Thermal decomposition products of polyacrylonitrile

The decomposition products of a polyacrylonitrile yarn thermally decomposed at temperatures of 400°, 600°, and 800°C, under a flow of either air or nitrogen, have been analyzed by GC and GCMS. Hydrogen cyanide and 16 other nitriles were identified and quantified. Decomposition products contained a series of aliphatic nitriles of various chain lengths, and HCN was the predominant toxic product.     

Thermal Dissolution of Coking Coals in the Anthracene Fraction of Coal Tar

The thermal dissolution of two samples of 1GZhR and ZhR coal in the anthracene fraction of coal tar is studied. The yield of quinoline-soluble products increases considerably in the temperature range of coal softening. Optimal thermal-dissolution conditions are determined for selective production of quinoline-soluble pitch-like products. At 350–380°C, the yield of quinoline-soluble products is 70–73% after 1–2 h. The yields of the distillate fraction and the gas are 0.9% and 0.2%, respectively. The ash-free pitch-like product is a plastic mass with a softening temperature of 76–81°C. It consists mainly of polycyclic aromatic hydrocarbons with a few short alkyl substituents in the aromatic rings. The spatial structure mainly includes poorly structured polycyclic aromatic molecules of the γ component. The proportion of relatively ordered graphitelike packets is 31–37%. Each packet contains five stacked polycyclic aromatic molecules of diameter 17 Å. In terms of its composition and plasticity, the product is suitable as a source of alternatives to coal pitch.     

Thermal degradation behaviour of aromatic poly(ester–imide) investigated by pyrolysis–GC/MS

The thermal degradation behaviours of a novel aromatic poly(ester–imide) (PEI) derived from pyromellitic dianhydride and 2,7-bis(4-aminobenzoyloxy)naphthalene have been investigated by thermogravimetric analysis (TGA) and by pyrolysis–gas chromatography/mass spectrometry (pyrolysis–GC/MS). The weight of PEI fell slightly in the temperature range of 350–450 °C in the TGA analysis, but the major weight loss occurred at 520 °C. Evolve gas analysis (EGA) of the PEI showed maximum release of pyrolyzates at 550 °C. The chemical structure of the volatile products resulted from the PEI pyrolysis at different temperatures was identified by pyrolysis–GC/MS. The cleavage of the ester linkage within the polymer chain initiated at 350 °C, and bond scission in the partially hydrolyzed pyromellitimide unit occurred in the temperature range of 450–500 °C. The bonds within the pyromellitimide unit started to cleave at 550 °C. The extensive decomposition of the pyromellitimide segment within the polymer backbone occurred at 600 °C. The possible thermal degradation pathways of this PEI are proposed on the basis of the pyrolysis products.     

Studien über die Autoxidation von 1-Phenylbuta-1,3-dien und 2-Phenylbuta-1,3-dien

Studies on the Autoxidation of 1-Phenylbuta-1,3-diene and 2-Phenylbuta-1,3-diene Hydrogenation of the polymeric peroxides formed during the autoxidation of 1-phenylbuta-1,3-diene ( 1 ) and 2-phenylbuta-1,3-diene ( 10 ) at 50°C in an autoclave yielded 1-phenylbutane-3,4-diol ( 5 ) and 2-phenylbutane-1,4-diol ( 12 ), respectively. The LiAlH₄ reduction of 1-phenylbuta-1,3-diene oxidate (50°C) yielded cinnamyl alcohols ( 4 ) as a major product. The oxygen-containing polymeric products formed along with Diels-Alder dimers during the oxidation of the title substances at 140°C showed no degradation after subjecting to hydrogenation and are therefore considered as polyethers.     

Exactly alternating silarylene—siloxane polymers: 6. Thermal stability and degradation behaviour

The thermal stability and degradation behaviour of a series of twelve different exactly alternating silarylene—siloxane polymers were investigated by several different methods including thermal gravimetric analysis (t.g.a.) in air and in nitrogen, long term (up to 48 h) high temperature (600° and 900°C) isothermal degradation in nitrogen, and rapid pyrolysis in helium. No weight loss was observed by t.g.a. until about 400°C, and two distinctly different mechanisms were observed, one for degradation in nitrogen (a single step process), and the other in air (a three step process). Under nitrogen, black, insoluble, carbon-hydrogen-silicon containing degradation products were obtained, which were stable in pure oxygen to at least 1100°C. In air, pure SiO₂ was obtained after heating to above 730°C. Isothermal investigations revealed that at temperatures of 600°C and above, weight loss by thermal degradation under a nitrogen atmosphere was completed in less than an hour, and the polymeric products which remained thereafter did not change any further even after 48 h at 900°C.     

Studies of heterocyclic polymers. V. poly (1, 3′-benzobis (iminopyrrolenones))

The synthesis of dimethyl-2, 5-dicyanoterephthalate from 2,5-dibromo-p-xylene and its conversion to 1,3′-benzobis (iminopyrrolenone) are reported. 1,3 -Benzobis (N-phenyliminopyrrolenone) was prepared by reaction of 1,3′-benzobis (iminopyrrolenone) with aniline. The product was a bright yellow crystalline solid which was also formed when dimethyl-2,5-dicyanoterephthalate was condensed with aniline under suitable conditions. Poly (1,3′-benzobis (iminopyrrolenones)) were synthesised by the condensation of 1,3′ -benzobis (iminopyrrolenone) with aromatic diamines and with 1,6-diaminohexane at high temperatures in dimethyl sulphoxide. The degrees of polymerisation of the polymers obtained were low, as judged by the completeness of the condensation reaction. Thermogravimetric analyses of these polymers in air showed that they have 10% weight-loss temperatures in the range 420 to 520°C, for the polymers prepared from aromatic diamines, and of 350°C for the polymer derived from 1,6-diaminohexane. The insoluble, intractable nature of these polymers precluded a thorough study of their structure.     

Hydrogenation of Liddell coal. Yields and mean chemical structures of the products

The products from the hydrogenation of an Australian medium-volatile bituminous coal (Liddell) in batch autoclaves have been investigated. Tetralin was used as a vehicle and Cyanamid HDS-3A as catalyst. The influences of temperature (315–400 °C), hydrogen pressure (3.4–17.2 MPa) and reaction time (0–4 h) on the yields of pre-asphaltene, asphaltene, oil and pitch were studied. The chemical compositions of these materials were investigated by nuclear magnetic resonance and infrared spectrometry, and high-pressure liquid chromatography. Higher temperatures (400 °C) and pressures (17.2 MPa) favour the formation of products with lower average molecular size, lower aromatic carbon and aromatic proton contents and smaller average aromatic fused-ring number. N.m.r. evidence is presented which shows that increasing the temperature from 370 °C to 400 °C or pressure to 17.2 MPa assists reactions which bring about hydrogenation and cleavage of aryl rings. Longer reaction times (4 h) promote reactions by which the oxygen content of the product is decreased and by which polymethylene becomes cleaved from other functional groups. The results show that asphaltenes are true intermediates in the formation of oil from coal.     

Thermal Isomerization of Azulene. Single-Pulse Shock Tube Investigation

The thermal isomerization of azulene was studied behind reflected shocks in a pressurized driver single-pulse shock tube. The temperature range covered was 1050–1400 K at overall densities of ∼2.5 × 10⁻⁵ mol/cm³. The main reaction of azulene under these conditions is a unimolecular isomerization to naphthalene, but it also isomerizes, although at a much lower rate, to another isomer. The suggested “tetracyclic triene” intermediate structure for the azulene-naphthalene isomerization can lead also to transition states that can describe isomerizations to 1-methylene-1H-indene and 1, 2,3-metheno-1H-indene,2,3-dihydro. Small quantities of C₂H₂, C₄H₂, C₆H₆, and C₆H₅-C≡CH were also found in the post-shock samples, particularly at high temperatures. The Arrhenius parameters of the two high pressure limit rate constants for the isomerization processes are: azulene → naphthalene, k₁ = 10^12.93 exp(–62.8 × 10³/RT) s⁻¹ azulene → second isomer, k₂ = 10^12.42 exp(–69.5 × 10³/RT) s⁻¹ A discussion of the mechanism for these isomerization processes is presented.     

Thermal degradation of polytetrafluoroethylene in flowing helium atmosphere II. Product distribution and reaction mechanism

The thermal degradation of polytetrafluoroethylene was studied in the helium flowing atmosphere and the temperature range 510–600°C. The products of the thermal degradation of polytetrafluoroethylene were analyzed by an on-line gas Chromatograph and the product distribution was obtained. The products consist of tetrafluoroethylene (TFE), perfluoropropene (PFP) and cyclic-perfluorobutane (c-PFB). Under most conditions the main product was TFE. The c-PFB was regarded as the secondary product formed from TFE because the formation of c-PFB strongly depended upon the degradation rate. However, the production of PFP was not related to the degradation rate, but it was influenced by diffusion limitation of gaseous product in the sample matrix. These phenomena were also verified with Curie-point pyrolyser. The results showed that the production of PFP reached a maximum point under diffusion limitation condition. The degradation mechanism of polytetrafluoroethylene was proposed in terms of unzipping mechanism and other mechanism like radical chain transfer reaction.     

1H n.m.r. study of tars from flash pyrolysis of three Australian coals

The structure and composition of tars from the flash pyrolysis of one brown and two bituminous Australian coals were investigated by ¹H n.m.r. spectroscopy. Reaction times in a fluidized bed were about 1 s. For each tar the aromatic hydrogen content increases slightly with pyrolysis temperature up to ≈650 °C and then rapidly up to 900 °C. The aromatic carbon content increases rectilinearly with temperature. The yield of aromatic carbon reaches a maximum at 600–700 °C, and then decreases; the yield of aromatic hydrogen is independent of temperature. The proportion of aromatic material with condensed ring structures increases with temperature. Three temperature zones of reactivity can be recognized. Polymethylene chains and aromatic groups are stable up to 600 °C. Between 600 and 700 °C aliphatic substituents, other than α groups, decompose; between 700 and 900 °C α-aliphatic and aromatic groups also decompose, resulting in lower yields of tar.     

A comparative study of the formation of aromatics in rich methane flames doped by unsaturated compounds

For a better modeling of the importance of the different channels leading to the first aromatic ring, we have compared the structures of laminar rich premixed methane flames doped with several unsaturated hydrocarbons: allene and propyne, because they are precursors of propargyl radicals which are well known as having an important role in forming benzene, 1,3-butadiene to put in evidence a possible production of benzene due to reactions of C₄ compounds, and, finally, cyclopentene which is a source of cyclopentadienyl methylene radicals which in turn are expected to easily isomerizes to give benzene. These flames have been stabilized on a burner at a pressure of 6.7 kPa (50 Torr) using argon as dilutant, for equivalence ratios (?) from 1.55 to 1.79. A unique mechanism, including the formation and decomposition of benzene and toluene, has been used to model the oxidation of allene, propyne, 1,3-butadiene and cyclopentene. The main reaction pathways of aromatics formation have been derived from reaction rate and sensitivity analyses and have been compared for the three types of additives. These combined analyses and comparisons can only been performed when a unique mechanism is available for all the studied additives.     

Omega−3 fatty acid ethyl ester from a simple catalytic non-oxidative dehydrogenation of a biobased oleochemical

Essential fatty acids and derivatives, such as ethyl esters, have acquired an important interest, lately. The reactivity of ethyl linoleate (di-unsaturated fatty acid ethyl ester, FAEE), specially the catalytic reactions of non-oxidative dehydrogenation and isomerization, in a fixed bed reactor using active carbon as a catalyst has been studied. Active carbon presented dehydrogenation properties under non-oxidative conditions and in a temperature range of 70–120 °C. Omega−3 tri-unsaturated FAEE and aromatic FAEE were the detected dehydrogenation compounds. Mono-unsaturated FAEE and isomers of ethyl linoleate were the products of hydrogenation and isomerization reactions, respectively. The dehydrogenation activity of active carbon remained stable with time. The non-oxidative dehydrogenation to omega−3 tri-unsaturated FAEE becomes more important than the isomerization and hydrogenation reactions at lower temperatures such as 70 °C. Up to a 7.2% of omega−3 tri-unsaturated FAEE has been obtained synthetically for the first time.     

Biologisch abbaubare Polyester-Copolymere aus petrochemischen und nachwachsenden Rohstoffen

Biological Degradable Polyester Copolymers from Petrochemical and Renewable Raw Material. Synthetic, biodegradable aliphatic polyesters often do not provide optimal properties of application (e.g. melting point of polycaprolactone: 60°C). Material properties of such polyesters can be improved by introducing aromatic compounds into polymers. It could be shown that random aliphatic/aromatic copolyesters consisting of components like 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, adipic acid, sebacic acid and terephthalic acid (35–55 mol-% with regard to the diacid components) exhibit melting points of up to 145°C. These copolyesters are still biodegradable making this material of great commercial interest. Significant weight losses of polyester films could be observed in three months soil burial experiments(up to 40mol-% terephthalic acid) and in compost simulation tests at 60°C (up to 50 mol-% terephthalic acid). From degradation experiments with aromatic model oligoesters from terephthalic acid and 1,2-ethanediol (1,3-propanediol, 1,4-butanediol, respectively) it could be concluded that, aromatic intermediates (oligomers) will be assimilated very fast by microorganisms, if the degree of polymerization is one or two. It seems that longer oligomers are not accessable for an enzymatic attack, but will probably be hydrolyzed chemically at elevated temperatures (60°C), too. Using especially screened thermophilic microorganisms (55°C) on agar plates and analysis of residual material by size exclusion chromatography, the above mentioned finding could be confirmed. Some of the components of polyesters, described here can be obtained from renewable resources. For instance. 1,3-propanediol can by produced by a fermentation process from glycerol and a number of aliphatic dicarboxylic acids are available from natural oils. This option can make biodegradable high-tech polyesters with a defined structure part of natural cycles.     

Thermal cis–trans isomerization of azo dye chrysophenine in cellulose matrices: Effect of morphology

Films obtained from native cellulose synthesized by Acetobacter xylinum and from cellulose obtained from cuproammoniacal solutions (cellulose II) were morphologically characterized by studying the cis-trans isomerization of azo dye Chrysophenine dispersed in their amorphous region. The kinetic measurements of the reaction showed that both films behave as glassy polymers in the temperature range explored (36–66°C). In going from native cellulose to cuproammoniacal cellulose, an increase of the isomerization rate was observed, revealing a more homogeneous distribution and likely larger extent of free volume in the amorphous phase of cellulose II.     

Thermal decomposition of strontium oxalate — effect of various atmospheres

Decomposition products have been prepared from strontium oxalate monohydrate by heating for 2 h at 410, 470 and 510 °C in presence of air, water vapour at various pressures, nitrogen, hydrogen or carbon dioxide atmosphere. Structural, textural and morphological changes have been studied by X-ray diffraction and electron microscopy; the influence of various atmospheres is discussed. Differential thermal analysis and thermogravimetry reveal that dehydration of the starting material proceeds in two steps: a main dehydration process takes place at 180 °C, followed by the release of a small amount of water (～5%) at 270 °C. Decomposition of oxalate into carbonate covers the range 400 – 480 °C; a very small endotherm is observed at 450 °C, masked by a strong exotherm (530 °C) due to the release of energy probably accompanying the conversion of the amorphous decomposition product of the oxalate into a crystalline form.     

Thermal and catalytic upgrading of a biomass‐derived oil in a dual reaction system

The thermal and catalytic upgrsding of bio‐oil to liquid fuels was studied at atmospheric pressure in a dual reactor system over HZSM‐5, silica‐alumina and a mixed catalyst containing HZSM‐5 and silica‐alumina. This bio‐oil was produced by the rapid thermal processing of the maple wood. In this work, the intent was to improve the catalyst life. Therefore, the first reactor containing no catalyst facilitated thermal cracking of blo‐oil whereas the second reactor containing the desired catalyst upgraded the thermally cracked products. The effects of process variables such as reaction temperature (350°C to 410°C), space velocity (1.8 to 7.2 h^?1) and catalyst type on the amounts and quality of organic liquid product (OLP) were investigated, In the case of HZSM‐5 catalyst, the yield of OLP was maximum at 27.2 wt% whereas the selectivity for aromatic hydrocarbons was maximum at 83 wt%. The selectivities towards aromatics and aliphatic hydrocarbons were highest for mixed and silica‐alumina catalysts, respectively. In all catalyst cases, maximum OLP was produced at an optimum reaction temperature of 370°C in both reactors, and at higher space velocity. The gaseous product consisted of CO and CO₂, and C₁‐C₆ hydrocarbons, which amounted to about 20 to 30 wt% of bio‐oil. The catalysts were deactivated due to coking and were regenerated to achieve their original activity.     

Thermal and catalytic degradation of waste high-density polyethylene (HDPE) using spent FCC catalyst

Thermal and catalytic degradation using spent fluid catalytic cracking (FCC) catalyst of waste high-density polyethylene (HDPE) at 430 °C into fuel oil were carried out with a stirred semi-batch operation. The product yield and the recovery amount, molecular weight distribution and paraffin, olefin, naphthene and aromatic (PONA) distribution of liquid product by catalytic degradation using spent FCC catalyst were compared with those by thermal degradation. The catalytic degradation had lower degradation temperature, faster liquid product rate and more olefin products as well as shorter molecular weight distributions of gasoline range in the liquid product than thermal degradation. These results confirmed that the catalytic degradation using spent FCC catalyst could be a better alternative method to solve a major environmental problem of waste plastics. This paper is dedicated to Dr. Youn Yong Lee on the occasion of his retirement from Korea Institute of Science and Technology.     

Thermal degradation of long‐chain polyunsaturated fatty acids during deodorization of fish oil

Long‐chain polyunsaturated fatty acids (LC‐PUFA) of the n‐3 series, particularly eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid, have specific activities especially in the functionality of the central nervous system. Due to the occurrence of numerous methylene‐interrupted ethylenic double bonds, these fatty acids are very sensitive to air (oxygen) and temperature. Non‐volatile degradation products, which include polymers, cyclic fatty acid monomers (CFAM) and geometrical isomers of EPA and DHA, were evaluated in fish oil samples obtained by deodorization under vacuum of semi‐refined fish oil at 180, 220 and 250 °C. Polymers are the major degradation products generated at high deodorization temperatures, with 19.5% oligomers being formed in oil deodorized at 250 °C. A significant amount of CFAM was produced during deodorization at temperatures above or equal to 220 °C. In fact, 23.9 and 66.3 mg/g of C20 and C22 CFAM were found in samples deodorized at 220 and 250 °C, respectively. Only minor changes were observed in the EPA and DHA trans isomer content and composition after deodorization at 180 °C. At this temperature, the formation of polar compounds and CFAM was also low. However, the oil deodorized at 220 and 250 °C contained 4.2% and 7.6% geometrical isomers, respectively. Even after a deodorization at 250 °C, the majority of geometrical isomers were mono‐ and di‐trans. These results indicate that deodorization of fish oils should be conducted at a maximal temperature of 180 °C. This temperature seems to be lower than the activation energy required for polymerization (intra and inter) and geometrical isomerization.     

Microstructure of a Pd/ceria–zirconia catalyst after high-temperature aging

Ga/ZSM-5 is an effective catalyst for the conversion of dilute (3%) ethylene-in-methane reactant streams into aromatic hydrocarbons at 500–550°C. A Ga loading as low as 0.5 wt% is sufficient to obtain maximum yields of aromatic products. At 520°C, an ethylene conversion of 93%, with an aromatics selectivity of 81%, was obtained over a 5 wt% Ga/ZSM-5 catalyst. The conversion of ethylene into aromatics over Ga/ZSM-5 catalysts involves a complex sequence of oligomerization, isomerization, cracking, and cyclization reactions that occur on Brønsted acid zeolites in the zeolite. The role of the gallium, which exists as both Ga³⁺ at zeolitic exchange sites and as Ga₂O₃ within the channels and on the external surface of the calcined catalyst, is to promote dehydrogenation of the acid-catalyzed oligomerization and cyclization products.     

Thermal behavior and reactivities of prepolymers prepared from aromatic biscyanamides and bismaleimide

Novel polymers obtained by reaction of aromatic biscyanamide and bismaleimide compounds were investigated. By heating 4,4′-methylene bis(o-methylphenylcyanamide) (BMCA) with 4,4′-methylene bis (phenylmaleimide) (BMI) at 120°C in N,N-dimethylformamide (DMF), prepolymers were obtained by the conversion of cyanamide to cyanoguanidine and the addition of an imino group on the double bond of maleimide. The prepolymer showed suitable behavior for thermosetting resin used in molding, i.e., it melted temporarily and then polymerized in an isochronal heating process (5°C/min). On heating above 170°C, the prepolymer could polymerize with ring formation of melamine and isomelamine. The cured product had good heat-resistant properties.