Evolution Of Gaseous Products Research Articles

Pyrolysis behavior and kinetics of the trapped small molecular phase in a lignite

Trapped small molecular phase is an important part in coal and strongly affects reactivity and volatile release during pyrolysis. In this work, it was separated by normal heptane leaching of extracts from thorough extraction of a lignite and was further fractionated into four sub-fractions by column chromatography. Chemical properties of each sub-fraction were evaluated first and then pyrolysis behavior, gaseous product evolution and kinetics of the raw coal and its four sub-fractions were systematically investigated using a thermogravimetric analyzer coupled with on-line Fourier Transform Infrared spectrometer. Determination results corresponding to the total yield and chemical properties of the sub-fractions proved the effectiveness of the separation procedure. Normal heptane eluate presented one mass loss stage and decomposition of aliphatic moieties in it mainly contributed to formation of methane, ethylene, and other high carbon number aliphatics. Toluene eluate exhibited one broad mass loss stage and produced largest quantities of light arenes and ether bond containing species, while two apparent mass losses occurred in pyrolysis profile of ethyl acetate eluate, during which ketonic bond containing species generated at the first pyrolysis stage. The formation of coke during pyrolysis was mainly caused by the presence of methanol eluate. Kinetic results revealed that distributed activation energy model was suitable for describing the pyrolysis process of raw coal and its four sub-fractions. Trapped small molecular phase could be easily pyrolyzed and the average bond energy of the components was in the order of raw coal≫ethyl acetate eluate>normal heptane eluate>toluene eluate>methanol eluate. In addition, the kinetic compensation effects were observed for almost the whole pyrolysis processes of both the raw coal and the four eluates.

Structural features and thermal degradation behaviors of extracts obtained by heat reflux extraction of low rank coals with cyclohexanone

Investigation on the properties of mobile phase in low rank coals and its pyrolysis characteristics is an alternative approach for understanding the pyrolysis mechanism and structure features of these coals. In this work, heat reflux extraction with cyclohexanone (CYC) was developed to dissolve the mobile phases in two low rank coals and afford one extract from Chifeng coal (ECF) and another extract from Hami coal (EHM). The structural features of the extracts were investigated using multiple analytical techniques first. Then, thermal reactivity and gaseous product evolution of the extracts, residues, and raw coals were evaluated by TG–FTIR. Detailed volatile specie composition during fast pyrolysis of extracts were further detected on the pyrolysis gas chromatography/time of flight mass spectrometer (Py–GC/TOF–MS). The results suggest that heat reflux extraction with CYC is an effective method for dissolving a fairly high fraction of the organic matters in low rank coals. Two low rank coals mainly showed one mass loss stage of devolatilization of the organic matters near 430°C and large numbers of gaseous products were released such as hydrocarbons (CH4, C2H4, C2+ aliphatics, and arenes), CO2, CO and CO bonds containing species, which were the result of the cracking and cleavage of the alkyl sides, strongly bonded functional groups, and bridged bonds, respectively. Forming of CO during pyrolysis of low rank coals was mainly derived from the cracking of the O-containing primary tar fragment and the condensation reactions of the aromatic clusters above 600°C rather than from the initial cleavage of the organic structures in low rank coals. Thermal dissolution effect of CYC can depolymerize the macromolecular structure of raw coals and thereby the dissociated coal structures (residues) are beneficial to crack the alkyl side chains and break the O-containing structures at lower temperatures. Two extracts can be pyrolyzed at temperatures lower than that of their parent coals and large quantities of O-containing gaseous products and C2+ aliphatics release during pyrolysis process. Furthermore, aliphatic hydrocarbons, arenes, ketones, phenols, and benzofurans are the most abundant species in the products during fast pyrolysis of both two extracts. Notably, the cleavage of CC bonds near the aromatic rings in longer-chain alkylbenzenes is a crucial reaction during fast pyrolysis of ECF and EHM.

Kinetics of the pyrolysis process of terpene acrylate homopolymers

The kinetics of the pyrolysis process along with the thermal behavior and evolution of gaseous decomposition products of differently structured, highly solvent and chemically resistant terpene acrylate homopolymers in inert atmosphere, poly(geranyl acrylate) and poly(citronellyl acrylate), were studied by means of the TG/DSC/FTIR-coupled method. In this work, two kinds of model-free-kinetic algorithms, differential Friedman and integral Kissinger–Akahira–Sunose (KAS) methods were combined to obtain the energetic profile in continuous mode as a function of the transformation degree (α). The obtained results were discussed in terms of energetic demand at each degradation stage through the dependence of E(α) on α, and its relationship with the global reaction rate (dα/dt).

On-Line Mass Spectrometry for Ethanol Oxidation on Well-Defined Sn/Pt(hkl) Electrode Surfaces

Onset potentials of ethanol oxidation reaction (EOR) and potential-dependent evolution of gaseous products from well-defined Sn/Pt(hkl) electrode surfaces were investigated. The electrode surfaces were prepared by vacuum deposition of Sn on a Pt(hkl) single-crystal substrate in ultra-high vacuum. The EOR onset potentials of anodic currents for Sn/Pt(hkl) shifted to lower potentials in comparison to unmodified Pt(hkl). Online electrochemical mass spectrometry (OLEMS) analysis of the gaseous products formed on the Sn/Pt(hkl) surfaces showed that acetaldehyde, rather than CO2, was generated at lower applied voltages and that the product evolution was sensitive to the atomic arrangement of the surface Pt (Pt(hkl)). EOR anodic current measurements and OLEMS analysis showed that EOR onset potential is the lowest for Sn/Pt(110). The findings can be attributed to the effectiveness of Pt(110) steps in ethanol C-C bond cleavage and an ensemble effect of the Pt and Sn atoms against CO poisoning.

A Combined DRIFTS and DR-UV–Vis Spectroscopic In Situ Study on the Trapping of CH3I by Silver-Exchanged Faujasite Zeolite

The mechanism of CH3I adsorption and thermal decomposition by a Ag/Y sorbent with 23 wt % of silver and a Si/Al ratio of 2.5 was investigated using two different spectroscopic techniques. On the one hand, DR-UV–vis spectroscopy was used to monitor the evolution of silver species and their transformation to silver iodide AgI clusters during increasing exposure to gaseous methyl iodide and upon heating under dry and wet atmospheres. On the other hand, the evolution of adsorbed organic species was investigated under similar conditions by DRIFTS. The latter data were correlated with the evolution of gaseous products to elucidate the mechanistic pathways involved in the trapping and catalytic decomposition of CH3I.

Initial moisture effects on herbal biomass torrefaction behavior: Gaseous products evolution and char structure analysis

ABSTRACTInitial moisture effects on biomass torrefaction were investigated by thermogravimetric (TG) and Fourier transform infrared spectrometer (FTIR) methods. Mass degradation properties, gaseous products’ evolution characteristics, and biomass char chemical structural features were studied. Results show that during torrefaction process, the evaporation of water will create a porous structure inside the solid particles, hence extend the mass loss time intervals. Gaseous products’ evolutions were favored, while tar was reduced because of enhanced secondary decomposition. Char structure analysis suggested that –OH stretch was slightly strengthened through water molecule decomposition and other radical reactions, which would increase the reactivity of char gasification and combustion.

Photoactive High Explosives: Substituents Effects on Tetrazine Photochemistry and Photophysics.

High explosives that are photoactive, i.e., can be initiated with light, offer significant advantages in reduced potential for accidental electrical initiation. We examined a series of structurally related tetrazine based photoactive high explosive materials to detail their photochemical and photophysical properties. Using photobleaching infrared absorption, we determined quantum yields of photochemistry for nanosecond pulsed excitation at 355 and 532 nm. Changes in mass spectrometry during laser irradiation in vacuum measured the evolution of gaseous products. Fluorescence spectra, quantum yields, and lifetimes were measured to observe radiative channels of energy decay that compete with photochemistry. For the 6 materials studied, quantum yields of photochemistry ranged from <10(-5) to 0.03 and quantum yield of fluorescence ranged from <10(-3) to 0.33. In all cases, the photoexcitation nonradiatively relaxed primarily to heat, appropriate for supporting photothermal initiation processes. The photochemistry observed was dominated by ring scission of the tetrazine, but there was evidence of more extensive multistep reactions as well.

Analytical Pyrolysis Study of Peanut Shells using TG-MS Technique and Characterization for the Waste Peanut Shell Ash

As an agricultural waste produced from the processing of peanut, the yield of peanut shells in China is quite abundant. Although numerous studies on the pyrolysis of peanut shells have been carried out, most of them were focused on the dynamics models for predicting kinetics parameter of biomass, and rarely on the evolution of gaseous products in pyrolysis. This study carried out a set of experiments on the pyrolysis of peanut shells under different heating rates in order to fill the knowledge gap. Besides, there is also a lack of information available concerning the characterization of resulting peanut shell ash. Thus, the aim of this study is to investigate the pyrolysis behaviors of peanut shells thoroughly and to characterize the properties of peanut shell ash that serves as predictors for its applications. The results show that the decomposition of peanut shells follows a stepwise mechanism, and the activation energy calculated by Flynn- Wall-Ozawa method varies from 58.3 to 88.6 kJ·mol–1. Compared with low heating rate, fast heating rate at low temperatures is more suitable for biogas production. Chemical and phase analysis shows that peanut shell ash has a high SiO2 content except for other oxides (K2O, CaO, MgO, Al2O3, etc.) that quite suitable in glass production, implying its potential for glass production and as a mineral admixture in concrete. Released volatile matters in pyrolysis create many pores in carbonaceous materials, thus low-cost adsorbents can be produced from these carbon residues.

On the feasibility of a friction-based staking joining method for polymer–metal hybrid structures

The increased use of hybrid structures to reduce weight currently faces the limitations of traditional joining methods. Consequently there is a niche for development of new joining techniques, which can reduce or overcome some of the existing limitations. This paper presents for the first time the new Friction-based Injection Clinching Joining technique (F-ICJ), describing the microstructure and changes in local properties of joints between polyetherimide (PEI) and aluminum alloy 6082-T6. A shear layer around the rotating tool composes a polymer thermomechanically affected zone (PTMAZ), which presents pores as a result of evolution of gaseous products. The PTMAZ shows decreases of 8% to 12% in local strength compared to the base material, as measured by microhardness. Ultimate forces of 1419±43N in lap shear and 430±44N in cross tensile were achieved for F-ICJ joints. These levels are similar to ultrasonic staking joints of the same material combination, but the hollow design of F-ICJ stakes accounts for improved strength-to-weight ratio (18% in lap shear, 21% in cross tensile). Although the F-ICJ process currently requires longer cycles (7.5s) than state-of-the-art ultrasonic staking (2.8–2.9s), generated results indicate that the F-ICJ process is a competitive staking joining method with potential for improvement.

Product Distribution during Co-pyrolysis of Bituminous Coal and Lignocellulosic Biomass Major Components in a Drop-Tube Furnace

Co-pyrolysis of the coal blend with lignocellulosic biomass has a significant influence on final product composition of co-gasification and co-combustion. Successful evaluation of the product distribution during co-pyrolysis is very important to understand the overall co-thermochemical process. In this paper, product distribution, especially the gaseous product evolution during a kind of bituminous coal from northern of China blended with lignocellulosic biomass, major model components (cellulose, hemicellulose, and lignin) were explored in a drop-tube furnace from 600 to 1000 °C. The addition of three model components showed different synergistic effects in the product yields and gaseous product composition. Positive synergistic effects in the gas and tar yields were observed during co-pyrolysis of bituminous coal and cellulose, indicating that the addition of cellulose promoted the formation of volatile products. On the contrary, gas yields from co-pyrolysis of bituminous and lignin mixtures showed a ne...

Study on pyrolysis behaviors of non-woody lignins with TG-FTIR and Py-GC/MS

To explore the potential values of lignins extracted from different agricultural wastes (e.g., walnut shell, wheat straw, cotton stalk, rice husk, bamboo, rape straw, corncob and peanut shell), pyrolysis behaviors of eight non-woody lignins were studied with TG-FTIR and Py-GC/MS. The TG-FTIR results indicated that the conversion of lignin and the evolution of main gaseous products were deeply influenced by the biomass species. Compared with the woody lignin, the phenylpropane unit present in the non-woody lignins would enhance the ability of condensation and lead to the formation of biochar. Also, differentiation of pyrolysis products was performed by Py-GC/MS. Corresponding to the classification of lignin types, the relative contents of syringol products from G type lignin were significantly less than those of the other two lignins (GS and HGS types). Compared with commercial alkali lignin (CAL, 6.7%), a high proportion of catechol type compounds was obtained from the peanut shell [37.5%] and cotton stalk [27.6%] lignins. Furthermore, the amount of styrene and 4-hydroxy-3-methoxystyrene was closely related to the content of hemicellulose in raw materials.

Thermal decomposition and evolved gas analysis (TG-MS) of lignite coals from Southwest China

Large amounts of lignite reserve in the southwest of China. However, there is little information about their thermal behaviors during the pyrolysis. In this work, five representative lignite samples which are characterized by high H/C atomic ratios (0.834–1.170) from Yunnan, Southwest China were investigated. The simultaneous thermogravimetry/mass spectrometry was used to study the thermal decomposition and evolved gas characteristics of the five samples. Besides, the Fourier-transform infrared (FTIR) analyzer was used to study the functional-group contents of the five samples in order to investigate the relationships between the thermal behaviors of the samples and their structures. The results revealed the influence of functional groups on the weight loss and gaseous products evolution of the lignite coals. The most prominent peaks of gaseous products were within the scope of 400–700 °C, and the maximum peaks of evolution of CO2, CO and H2O gases well corresponded to the maximum rate of mass loss in the range from 421 to 453 °C. The lignite coals from Southwest China were suitable for low temperature pyrolysis.

Water electrolysis with Zirfon® as separator and NaOH as electrolyte

Composite membranes are aimed at employing and enhancing some characteristics of the two materials they consist of: organic and inorganic materials. In this research work, a member of the composite membrane family, Zirfon®, was studied. This material consists of a polysulphone matrix and zirconium oxide, in the form of powder. The presence of zirconium oxide improves the wettability of the material, an important issue if the process includes the evolution of gaseous products as in water electrolysis. Zirfon® was tested in a crystal acrylic electrolytic cell with rectified blocks, which established the different distances between electrodes. The material selected for the cathode and the anode was stainless steel 316 L. In this experience, 20% w/w NaOH was used as electrolytic solution at room temperature. The experiment was carried out by applying a range of differential potential to the electrolytic cell. Six different distances between electrodes were studied: 7.5, 6.5, 5.6, 4.45, 4.25 and 3.10 mm. The control parameters were current, voltage and temperature. These parameters allowed us to calculate the following: decomposition voltage, resistance and conductance of the electrolytic solution. Resorting to this data set, the distance between electrodes selected was 3.10 mm, where the best performance of the system is obtained.

Kinetic parameters of CaCO3 decomposition in vacuum, air and CO2 calculated theoretically by means of the thermochemical approach

Fundamental advantages of the thermochemical approach compared with the activation approach were supported in this work by the results of theoretical calculations of the A and E kinetic parameters of CaCO3 decomposition in vacuum, air and CO2 and their comparison with experimental data. The temperature of the reaction in CO2 increases from 800 K (in vacuum) up to 1,200 K at equal rates of decomposition. This effect (unexplained in the framework of the activation approach) is of tremendous importance for estimating the thermal stability and lifetime of materials. It has been shown that the pre-exponential factor A in the Arrhenius equation is related to the entropy change of decomposition reaction and, in the isobaric mode, additionally, to the pressure of the external gaseous product. The mysterious effect of “variable activation energy” observed in many non-isothermal studies of solid decompositions, in particular, for CaCO3, was explained by the change of the reaction regime from the isobaric mode at low temperature (and decomposition degree) to the equimolar mode at higher temperatures (and higher decomposition degrees). This effect manifests itself for reactions related to the evolution of O2, H2O and CO2 gaseous products, which can be present in the reactor media as impurities.

Tar evolution in a two stage fluid bed–plasma gasification process for waste valorization

This work focuses on systematic studies of the plasma reforming of newly evolved vapors from a fluid bed gasifier, and on the resulting evolution of individual gaseous cracking products to hydrogen-rich syngas. The aim of this study is to compare some previously developed mechanisms of thermal cracking and to identify the main elementary reactions and the most sensible ones for tar decomposition in a two-stage process. Evaluation of plasma chemistry is performed by a comparison between experimental data and thermal kinetic predicted results. Distribution analysis of condensable organics shows that for all the representative species, the levels of tars are distinct in the first stage and almost negligible after the plasma treatment. Under the given reaction conditions, the organic cracking products such as methane and C2-species are completely converted to carbon monoxide and hydrogen, and no soot significantly formed. Oxygen atoms initially formed from CO2 were identified as the major active species involved in the oxidative decomposition of hydrocarbon intermediates and soot precursors. As a result, a two-stage system shows better reforming results, large treatment capacity and almost complete carbon conversion.

The effects of varying CaO content and rehydration treatment on the composition, yield, and evolution of gaseous products from the pyrolysis of sewage sludge

Sewage sludge samples with CaO contents of 0%, 5%, and 10% as well as rehydrated (50wt% moisture) versions of these three samples were examined. The chemical analyses of the dry sewage sludge samples revealed the inhibition of fatty acids by the formation of calcite (CaCO3) as a result of the generation of calcium carboxylate salts. Pyrolysis experiments were conducted on the dry and rehydrated samples in a fixed-bed reactor under a nitrogen atmosphere and at rate of 5°C/min to a final temperature of 750°C. The effects of varying CaO content and rehydration treatment on the composition, yield, and evolution profiles of the gaseous products that were released during pyrolysis were evaluated. The gaseous products of pyrolysis consisted primarily of CH4, H2, CO2, CO, C2H6, and C3H8. An excess of CaO favored the reverse water-gas shift (WGS) reaction and therefore increased the formation of CO, whereas the rehydration treatment weakened the effect of CaO on the evolution of the gaseous products. The combination of both treatments, CaO addition and rehydration, resulted in (i) a substantial increase in CO formation, (ii) a reduction in the formation of CH4 and CO2, and (iii) CaCO3 decomposition.

Effect of exogenous softwood on thermal decomposition of reconstituted tobacco sheet

In recent years, reconstituted tobacco sheet (RTS) has played an increasingly vital role in reducing tumorigenicity for tobacco industry. In this paper, two plant fibers of tobacco pulp (TP) and softwood pulp (SP) were added independently as strengthening agents during the paper-making process to manufacture RTS (TP-RTS and SP-RTS). The effects of exogenous SP on the CO yield in cigarette mainstream smoke, thermal behavior, and gaseous products evolution properties of RTS were evaluated and compared with TP. The CO yield in cigarette mainstream smoke was studied using smoking machine and CO analyzer. The thermal behavior of two RTS was studied by thermogravimetric (TG) analysis, and the gaseous products were investigated by Fourier transform infrared spectrometer (FTIR). CO yield in cigarette mainstream smoke results demonstrated that SP-RTS (3.16 mg per puff) presented higher CO yield per puff than TP-RTS (2.83 mg per puff). TG analysis results demonstrated that the maximum mass loss rate of SP-RTS (23.3 % min−1) was drastically higher than that of TP-RTS (15.8 % min−1). FTIR results illustrated that SP-RTS presented stronger absorbance intensity associated with generation of more gaseous products than TP-RTS. In the thermal decomposition stage, the maximum mass loss rate of SP (78.6 % min−1) was clearly higher than that of TP (38.4 % min−1), and SP increased the generation of gaseous products compared to TP.

Influence of Ammonium Polyphosphate on Thermal Decomposition of Reconstituted Tobacco and CO Evolution

The thermal behaviors and burning characteristics of reconstituted tobacco (RT) are strongly related with evolved gaseous products. The effect of ammonium polyphosphate (APP) as an additive of RT on the pyrolysis behavior and CO evolution was studied, emphasizing the role of heating velocity in reducing CO delivery of the mainstream smoke by APP. Thermogravimetric analysis (TGA) was employed to investigate the influence of APP on RT thermal behavior. Slow and flash pyrolysis of RT were compared to discuss the role of heating rate in decreasing CO by APP. TGA results demonstrated that, in dependence on APP concentration, APP influenced exothermal amount and weight loss rate during RT thermal decomposition, promoted the formation of char and retarded the thermal decomposition of RT. In addition, APP had a considerable influence on the evolution of gaseous products during thermal decomposition of RT. Both CO delivery per cigarette and that per puff in the smoking process were significantly reduced in dependence on APP content in RT. Comparative analysis of CO evolution patterns in the flash and slow pyrolysis elucidated that heating rate played a key role in decreasing CO evolution by APP. The results suggest that APP is a potential burning additive for controlling CO delivery in mainstream smoke of RT.

Dynamic evolution of emitted volatiles from thermal decomposed bituminous materials

Bituminous material is widely utilized in building waterproof, pavement engineering, etc. However, when the fire happens, hazardous fumes are released due to bitumen decomposition, affecting adversely the environment and human health. The thermal decomposition behavior of bitumen is the first step of its conversion process, such as combustion, and carbonization. To better understand the bitumen conversion when exposed to fire, the decomposition characteristics of bitumen was investigated and the dynamic evolution of gaseous products was characterized in this study. The results from thermogravimetry (TG) indicate that the decomposition of bitumen shows a single-step decomposition mechanism. The spectrum profiles from Fourier transform infrared spectroscopy (FTIR) further characterizes the decomposition mechanism and the overall evolution of volatiles from bitumen at flash and fire points. The evolved volatiles include carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), water (H2O), nitrogen dioxide (NO2), sulfur dioxide (SO2), hydrocarbon, methanol, formic acid, phenols, aromatic compounds, etc. The vapor pressure is a main factor to determine the concentration and hazards of gaseous products during bitumen decomposition. It was found that the evolution of each gaseous product was concentrated from 60min to 110min and each volatile was emitted from different chemical compositions of bitumen at various temperature ranges.

Epoxy-foam adhesives

The historical aspects of creation of domestic epoxy-foam adhesives (FA) for sealing radio-engineering equipment are briefly discussed, and the advantages (adhesion, cohesion strength etc.) over FAs based on other polymers are shown. The characteristics of modern FAs of the VKV series that are used in aircraft engineering are presented. The possibility of application of alternative foaming agents (azo compounds) is shown after which evolution of gaseous products form reactive modifying agents that provide an increase in the strength and operational characteristics compared to the known analogs.