Carbon Coke Research Articles

Hydrogen production by biomass gasification in supercritical water over Ni/γAl 2O 3 and Ni/CeO 2-γAl 2O 3 catalysts

Hydrogen production by supercritical water gasification (SCWG) is a promising technology for wet biomass utilization. Ni catalyst can realize the high gasification efficiency of biomass near the critical temperature of water. In this paper, Ni/γAl 2O 3 and Ni/CeO 2-γAl 2O 3 catalysts were prepared by an impregnation method. The catalyst performance for glucose gasification in supercritical water was tested in autoclave reactor. All experiments were carried out in the autoclave at 673 K, 24.5 MPa, and the concentration of glucose was 9.09 wt.%. The catalysts before and after reaction were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area measurements, X-ray fluorescence spectrum (XRF) and Thermo-gravimetric analyses (TGA) in order to investigate on the chemical property and catalytic mechanism. The experimental results showed that hydrogen yield and hydrogen selectivity increased sharply with addition of Ni/γAl 2O 3 and Ni/CeO 2-γAl 2O 3 catalysts. The catalytic activity and H 2 selectivity of Ni/CeO 2-γAl 2O 3 was higher than that of Ni/γ-Al 2O 3 catalyst. The results revealed that carbon deposition and coking led to the deactivation of the catalysts. Ce in the Ni/CeO 2-γAl 2O 3 catalyst had a certain role in the inhibition of carbon deposition and coking.

Structural Analysis of Coke on Used Catalysts during Residue Hydrotreating by Ruthenium Ion Catalyzed Oxidation Reaction

The structure of coke from five spent residue hydrotreating catalysts was investigated based on ruthenium ion catalyzed oxidation reaction. The distribution of n-alkyl chains and bridges attached to aromatic carbon of coke on catalysts was quantified. Results showed the concentrations of n-alkyl chains and bridges in coke were declined with the increase of carbon number. The substituential group is methyl mainly, and it had no >C5 alkyl chains in coke. Various isomeric benzenepolycarboxylic acids from oxidated products were identified. Then the condensation mode of some aromatic structure was discussed. The precursor of coke affected the coke structure. Catalysts made coke dehydrogenate to form graphite type aromatic condensate. About 60% of coke was graphite type.

Methane Dissociation on the Ceria (111) Surface

The complete oxidation of methane into water and carbon dioxide on the (111) surface of ceria is considered within a DFT + U framework in order to gain insight into the coke-free operation of solid oxide fuel cells with ceria-containing anodes. Preferred adsorption sites and energies are determined for CHx (x = 0, ..., 3), H, and CO, together with transition states and kinetic barriers along the complete pathway from CH4 to H2O and CO2. The results presented are in excellent agreement with existing theoretical and experimental work suggesting that ceria is more easily reduced by CO than by H2 and offer an explanation for the apparently inconsistent observations of carbon coke formation in Ni−ceria anodes and the stable, coke-free oxidation of methane in Cu−ceria anodes.

Removal of endocrine disruptors and cytostatics from effluent by nanofiltration in combination with adsorption on powdered activated carbon

Direct capillary nanofiltration also in combination with an upstream powdered activated carbon treatment was tested for high quality water reuse of tertiary effluent from a municipal wastewater treatment plant. Two endocrine disruptors (BPA and EE2) and two cytostatics (CytR and 5-FU) were spiked in concentrations of 1 to 2 microg/L to evaluate the process performance. In direct NF the real total removal of the micropollutants was between 5 and 40%. Adsorption to the membrane played a major role leading to a seemingly total removal between 35 and 70%. Addition of powdered activated carbon and lignite coke dust largely reduced the influence from adsorption to the membrane and increased the total removal to >95 to 99.9% depending on the PAC type and dose. The cytostatics showed already in direct NF a very high removal due to unspecified losses. Further investigations are ongoing to understand the underlying mechanism. The PAC/NF process provided a consistently high permeate quality with respect to bulk and trace organics.

Information content of methods of determining coke reactivity

The reactivity of coke plays an important role in blast-furnace smelting. The reaction of carbon in coke with oxygen generates the heat required for various chemical reactions in the blast furnace. The reaction of carbon in coke with carbon dioxide and water vapor forms carbon monoxide and hydrogen, which reduce the iron and alloying elements from their oxides. As a result of these reactions, the strength of the coke pieces in the blast furnace is reduced, and they break down more as they move in the furnace batch, with consequent decrease in gas permeability of the batch column.

Study on the carbon deposition in steam reforming of ethanol over Co/CeO2 catalyst

Abstract In this work, coke formation over Co/CeO2 catalysts for the steam reforming of ethanol was studied. Variations of ethanol conversion and product distribution with reaction temperature and time were investigated and the used catalysts were characterized with thermal analysis method and transmission electron microscopy. The results indicate that the reaction temperature exerts influences on coke formation and its property significantly. As the reaction temperature is 450 °C or lower, catalyst particles are heavily enclosed by cokes, leading to severe deactivation. As the reaction temperature is 500 °C or 550 °C, the encapsulation of catalyst particles is rarely observed due to the formation of another kind of carbon, namely, tube- or fiber-like carbon, which results in mild deactivation. When the reaction temperature is over 600 °C, carbon deposition is not a major problem for the steam reforming of ethanol over Co/CeO2 catalysts, for carbon deposition or coke formation under these temperatures is not notable.

Formation of coke in thermal cracking of jet fuel under supercritical conditions

Continuous-flow reactor experiments were carried out to study coke formation from thermal cracking of home-made jet fuel RP-3 under supercritical conditions. The mechanism and precursor of coke forming were analyzed. The starting cracking temperature of RP-3 fuel was determined to be 471.8°C by differential scanning calorimetry (DSC). Temperature-programmed oxidation and scanning electron microscopy (SEM) characterizations of the stressed tubes showed that there are three different coke species including chemisorbed carbon, amorphous carbon and filamentous coke in the solid deposits. More than 90% of coke deposits are carried away by the supercritical fluid, which has strong capabilities of extraction for coke deposits and their precursors. There were 17.1 wt-% of iron and 11.1 wt-% of chromium found on the coke surface detected by energy dispersive spectroscopy (EDS) which suggests carburetionon alloy. RP-3 fuel and its cracking liquids were analyzed by GC-MS,which showed that the content of alkyl benzene and alkyl naphthalene increased evidently in cracking liquids.

Experimental Investigation of Hydrogen Production from Glycerin Reforming

A series of tests were performed to investigate reforming of reagent-grade propane-1,2,3-triol, (C3H8O3) commonly called glycerin, to produce a H2 rich gas. Effects of the operating parameters, oxygen to carbon ratio, steam to carbon ratio, and temperature, were determined using a factorial experimental design. A mathematical model defining the effect of the three parameters was derived and used to improve the hydrogen yield. From the range of experimental conditions, it was concluded that the oxygen to carbon ratio, as well as the interaction between oxygen to carbon ratio and temperature had the most important effects on H2 yield. A 4.5 mol quantity of hydrogen was produced per mole of glycerin at experimental conditions of oxygen to carbon ratio of 0, steam to carbon ratio of 2.2, and temperature of 804 °C. This is 65% of the maximum theoretical H2 yield, and 90% of the H2 yield predicted by thermochemical equilibrium. A 1.4 mol quantity of CO was also produced per mole of glycerin, presenting the potential for additional production of 1.4 mol H2/mol glycerin. A water gas shift reactor was added to the process and operated at 369 °C, producing a final yield of 5.3 mol H2/mol glycerin, 75% of the maximum stoichiometric hydrogen yield. Crude glycerin obtained from biodiesel production was finally tested (without the water gas shift reactor) as a feed and compared with reagent-grade glycerin results. The initial crude glycerin hydrogen yield, 4.4 mol H2/mol glycerin, was almost identical to that of reagent-grade glycerin, but carbon formation and coking increased the pressure drop through the catalyst bed causing the test to be terminated. Possible contaminants, chloride and sodium cations, present in crude glycerin as byproducts of biodiesel synthesis were added to reagent-grade glycerin and tested in the reformer, producing results similar to those observed for the crude glycerin reforming test.

Density functional theory studies of methane dissociation on anode catalysts in solid-oxide fuel cells: Suggestions for coke reduction

We studied the dissociation of methane into adsorbed carbon and hydrogen atoms on various surfaces to gain insight into carbon coke formation on solid-oxide fuel cell anodes. Preferred adsorption sites and energies were calculated for CH x ( x = 0 , … , 3 ) and H on Ni and Cu (111) planar and (211) stepped surfaces, on Cu Ni and Cu Co surface alloys, and on Ni(211) surfaces with step edge sites blocked by Au- and S-promoter atoms. Transition states and kinetic barriers were calculated on Cu(111) and Cu(211) and on the S Ni(211) surface. Our results are in excellent agreement with existing experimental and theoretical studies, suggesting that copper anodes have very low activity and high resistance to coking, and that step-blocking on the nickel surface can increase the tolerance of nickel-based anodes to carbon coke formation.

Peculiarities of Rapid Pyrolysis of Biomass Covering Medium- and High-Temperature Ranges

Rapid pyrolysis of Hinoki cypress sawdust was conducted over a wide temperature range from 600 to 1400 °C in a lab-scale drop-tube furnace (DTF). Attention was paid to the influence of temperature on carbon conversion, gas yield, tar destruction, and coke deposition. A new observation was the decrease in carbon conversion from 900 to 1100 °C followed by a positive increase as the temperature was raised. Gravimetric analysis and gas chromatography were used as tools for determining heavy tar and light tar, respectively. It was found that temperature had a significant effect on tar destruction. The achievement of complete tar destruction in the product gas required an extremely high pyrolysis temperature of at least 1200 °C. An attractive result of this study was the satisfactory separation of the char and coke produced in pyrolysis, which described an unfamiliar behavior of the char formation and coke deposition. Char yield indicated a sharp drop between 600 and 800 °C then followed an almost plateau up to 1100 °C. Apparent coke deposition was observed from 900 °C accompanied by the secondary decomposition of tars and light hydrocarbon gases. It was concluded that the enhanced carbon conversion at the pyrolysis temperatures above 1100 °C was attributed to the enhancement of the gasification reactions between solid products (char and coke) and reactive gases (H2O and CO2).

Kinetics and mechanisms of nickel metal dusting I. Kinetics and morphology

Abstract The kinetics of nickel metal dusting were investigated at different gas compositions at 680 °C. The carbon uptake rate on nickel exposed to supersaturated H 2 /CO/H 2 O gas mixtures (nominal a C = 19) increased as p CO increased from 0.31 to 0.68 atm, but decreased with further increase in p CO . This behaviour was ascribed to the existence of parallel, independent reaction paths, and the rate was well described by Rate = k 1 p CO p H 2 + k 2 p CO 2 - k 3 p H 2 2 where the k i are constants. Examination of reacted cross-sections showed that general coke layer formation at the nickel surface was accompanied by internal precipitation of graphite along grain boundaries deep inside the nickel. The internal precipitation reflected the large grain of the nickel. Prior cold working of the surface caused its recrystallisation, which affected carbon deposition and coke morphology. The carbon morphologies formed on the sample surface could generally be classified as bulk graphite, carbon filaments and graphite particle clusters. Carbon filaments were nanoscale in size, and uniform. The particles in the graphite particle clusters were relatively large (0.1–2.5 μm) and non-uniform. The morphological development of the carbon deposit differed from one sub-grain to another.

Modelling of carbon and hydrogen oxidation kinetics of a coked ferrierite catalyst

The hydrocarbons in an alkene skeletal isomerisation process cause catalyst deactivation by forming coke that blocks the active sites. Oxidation of the coke is carried out in a regeneration unit to reactivate the catalyst. A kinetic model for the combustion is essential for purposes of designing the regeneration unit, since the highly exothermic oxidation releases heat that can damage the catalyst and the unit. Kinetic models were derived and tested by non-linear regression against the results of temperature programmed oxidation experiments with a coked ferrierite catalyst. Two methods for the measurement of carbon oxides in the reactor outflow – a direct analysis by mass spectrometry and an indirect analysis by a methanation method – were compared, and both were found appropriate. The determination of water by mass spectrometry was found adequate. The derived models cover the oxidation of both coke carbon and hydrogen. A power law model with an oxygen concentration order of half in carbon oxidation and zero order in hydrogen oxidation described the experimental results well. Two other models, in which active intermediate species are formed in fast equilibrium reactions, performed as well as the power law model. The estimated parameters of the models were in the physically meaningful range.

Characterization of Thermal Annealing Effects on the Evolution of Coke Carbon Structure Using Raman Spectroscopy and X-ray Diffraction

An experimental study was conducted to monitor the evolution of coke carbon structure during thermal annealing in a temperature range from 1273 to 2473 K in a bench-scale reactor. Coke carbon structure was characterized by using Raman Spectroscopy and the X-ray Diffraction. The Raman spectra of most of the cokes displayed two broad peaks G* (1620 cm−1) and D* (1360 cm−1). Both Raman peaks were deconvoluted into five peaks namely G, D, D′, R1 and R2. On the basis of area under the respective band peaks, new structural parameters were obtained to quantify graphitic (G), graphitic defect (D) and random (R) carbon fractions of cokes.XRD analysis was used to show that stack height carbon crystallite, Lc, of coke increases with increasing annealing temperature while the impact of annealing duration was not significant particularly up to 1873 K. On the other hand, average carbon crystallite width, La, did not improve significantly up to 1873 K, and increased rapidly after subsequent rise in the annealing temperature. It appears that during annealing up to 1873 K, modification of coke carbon structure could occur due to loss of basal carbon as a consequence of in-situ gasification.The lateral expansion of carbon crystallite, La, was related to relative intensity or shape of Raman band peaks such that both parameters did not change significantly up to an annealing temperature of 1873 K. At higher annealing temperatures, La values of coke increased with decreasing D/G ratio. Lateral expansion of carbon crystallite was attributed to progressive reduction of defects of graphitic carbon of coke, which can be monitored by D fraction of Raman Analysis. Combined Raman and XRD analysis suggested that rapid graphitization of coke may not occur along all dimensions until the annealing temperature exceeds 1873 K.Combining XRD and Raman analysis would provide a comprehensive evaluation of the evolution of coke carbon structure at different temperatures and their subsequent implications on the efficiency of various ironmaking operations.

혼합가스 주입형 연료전지를 위한 전지 디자인

In this study, we fabricated honeycomb type Mixed-Gas Fuel Cell (MGFC) which has advantages of stacking to the axial direction and increasing volume power density. Honeycomb-shaped anode with four channels was prepared by dry pressing method. Two alternative channels were coated with electrolyte and cathode slurry in order to make cathodic reaction sites and the others were filled with partial oxidation (POX) catalyst to increase fuel conversion. Furthermore we employed the sol-gel technique which can increase cell performance and decrease carbon coking.

The use of sulfur to extract hydrogen from coal

Abstract The world's recoverable coal reserves contain about 3 × 10 10 tons of hydrogen. The reaction of sulfur vapor with medium-volatile bituminous coal produces hydrogen sulfide in yields up to 97% (based on sulfur), and utilizes 70–75% of the hydrogen from the coal. The conversion of hydrogen sulfide to hydrogen can be effected through commercially proven processes; several laboratory-scale processes could also be scaled up for future use. The solid by-product of the coal–sulfur reaction meets or exceeds specifications for fixed carbon, ash, and friability of conventional metallurgical coke, though produced at lower temperatures than typical by-product coke ovens. A conceptual process is presented in which sulfur is converted to hydrogen sulfide by reaction with coal, the hydrogen sulfide in turn is converted to the desired hydrogen and to sulfur, and the sulfur is recycled through the reactor. The by-product is a good quality coke, but may also have other applications as a carbon material.

Carbon structure of coke at high temperatures and its influence on coke fines in blast furnace dust

A thermal annealing study of three industrial cokes was carried out in a horizontal tube furnace at a range of temperatures up to 1600 °C under N2. Evolution of the carbon structure of cokes was established by determining the stack height (L002) of aromatic carbon layers on the basis of the 002 carbon peak in their X-ray diffraction (XRD) spectra by using the classical Scherrer’s approach. The heat-treatment temperature is shown to have a strong impact on the growth of crystalline order of coke carbon by demonstrating a linear correlation between the carbon crystallite height (L002) and the annealing temperature. The intensity of the thermal effects on the growth of the crystalline order of coke carbon is influenced by the coke ash chemistry, particularly with the iron content of the coke. The carbon structure of blast furnace (BF) dust samples was also analyzed by using XRD and scanning electron microscopy (SEM). Under a similar range of heat-treatment temperatures, growth of the carbon crystallite (L002) of coke, in both the laboratory and the industrial BF, was found to be of the same order of magnitude. The correlation between the carbon structure (L002) of coke and the annealing temperature is used to ascertain the temperature of the origin of coke fines in a BF. The carbon structure of coke is shown to have a significant influence on the coke behavior in a BF such that highly ordered coke displayed lower reactivity as well as higher proportion of coke fines in the dust. The carbon structure of coke fines in BF dust has been shown as an indicator of the crystallite dimension (L002) of the coke in a BF, and has a potential to assess coke performance, particularly of the coke fine generations from different thermal regimes of a BF and also their subsequent consumption.

Synthesis of Polyynes with Electric Arc Part 5: Detection of PAHs as Minor Products

The main products of the submerged electric arc between graphite electrodes in n‐hexane and in methanol are the polyynes series. The liquid chromatographic analysis (HPLC) of the arcing products in n‐hexane reveals also the presence of a mixture of polycyclic aromatic hydrocarbons (PAHs) as minor products. Naphthalene, acenaphthylene, phenanthrene, perylene, fluoranthene, benzo[b]fluoranthene, pyrene, and the related compound cyclopenta[c,d]pyrene have been identified. Even crysene and acenaphthene were reasonably identified from the PAHs mixture. The PAHs mixture appears to derive essentially from the plasmalysis of the solvent where the electric arc is conducted, while the polyynes are formed from the elemental carbon supplied from the graphite electrodes. Another minor product is represented in all cases by the formation of carbon black or carbon coke, which appears more abundant in n‐hexane rather than in methanol. The different results are explained thermodynamically in terms of different carbonization tendency of the solvents used.

Degradation Behaviour of a High CSR Coke in an Experimental Blast Furnace: Effect of Carbon Structure and Alkali Reactions

A high CSR coke was tested in the LKAB’s Experimental Blast Furnace (EBF) at Lulea. The evolution of physical and chemical properties of the centre-line coke samples were analysed by Light Optical Microscopy (LOM), BET N2 absorption and SEM/XRF/XRD. Alkali distribution in the EBF cokes was examined by XRF/SEM and EDS. Thermo Gravimetric Analysis (TGA) was used to measure isothermal and nonisothermal CO2 reactivity of the cokes. The crystalline order of carbon and the concentration of alkalis were found to increase as the coke descended through thermal reserve zone to the cohesive zone of the EBF. The crystallite height (Lc) of EBF coke carbon displayed a linear correlation with the measured EBF temperatures demonstrating the strong effect of temperature on carbon structure of coke in the EBF. Alkali concentration of the coke was increased as it descended into the EBF, and was uniformly distributed throughout the coke matrix. The CO2 reactivity of lower zone cokes was found to increase when compared to the reactivity of the upper zones cokes, and was related to the catalytic effect of increased alkalis concentration. The deterioration of coke quality particularly coke strength and abrasion propensity were related to coke graphitisation, alkalization and reactivity. Coke graphitisation is shown to have a strong influence on the coke degradation behaviour in the EBF.

New approaches to hydroprocessing

Heavy oil conversion adds a new dimension to refinery operations that requires the use of units to prevent high yields of coke and more beneficial yields of distillate products. Typically, heavy oil conversion involves two general routes: (1) carbon (coke) removal as a product having a low atomic hydrogen/carbon ratio and, at the same time, to produce overhead material (distillate) having a high atomic hydrogen/carbon ratio; and (2) hydrogen addition by a hydrocracking/hydrogenolysis mechanism by which the yield of coke is reduced in favor of enhanced yields of liquid products. Efficient conversion of heavy oil by fluid catalytic cracking or by hydrotreating requires serous efforts to develop adequate catalysts as well as the modification of existing, or the development of new, processes. The constituents of heavy oil are deleterious to catalyst activity and to on-stream lifetime and there is the need to develop catalysts that are tolerant to the high molecular weight and metal constituents of the feedstocks. Alternative processes include hydrotreating coupled with coking or visbreaking. Such options combine the benefits of higher liquid yields from hydrogen addition with the benefit of the added hydrogen during the thermal process. Furthermore, hydrovisbreaking is receiving some attention as a possible alternate to visbreaking and coking. Hydrovisbreaking heavy oil and thermal cracking (e.g., coking, fluid catalytic cracking) the liquid product process (coking) offers the potential for higher yields of distillate with corresponding decreases in the yield of coke. Further development of these and process other concepts are needed to enhance the conversion of heavy oils.

In situ IR investigation of n-hexane isomerization over Pt containing sulfated zirconia

Isomerization of n-hexane over Pt containing sulfated zirconia (Pt/SZ) and SZ was followed by in situ IR measurements. A constant conversion and high selectivity to iso-hexanes were only observed with Pt under hydrogen as carrier gas. In the IR spectra only subtle changes in comparison to the spectrum after activation of Pt/SZ were observed. In the active state of Pt/SZ neither the OH groups nor the sulfates are involved as adsorption sites for n-hexane. Therefore, Pt-proton adducts near sulfate groups and hydride ions connected to Lewis acidic sites are proposed as active sites on Pt/SZ. Over SZ and Pt/SZ using He as carrier gas the isomerization started with an oxidative dehydrogenation of n-hexane followed by a rapid deactivation. The latter reaction is characterized by water formation, by a band near 1670 cm −1 and a broad band in the range of 1540–1580 cm −1 assigned to oxidized carbon species and coke precursors or coke, respectively. The oxidized species are transformed during TOS into coke. Reactivation of the catalysts could only be achieved by oxidation in air.