Flash pyrolysis of coals. Devolatilization of bituminous coals in a small fluidized-bed reactor

The devolatilization behaviour of ten bituminous coals was investigated under rapid heating conditions using a small-scale fluidized-bed pyrolyser. The pyrolyser operated continuously, coal particles being injected at a rate of 1–3 g h^?1 directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbon gases, and total volatile-matter and an agglomeration index are reported for all coals. Maximum tar yields were obtained at about 600 °C and were always substantially higher than those from the Gray-King assay. Total volatile-matter yields were also substantially higher than the proximate analysis values. The maximum tar yields appear to be directly proportional to the coal atomic $\text{H}\text{C}$ ratio. The elemental analysis of the tar is strongly dependent on pyrolysis temperature. The tar atomic $\text{H}\text{C}$ ratio is proportional to that of the parent coal. The effect on the devolatilization behaviour of two coals produced by changes in the pyrolyser atmosphere and the nature of the fluidized-bed material were also investigated. Substituting an atmosphere of hydrogen, helium, carbon dioxide or steam for nitrogen, has no effect on tar yield and, with one exception, little effect on the hydrocarbon gas yields. In the presence of hydrogen the yield of methane was increased at temperatures above 600 °C. Tar yields were significantly reduced on substituting petroleum coke for sand as the fluid-bed material. A fluidized bed of active char virtually eliminated the tar yield.     

Flash pyrolysis of coals: comparison of results from 1 g h−1 and 20 kg h−1 reactors

The performances of 1 g h^?1 and 20 kg h^?1 flash pyrolysers are compared for three Australian coals: Loy Yang brown coal (Victoria), Liddell bituminous coal (New South Wales), and Millmerran sub-bituminous coal (Queensland). The two reactors gave comparable yields of tar, char and C₁–C₃ hydrocarbon gases over a range of operating conditions for each particular coal. The yield of total volatile matter from Millmerran coal was similar from both reactors, as were the compositions of chars from Loy Yang coal and tars from the Liddell and Millmerran coals. For Millmerran coal, the yields of tar, C₁–C₃ gases and volatiles from the large reactor below 650 °C, were slightly lower than for the small reactor, possibly owing to a shorter retention time of Millmerran coal particles in the large-scale reactor. At a temperature near 600 °C tar yields were independent of tar concentration in the effluent gas, over a range 0.0025–0.1 kg m^?3 for Liddell coal, 0.005–0.26 kg m^?3 for Millmerran coal and 0.0045–0.09 kg m^?3 for Loy Yang coal. The tar yields from Millmerran and Liddell coals at 600 °C in the large reactor, correlate directly with the atomic $\text{H}\text{C}$ ratio of the parent coal, in the same manner as that found for a wider range of bituminous coals in the small-scale reactor.     

Gel permeation chromatographic analysis of solubilized lignite asphaltenes and preasphaltenes

GPC data have been measured for a series of acetylated solvent refined lignite (SRL) asphaltenes and preasphaltenes and model compounds. Two structural parameters, the degree of aromatic condensation ($\text{H}{}_{\mathrm{aru}}\text{C}{}_{\mathrm{ar}}$) and the molar hydrogen to carbon ratio ($\text{H}\text{C}$), were employed to correct the molecular weight of the samples for linear molecular size. For the model compounds, $\text{H}{}_{\mathrm{aru}}\text{C}{}_{\mathrm{ar}}$ was more effective, whereas the SRL materials were better adjusted by $\text{H}\text{C}$. The calibration standards deemed most suitable for determination of molecular weight of SRL by GPC are the SRL samples themselves.     

Flash pyrolysis of coals: influence of cations on the devolatilization behaviour of brown coals

The influence of cations on the pyrolysis behaviour of brown coals under flash heating conditions was investigated by means of a small fluidized-bed pyrolyser. A stream of coal particles in nitrogen was injected at rates of 1–3 g coal/h directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbons and total volatile matter from four Gelliondale brown coals and a Montana lignite were determined as a function of pyrolysis temperature. With all coals the maximum tar yield was obtained at 600 °C. Removal of cations present in the coals markedly increased the yields of tar and total volatile matter, with little effect on the yields of hydrocarbon gases. The converse was also observed in that the addition of Ca²⁺ to a cation-free coal decreased the yields of tar and total volatile matter. The extent of the reduction in tar yield at 600 °C in the presence of cations was found to be similar for all coals. After acid washing, tar yields appear to correlate with the atomic $\text{H}\text{C}$ ratios of the coals in a manner similar to that observed previously with bituminous coals.     

Electrochemical reduction of polymeric carbon

It was found that the electrochemical reduction of poly (tetrafluoroethylene) with lithium amalgam leading to the mixture of polymeric carbon and lithium fluoride as solid product is followed by a consecutive electrochemical reaction via a polymeric anion radical, [$\text{(}\text{?}$C_n$\text{)}\text{?}$^?]_m. The value of n was determined as 4.75 and was found to be independent of the reaction conditions. The charge of this radical is during the reaction neutralised with Li⁺ ions diffusing through the solid phase to form a chemical compound $\text{(}\text{?}$C_nLi$\text{)}\text{?}$_m whose CLi bonds have a localized character. Therefore, this compound does not evolve hydrogen in contact with water as the intercalation compounds C_nLi, but hydrolyses to a solid hydrocarbon $\text{(}\text{?}$C_nH$\text{)}\text{?}$_m.     

The significance of heating rate on char yield and char properties in the pyrolysis of cellulose

The carbonization of powdered cellulose was investigated in the temperature range 200–950°C by measuring weight loss, carbon and hydrogen content, BET-adsorption of nitrogen and carbon dioxide, mercury penetration and particle-size distribution. Evidence is presented in support of a kinetic model according to which cellulose decomposition is controlled by dehydration at low temperature and by cleavage/scission at high temperature. Increased char yield and lower $\text{O}\text{C}$ ratio at low heating rate, as well as kinetic investigations into the effect of potential catalysts, support this model. The difference in reaction mechanism according to the heating rate appeared to influence the char properties considerably. Yield in micropore volume and surface area of slowly carbonized cellulose is up to four times larger than that of rapidly heated cellulose. Mercury pore volume, density and particle diameter depend on the heating rate, also. By adsorption of various gases, differences in relative size of the pore openings of different chars can be discerned. Micropore volumes measured with carbon dioxide were as much as seventy times larger than the corresponding volume measured with nitrogen. Thus, it is possible to obtain chars with molecular sieve properties by simple pyrolysis heating schemes.     

Twenty-five years of Brown and Ladner's parameters

Brown and Ladner's parameters have been compared with those of Williams for the same conditions. The combination of experimental data from ¹H n.m.r. and ¹³C n.m.r. spectra gives the value of the Brown and Ladner's parameter $\text{H}{}_{\mathrm{aru}}\text{C}{}_{\mathrm{ar}}$. A comparison of the $\text{H}{}_{\mathrm{aru}}\text{C}{}_{\mathrm{ar}}$ values was performed on a group of different coal oil samples.     

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.     

Development of aromaticity in cellulosic chars

Cellulosic chars prepared at HTTs ranging up to 500°C contain aromatic structures as evidenced by the production of benzene polycarboxylic acid derivatives on permanganate oxidation. Analysis of these products indicates the concentration of the aromatic units and the degree of substitution of benzene polycarboxylic acids represents the extent of condensation or crosslinking of the structures. Further information on this subject is obtained by elemental composition of the char and the $\text{H}\text{C}$ ratio. These studies indicate a rapid weight loss and development of aromatic structures between 350 and 400°C, as the $\text{H}\text{C}$ ratio is gradually reduced from 1.5 to 0.7 and the aromatic carbon of the benzene polycarboxylic acids formed is increased to 2.5% of the carbon content of the original cellulose. Above 400°C the rate of weight loss is reduced with the formation of the “stable” char and the yield of the aromatic carbon remains constant. However, the aromatization process continues with rapid reduction in $\text{H}\text{C}$ ratio, due to the condensation and growth of the aromatic clusters as evidenced by the increased formation of the highly substituted benzene polycarboxylic acids. The presence of inorganic additives, representing flame retardants results in increased charring and enhancement of aromaticity and condensation.     

Carbon-supported sulfide catalysts

The activities of sulfided $\text{Mo}\text{C}$, $\text{W}\text{C}$, $\text{Co}\text{C}$, $\text{Ni}\text{C}$, $\text{Co-}\text{Mo}\text{C}$, and $\text{Ni-W}\text{C}$ catalysts for thiophene hydrodesulfurization and butene hydrogenation were studied using a flow microreactor operating at atmospheric pressure. The following parameters were varied: type of carbon support, carbon pretreatment, catalyst preparation method, and content of active material. The results are compared with those obtained for series of sulfided Mo/γ-Al₂O₃, W/γ-Al₂O₃, $\text{Mo}\text{SiO}{}_2$, and $\text{W}\text{SiO}{}_2$. Some samples, viz., $\text{Mo}\text{C}$, $\text{Co}\text{C}$, and $\text{Co-Mo}\text{C}$, were also studied by X-ray photoelectron spectroscopy (XPS). The carbon-supported catalysts demonstrated outstanding performance for thiophene hydrodesulfurization. XPS analysis showed the presence of low-valence-state sulfur, e.g., S^? or (S-S)^2?, in $\text{Mo}\text{C}$ and $\text{Co}\text{C}$ catalysts with low molybdenum or cobalt content. These sulfurspecies are supposedly connected with the catalytic activity for hydrodesulfurization. $\text{Co}\text{C}$ and $\text{Ni}\text{C}$ were found to have a hydrodesulfurization activity which was higher (Co) or the same (Ni) as that measured for $\text{Mo}\text{C}$ or $\text{W}\text{C}$. Therefore Co (Ni) ions in Co $\text{(Ni)-Mo (W)}\text{C}$ catalysts are considered as promoters for the MoS₂ (WS₂) phase (low $\text{Co}\text{Mo}$ or $\text{Ni}\text{W}$ ratios) or as additional active species.     

Constitution of tars from flash pyrolysis of Australian coals: 3. A structural study of Millmerran asphaltene components by hydrogenolysis

Asphaltenes derived from tar from the flash pyrolysis of Millmerran coal have been separated into acid, base, polyfunctional and neutral fractions by ion-exchange chromatography. Each fraction was studied by high-pressure catalytic hydrogenolysis followed by g.c.-m.s. analysis of the volatile products. The high content of n-alkanes from C₉ to C₃₂ in the organic products highlights the unusual maceral composition of Millmerran coal and its high $\text{H}\text{C}$ ratio. The results show that most of the asphaltenes are made up of small 1 — or 2-ring aromatic units probably linked by methylene chains bonded through intermediate functional groups. In some cases, the asphaltene structures appear to be ‘simpler’ than the corresponding coal-tar resin structures in the maltenes. Because no amphoteric molecules were detected these results support the concept of an acid-base structure for coal-derived asphaltenes.     

A novel semi-empirical relationship between aromaticities measured from 1H and 13C n.m.r. spectra

An empirical correlation between ¹H n.m.r. measured aromaticity (H_ar) and ¹³C n.m.r. measured aromaticity (C_ar) has been found. Over 300 samples which are diverse in origins and structural characteristics have been studied. A semi-empirical functional relationship between H_ar and C_ar has been devised. It is suggested that for distillable samples with, nominally, less than 50% boiling above 320 °C, the derived function can be used to rapidly and conveniently approximate C_ar from H_ar. The difference between observed and calculated C_ar values for 303 such samples shows a standard deviation of just 1.8%.     

Differential thermal method of estimating calcium hydroxide in calcium silicate and cement pastes

DTA is applied to estimate Ca(OH)₂ in cementitious phases by determining the peak areas caused by the decomposition of Ca(OH)₂ to CaO+H₂O. In the hydration of C₃S generally, the chemical method yields slightly higher values. DTA is also used as a monitoring technique in preparing a practically Ca(OH)₂-free product from hydrated portland cement or hydrated C₃S. Hydrated portland cement or C₃S has now been exposed to an unsaturated Ca(OH)₂ solution and extraction continued until the sample indicate no endothermal peak for Ca(OH)₂. The thermal method permits determination of the rate of formation of Ca(OH)₂ in portland cement hydrated in the presence of 0, 1, 2 and $\text{3}\text{1}\text{2}$ per cent CaCl₂.     

The production of active carbon from brown coal in high yields

The acid-leached char produced in high yield by the pyrolysis of the potassium salt of a brown coal (Yallourn seam, Victoria, Australia) is shown to have an internal surface area in excess of $\text{1100}\text{m}{}^2\text{g}$ without the need for activation. Tabletting, or extrusion, of the potassium salt of the coal permits production of a hard, active carbon as shaped granules. Of the cations investigated — sodium, potassium and magnesium — potassium was unique with regard to the formation of such a highly active char.     

The characterization of asphaltenes and preasphaltenes obtained under various coal liquefaction conditions

A CP-MAS ¹³C NMR study of asphaltenes and preasphaltenes obtained under various coal liquefaction conditions is reported. The carbon aromaticity, f_a, of the solid extracts from the reaction products has a close relation with the reaction conditions. By plotting f_a against the atomatic $\text{H}\text{C}$ ratio for these solid products on the characterization chart for model polycyclic aromatic compounds, the molecular structures with relation to the liquefaction pathway from coal to oil can be proposed.     

The chemical vapor deposition of carbon on carbon fibers

The relations between chemical vapor deposition (CVD) parameters and the resultant pyrolytic carbon microstructures have been examined for matrix deposition in fibrous carbon substrates. The parameters considered are temperature (1200–1450°C), pressure (20–630 Torr), C/H ratio ($\text{1}\text{4}\text{–}\text{1}\text{14}$), total flow rate (2–16) 1/min), and carbon felt density (0·12–0·23 g/cm³). Most of the data obtained are in agreement with a CVD model for carbon; where agreement is not obtained, it is surmised that the assumptions of the model may not be satisfied.     

Effect of gas phase conditions on resultant matrix pyrocarbons in carbon/carbon composites

The various microstructures obtained by the low temperature (< 1500°C) chemical vapor deposition (CVD) of carbon in carbon fiber substrates fall into three major types identified as rough laminar, smooth laminar, and isotropic. It is shown that the type of microstructure is a function of the temperature of deposition, the total gas pressure, and the carbon to hydrogen ratio of the source gas. These experimental results are found to be in good agreement with a previously reported carbon CVD model which relates the microstructure to a single parameter, the equilibrium gas phase $\text{C}{}_2\text{H}{}_2\text{C}{}_6\text{H}{}_6$ molar ratio.The densities and crystallographic parameters of the heat-treated composites are significantly affected by the type of microstructure. The rough laminar material has by far the most graphitic characteristics and is followed by the smooth laminar and isotropic materials, in that order.