Experimental evaluation of molten caustic leaching of an oil sand coke residue

An evaluation of molten caustic leaching, MCL, for the desulfurization and demineralization of Syncrude fluid coke has been carried out. The results obtained indicate that with the incorporation of an acid washing step, a treated coke product having sulfur and ash contents of less than 1 % may be obtained. Scanning electron microscopy confirm that vanadium is released during molten caustic leaching. At caustic to coke mass ratio in the range 1.8 - 2.0, the dedlurization reaction was determined to be independent of particle size, thus suggesting chemical reaction control.     

Desulphurization of Athabasca petroleum coke by (a) chemical oxidation and (b) solvent extraction

This study concerns the desulphurization of petroleum coke produced by delayed coking of Athabasca bitumen. The coke contains 7.5 wt % sulphur, 99.6% of the sulphur in coke being organic and the remainder pyritic. The coke was treated both with nitric acid and by solvent extraction. During nitric acid treatment, sulphur removal was found to increase with reaction time and the concentration of nitric acid, and to decrease slightly with increase in particle size. About 30% of organic sulphur was removed from ?250 Tyler mesh coke particles by 6 N nitric acid for 4 h at 102 °C. The basic mechanism for this treatment is oxidation and solution of organic sulphur compounds by nitric acid. About 50% ash was also removed from the coke. For solvent extraction, o-chlorophenol was used. Sulphur removal was found to increase with extracting temperature and time, and to decrease with increase in particle size of coke. About 19% of the sulphur was removed from ?250 mesh coke particles by o-chlorophenol at 160 °C in 2 h. When treated consecutively with nitric acid and o-chlorophenol, about 40% of sulphur was removed from the ?250 mesh coke particles.     

Distribution of potassium during chemical activation of petroleum coke: Electron microscopy evidence and links to phase behaviour

In this study, direct evidence for chemical penetration into petroleum coke particles during activation is presented. In addition, the porosity development was directly related to the sulphur loss and phase behaviour of the species present. Petroleum coke (petcoke, 6 wt.% sulphur) was activated with KOH and NaOH at temperatures between 400 and 800°C. The C S bonds were broken before 400°C in the presence of KOH and before 500°C in the presence of NaOH. Electron microscopy analysis of cross-sectioned and ultramicrotomed samples revealed that sulphur was still present within the particles and that the hydroxide activation agents had penetrated to the centre of the particles (90–150 μm). After heating to 800°C and washing with a weak acid aqueous solution, essentially all the sulphur was removed, as was any remaining chemical agent. The characterization results, phase diagrams, and complementary experiments with carbonate chemical agents or steam suggest that, during heating, a molten phase formed around the petcoke particles. The composition of this molten phase changed as activation proceeded and both sulphur and ash components were liberated from the petcoke. This better understanding of the activation process will improve the efficiency of preparing activated carbon.     

Thermal desulphurization of ultra-high-sulphur petroleum coke

A study has been made of the desulphurization of Syrian petroleum coke, containing 8.83% sulphur, by calcination in a Tamman furnace at high temperatures (1000–1600 °C) using heating times up to 4 h. Sulphur elimination (up to 96% in 30 min at 1600 °C) was found to increase with calcination temperature and heating time and to decrease with increase in ash. Reactivity of petroleum coke increases with the extent of sulphur elimination, but this is counteracted to some extent by the annealing effect of the higher temperature.     

Wettability and interfacial phenomena investigations on high-density polyethylene and petroleum coke

An in-depth wettability and interfacial phenomena investigation was carried out to study interactions between high density polyethylene (HDPE) and petroleum coke. The aim is to investigate the effect of temperature and contact times on possible interactions and adhesion characteristics for partially substituting coal-tar pitch binder with waste polymers. Using a sessile drop arrangement, experimental assemblies consisting of ground HDPE and a petroleum coke substrate were heat treated in the temperature range of 150–350°C for 15–60 min. Contact angles between molten HDPE and petroleum coke surface and depth of penetration of HDPE into petroleum coke substrate were measured. The highest contact angle (131.5°) was observed at 250°C after 15 min. and lowest contact angle (30.9°) was observed at 350°C after 60 min. Highest penetration depth (75 μm) was observed at 350°C after 60 min and lowest penetration (13 μm) at 200°C after 15 min. Analysis of results showed that increasing time and temperature of heat treatment had a significant impact on the interactions of molten HDPE with petroleum coke. Longer residence time and higher temperatures increased the extent of melting of HDPE, which in turn resulted in improved wettability and deeper penetration into petroleum coke substrate. HDPE was found to bind and adhere strongly with petroleum coke. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Comparison of physical,chemical, and thermal characteristics of water‐, dew‐, and enzyme‐retted flax fibers

Assessments of dew‐, water‐, and enzyme‐retted fibers for differences in fineness, strength, caustic weight loss, acid detergent fiber, neutral detergent fiber cellulose, hemicellulose, lignin, carbon, hydrogen, nitrogen, lipid, ash, and nine minerals were compared in this study. Distinct differences in retted‐fiber samples were observed in all the parameters tested. The samples also were analyzed by derivative thermogravimetry, which revealed that weight losses in two decomposition bands of 240–400°C and 400–520°C correlated with the fiber fineness and the caustic weight‐loss measurements of the samples. The variations in quality of the fiber samples were mainly due to differences in the proportion of residual noncellulosic polysaccharides, lipid, lignin, and certain minerals. The key parameters for determining fiber quality are fiber fineness, strength, ash, caustic weight loss, and the derivative thermogravimetry weight‐loss parameters. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 139–143, 1999     

Enhanced hydrodesulphurization of cokes deposited on iron ore by air gasification

The influence on air-gasification of cokes deposited on iron ores were studied in under successive desulphurization at 750 °C under atmospheric hydrogen. Gasification promoted by steam (water: 40 μl min⁻¹) at 350 °C for 125 min gasified 21% of the coke and allowed 25% oxidative desulphurization (based on sulphur in the coke) during the gasification and enhanced the successive hydrodesulphurization level up to 63% giving a total desulphurization of 88%. This level is comparable with that achieved after grinding. Gasification at higher temperatures, which burned more coke, was less effective in enhancing hydrosedulphurization. Gasification increases the access of hydrogen molecules to sulphur atoms in the coke. Gasification, which increases the surface area of the coke and removes the sulphur preferentially, is discussed in terms of reactivity.     

Desulphurization of a fluid coke similar to the Athabasca oil sands coke

Almost complete desulphurization of a high-sulphur fluid coke was achieved by impregnating the coke with suitable alkaline reagents followed by high-temperature calcination in an inert atmosphere and subsequent leaching of the coke to remove soluble metal sulphides formed during calcination. Sodium hydroxide and sodium carbonate were found to be the most effective bases. Sodium sulphide was detected in the calcined, non-leached coke by X-ray diffraction. Methane, carbon monoxide, carbon dioxide, ammonia and water, in addition to hydrogen sulphide, were detected in the gaseous product stream by gas chromatography. Flow rate of the inert gas and the particle size of the coke employed in this investigation had no effect on the extent of desulphurization. A maximum desulphurization was observed at a calcination temperature of 850 °C.     

Ultrasonic-assisted leaching kinetics in aqueous FeCl<Subscript>3</Subscript>-HCl solution for the recovery of copper by hydrometallurgy from poorly soluble chalcopyrite

We studied the ultrasonic effect on the leaching of copper from poorly soluble chalcopyrite (CuFeS₂) mineral in aqueous FeCl₃ solution. The leaching experiment employed two methods, basic leaching and ultrasonic-assisted leaching, and was conducted under the optimized experimental conditions: a slurry density of 20 g/L in 0.1M FeCl₃ reactant in a solution of 0.1M HCl, with an agitation speed of 500 rpm and in the temperature range of 50 to 99 °C. The maximum yield obtained from the optimized basic leaching was 77%, and ultrasonic-assisted leaching increased the maximum copper recovery to 87% under the same conditions of basic leaching. In terms of the leaching mechanism, the overall reaction rate of basic leaching is determined by the diffusion of both the product and ash layers based on a shrinking core model with a constant spherical particle; however, in the case of ultrasonic-assisted leaching, the leaching rate is determined by diffusion of the ash layer only by the removal of sulfur adsorbed on the surface of chalcopyrite mineral.     

Sodium hydroxide-assisted desulphurization of petroleum fluid coke

Desulphurization of a fluid coke produced commercially from a conventional petroleum crude oil was attempted. Direct hydrodesulphurization of the coke at 700°C resulted in ≈31 wt% sulphur removal; however, impregnation of the fluid coke with trace amounts of sodium hydroxide and subsequent hydrodesulphurization resulted in > 80 wt% sulphur removal primarily as H₂S. A significant part of the alkaline reagent could be recovered by hot water leaching of the desulphurized coke. The calorific value of the desulphurized coke is slightly lower than that of the starting material. The mechanism appears to be complex as the change in surface area was negligible upon impregnation and hydrodesulphurization. Economic evaluation of the desulphurization process, carried out at the Alberta Research Council, indicates that it has significant economic advantages over fluidized-bed combustion of the coke with limestone or combustion of the coke with flue gas desulphurization.     

Sulfur dioxide as an activating agent for sulfur-impregnated activated carbon produced from dense petroleum coke

To develop novel sorbent materials for capturing vapor mercury from industrial flue gases at high temperatures, high-sulfur oil-sands fluid coke was activated using 50% sulfur dioxide (SO₂) at 700°C under various pre-treatment conditions. Pyrolysis in nitrogen prior to activation significantly decreased specific surface area (SSA) of the product, which was attributed to the thermoplastic behavior of coke at high temperatures. Air pre-oxidation suppressed this effect and provided an enhancement over non-pyrolyzed coke, with SSA peaking at 447 m²/g after 5 h activation. Acid washing of air pre-oxidized activated coke in 10% hydrochloric acid increased SSA by removal of inorganic ash which added weight but contributed minimal surface area. Decreasing initial particle size range from 212–300 to 53–106 μm significantly increased SSA, which was attributable to an outer porous layer of constant thickness. Under optimized conditions, an SSA of 531 m²/g was achieved – the highest reported in literature for physically activated fluid coke. Coke activated with SO₂ displays a high mesoporous fraction and pore surface coverage by sulfur groups that were thermally stable up to 500°C.     

Thermocatalytic treatment of petroleum residues in the presence of zeolites and oil shale

Thermolysis of atmospheric and vacuum residua in the presence of both organomineral activators and zeolites, solid Broñsted acids, was studied. It was shown that the thermolysis of heavy petroleum residues is a thermocatalytic process that occurs under relatively mild conditions (415–425°C). Oil shale and/or zeolite admixtures act as both a catalyst for the process and a coke adsorbent. Under optimal conditions (415–425°C, 50 min, 10–12% shale), light petroleum fractions boiling in the motor-gasoline and diesel ranges can be obtained from atmospheric and vacuum residua with a yield up to 60 wt %.     

Desulphurization of petroleum coke by butagas

The work described concerns the desulphurization of Egyptian petroleum coke by butagas in a fixed-bed reactor. Optimum values for reaction temperature and coke particle size were observed; but increased gas flow rate, prolonged reaction time, and decreased coke bed depth all favoured increased sulphur removal throughout the ranges studied. The effects of the different factors could be interpreted satisfactorily in terms of the thermodynamic potential of the desulphurization reaction and the diffusion of gases into and out of the coke particles. While gas/coke ratio governs the former, the latter is mainly influenced by sintering of the coke particles. For comparison, some desulphurization runs were carried out using hydrogen in place of butagas, and Syrian petroleum coke instead of the Egyptian coke. The Syrian coke proved difficult to desulphurize.     

The effect of catalyst temperature zoning on hydrotreating a coal-derived liquid

The effect of catalyst temperature zoning on hydrotreating reactions, coke formation, and changes in catalyst surface area and pore volume was examined. A coal liquid was hydrotreated with the top zone operated in the range of 400–500° C (752–932° F) while the lower zone was maintained at 400° C (752° F). Increasing the top zone from 400° C (752° F) to 450° C (842° F) had beneficial effects on hydrogenation, HDN, and HDM at no cost of increased catalyst coke content. A further temperature increase was detrimental because of excessive coking and possible thermodynamic equilibrium limitations.     

Chemical cleaning of Turkish lignites by leaching with aqueous hydrogen peroxide

Two Turkish lignites (Beypazari and Tunçbilek) were leached with the solutions of hydrogen peroxide in water or in 0.1 N H₂SO₄. The effects of some process parameters, such as concentration, time and temperature, on the removal of ash and sulphur have been investigated. The rate of ash and sulphur removal are relatively high in the first 30 min, but slow after 60 min of the reaction time. Depending on the type of lignite, the maximum reductions ranged from 30 to 70% in ash, from 70 to 95% in pyritic sulphur, and from 42 to 58% in total sulphur. A relatively small reduction (a maximum of 25%) was estimated for organic sulphur. The optimum process conditions were established as a hydrogen peroxide concentration of 15 wt.%, a temperature of 30 °C and a leaching time of 60 min. High peroxide concentration or high temperature did not result in an appreciable further reduction in ash and sulphur. Due to partial dissolution or oxidation of the lignites, some organic material losses occurred but no heating value loss was estimated. An overall kinetic approach was also applied for pyritic sulphur removal, and the conversion data were analyzed by using both homogenous and heterogeneous reaction models.     

湿法冶金提纯废弃焦粉的热力学研究

湿法冶金反应过程中的热力学研究可以揭示反应过程中反应热变化规律、反应进行的可能性以及反应自动进行的条件。选用云南某地产出的废弃焦粉作为研究对象，对其采用湿法冶金两段浸出过程进行了热力学分析。研究结果为采用湿法冶金方法降低废弃焦粉灰分含量的实验研究提供理论依据。所获得优质焦粉经造球成型后，作为冶金、化工（主要指电石）等行业替代还原剂使用具有较好的应用前景。     

Desulphurization of organic sulphur from coal by electron transfer process with Co2+ ion

This paper reports the results of desulphurization of organic sulphur from a subbituminous Meghalaya coal by the electron transfer process accomplished with the metal ion Co²⁺. The process was studied both in presence and absence of naphthalene which is used as an electron transfer agent. Temperature dependence on desulphurization unfolded that as the temperature is raised from 25 to 50 °C, there is increase in desulphurization performance. Model organic sulphur compounds study revealed that the desulphurization process is effective with aliphatic type of compounds. Infrared spectroscopic study revealed the release of easily removable sulphur compounds as the band intensities due to −SO and −SO₂ groups have declined considerably in their respective regions in the desulphurized coals. The degree of desulphurization is 28.5 wt.% in the presence of naphthalene and 24.6 wt.% in absence of naphthalene, both at 4 h and 50 °C. The sulphur extrusion process is continuous and application of a first-order kinetic model produced specific rate constants of the desulphurization reaction in the two systems, at different temperatures, which falls in the range of (1.3–2.9)×10⁻⁵ s⁻¹. The activation energy of the sulphur-loss reaction in the system containing naphthalene (26.8 kJ mol⁻¹) is about 12% lower than that of the system without naphthalene (30.6 kJ mol⁻¹). The frequency factor of the sulphur removal reaction in the systems have been found to be in the range of 0.8–3.2 s⁻¹, suggesting low amount of successful collisions and an associated type of reaction. The desulphurization reaction is nonspontaneous in nature, proceeds with the absorption of heat and there is reduction in the degree of disorderliness in the system as predicted by the transition state theory.     

Supercritical desulfurization of high rank coal with alcohol/water and alcohol/KOH

A high rank coal with total sulfur of 4.90% was extracted employing alcohol/KOH and alcohol/water under supercritical conditions both in a semi-continuous reactor and in a batch reactor. In the semi-continuous reactor it was found that supercritical desulphurization is mainly taking place within about one hour at 400°C. Pretreatment of coal with KOH up to 5% concentration was favourable for sulfur removal, but greater KOH concentration and longer soaking time brought about the opposite results. When the ethanol concentration was 95 vol % the organosulfur removal achieved the maximum. Ethanol/KOH solution as supercritical solvent enhanced the desulfurization process, in which the inorganic sulfur was removed preferentially. In the batch reactor it was found that there was reincorporation of both organic sulfur and inorganic sulfur. KOH addition can improve the sulphur removal greatly. When KOH/coal ratio was greater than 0.5, the tendency for sulfur removal was gradually slow.     

Production of isotropic coke by thermocracking of the anthracene fraction of coal tar

The properties of coke obtained by heat treatment of the anthracene fraction of coal tar under pressure (by thermocracking) are investigated. Pressures up to 5 MPa are used; the temperature is 500 or 550°C. For comparison, pitch coke is obtained from oxidized pitch with softening temperatures of 166.2 and 190.2°C. The coke yield from thermocracking is 70–75%. The following properties of the coke are determined: the actual density, the ash content, the yield of volatiles, the optical microstructure, the elementary composition, the change in volume on heating to 2400°C, the impurity composition, and the X-ray structural characteristics. High temperatures (at least 550°C) and heating rate of the anthracene fraction facilitate the formation of a large quantity of active radicals, which instantaneously form the three-dimensional coke structure, preventing the growth and coalescence of mesophase particles; isotropic coke is formed, with a microstructure score of 2.2. At 500°C, anisotropic coke is formed, with a microstructure score of 4.3. Despite the high softening temperature and the content of the α1 fraction, the high-temperature pitch does not form isotropic coke on carbonization. The macrostructure of the coke obtained by thermocracking is monolithic, with fine pores. The thermocracking conditions (temperature, pressure, presence of H₂) facilitate partial destruction and hydrogenation of the heterocyclic compounds. As a result, the coke has a reduced N, S, and O content. For pitch coke, the nitrogen content is 20–40% higher. The lack of ash in the anthracene fraction of coal tar results in ash- and metal-free coke. The coke obtained by thermocracking also has satisfactory X-ray structural characteristics and undergoes practically no expansion on graphitization, in contrast to pitch coke. In view of the technological convenience (absence of liquid products, high coke yield) and the quality of the coke, the production of isotropic coke by thermocracking may be regarded as a promising means of supplying the raw material used to produce artificial graphite.