THERMAL DECOMPOSITION OF SAUDI CRUDE OIL ASPHALTENES

Abstract

Asphaltenes precipitated by the use of pentane, heptane and decane solvents from Saudi Arabian Light (AL) and Saudi Arabian Heavy (AH) crude oils 370^°C + residua have been investigated by thermal gravimetric analysis and pyrolysis - gas chromatographic analysis at 350^°C and 520^°C. Gas chromatographic analysis of the gases evolved during pyrolysis has shown that CO, CO₂ and CH₄ constitute the major portion of the gases evolved at 350^°C from pentane and heptane asphaltenes of AH residue and from pentane asphaltenes of AL residue. Whereas gases evolved from decane asphaltenes are dominated by CO₂ and C₂-C₄ hydrocarbon gases. At 520^°C, hydrogen and methane represent 56-80 vol %of the gases evolved from all the four asphaltenes. The amounts of C₁-C₄ hydrocarbon gases increased with an increase in the carbon number of the precipitating solvent at 350^°C and decreased at 520^°C. The presence of up to C₃₆ normal alkane hydrocarbon has been indicated in the maltenes produced from these asphaltenes. The loss of nitrogen from AH asphaltenes during pyrolysis remained low (1-6 wt %), whereas the losses of oxygen and sulphur ranged from 58 to 74 wt % and 10 to 29 wt %, respectively.     

The catalytic effect of manganese carbonate on kerogen pyrolysis in the absence and presence of water

To investigate the effect of Mn ore on the chemical components and isotopic compositions of gas products during kerogen pyrolysis in the absence or presence of water, a series of pyrolysis experiments on Type-I kerogen with manganese carbonate and/or water were conducted in closed gold capsules at 325–600?°C for 72?h with 300?bar. The heavy hydrocarbon gas yields increased significantly over 450?°C due to the participation of manganese. As for isotopic compositions, the manganese catalysis caused a decrease in the ¹³C_CH4 and an increase in the ¹³C_C2H6 over 475?°C; the δD values of methane generated during anhydrous pyrolysis with manganese carbonate are much lower than those produced by the pyrolysis of kerogen alone. Furthermore, the δD values are the most negative during hydrous pyrolysis with manganese ore. In addition to the thermal decomposition of manganese carbonate to form carbon dioxide, water provides sources of hydrogen and oxygen to form H₂ and CO₂. Manganese carbonate inhibits the association of sulfur-free radicals to hydrogen to form H₂S. The i-C₄/n-C₄ ratio for gas products was evidently higher due to the existence of manganese and water, they can enhance the carbocation mechanism.     

PYROLYSIS OF SUNNYSIDE (UTAH) TAR SAND: CHARACTERIZATION OF VOLATILE COMPOUND EVOLUTION

ABSTRACT

Sunnyside (Utah) tar sand was subjected to programmed temperature pyrolysis and the volatile products were detected by tandem on-line mass spectrometry (MS/MS) in real time analyses. A heating rate of 4°C/min from room temperature to 900°C was employed.

Evolution of hydrogen, light hydrocarbons, nitrogen-, sulfur-, and oxygen-containing compounds was monitored by MS or MS/MS detection. Evolution of volatile organic compounds occurred in two regimes: 1) low temperature (maximum evolution at 150 to 175°C), corresponding to entrained organics, and 2) high temperature (maximum evolution at 440 to 460°C), corresponding to cracking of large organic components. Alkanes and alkenes of two carbons and higher had temperatures of maximum evolution at approximately 440°C, and methane at approximately 474°C. Aromatic hydrocarbons had temperatures of maximum evolution slightly higher, at approximately 450° C. Some nitrogen-, sulfur-, and oxygen-'ccntaining compounds were also detected in the volatile products.

Comparing the Sunnyside pyrolysis to the pyrolysis of other domestic tar sands indicated the following for hydrocarbon evolution: 1) the evolution of entrained organics relative to the total evolution was much less for Sunnyside tar sand, 2) the temperatures of maximum evolution of hydrocarbons due t o cracking reactions were slightly lower, and 3) the temperatures of maximum evolution for benzene and toluene are slightly higher than observed for other tar sands.

In general, the noncondensible gases, H₂, CO, and CO₂, exhibited evolution associated with hydrocarbon cracking reactions, and high temperature evolution associated with mineral decomposition, the water-gas shift reaction, and gasification reactions. Pyrolysis yields were dominated by the evolution of carbon oxides and water. The CO₂ primarily appeared t o cane from the decomposition of carbonate minerals. Compared t o other domestic tar sands, the gas evolution reflected more mineral decomposition character for Sunnyside tar sand.     

EFFECTS OF HEATING RATE AND PARTICLE SIZE ON THE PRODUCTS YIELDS FROM RAPID PYROLYSIS OF BEECH-WOOD

ABSTRACT

Effects of pyrolysis temperature (300–1000 ^°C), heating rates (100, 500, 1000, and 10,000 ^°C/s), and particle sizes (53–63,104–120,177–270, and 270–500 urn) on the yields and formation rates of tar, light oils, total gases, and char from pyrolysis of beech-wood under 1 atm helium pressure were studied. Wood particles were pyrolyzed in strips of stainless steel wire mesh in a captive sample apparatus; and yields of products were measured in weight percent of original wood as a function of temperature for different heating rates and particle sizes. The overall weight loss achieved from pyrolysis of this wood was about 90%. The total yields of tar and light oils from pyrolysis of this wood accounted for up to 80% of the original wood above 400 ^°C. Due to the post-pyrolysis reactions of tar and light oils, the tar and light oils yields go through a maximum with pyrolysis temperature for all particle sizes and most heating rates studied here. As particle size increases from 53–63 μm to 270–500 μm the maximum tar yield decreases from 53% to about 38%. The maximum tar yield also decreases with increasing the heating rate from 70% at 100 ^°C/s to 48% at 10,000 ^°C/s heating rate. Theses results indicate that as the intra-panicle post-pyrolysis cracking reactions of tar increases at higher heating rates and with larger particles the tar yield decreases. Tar was also analyzed with GPC for the effects of above pyrolysis parameters on the tar molecular weight. The tar average molecular weight. remains relatively constant (M_w = 300 amu, M_n = 155 amu, and M_z = 483 amu) under helium atmosphere with pyrolysis temperature at 1000 ^°C/s heating rate and with 53/63 u m particle size. The average molecular weight of tar does not significantly varies with heaung rate, but it decreases as the particle size increases.     

Features of liquid hydrocarbon and biomarker maturity ratios during HTHP semi-open system pyrolysis of type II and III source rocks

In order to study the liquid hydrocarbon generated by laboratory pyrolysis and the biomarker maturity ratios in expelled oil with the increasing simulation temperature, the Hydrous semi-open system high temperature high pressure (HTHP) pyrolysis experiments was performed on Type II and III source rocks from 350°C to 540°C. The results showed that expelled oil yields in both samples have a trend of increased first and then decreased with the increasing temperature, while an opposite tendency occurred in the residual oil. The biomarker maturity ratios, such as ∑C_21?/∑C₂₂₊ ratio in n-alkanes, Pr/Ph ratio in isoprenoid alkenes, Ts/Tm in terpenes, and C₂₉ββ/(αα + ββ) ratios in steranes are all better indicators in terms of maturity in pyrolysis. However, the maturity biomarkers ratios interpreted by the mechanism of isomerization such as C₃₁-homohopanes 22S/(22S?+?22R) and ααα C₂₉-sterane 20S/(20S + 20R), which had already reached their equilibrium values, indicating that microbiological deterioration is one reason for the failure indicative function of αααC₂₉sterane20S/(20S + 20R) ratio. This research may also play an important role in the studies about the evolution of sedimentary organic matters in geology.     

Thermogravimetric analysis and kinetic study of heavy oil pyrolysis

Pyrolysis, so-called devolatilization, is one of the first steps of all thermochemical processes occurring in an inert atmosphere. The authors discuss the main kinetic features of heavy oil pyrolysis, on the basis of the data derived m from a TGA analysis and by using a kinetic model. The samples were heated over a range of temperature from 400 K to 430°C at various heating rates between 10 and 80°C/min. Experimental results showed that the effect of time is considerable in the case of tar conversion, compared to char and gases.     

The Influence of Basic Volcanic Fluids on Gaseous Products of Source Rocks

The aspects, such as composition, temperature, viscosity, and fluidity, of basic volcanic fluids are greatly different from acidic volcanic fluids. In order to further complement the conceptual model of the influence of volcanic fluids on source rocks in petroliferous basins, this research uses the thermal simulation experiment to analyze the characteristics and reasons of the ratio of alkanes to acid, dry coefficient, and carbon isotope in the dry and fluid systems. The results show that, the ratio of alkanes to acid of all samples in the two systems will increase with the rise of temperature and presents features of the dry system higher than the fluid system, which indicates that the basic volcanic fluids restrain the generation of gaseous hydrocarbons. The dry coefficient of the fluid system at the range of 300–400°C is greater than that of the dry system, while smaller at the range of 400–450°C, which indicates that the basic volcanic fluids promote the generation of CH₄ in low temperature. In the two systems, δ¹³CO₂ of all samples have no obvious change as the rising of temperature, but in the fluid system the proportion of carbon isotopic will increase with the rising of temperature, which shows that carbonate exists in the volcanic fluids. The carbon isotopes of gaseous hydrocarbon in three samples are presented as δ¹³C₁ < δ¹³C₂ < δ¹³C₃, and it accords to general pyrolysis regularity without reversal phenomenon, which indicates alkane gases produced by pyrolysis of three samples are of organic origin.     

塔里木盆地煤岩在不同介质条件下热模拟实验中烷烃系列有机地球化学特征

对塔里木盆地侏罗系煤岩在不同介质下的热模拟实验和正构烷烃系列色质测试分析结果表明,在400℃前后煤岩成烃机理不同。结合对峰型、ΣC21-/ΣC22+值、OEP指数和P r/Ph值等地球化学参数的研究,指出了不同热演化阶段的成烃机理:在低温阶段(<350℃)煤岩主要是裂隙、晶格间吸附烃和结构边缘烃的排出;在350~400℃之间,脱甲基及链断裂效应使得煤岩排烃进入高峰期;在高演化阶段(≥450℃),大量内部结构烃发生断裂重排,550℃以上温度达到第二个热降解高峰,产出烃发生脱甲基、链断裂和开环效应。模拟实验还表明,OEP指数变化较大,其每次变化都伴随一次生烃高峰;P r/Ph值随着热演化程度呈降低趋势;有水、伊利石和蒙脱石存在时,会改变煤岩在热演化过程中高碳数烃的热降解速率,有利于液态烃的形成。     

A kinetic model for pyrolysis of petroleum residue under nonisothermal conditions

Kinetic study on pyrolysis of petroleum residue was carried out by an accurate Arrhenius type equation at heating rate of 0.5–30.0°C/min under nonisothermal conditions. The influence of some critical parameters including temperature, heating rate and activation energy on mass conversion was evaluated. The apparent activation energies for during the pyrolysis process were in the range of 198–361 kJ/mol at various mass conversions of 5–94%. The reaction temperature was introduced as the most important parameter for the improvement of mass conversion, compared to that of other parameters. The pyrolysis of petroleum residue was occurred in a broad temperature range, from 150–650°C, yielding 33 wt% unpyrolyzed residue. It also was found that an increase in heating rate has a minor impact in the process. Model predictions were compared with experimental data, which showed fully good agreement.     

Catalytic Dewaxing for Lube Oil Production

Abstract

The selective cracking of long-chain normal paraffin's of medium neutral raffinate, derived from a lube oil-phenol extraction unit, by the catalytic dewaxing technique over H-ZSM-5 and NiMo-H-mordenite catalysts was studied. The runs were conducted to produce lube oils with acceptable cold flow properties. The influences of zeolite types, metals loading, and operating reactor temperatures (290°C–475°C) can have a great effect on cracking high pour point n-paraffins into lower ones, and hence a reduction in pour points. An increase in temperature (between 290°C and 375°C) increased wax conversion (percent dewaxing) on H-ZSM-5 compared with NiMo-H-mordenite catalysts due to its higher cracking activity. As a result, large amounts of C₁-C₄ gases and C₅-170°C naphtha were produced. The low pour point lube oils produced from catalytic dewaxing over H-ZSM-5 compared with NiMo-H-mordenite catalyst indicates that the former was more selective for removing wax components than the later. On the other hand, high concentrations of aromatics were obtained on both catalysts, since the waxy paraffins are converted to lower boiling products. The reduction in dewaxed pour points (Δpp) was observed to be in the range of 38°C–42°C over H-ZSM-5, compared to 37°C–40°C over NiMo-H-mordenite at the same reaction temperature ranges (290°C–375°C), but NiMo-H-mordenite has advantages at higher temperature ranges (above 375°C) in pour point reduction (Δpp range: 41°C–42.5°C). The addition of bimetallic components to the mordenite-catalyst enhances its activity, and the rate of normal paraffin cracking was increased due to the hydrogenolysis activity of the active metals. This means that the bimetallic H-mordenite catalyst has the advantage over H-ZSM-5 in its refining activities (hydrodesulfurization [HDS] and hydrodenitrogenation [HDN]) under the tested operating conditions. These results may be attributed to shape-selective discriminating behavior due to differences in zeolite pore openings (i.e., 6.5 × 7.0 Å for mordenite and 5.3 × 5.6 Å for ZSM-5). In other words, a combination of isomerization and selective cracking reactions of high n-paraffins may occur during the dewaxing process using NiMo-H-mordenite catalyst. The influences of process parameters (temperature, pressure, and liquid hourly space velocity [LHSV]) on the relations between wax conversion to maintain maximum low pour points and maximum dewaxed oil yields or minimum yields of the least desired gases were optimized to produce dewaxed lube oils of acceptable characteristics.     

塔里木盆地煤及其显微组分超高温开放体系热模拟实验气态产物对比研究

通过对塔里木盆地煤及其显微组分进行以1 K/min升温速率的开放体系热模拟实验(最高实验温度为1 200℃),获得了煤岩与各显微组分气态产物产率与累计产量变化。对比分析了煤及其显微组分生成气态产物CH₄、N₂和CO变化特征,其中 N₂生成温度高于CH₄和CO; H₂生成时间与CH₄相一致(说明了氢为烃类气体形成的关键因素）。煤及其显微组分生烃潜力具有壳质组>镜质组>煤>半丝质组≥ 丝质组的特征,说明煤岩生烃潜力主要由其显微组分控制;虽然壳质组在煤岩中含量很低,但生烃潜力高于其他显微组分。煤岩生成的N2具有双峰型特征,说明了前后峰N₂具有不同来源,前者来源于无机矿物（如含铵粘土）的分解,后者来源于有机质热降解;显微组分生成N₂主要为高温阶段,说明了显微组分在分离过程中可能造成部分无机矿物的损失。     

KINETIC PECULIARITY OF CO-PRODUCTION OF BENZENE AND NAPHTHALENE FROM AROMATIC MIXTURES BY THERMAL HYDRODEALKYLATION

ABSTRACT

The kinetic peculiarity of aromatic and non-aromatic hydrocarbons under co-production process conditions of benzene and naphthalene from pyrolysis gasoline or other industrial aromatic mixtures through thermal hydrodealkylation was experimentally investigated. In these experiments, various model mixtures of such pure hydrocarbons as benzene, toluene, naphthalene, 1-, 2-methylnaphtalenes and n-heptane were used as raw materials, and under thermal hydrodealkylation conditions, conversion kinetics of these hydrocarbons and their effects to each other were studied. According to the experimental results obtained, the conversion rates in descending order are as n-heptane > 1-methylnaphthalene (1-MN) > 2-methylnaphthalene (2-MN) > toluene. N-heptane considerably accelerates the hydrodealkylation reactions of both toluene and 1-MN and 2-MN. While 1- MN and 2-MN increase the rate of toluene's conversion to some extent, toluene can prevent their conversion. Furthermore, n-heptane has an increasing impact on the reaction rate of benzene's conversion into biphenyl. At temperature of 625°C and in a long contact time (60 s or more) almost all of n-heptane is converted into mostly alkanes, C1–C3 gases.     

Organic geochemistry of the Upper Triassic–Middle Jurassic Shemshak Group (Alborz Mountains,NE Iran)

Abstract

The organic geochemistry of shale samples of Shemshak Group at Dehmolla section in Eastern Alborz Mountains in the present study are discussed throughout the Rock-Eval pyrolysis. The results used to describe the quantity, type, maturity, and petroleum potentials of the Shemshak Group sediments. The pyrolysis data show that the total organic carbon values of the shale samples are between 0.08 and 20.98?wt% and the generation potential (S1+ S2) of the studied samples ranges from 0.02 to 9.47?mg HC/g rock revealing the organic richness of these samples varies from poor to good. The type of hydrocarbon products (S2/S3) ranging from 0.06 to 2.33 and the type of hydrocarbon determined from Tmax versus HI indicate mainly well for gas generation. Based on the HI versus OI plot diagram, the type III of kerogen is the main type of organic matter in studied samples. These data also show that most of the samples were deposited in oxic environments with low sedimentation rate and high amount of organic matter from the terrestrial source. “Tmax” values ranging from 416?°C to 602?°C in studied samples indicate that most of the samples are over mature and located in gas zone.     

Characteristics of organic acids in lacustrine organic-rich shale,Ordos Basin,China

Organic acids are critical to studying the formation of secondary porosity in tight lacustrine reservoirs, Ordos Basin. The expelled fluids produced through hydrocarbon evolution in a semi-closed system under different pressure and temperature settings (16.9?MPa, 250?°C; 22.1?MPa, 300?°C; 32.5?MPa, 350?°C; 37.7?MPa, 370?°C; 42.9?MPa, 400?°C; and 52.2?MPa, 450?°C) were collected. In this study, 12 different organic acids were identified using ion chromatography, and both the concentration and species of organic acids indicate a two-step process.     

Analysis of the thermal hydrocracking of heavy fuel oil

The thermal hydrocracking of Mexican heavy fuel oil was studied at 1200 psia and different reaction temperatures (370, 380, 390 and 400°C). The results show that the vacuum residue which constitutes 62 wt. % of the heavy fuel oil and contains 47 wt. % resins and 23.3 wt. % asphaltenes, reacts to form lighter hydrocarbons (IBP-540°C), solid and gas. Resins transform more easily to saturates, and gases are produced mainly from the asphaltene fraction, indicating that the terminal alkyl groups in this fraction are shorter than those present in the resin fraction. The C-C scission reactions dominate the transformation of heavy fuel oil in the interval from 370 to 390°C, whereas the carbon rejection reactions are dominant at 400°C. Finally, the thermal hydrocracking of heavy fuel oil at 390°C appears suitable since at this temperature the reaction produces the greater amount of atmospheric distillates (+20.5 wt. %) and a low content of solid (2.0 wt. %) and gas (2.1 wt. %).     

低成熟度页岩油加热改质热解动力学及地层渗透性

低成熟度页岩油加热改质是采用加热井对地层进行加热，将地层中滞留的重质烃转化为轻质烃，同时将尚未转化的固体有机质热解生成油气后采出。热解油气生成量预测及地层孔渗变化是页岩油改质开采研究的难点和挑战之一。利用页岩井下取心样品，采用黄金管实验装置，研究了页岩加热过程中的有机质热解规律及组分动力学，获得了烃类气体、轻质油及重质油的生成动力学参数。结果表明，在温度为280~500℃范围内，油的生成量先增后减，而气体量持续增加；低速升温条件下的转化率随温度变化曲线左移，热解温度变低。重质油、轻质油和气态烃的活化能分别为39~49，57~74和56~59 kcal/mol；动力学模型可预测任意时间的烃类生成量。应用三轴高温渗透率测试装置，获得了页岩从室温到高温（550℃）条件下的氮气测试渗透率动态变化规律。结果显示，页岩加热过程中的渗透性变化分为下降段、上升段和稳定段，在温度达到有机质热解温度后，基质及裂缝渗透率均出现明显改善，比初始渗透率提高1~2个数量级。热解油气生成量及渗透率变化可为低成熟度页岩油加热改质开采的产量预测提供依据。     

KINETIC AND STRUCTURAL STUDIES OF CALCIUM-BASED SORBENTS FOR HIGH-TEMPERATURE COAL-GAS DESULFURIZATION

ABSTRACT

The absorption of H₂S by large particles of limestone, dolomitic limestone and dolomite (average mass-radius of 0·40 mm) was tested under simulated coal gases. Below the calcination temperature of CaCO₃ (about 900^°C under 1 bar of CO₂), complete conversion of the calcium carbonate to calcium sulfide can only be achieved with dolomite. Above the calcination temperature of CaCO₃, the conversion to CaS is complete for all three sorbents in about one hour when 10,000 ppm H₂S is present in the gas phase. Large particles of limestone thus appear to be a suitable sorbent for high-temperature coal-gas desulfurization (above about 900 ^°C). A mathematical model based on the kinetic information collected in this work predicts the desulfurization performance of a packed or moving bed of limestone particles. Finally, a low-temperature regeneration scheme for the spent sorbent (CaS) in which sulfur can be subsequently recovered as the element is suggested.     

Developing a free-fall reactor for rice straw fast pyrolysis to produce bio-products

Recently, the world energy demand is increasing due to the growing world population. Accordingly, many research works are directed toward the new resources of renewable energy in order to compensate the shortage in petroleum based products. The use of biomass as a source for renewable energy is of growing importance. One of the most problematic agriculture wastes in Egypt is rice straw which is generated in huge amounts over a limited harvesting period. In this study the main objective is to develop and design a new rice straw fast pyrolysis reactor that improves some inefficiencies in traditional reactors while maintaining high bio-oil yields. To accomplish this target, a laboratory scale plant with a free-fall reactor was designed to avoid lack of moving parts; Compared it with other plants, the designed under investigation plant has the advantage of simple design. Two basic principles were combined in the design of the free-fall reactor; the first principle dealt with the particle heating rate, while the second considered the particle’s free-fall velocity. Based on this developed and designed free-fall reactor, the fast pyrolysis process of rice straw was carried out at temperatures ranging from 450?°C to 700?°C. The obtained bio-products from this process are liquid bio-oil, bio char and non-condensable gases. The characterization and chemical composition of the bio-oil and non-condensable gases were determined, respectively. It was concluded that the above mentioned free-fall reactor can be used for producing useful bio-products from rice straw and sharing to solve the most problematic agriculture waste.     

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??The thermal simulation experiment of coal rock can provide a scientific basis for understanding the evolution of hydrocarbon generation in coal??bearing basin and the geochemical characteristics of coalbed methane and its resource prediction. The thermal simulation experiments of gas generation of the upper Paleozoic coal rock samples collected from Qinshui Basin were carried out at the temperatures of 336.8-600 ?棬 the pressure of 50 MPa and the temperature??rising rates of 20 ??/h and 2 ??/h. The results indicated that the gaseous products (relative percent content) were mainly composed of methane?? C_2-5 hydrocarbon gases and carbon dioxide?? the bydrogen content and hydrogen sulfide content being extremely low?? along with the increase in simulation temperature?? the methane and hydrogen increased but carbon dioxide decreased?? and the C_2-5 hydrocarbon gases and hydrogen sulfide increased first and decreased afterwards?? the low temperature??rising rate was favourable to the generation of methane?? C_2-5 hydrocarbon gases?? hydrogen and carbon dioxide?? their formation being stage?? the relative productivity of carbon dioxide or hydrogen was positively correlated with that of methane at the same temperature??rising rate?? which reflects that they and the methane were the products of simultaneous parallel reaction in the process of the pyrolysis of coal rocks?? and the ability of generating methane and C_2-5 hydrocarbon gases of Shanxi Formation coal rocks was higher than that of Taiyuan Formation coal rocks at the same simulation temperature and temperature??rising rate?? which means that the Shanxi Formation coal rocks were more beneficial to coalbed methane formation in natural conditions. Finally?? the significance tracing coalbed methane formation is discussed in the paper according to the experimental results. (Financed by the National Basic Research Program Project??No. 2002CB211701)     

PRODUCTS FROM FLASH PYROLYSIS OF A TURKISH LIGNITE IN A FREE-FALL REACTOR UNDER VACUUM

ABSTRACT

Flash pyrolysis of a Turkish lignite under vacuum in a free-fall reactor was examined at a temperature range of 400 - 800 °C. Gaseous products were analysed with an on-line GC equipped with a manuel injection valve. Solvent fractionation was applied to the liquid product to separate preasphaltenes, asphaltenes and oils fractions. Two particle distributions of the lignite were used: ?0.315+0.2 mm and ?0.1 mm. The liquid yield increased with temperature up to 650 °C and, thereafter decreased for the larger particles. The maximum liquid yield, excluding pyroltic water, was found to be 8 % wt (dal) at 650 °C. In the case of the smaller particles the liquid yield increased steadily with temperature and the yield of liquid, excluding pyrolytic water, was 5.9 % wt (da) at 850 °C. The gaseous product yield also increased with temperature for both size fractions, and CO and CO₂ in the gaseous products were present in large amounts.