The chemical nature of flash pyrolysis tars. An N.M.R. study

Flash pyrolysis tars from one brown and two bituminous Australian coals were separated into oils, asphaltenes and pre-asphaltenes. The oils were further separated by chromatography while the asphaltenes were separated into basic and acid/neutral fractions. The pre-asphaltenes were silyalated prior to ¹³C- and ¹H-n.m.r. studies. The brown coal tar was less aromatic and contained more long alkyl chains than the tars from the bituminous coals. Aliphatic constituents of the oils, which were relatively abundant, consisted mainly of n-alkanes and straight chain 1-alkenes with an average chain length of ca. C₁₃. The pre-asphaltenes were no more aromatic than the asphaltenes from the same tar but had higher molecular weights.     

Fate of aliphatic groups in low-rank coals during extraction and pyrolysis processes

Information on the nature of aliphatic groups in some bituminous coals and lignites was obtained by determining their fate during extraction and pyrolysis processes of differing severity. Aromatics (neutral oils) and asphaltenes from supercritical gas and hydrogen-donor solvent extracts and from pyrolysis and hydropyrolysis tars have been characterized by an n.m.r.-based structural analysis method which identifies hydroaromatic, methyl and long alkyl (?C₈) groups. The results indicate that methyl and other alkyls account for about half of the aliphatic carbon, long alkyl chains being the major aliphatic group in the lignites. There is evidence to suggest that some of the long alkyl chains are joined to aromatic structures. Hydroaromatic groups are small consisting of only 1–2 rings and account for less of the aliphatic carbon in bituminous coals than previously thought. Their concentrations and those of long alkyl chains in the aromatics and asphaltenes generally decrease with increasing process severity.     

The influence of catalyst regeneration on the composition of zeolite-upgraded biomass pyrolysis oils

The composition of oils derived from the on-line, low pressure zeolite upgrading of biomass pyrolysis oils from a fluidized bed pyrolysis unit have been investigated in relation to the regeneration of the zeolite catalyst. The catalyst used was H-ZSM-5 zeolite. The gases were analysed by packed column gas chromatography. The composition of the oils before catalysis and after catalyst upgrading were analysed by liquid chromatography fractionation, followed by coupled gas chromatography—mass spectrometry of each fraction. In particular, the aromatic and oxygenated aromatic species were identified and quantified. In addition, the oils were analysed for their elemental composition and molecular weight range using size exclusion chromatography. Before catalysis the biomass pyrolysis oil was highly oxygenated but after catalysis a highly aromatic oil was formed with high concentrations of monocyclic aromatic hydrocarbons. In addition, significant concentrations of polycyclic aromatic hydrocarbons (PAH) were formed. Regeneration of the zeolite catalyst showed that continued regeneration reduced the effectiveness of the catalyst in converting biomass pyrolysis oils to an aromatic product. Elemental analysis of the upgraded oils showed an increase in the oxygen content of the oil with increasing regeneration of the catalyst. The molecular weight range of the oils was found to decrease markedly after catalysis, but continued regeneration of the catalyst increased the molecular weight range of the upgraded oils. Detailed analysis of the uncatalysed oils showed they contained low concentrations of aromatic and PAH species which markedly increased in concentration after catalysis. The overall effect of increasing catalyst regeneration was a decrease in the concentration of aromatic hydrocarbons and PAH. Also as the catalyst was regenerated, the number of methyl groups on the parent single ring aromatic compound or PAH increased. The oxygenated aromatic species in the oil before catalysis were mainly, phenols and benzenediols and their alkylated homologues. After catalysis some of the oxygenated species were reduced and some increased in concentration. A dual mechanistic route is suggested for the formation of aromatics and PAH during the catalytic upgrading of biomass pyrolysis oils: (1) the formation of low-molecular-weight hydrocarbons on the catalyst which then undergo aromatization reactions to produce aromatic hydrocarbons and PAH; (2) deoxygenation of oxygenated compounds found in the non-phenolic fraction of the pyrolysis oils which directly form aromatic compounds.     

Structural relationships between kerogens and their pyrolysis products determined with a wire-mesh reactor

Two samples, of different geological age, of each of the three major types of kerogen were pyrolysed in a wire-mesh reactor, allowing tars to be recovered quantitatively under conditions minimizing extraparticle secondary reactions. To gain improved understanding of the reactions leading from kerogens to oil, the structures of the kerogens and their pyrolysis tars were compared by FT-i.r. spectroscopy. Tars were also characterized by size exclusion and planar chromatography. For each type of kerogen, the geologically younger sample gave the greater oil and total volatile yields. The aliphatic hydrogen contents of the kerogen samples were correlated with the oil yields from the wire-mesh reactor. The infrared spectra showed that the tars had substantially higher aliphatic hydrogen and slightly higher aromatic hydrogen contents than those of the original kerogens. Concentrations of phenolic-OH and carbonyl groups were also somewhat higher than in the original kerogen, at the expense of etheric structures, which tend to be present in very low concentrations in kerogen tars. Initial results indicate that a more comprehensive treatment needs to be formulated than that provided by conventional elemental analysis in predicting hydrocarbon production from kerogens.     

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.     

The pyrolysis of scrap automotive tyres: The influence of temperature and heating rate on product composition

Shredded automotive tyre waste was pyrolysed in a 200 cm³ static batch reactor in a N₂ atmosphere. The compositions and properties of the derived gases, pyrolytic oils and solid char were determined in relation to pyrolysis temperatures up to 720 °C and at heating rates between 5 and 80 °C min⁻¹. As the pyrolysis temperature was increased the percentage mass of solid char decreased, while gas and oil products increased until 600 °C after which there was a minimal change to product yield, the scrap tyres producing approximately 55% oil, 10% gas and 35% char. There was a small effect of heating rate on the product yield. The gases were identified as H₂, CO, CO₂, C₄H₆, CH₄ and C₂H₆, with lower concentrations of other hydrocarbon gases. Chemical class composition analysis by liquid chromatography showed that an increase in temperature produced a decrease in the proportion of aliphatic fractions and an increase in aromatic fractions for each heating rate. The molecular mass range of the oils, as determined by size exclusion chromatography, was up to 1600 mass units with a peak in the 300–400 range. There was an increase in molecular mass range as the pyrolysis temperature was increased. FT-i.r. analysis of the oils indicated the presence of alkanes, alkenes, ketones or aldehydes, aromatic, polyaromatic and substituted aromatic groups. Surface area determination of the solid chars showed a significant increase with increasing pyrolysis temperature and heating rate.     

Viscosity modification of flash pyrolysis tars

A study was made of the effect of a number of additives on the viscosity of a characteristic tar produced by the flash pyrolysis of indigenous Australian coals. The results indicate that aliphatic compounds are more effective than aromatic compounds in lowering the viscosity. This observation is of significance in the selection of suitable recycle solvents and the dissolution of aged tars.     

The pyrolysis of propane. I. Production of gases,liquids and carbon

Studies have been carried out on the formation of gases, tars and carbon from the pyrolysis of propane under conditions pertinent to steam cracking. Careful analysis has been carried out to relate the production of gases, liquids and solids in the presence and absence of hydrogen and helium diluents. The experimental observations agree with predictions of gas production from a mathematical model. The reactor surface is shown to influence the production of carbon and possibly the production of gases and tars. Minimisation of coke formation in steam cracking is shown to depend, at least in part, on the correct choice of material for reactor construction.     

Pressure and temperature effect on the mean chemical structure of coal hydrogenolysis product

The hydrogenolysis reaction of coal using red-mud and sulphur as catalyst has been carried out at 400 and 450 °C, 10 MPa or 3 MPa of hydrogen, and 3 MPa of hydrogen plus 7 MPa of nitrogen. The mean chemical structures of the asphaltenes and oils produced show that at first the portion with relatively fewer aromatic rings and more aliphatic structures becomes soluble because of the saturation of the aromatic rings, and then gradually that having more aromatic rings and less of the aliphatic structures does likewise. The higher pressure contributes more to the saturation of aromatic rings and yields more extract. The higher temperature causes thermal decomposition of the aliphatic structures without changing the aromatic structures. When only the total reaction pressure is high, though the hydrogen density is unchanged, the chemical structure of the product is the same, but the reaction rate is accelerated because the reaction proceeds to a greater extent in the liquid state by the suppression of vaporization of low-molecular-weight matter under the higher pressure.     

Coal flash pyrolysis: 2. Polymethylene compounds in low temperature flash pyrolysis tars

Pyrolysis of coals at low temperatures (< 600 °C) produces tars containing the precursors of the low molecular weight aliphatic hydrocarbons, such as ethylene and propylene, observed on flash pyrolysis of the coals at higher temperatures (700–800 °C). This is shown by further pyrolysis of these low temperature tars at high temperatures. Various methods, including isolation by h.p.l.c. were used to confirm the presence of straight chain paraffin and olefin pairs (C₁₄C₂₆ and above) in the low temperature tars. Pyrolysis of pure paraffins and olefins in this molecular weight range at temperatures > 700 °C produce ethylene, propylene and other cracking products similar to those obtained on flash pyrolysis of coal.     

Characterization of pyrolysis tars from Canadian coals

Tars produced by rapid pyrolysis of several Canadian coals have been characterized. Raw tars were separated into solvent fractions which were analysed by a combination of PONA separation by high-performance liquid chromatography, high-resolution capillary gas chromatography and chromatography-mass spectrometry. The alkane-alkene pairs and poly nuclear aromatics found in hexane and benzene fractions are reported for four coals pyrolysed under a range of conditions. The predominance of C₈ to C_14–18 alkane-alkene pairs together with alkyl-substituted benzenes and naphthalenes in the hexane-soluble oils, and three-to five-membered ring aromatics in the benzene-soluble asphaltenes from bituminous coal tars was established. Effects of pyrolysis temperature on aromatic homologues and key nitrogen, sulphur and oxygen heterocyclic homologues are shown.     

Upgrading of flash pyrolysis tars to synthetic crude oil: 4. Hydrotreatment with iron catalyst in a slurry-phase reactor

Flash pyrolysis tars, produced from Millmerran (Queensland subbituminous) and Piercefield (New South Wales bituminous) coals, have been hydrogenated in a slurry-phase bubble-column reactor using red mud and sulphur as catalyst. Oils of low coking propensity and high volatility were produced from both coal tars. The slurry-phase reactor successfully overcame the severe coking problems previously encountered when hydrogenating flash pyrolysis tars in fixed-bed reactors, completely eliminating coke formation. For Millmerran coal tar the effect of reaction temperature on reactor performance was investigated in the range 420–460 °C. The major effects of increasing temperature were to reduce the coking propensity of the product oil and to increase its volatility. Product oils from both tars were high in aromatics and heteroatoms, and the distillate fractions derived from these oils would require further refining to produce finished products (i.e., gasoline and diesel). It should be possible to achieve this using conventional refining technology.     

Flash pyrolysis of coals: behaviour of three coals in a 20 kg h−1 fluidized-bed pyrolyser

Flash pyrolysis of Loy Yang brown coal, and Liddell and Millmerran bituminous coals has been studied using a fluidized-bed reactor with a nominal throughput of 20 kg h^?1. The apparatus and its performance are described. The yields of tar and hydrocarbon gases are reported for each coal in relation to pyrolysis temperature, as also are analytical data on the pyrolysis products. The peak tar yields for the dry, ash-free Loy Yang and Millmerran coals were respectively 23% wt/wt (at ≈ 580 °C) and 35% wt/wt (at $\text{\$}\text{?}$600 °C). The tar yield from Liddell coal was 31% wt/wt at ≈ 580 °C. Hydro-carbon gases were produced in notable quantities during flash pyrolysis; e.g. Millmerran coal at 810 °C gave 6% wt/wt (daf) methane, 0.9% wt/wt ethane, 6% wt/wt ethylene, and 2.5% wt/wt propylene. The atomic $\text{H}\text{C}$ ratios and the absolute levels of hydrogen in product tars and chars decreased steadily with increasing pyrolysis temperature.     

Investigations into the characteristics of oils produced from microwave pyrolysis of sewage sludge

GC–MS was used to determine the main components of high temperature oils obtained from the microwave pyrolysis of sewage sludge under different conditions. The effect of a multimode and a singlemode microwave oven and graphite and char as microwave absorbers on the pyrolysis process was investigated. The pyrolysis of sewage sludge was rapid with both absorbers, temperatures of up to 1000 °C being reached within a few minutes. Although the qualitative composition of the pyrolysis oils was the same for both microwave ovens and absorbers, certain quantitative differences were observed. For example, the use of graphite instead of char produced more cracking in the large aliphatic chains, a higher proportion of 1-alkenes than alkanes and an increase in the proportion of monoaromatics. The multimode microwave oven also favoured cracking and dehydrogenation reactions to a greater extent than the singlemode microwave oven. Compared with the electrical furnace, microwave-assisted heating required shorter times for pyrolysis. Moreover, the microwave pyrolysis oils were more aliphatic and oxygenated and did not contain environmentally harmful compounds such as heavy PAHs. Conversely, the pyrolysis of the sludge at high temperatures using conventional methods gave rise to an oil rich in PAHs including compounds such as benzo[e] and benzo[a]pyrene and benzo[ghi]perylene with 5 or 6 aromatic rings.     

Flash pyrolysis of an Italian low rank coal

Flash pyrolysis of low rank Italian coal (Sulcis coal) has been studied in a fluidized bed pyrolyser using temperatures between 460 and 900°C. The maximum yield of oils (tars) was obtained at about 600°C. Yields of C₁C₃ hydrocarbons increased with increasing temperature, reaching 6% at 900°C. Fractionation of tars showed that the composition was strongly dependent on pyrolysis temperature. By the behaviour of the composition of tars on temperature, a possible reaction mechanism is suggested.     

Kinetics of Colorado oil shale pyrolysis in a fluidized-bed reactor

Previous hydrocarbon evolution data were reanalysed to determine improved rate expressions for oil generation from Colorado oil shale under rapid pyrolysis conditions. Contributions from low-molecular-weight gases were subtracted from flame-ionization detector data to obtain the rate of oil generation alone. Equally good fits to the data were obtained using two parallel first-order reactions or a single reaction with an effective reaction order of 1.51. The latter expression was easier to incorporate into global process models. The rate expressions were independent of shale source (Anvil Points or Tract C-a) and particle size (0.5–2.4 mm). The kinetic data were consistent with the previous conclusion that the small incremental oil yield possible for fluidized-bed pyrolysis requires a longer residence time than that estimated by kinetic expressions derived from slow-heating data.     

Performance studies of various cracking catalysts in the conversion of canola oil to fuels and chemicals in a fluidized-bed reactor

Studies were conducted at atmospheric pressure at temperatures in the range of 400–500°C and fluidizing gas velocities in the range of 0.37–0.58 m/min (at standard temperature and pressure) to evaluate the performance of various cracking catalysts for canola oil conversion in a fluidized-bed reactor. Results show that canola oil conversions were high (in the range of 78–98 wt%) and increased with an increase in both temperature and catalyst acid site density and with a decrease in fluidizing gas velocity. The product distribution mostly consisted of hydrocarbon gases in the C₁–C₅ range, a mixture of aromatic and aliphatic hydrocarbons in the organic liquid product (OLP) and coke. The yields of C₄ hydrocarbons, aromatic hydrocarbons and C₂–C₄ olefins increased with both temperature and catalyst acid site density but decreased with an increase in fluidizing gas velocity. In contrast, the yields of aliphatic and C₅ hydrocarbons followed trends completely opposite to those of C₂–C₄ olefins and aromatic hydrocarbons. A comparison of performance of the catalysts in a fluidized-bed reactor with earlier work in a fixed-bed reactor showed that selectivities for formation of both C₅ and iso-C₄ hydrocarbons in a fluidized-bed reactor were extremely high (maximum of 68.7 and 18 wt% of the gas product) as compared to maximum selectivities of 18 and 16 wt% of the gas product, respectively, in the fixed-bed reactor. Also, selectivity for formation of gas products was higher for runs with the fluidized-bed reactor than for those with the fixed-bed reactor, whereas the selectivity for OLP was higher with the fixed-bed reactor. Furthermore, both temperature and catalyst determined whether the fractions of aromatic hydrocarbons in the OLP were higher in the fluidized-bed or fixed-bed reactor.     

Comparative analysis of pyrolysis oils and its subfractions under different atmospheric conditions

In this paper comparative analysis of bio-oils and their subfraction from static, sweeping gas and steam pyrolysis of apricot pulp, a food industry waste, was investigated. Experimental studies were conducted in a well-swept fixed-bed reactor with a heating rate of 5 °C min^{− 1}, to a final pyrolysis temperature of 550 °C. The oil yield which was 22.4% at the static atmosphere reached to the value of 23.2% in the sweeping gas atmosphere by using 100 cm³ min^{− 1} N₂ flow rate. The yield of liquid product in steam pyrolysis was higher (27.2%) than the static and inert gas atmosphere.The elemental analyses of the pyrolysis oils were determined, and the chemical compositions of the oils were investigated using chromatographic and spectroscopic techniques. The liquid products were fractionated into pentane solubles and insolubles (asphaltenes). Pentane solubles were then solvent fractionated into pentane, toluene, and methanol subfractions by fractionated column chromatograpy. The aliphatic subfractions of the oils were then analysed by capillary column gas–liquid chromatography and GC/MS. For further structural analysis, the pyrolysis oils' aliphatic, aromatic and polar subfractions were conducted using FTIR and ¹H NMR spectra.     

Kinetics of reactions involved in pyrolysis of cellulose I. The three reaction model

Kinetics of reactions involved in pyrolysis of cellulose has been modeled in terms of a three reaction model. In this model it is assumed that cellulose decomposes to tars, chars and gaseous products via three competitive first-order reactions. Arrhenius parameters have been obtained to describe the rate constants of these reactions. The three reaction model predicts the weight loss data reasonably well. Product yields of tars, chars and gases predicted by the three reaction model are compared over the temperature range 250 to 360°C. In this communication a technique for analyzing experimental data of a solid state reaction is presented.     

塑料与煤低温共焦化的液体产物性质分析

利用GC -MS考察了不同种类塑料 (PDPE ,PP ,PPVC)单独热解及与八一焦煤低温共焦化焦油的组成。结果表明 :添加HDPE、PP使煤焦油中脂肪烃的相对收率提高 ,焦油中脂肪烃的含量明显增加和轻质化 ,可作为加氢精制汽油的原料 ;而PPVC则使脂肪烃和芳香化合物的相对收率均增加 .塑料与煤共焦化过程中同时存在物理和化学协同作用 ,减少了二次反应的机会 ,增加了焦油收率 ,同时促进了焦油中芳香化合物的甲基化 .