superior for other chemical systems. The greater efficacy of the PD/MW technique appears to be the result of the following two considerations: (i) there is enhanced formation of reactive oxygen species (.OH radicals), as attested to by DMPO spin-trap ESR methods and their attack on the dye; and although speculative at this time, (ii) the activity of bulk water or the TiO2 particle surface is somehow affected by microwave radiation. The greater efficacy of the PD/MW degradation method was also observed at low concentrations of molecular oxygen and at low radiant excitance of the light source. A brief mechanistic description is given on the basis of results obtained on the two model compounds, (i) benzoic acid and (ii) pyronin-B dye.