Microwave-assisted organic synthesis versus conventional heating. A comparative study for Fisher glycosidation of monosaccharides

The Fisher glycosidation of monosaccharides (d-glucose and d-mannose) with fatty alcohols was studied under microwave irradiation and conventional heating with strict internal temperature control using a fiber optic sensor. Surfactants were obtained in only 3 minutes under microwave at maximum power of 5 W to avoid overshoot and products decomposition. In contrast with the typical reported glycosidation methods, the reaction under conventional heating can be carried out at the same time and temperature with high conversion.     

Green Synthesis of Some Calix[4]Resorcinarene Under Microwave Irradiation

A green synthetic procedure for the preparation of some calix[4]resorcinarenes using a household microwave oven has been carried out. This method represents a very rapid heating alternative to the conventional method that involves very long time of reactions (from 20-24 h in conventional heating to 5-8 min in microwave irradiation). C-4-hydroxy–3-methoxycalix[4]resorcinarene (CHMPCR), C-4-methoxyphenylcalix[4]resorcinarene (CMPCR) and C-2–phenylethenilcalix[4]resorcinarene (CPECR) was achieved by placed of resorcinol, an aldehyde, HCl and ethanol inside a household microwave oven. The product was recrystallized by methanol and analyzed by spectral analysis (FTIR, H-NMR and MS). Optimization of reaction was carried out in variation of microwave power, reaction times and reactant composition. The result shows that optimum condition of synthesis of C-4-hydroxy-3–methoxycalix[4]resorcinarene (CHMPCR) with microwave irradiation were at microwave power 332 W, reaction time 8 min and the mole ratio of resorcinol and 4-hydroxy-3-methoxyphenylbenzaldehyde 1:1. This parameter gave product in 97.8% (53.7% after recrystallization). The CPECR synthesis using resorcinol and cynnamaldehyde (1:1) at microwave power 332 W for 5 min afforded the product in 97.3% (44.5% after recrystallization). Whereas the reaction of resorcinol and 4-methoxyphenylbenzaldehyde (1:1.2) at microwave power 264 W for 5 min gave CMPCR in 99.5% (68.6% after recrystallization).     

Conventional and microwave induced pyrolysis of coffee hulls for the production of a hydrogen rich fuel gas

This paper describes the conventional and microwave-assisted pyrolysis of coffee hulls at 500, 800 and 1000 °C. The influence of the pyrolysis method and temperature on the product yields and on the characteristics of the pyrolysis products is discussed. It was found that the pyrolysis of this particular residue gives rise to a larger yield of the gas fraction compared to the other fractions, even at relatively low temperatures. A comparison of microwave-assisted pyrolysis and conventional pyrolysis showed that microwave treatment produces more gas and less oil than conventional pyrolysis. In addition, the gas from the microwave has much higher H₂ and syngas (H₂ + CO) contents (up to 40 and 72 vol.%, respectively) than those obtained by conventional pyrolysis (up to 30 and 53 vol.%, respectively), in an electric furnace, at similar temperatures. From the pyrolysis fraction yields and their higher heating values it was found that the energy distribution in the pyrolysis products decreases as follows: gas > solid > oil. Moreover, the energy accumulated in the gas increases with the pyrolysis temperature. By contrast, the energy accumulated in the char decreases with the temperature. This effect is enhanced when microwave pyrolysis is used.     

Characterization of the different fractions obtained from the pyrolysis of rope industry waste

A study of the possibilities of pyrolysis for recovering wastes of the rope's industry has been carried out. The pyrolysis of this lignocellulosic residue started at 250 °C, with the main region of decomposition occurring at temperatures between 300 and 350 °C. As the reaction temperature increased, the yields of pyrolyzed gas and oil increased, yielding 22 wt.% of a carbonaceous residue, 50 wt.% tars and a gas fraction at 800 °C. The chemical composition and textural characterization of the chars obtained at various temperatures confirmed that even if most decomposition occurs at 400 °C, there are some pyrolytic reactions still going on above 550 °C. The different pyrolysis fractions were analyzed by GC–MS; the produced oil was rich in hydrocarbons and alcohols. On the other hand, the gas fraction is mainly composed of CO₂, CO and CH₄. Finally, the carbonaceous solid residue (char) displayed porous features, with a more developed porous structure as the pyrolysis temperature increased.     

Kinetic study of low-temperature conversion of plastic mixtures to value added products

Batch-mode pyrolysis of 200.0 g samples of polymers was studied at low temperature. The cracking reaction was carried out in a stainless-steel autoclave with reaction temperatures of 360, 380, 400 and 420 °C, initial pressure of 6.325 kPa (absolute pressure) and reaction times of 0–240 min. Based on the experimental results, a four-lump kinetic model has been developed to describe the production distribution of the light fractions, middle distillates and heavy fraction. This model reasonably fitted the results in each reaction of operation conditions. It was also found that the pyrolysis kinetics of separated plastic, mixed plastic and mixed plastic containing additives can be described by the same kinetic model. The plastic additives have not had a great influence on the product distribution and kinetics of the mixed plastic pyrolysis. Finally, the optimum conditions of low-temperature conversion of plastic mixtures to value-added products were established. The formation of heavy fractions from HDPE was as high as 70 wt% at 380 °C at a reaction time of 250 min. During the thermal degradation of plastic mixtures, the heavy fractions yielded up 50 wt% for 30 min reaction time at 400 °C. The total activation energies for the conversion of HDPE and the plastic mixtures were estimated to be 217.66 kJ mol⁻¹ and 178.49 kJ mol⁻¹, respectively.     

Catalytic stepwise pyrolysis of packaging plastic waste

In this paper the combination of catalytic and stepwise pyrolysis is explored. A mixture of polyethylene (PE), polypropylene (PP), polystyrene (PS), poly(ethylene terephthalate) (PET) and poly(vinyl chloride) (PVC), which resembles real municipal plastic waste, has been pyrolysed in a 3.5 dm³ semi-batch reactor at 440 °C for 30 min using a ZSM-5 zeolite as catalyst. A low temperature (300 °C) dechlorination step has been carried out both with and without catalyst. It has been proved that the application of such dechlorination step gives rise to a 75 wt% reduction of chlorine in the liquid fraction. However, such step has a negative influence on the catalyst, which loses some catalytic activity. The optimum procedure in terms of quality and chlorine content of the products is the combination of first a low temperature step without catalyst, and second the catalytic pyrolysis step.     

New power source from fractional quantum energy levels of atomic hydrogen that surpasses internal combustion

Extreme ultraviolet (EUV) spectroscopy was recorded on microwave discharges of helium with 2% hydrogen. Novel emission lines were observed with energies of q·13.6 eV where q=1,2,3,4,6,7,8,9, or 11 or these lines inelastically scattered by helium atoms wherein 21.2 eV was absorbed in the excitation of He (1s²) to He (1s¹2p¹). These lines were identified as hydrogen transitions to electronic energy levels below the ‘ground’ state corresponding to fractional quantum numbers. Significant line broadening corresponding to an average hydrogen atom temperature of 33–38 eV was observed for helium–hydrogen discharge plasmas; whereas pure hydrogen showed no excessive broadening corresponding to an average hydrogen atom temperature of ≈3 eV. Since a significant increase in H temperature was observed with helium–hydrogen discharge plasmas, and energetic hydrino lines were observed at short wavelengths in the corresponding microwave plasmas that required a very significant reaction rate due to low photon detection efficiency in this region, the power balance was measured on the helium–hydrogen microwave plasmas. With a microwave input power of 30 W, the thermal output power was measured to be at least 300 W corresponding to a reactor temperature rise from room temperature to 900 °C within 90 s, a power density of 30 MW/m³, and an energy balance of about −4×10⁵ kJ/mol H₂ compared to the enthalpy of combustion of hydrogen of −241.8 kJ/mol H₂.     

Study of products yield of bagasse and sawdust via slow pyrolysis and iron-catalyze

In this paper, the via slow pyrolysis behavior of the bagasse and sawdust were studied at the different heating rates, the different iron-containing blend pyrolysis and the treatment temperature, the further understood for the pyrolysis of agricultural residues. The distribution of the products yield of the slow pyrolysis process, it is typically performed at temperature between 200 and 600 °C, the pyrolysis temperature increased, the bio-liquids and gas yields tended to increase, which at 400 °C was able to achieve maximum bio-liquids yields, the biochar yields tended to downward. For different heating rate, in the heating rate ranges for 80–100 W, the bio-liquids products yield curve increased from 44.5 wt% to 46.5 wt% for bagasse; the sawdust products yield increased from 41 wt% to 42.75 wt%. Iron-catalysts blend pyrolysis (0, 10, 25, 40 and 50 wt%), the bagasse bio-liquid yields respectively 56.25 wt% in the presence 50% iron-catalysts blend pyrolysis; the sawdust bio-liquid yields respectively 52.5 wt% in the presence 40% iron-catalysts blend. The pyrolysis process were calculated according to the kinetic mechanism were examined, the pyrolysis activation energy was between 6.55 and 7.49 kcal/mol for bagasse. Sawdust the pyrolysis activation energy was between 11.52 and 11.76 kcal/mol. Therefore, in this study a pyrolysis model of bagasse and sawdust thermal treatment may provide both agricultural and forestry transformation importance of resources.     

Rotary kiln pyrolysis of straw and fermentation residues in a 3 MW pilot plant – Influence of pyrolysis temperature on pyrolysis product performance

The idea of co-firing biomass in an already existing coal-fired power plant could play a major contribution in the reduction of carbon dioxide emissions. Huge amounts of unused biomass in terms of agricultural residues such as straw, which is a cheap and local feedstock, are often available. But due to the high amount of corrosive ash elements (K, Cl, etc.), the residues are usually not suitable for co-firing in a thermal power plant. Therefore, the feedstock is converted by low temperature pyrolysis into gaseous pyrolysis products and charcoal. A 3 MW pyrolysis pilot plant located next to a coal-fired power plant near Vienna was set up in 2008. For the process, an externally heated rotary kiln reactor with a design fuel power of 3 MW is used which can handle about 0.6–0.8 t/h straw. The aim is to investigate the fundamentals for scale-up to the desired size for co-firing in a coal-fired power plant. In addition to the desired fuel for the process, which is wheat straw, a testing series for DDGS was also performed. The high amount of pyrolysis oil in the gas had positive effects on the heating value of the pyrolysis gas. Chemical efficiencies of this pyrolysis pilot plant of up to 67% for pyrolysis temperatures between 450 °C and 600 °C can be reached. The focus of this work is set on the pyrolysis products and their behavior at different pyrolysis temperatures as well as the performance of the pyrolysis process.     

Pyrolysis of textile wastes: I. Kinetics and yields

Thermal behavior of textile waste was studied by thermogravimetry at different heating rates and also by semi-batch pyrolysis. It was shown that the onset temperature of mass loss is within 104–156 °C and the final reaction temperature is within 423–500 °C. The average mass loss is 89.5%. There are three DTG peaks located at the temperature ranges of 135–309, 276–394 and 374–500 °C, respectively. The first two might be associated with either with decomposition of the hemicellulose and cellulose or with different processes of cellulose decomposition. The third peak is possibly associated to a synthetic polymer. At a temperature of 460 °C, the expected amount of volatiles of this waste is within 85–89%. The kinetic parameters of the individual degradation processes were determined by using a parallel model. Their dependence on the heating rate was also established. The pyrolysis rate is considered as the sum of the three reaction rates. The pyrolysis in a batch reactor at 700 °C and nitrogen flow of 60 ml/min produces 72 wt.% of oil, 13.5 wt.% of gas and 12.5 wt.% of char. The kinetic parameters of the first peak do not vary with heating rate, while those of the second and the third peak increase and decrease, respectively, with an increasing heating rate, proving the existence of complex reaction mechanisms for both cases.     

Product characterization of waste printed circuit board by pyrolysis

This paper is part of a project which studies pyrolysis as an alternative for recycling printed circuit board (PCB); the sample (2.0 cm × 2.0 cm) was pyrolyzed under nitrogen atmosphere, at 300, 400, 500, 600 and 700 °C in a tubular type oven, maintaining 30 min, and during the pyrolysis process the organic part is decomposed to pyro-oils and pyro-gases, which can be used as fuels or chemical material resources: the solid residues of about 75–80 wt.%, liquid yields of ∼9.0 wt.% and gas yields of 12–14 wt.%. No significant influence of temperature was observed over 500 °C, however, there was certainly influence under 500 °C in both volatile substance. The pyro-oils have fairly high gross calorific values (∼30 kJ/kg), mainly with aromatic and with oxygenated compounds. The pyro-gas is very rich in CO, CO₂, H₂, CH₄ and in small part of O₂; after being purged it can be combusted for the pyrolysis self-sustain. The tensile strength decreases about 35% at 773 K, while the impact and tear strength increases above 773 K, and then decreases along with the temperature increase. The strength changes can offer guidance for used as a replacement for virgin fibres in SMC manufacture. The residues are better laminated can be easily liberated for metals recovery.     

Pyrolysis of cohesive meat and bone meal in a bubbling fluidized bed with an intermittent solid slug feeder

Meat and bone meal (MBM) is a mass-produced by-product of the meat rendering industry. It has great potential as a feedstock for the production of bio-fuels. Meat and bone meal, however, is a highly cohesive and temperature sensitive material and has traditionally been found to be very difficult, if not impossible, to feed properly into pyrolysis reactors or bubbling fluidized beds. This study showcases an application of the ICFAR intermittent solid slug feeder technology and its capability of successfully feeding the MBM regularly at an average feeding rate of 0.34 g/s into the reactor.A highly automated and instrumented fast pyrolysis pilot plant has been used to process meat and bone meal residues and to operate within a wide range of temperatures (450–600 °C). This is the first study dealing with the pyrolysis of pure meat and bone meal at various operating conditions continuously fed into a laboratory-scale fluidized bed reactor. All liquid and solid products have been analyzed (yields, HHV, GC–MS, elemental analysis, and ash mineral analysis). The homogenous bio-oil produced is an attractive fuel with a significant high heating value (HHV) of 31.5 MJ/kg and an average liquid yield of 43 wt% at 550 °C. The highest water-free HHV (36.7 MJ/kg) was found at 500 °C, with a liquid yield of 35 wt% at this temperature. The optimized pyrolysis temperature, at which the heat from the gas combustion can provide the heat required for processing MBM, while maximizing the bio-oil liquid yield and process energy yield, is 550 °C. Under these conditions, the pyrolysis process energy yield is 91%.The study also demonstrates a new technique to accurately determine the heat of pyrolysis reaction energy required by the process, using a non-invasive water calibration method.     

Effect of gamma irradiation on physico-mechanical properties of spice packaging films

Physico-mechanical properties of two types of laminated films, commercially used for spice packaging, are investigated after gamma irradiation at 8, 10 and 15 kGy. Data showed that polyethylene terephthalate/polyethylene terephthalate/linear low density polyethylene (PET/PET/LLDPE) was more resistant to radiation compared to biaxially oriented polypropylene/cast polypropylene (BOPP/CPP) and its barrier properties slightly improved up to 15 kGy. Oxygen transmission rate of BOPP/CPP was increased by 25%, and the melting peak temperature was decreased by 3.9% at 15 kGy, which may lead to oxidation of packaged spices and loss of their aroma/flavour, respectively.     

Chemical recycling of cycloolefin-copolymers (COC) in a fluidized-bed reactor

The pyrolysis of cycloolefin-copolymers (COC) in a fluidized-bed reactor was studied under various parameters like pyrolysis temperature, fluidizing gas or residence time. It was proven to reduce the undesired tar fraction to a minimum of around 10 wt.% and to obtain up to 44 wt.% valuable gases and 45 wt.% aromatic light oils with a reactor temperature of 700 °C.Furthermore, the mechanism of the pyrolytic degradation has been analyzed to determine if the comonomer 2-norbornene can be obtained by pyrolysis. In all experiments, only traces of around 0.05 wt.% were detected. It was learned that 2-norbornene is not stable enough to resist drastic pyrolysis conditions; rather it undergoes a Retro–Diels–Alder reaction to form ethene and cyclopentadiene.     

Catalytic pyrolysis of Phragmites (reed): Investigation of its potential as a biomass feedstock

In this paper, thermogravimetry, TG, and pyrolysis are used for the thermochemical evaluation of the common reed (Pragmites australis) as a candidate biomass feedstock. The TG analysis indicated that the material loses 4% of its weight below 150 °C through dehydration. The main decomposition reaction occurs between 200 and 390 °C. The rate of weight loss, represented by the derivative thermogravimetric, DTG, signal indicated a multi-step reaction. Kinetic analysis helped in the resolution of the temperature ranges of the overlapping steps. The first step corresponds to the degradation of the hemi-cellulosic fraction and the second to the cellulosic fraction degradation. The TG and DTG signals of reed samples treated with increasing concentration of potassium carbonate (0.6–10 wt%) indicated a catalytic effect of the salt on reed decomposition. The temperature of maximum weight loss rate, DTGmax, exponentially decreased with increasing catalyst content, whilst the initial temperature of the decomposition decreased linearly. The pyrolysis studies were carried out in a Pyrex vertical reactor with sintered glass disc to hold the sample and to aid the fluidization with the nitrogen stream flowing upwards. The reactor was connected to a cyclone and condenser and a gas sampling device. Tar and char are collected and weighed. The gas chromatographic analysis of the evolved gases demonstrated the effect of pyrolysis temperature (400, 450, and 500 °C) on their composition. The temperature increase favors the yields of hydrocarbons, carbon monoxide and hydrogen at the expense of methanol and carbon dioxide. Similarly, reed samples treated with K2CO3 at 10 wt% were pyrolyzed and analyzed. Comparisons for the various parameters (yields, gas composition and carbon–hydrogen recovery) between the untreated and catalyzed reed conversion were also made.     

Investigation of the evolved gases from Sulcis coal during pyrolysis under N2 and H2 atmospheres

The evolution of gases and volatiles during Sulcis coal pyrolysis under different atmospheres (N₂ and H₂) was investigated to obtaining a clean feedstock of combustion/gasification for electric power generation. Raw coal samples were slowly heated in temperature programmed mode up to 800 °C at ambient pressure using a laboratory-scale quartz furnace coupled to a Fourier transform infrared spectrometer (FTIR) for evolved gas analysis. Under both pyrolysis and hydropyrolysis conditions the evolution of gases started at temperature as low as 100 °C and was mainly composed by CO and CO₂ as gaseous products. With increasing temperature SO₂, COS, and light aliphatic gases (CH₄ and C₂H₄) were also released. The release of SO₂ took place up to 300 °C regardless of the pyrolysis atmosphere, whilst the COS emissions were affected by the surrounding environment. Carbon oxide, CO₂, and CH₄ continuously evolved up to 800 °C, showing similar release pathways in both N₂ and H₂ atmospheres. Trace of HCNO was detected at low pyrolysis temperature solely in pure H₂ stream. Finally, the solid residues of pyrolysis (chars) were subjected to reaction with H₂ to produce CH₄ at 800 °C under 5.0 MPa pressure. The chars reactivity was found to be dependent on pyrolysis atmosphere, being the carbon conversions of 36% and 16% for charN₂ and charH₂, respectively.     

Recycling of waste poly(ethylene terephthalate) with castor oil using microwave heating

The chemical recycling of waste poly(ethylene terephthalate) (PET) using castor oil (CO) as a reagent is reported. CO presents a renewable alternative to petrochemical based reagents, e.g. glycols, and enables also substantial modification of final physico-chemical properties of a received product. Advantageously, microwave irradiation was used to accelerate the depolymerization of PET. A composition of obtained product was strongly influenced by the reaction temperature. When the decomposition of PET was performed at temperature higher than 240 °C, then a significant extent of side products based on PET oligomers and transesterified CO was observed due to dehydration and hydrolysis of CO. Contrary to that, PET decomposition took place at slow rate below 230 °C and the optimal reaction temperature lies in the relatively narrow interval from 230 °C to 240 °C. The product prepared in the optimal temperature range did not contain any high molecular weight PET oligomers. MALDI-TOF mass spectrometry enabled to identify the structures included in the obtained polyol product. The maximum number of six repeating monomeric unit of PET was found in the product, which confirmed practically the complete depolymerization of PET chain and good reactivity of the acylester hydroxyl groups of CO.     

Synthetic Liquid Fuels Obtained by Thermolysis of Animal Waste

Modern methods of recycling organic waste are not considered viable today. Therefore, an important advantage of the proposed technology is to obtain mineral fuel products as an output. The technologies of high-temperature processing are based on thermal decomposition of waste without oxygen at high temperature. In pyrolysis, wastes are converted into gaseous, liquid and solid fuels. Thereby, the properties and composition of the liquid feedstock obtained by pyrolysis with a boiling temperature in the range of X.I. (38) - 180 °C, 180 - 320 °C and more than 320 °C were investigated. Residue with a boiling temperature over 320° C (52.4% vol.) is the main portion of the synthetic liquid fuels (SLF). It can be attributed to fuel oil grade 100 and used as boiler fuel or fuel oil additives according to the studied physicochemical parameters.     

Optical emission spectroscopy for quantification of ultraviolet radiations and biocide active species in microwave argon plasma jet at atmospheric pressure

This work deals with absorption and mainly emission spectrometry of a microwave induced surfatron plasma jet launched in ambient air and using an Argon flow carrier gas. The Ar flow rate varies between 1 and 3 L/min and the microwave power between 40 and 60 W. The analysis of the various spectra has led to the determination of the ozone and atomic oxygen concentrations, ultraviolet (UV) irradiance separating UVA, UVB and UVC, gas temperature, plasma electron density and excitation temperature. Most of these diagnostics are spatially resolved along the plasma jet axis. It is shown more particularly that rotational temperature obtained from OH(A-X) spectra ranges between 800 K to 1000 K while the apparent temperature of the plasma jet remains lower than about 325 K which is compatible with biocide treatment without significant thermal effect. The electron density reaches 1.2 × 10¹⁴ cm^− 3, the excitation temperature is about 4000 K, the UVC radiation represents only 5% of the UV radiations emitted by the device, the ozone concentration is found to reach 88 ± 27 ppm in the downstream part of the plasma jet at a distance of 30 mm away from the quartz tube outlet of the surfatron and the atomic oxygen concentration lies between 10 and 80 ppm up to a distance of 20 mm away from the quartz tube outlet. Ozone is identified as the main germicidal active species produced by the device since its concentration is in accordance with bacteria inactivation durations usually reported using such plasma devices. Human health hazard assessment is carried out all along this study since simple solutions are reminded to respect safety standards for exposures to ozone and microwave leakage. In this study, an air extraction unit is used and a Faraday cage is set around the quartz tube of the surfatron and the plasma jet. These solutions should be adopted by users of microwave induced plasma in open air conditions because according to the literature, this is not often the case.     

Scale-up of microwave heating process for the production of bio-oil from sewage sludge

A pilot-scale microwave heating apparatus was constructed for the production of bio-oil from sewage sludge, and the effects of important microwave processing parameters and chemical additives on the quality and yield of bio-oils were investigated. It was found that bio-oil was mainly formed at the pyrolysis temperature range of 200–400 °C. A higher heating rate (faster pyrolysis) not only increased the yield of bio-oil, but also improved the quality of bio-oil according to the elemental composition and calorific values. The maximum bio-oil yield was 30.4% of organic fraction, obtained from the pyrolysis of original sewage sludge at microwave radiation power of 8.8 kW and final pyrolysis temperature of 500 °C. All of five simple additives (KOH, H₂SO₄, H₃BO₃, ZnCl₂, and FeSO₄) reduced the bio-oil yield, but the composition and property of bio-oil varied with the additive types greatly. KOH, H₂SO₄, H₃BO₃ and FeSO₄ were found to improve the quality of bio-oils remarkably according to the calorific value, density, viscosity and carbon content of bio-oils, but ZnCl₂ treatment went against that. GC–MS analysis of the bio-oils showed that, alkali treatment promoted the formation of alkanes and monoaromatics, while acid treatment favored the formation of heterocyclics, ketones, alcohols and nitriles. Compared with sulfate slat FeSO₄, chloride salt ZnCl₂ was a better catalyst for selective catalytic pyrolysis of sewage sludge. The addition of ZnCl₂ only promoted the formation reactions of a few kinds of nitriles and ketones remarkably. It is technologically feasible to produce bio-oil form microwave-induced pyrolysis of sewage sludge by optimizing pyrolysis conditions and selecting appropriate additives.