Pyrolysis Coke Research Articles

Effect of molecular structure on pyrolysis coking performances of hydrocarbons at different temperatures

Methylcyclohexane (MCH) and n-heptane (nC7) were used to perform experimental studies in high-temperature oxidation pretreated STS304 reactor (ϕ2 × 0.5 × 1000 mm) at 873–1073 K, 1.0 MPa, and 1.0 mL/min feed rate. The heat sinks of the two fuels were calculated based on the conversion and product distribution. MCH was found to have difficulty in achieving high heat sink at low and high temperatures. The formation pathways of ethylene and benzene were then compared. Results showed their main precursors were similar, but the contribution proportion of each path was different affected by initial cracking reactions of MCH and nC7. The coking rate of MCH was lower than that of nC7 at low temperatures, while the trend was the opposite at high temperatures. The variation in C/H ratio of coke for MCH and nC7 with temperature was the same, whereas the C/H ratio of the former was significantly lower. The unique unimolecular demethylation and intramolecular stepwise dehydrogenation reactions of MCH caused its coking rate to be higher than that of nC7. An experimental method was proposed to determine the coking active site density based on composition and structure of coke. Finally, a coking mechanism based on the growth of spherical coke particles was proposed.

Co-pyrolytic interactions, kinetics and products of biomass pyrolysis coke and rapeseed cake: Machine learning, DAEM and 2D-COS analysis

In this study, an efficient strategy for synergistic disposal of biomass pyrolysis coke (PC) and rapeseed cake (RC) was proposed to explore their clean utilization, with the purposes for evaluating the co-pyrolytic interactions, kinetics, mechanism and products. The results indicated that synergistic effect was strengthened by lower PC ratio and temperature. A multiple distributed activation energy model (MDAEM) was applied to obtain accurate activation energy distributions. Co-pyrolysis resulted in lower average activation energy and wider distribution, from which the activation energy E0 and σ were in the range of 103.99–214.16 kJ/mol and 3.18–38.09 kJ/mol. MDAEM was also innovatively combined with machine learning to describe and predict co-pyrolysis process, with the determination coefficient R2 beyond 0.999923. Sensitivity analysis and principal component analysis were applied, indicating RC was more sensitive to the heating rate, and preferred dominating reactions at high-temperature region. Temperature dependences of pyrolysates was obtained by two-dimensional correlation spectroscopy method.

Modelling and understanding deposit formation of hydrocarbon fuels from the coke characteristics

Coking during the hydrocarbon fuel pyrolysis is a key problem that needs to be considered. To get more insights into coke, this work explored deposit formation of hydrocarbon fuels from the coke characteristics. Pyrolytic deposition experiments of n-decane and HF-01 were experimentally performed by using electric heating stainless steel and TiN-coated tubes to investigate the different growth pathway of coke. The morphology, graphitization degree and mass of coke produced under different experimental conditions were analyzed by means of scanning electron microscopy, Raman spectroscopy and carbon burn-off method, respectively. Results reveal that the differences in physical properties and reactivity of coke between different tubes are due to the different growth mechanism. The graphitization degree of coke can distinguish the main growth mechanism. It is also found that the low reactive filamentous carbon with ID/IG value below 2.7 produced by metal catalytic coking is the primary cause of pipeline blockage. TiN coating effectively inhibits the production of filamentous carbon, meanwhile, the coking inhibition efficiency can reach above 70%. The simplified coking kinetic models and semi-empirical coke combustion models are established to explore the coke formation and oxidation process. The models are performed to investigate the coke characteristics, for further exploring and understanding intrinsic hydrocarbon fuel pyrolysis coking mechanism.

Study on SO <sub>2</sub> Reduction to Element Sulfur with Pyrolytic Coke of High Sulfur Coal

Study on SO <sub>2</sub> Reduction to Element Sulfur with Pyrolytic Coke of High Sulfur Coal

Study on the Effect of Heat Transfer Enhancement on Pyrolysis Coking Process for N-Decane at Supercritical Pressure in Corrugated Tube

Study on the Effect of Heat Transfer Enhancement on Pyrolysis Coking Process for N-Decane at Supercritical Pressure in Corrugated Tube

Study on durability of online catalytic upgrading of bio-oil based on Ru/HZSM-5

Ru/HZSM-5 was prepared and used to upgrade bio-oil online and the changes of bio-oil yield and physicochemical properties were analyzed through the total quality index (TQI). The changes of the chemical compositions of the bio-oils were compared; simultaneously, the coking situation of the catalyst was characterized. The results showed that the yield and physicochemical properties of bio-oil obtained by using fresh catalyst were high, and the TQI increased from 0.15 to 6.45; with the increase of using times, the TQI first increased slightly to 6.68, then decreased rapidly to 1.25, and reduced to only 0.27 after the fourth usage. In the initial stage, a small amount of coking reactions made the strong acid sites partially passivated, which improved the aromatization performance. When the catalyst was used twice, the relative content of hydrocarbons in the bio-oil reached 53.79%, of which the relative content of light aliphatic hydrocarbons was 16.87 %, and the relative content of monocyclic aromatic hydrocarbons was 32.65%. After the fourth usage, the relative content of hydrocarbons in the bio-oil was only 9.32 %, and the catalyst layer basically lost the upgrading effect, and had adverse effects on pyrolysis vapors such as secondary cracking or polymerization. Before the third usage, the low-temperature pyrolytic coke attached to the catalyst surface was dominant. After the third usage, the low-temperature pyrolytic coke and high-temperature catalytic coke increased significantly, and the catalyst activity decreased sharply. Continuous usage of catalyst slightly increased coke, of which the pyrolytic coke increased mainly.

Low temperature oxidized coke of the ultra-heavy oil during in-situ combustion process: Structural characterization and evolution elucidation

Fundamental knowledge on the evolution of low temperature oxidized coke was a prerequisite towards a deep understanding of coke deposition and subsequent combustion of ultra-heavy oils during in-situ combustion (ISC) process. This study investigated the structural characterization (oxidation behavior, elemental composition, functional groups, and morphology) and elucidated evolution mechanism of cokes generated from the low temperature oxidation/pyrolysis of the ultra-heavy oil during ISC process. The results shown that, compared with pyrolytic coke, the intermediate groups of C-O/C-OH (1260–1060 cm−1) were further oxidized into C = O (1850–1650 cm−1) groups and finally converted into C = C groups (“coke peak”, 1590 cm−1) in highly conjugated aromatic structures for oxidized cokes. Besides, the oxidized coking condition would result in a higher degree of substitution (γCHAr1, γCHAr4) of aromatic rings (900–700 cm−1) and promote the evolution of N- and S- functional groups. Although >78 % of C 1 s belonged to the graphitic carbon for four cokes, morphologies of oxidized cokes were relatively coarse with much looser distribution. In addition, the corresponding enthalpies were in the order cokeLTO3 (25.51 kJ·g−1) > cokeLTP (24.22 kJ·g−1) > cokeLTO2 (23.23 kJ·g−1) > cokeLTO1 (17.45 kJ·g−1), indicating a considerable contribution of low temperature oxidation reactions on derived coke morphology, oxidizability and exothermicity, which contained complicated and crucial dehydrogenation, crosslinking and polymerization reactions to accelerate coke evolution.

Experimental investigation of n-heptane unsteady-state pyrolysis coking characteristics in microchannel

Coke deposition is considered a challenging problem during hydrocarbon pyrolysis. To get more insights into pyrolysis coking characteristics in the regenerative cooling channels, the unsteady-state experiments of n-heptane were performed in a 2.0 mm (internal diameter) passivated STS304 tube at 873–1073 K and 1.0 MPa with a feeding flow rate of 1.0 mL/min during pyrolysis for 5–60 min. The unsteady-state and spatial coke distributions were obtained. Results showed three distinct stages of coking, namely, catalytic coking, the transition stage, and pyrolytic coking. Coke samples obtained under different temperatures were characterized by element analyzer, scanning electron microscope (SEM), thermogravimeter coupled with a Fourier transform infrared spectroscopy (TG-FTIR), X-ray diffraction (XRD), and Raman spectra apparatus. The coke could be classified into two or three types according to its oxidative activity, and was composed of aromatic carbon and aliphatic hydrocarbons. The morphology of the coke transitions from filamentous to spherical with temperature and pyrolysis time. The C/H ratio of coke increased with the temperature in the catalytic coking stage, but decreased in the pyrolytic coking stage. High H contents and extensive defects of the coke observed at high temperatures could attributed to the generation of large amounts of pyrolytic coke and high coking rate, which resulting a lower degree of dehydrogenation. The presence of metallic substances in the coke verifies the catalytic effect at the beginning of coking and indicates the occurrence of carburization corrosion.

Experimental Study on Co-Pyrolysis Characteristics of Household Refuse and Two Industrial Solid Wastes

The calorific value of household refuse (HR) is greatly improved after classification, which includes the implementation of sufficient pyrolysis conditions. Therefore, a better pyrolysis effect can be achieved by co-pyrolysis with industrial solid waste (ISW) with high calorific value. In this work, HR and ISW were used as raw materials for co-pyrolysis experiments. The influence on the distribution of three-phase products after co-pyrolysis, the concentration of heavy metals and dioxins in the flue gas, and the distribution of PCDD/Fs isomers were studied. The results showed that, at a temperature of 600 °C and H/C = 1.3, of the formed material, the quantity of pyrolysis gas was approximately 27 wt.%, and the quantity of pyrolysis oil was approximately 40.75 wt.%, which mainly contained alkanes, olefins, and aromatic hydrocarbons. When S/C = 0.008, pyrolysis gas accounted for 25.95 wt.% of the formed material, and pyrolysis oil for 41.95 wt.% of the formed material. The ignition loss rate of pyrolysis coke was approximately 20%, and the maximal calorific value was 14,217 KJ/kg. According to the thermogravimetric experiment, the co-pyrolysis of HR and ISW can promote the positive reaction of pyrolysis, and the weight loss reached 62% at 550 °C. The emission of gaseous heavy metals was relatively stable, and the concentration of heavy metals slightly decreased. The main heavy metals in the ash were Cu, Fe, and Zn. The emission of dioxins could be effectively reduced by the pyrolysis of HR with ISW, and the produced dioxins were mainly synthesized from de novo synthesis. After pyrolysis, the toxic equivalent of dioxins in the flue gas was reduced from 0.69 to 0.29 ng I-TEQ/Nm3, and the distribution of dioxin isomers in the flue gas had little influence. The experimental results provide a theoretical basis for the application of co-pyrolysis technology with HR and ISW.

Agglomeration of coke particles by aliphatic binders: A hidden pollutant in effluent of steam crackers

This work is aiming at exploration of agglomeration process leading to the increasing pollution potential of pyrolytic coke particles in effluent of steam crackers before entering the water resources. The submicron particles of pyrolytic coke are formed in steam crackers in diameter range of 0.2–5.0μm and enter the oceans as industrial effluent while the COD, TDS, TSS, odor and turbidity values are in acceptable range. The agglomeration tendency of submicron pyrolytic coke fines was attributed to selective adsorption of self–assembled monolayers (long–chain normal aliphatic alkanes, C14–C24) on the surfaces of pyrolytic coke particles. The monolayer scaffold forms a thermal sensitive adhesive coating for agglomeration of suspended particles. The results of liquid chromatography–mass spectrometry (LC–MS) revealed no polymeric or oligomeric substrates in the monolayer scaffolds since the maximum molecular weight of adsorbed solutes was determined to be below 500 Da. The outcomes showed that the amount of submicron particles of pyrolytic coke in the industrial effluents can be reduced by removing long–chain normal aliphatic alkanes (C14–C24) as the source of self–assembled monolayers. Finally, the mechanism of temperature dependent vertical/horizontal adsorption modes was examined.

Evaluation of thermokinetics methodology, parameters, and coke characterization of co-pyrolysis of bituminous coal with herbaceous and agricultural biomass

In this paper, conventional thermogravimetric analysis and a new congruent–mass thermogravimetric analysis were used to study the reaction mechanism of the co-pyrolysis process of coal and biomass in the thermogravimetric analyzer, the effects of heating rate and carrier gas flow rate on co-pyrolysis were investigated, and kinetic analysis was conducted for the major pyrolysis stages to explore whether there was a synergistic effect in the co-pyrolysis process. The surface morphology of pyrolytic coke was evaluated by the fractal dimension method. The results show that congruent–mass thermogravimetric analysis can compare the interactions in the co-pyrolysis process more intuitively and reduce the influence of initial mass on the determination of interaction relationship. Synergistic effect appears in co-pyrolysis of coal and biomass. With the increase of heating rate, the thermogravimetric hysteresis appeared and the thermogravimetric curve gradually moved to the high temperature region. With the increase of carrier gas flow rate, the synergistic effect weakens. The kinetics of different reaction stages was analyzed by Coats–Redfern method; the results show that the activation energy required in the main co-pyrolysis stage of the mixture is lower than that in the pyrolysis stage alone. The micromorphology shows that biomass coke has a more developed pore structure than coal, and the box dimension indicates that co-pyrolysis increases the surface irregularity of coke. It is of great significance to judge the interaction mechanism of two or even multiple mixed samples in the process of co-pyrolysis.

Influence of scale and atmosphere on the pyrolysis properties of large-scale bituminous coal

In order to explore the influence of scale and atmosphere on the pyrolysis properties of coal in the underground coal gasification process, bituminous coal samples measuring 5, 8, and 10 cm were separately pyrolyzed in N2 and CO2, and the functional groups and pore structure at various scales were also analyzed. The results indicated that the main influences on large-scale bituminous coal pyrolysis were both the inner and outer temperatures, and the inner temperature was lower than the outer temperature. The production rate of pyrolysis tar in CO2 is higher than that in N2. The pyrene, naphthalene, and benzene concentrations in the pyrolysis tar decreased, but the indene increased with the increase of scale. The specific surface area and pore volume of pyrolysis coke were significantly increased in CO2 with the increase of scale. The average pore diameter of pyrolysis coke showed a decreasing trend with the increase of scale. In a N2 atmosphere, the average pore diameter and the most probable diameter were both greater than those in CO2. The −OH, CH2, and CH3 concentrations in the coke in CO2 were lower than those in N2. The larger the scale, the more −OH was contained in the coke.

Fouling propensity of pyrolytic coke particles in aqueous phase: Thermal and spectral analysis

AbstractAgglomeration–deposition of pyrolytic coke particles has been assigned as the main concern of fouling formation of olefin units in heat exchangers, vessels, and towers. The aim of this study is to investigate the agglomeration and the fouling propensity of aliphatic‐coated pyrolytic coke particles in the aqueous phase of quench water. Unusual surface properties of pyrolytic coke particles refer back to selective adsorption and formation of self‐assembled monolayers of long‐chain aliphatic hydrocarbons C14–C24 on the micropores of pyrolytic coke scaffold leading to formation of a thermal sensitive coating for agglomeration of suspended particles. Agglomeration of pyrolytic coke particles on solid surfaces was demonstrated using scanning electron microscopy (SEM) observations, and the morphology of fouling layer was studied. The experimental results revealed that the aliphatic coating, which encompasses about 40 wt% of the pyrolytic coke particles, is responsible for fouling propensity and particulate agglomeration of pyrolytic cokes in hot quench water. Thermal analysis as well as Fourier transform infrared spectroscopy (FT‐IR) and energy‐dispersive X‐ray spectroscopy (EDS) spectra showed that adsorbed layer of hydrocarbons follows a first‐order burning reaction and contains negligible amounts of heteroatoms, mainly aliphatic hydrocarbons.

Gas-Modified Pyrolysis Coke for in Situ Catalytic Cracking of Coal Tar.

Modified pyrolysis coke can be used as a catalyst for tar cracking. In this paper, pyrolysis coke was used as a carrier for modification by using gases (H2O, CO2, and NH3), and the optimal modified gas was selected. On the basis of this, pyrolysis coke with different modified flow rates, temperatures, and times were prepared to catalyze the cracking of tar. The effect of gas-modified pyrolysis coke on tar cracking products was studied. Also, pyrolysis coke was characterized by Fourier-transform infrared spectroscopy, Brunauer–Emmett–Teller analysis, and scanning electron microscopy. The results show that the optimal gas is H2O, and the optimal preparation conditions are 450 mL/min, 650 °C, and 60 min. The pyrolysis coke catalyst under the optimal conditions has the best cracking effect on tar. Also, the gas and tar yields have been further improved.

Study on In Situ Catalytic Cracking of Coal Tar by Plasma Preparation of the Pyrolysis Coke Catalyst.

A two-stage pyrolysis fixed bed was used, and the vapor-modified pyrolysis coke was used as a carrier. A ZHPC catalyst was prepared by plasma calcination. Gas-phase tar produced by the pyrolysis of raw coal was subjected to in situ catalytic cracking to improve tar and gas yield. The effects of plasma calcination power, calcination time, and ZnO loading on in situ cracked products were studied. The prepared catalyst was characterized by X-ray electron spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller, and scanning electron microscopy. The results showed that (1) compared with traditional catalysts, the catalyst prepared by plasma has better performance; (2) the optimal calcination time of the ZHPC catalyst is 5 min, calcination power is 60 W, and ZnO loading is 10%; (3) compared with raw coal pyrolysis, the optimal ZHPC catalyst on in situ catalytic cracking tar, gas yield increased by 66.16%; the cracking rate of tar increased by 54.46%, and the content of light components increased to 60.7%; (4) in situ catalytic cracking of tar with the optimal PC, the light tar has been greatly improved, in which the light oil, phenol oil, naphthalene oil, and wash oil have increased by 93.04, 126.31, 257.28, and 108.08%, respectively. The anthracene oil and asphalt have decreased by 26.98 and 58.71%; the tar cracking rate has increased.

Study on solid waste pyrolysis coke catalyst for catalytic cracking of coal tar

Low value solid waste pyrolysis coke was used as a catalyst to catalytically crack gas-phase tar to improve tar yield and gas production. Pyrolysis coke with different pyrolysis final temperature and pyrolysis time were prepared, the effect of tar cracking products was studied, and the optimal pyrolysis coke were screened. The pyrolysis coke catalyst was characterized by BET, FTIR, SEM. The results show that the optimal preparation final temperature of pyrolysis coke is 750 °C, and the optimal preparation pyrolysis time is 2 h. Compared with the pyrolysis of raw coal, the tar cracking rate increased by 9.3%, after added the pyrolysis coke catalyst, the gas increased by 23.2%, and the light component increased to 36.6%. And the OH, C–N and C–O–C functional groups present on coke are the factors that affect the catalytic cracking.

Preparation of NiO / PC catalyst with plasma for cracking tar to produce flammable gas

To increase the use of lignite, the tar was pyrolyzed with pyrolysis coke (PC) to produce more combustible gases such as H2, CH4, and CO. NiO/PC catalyst with plasma was prepared, and the influence of PC and NiO/PC catalyst on flammable gas was investigated in a two-stage fixed reactor. The catalysts were characterized by SEM, BET, XPS and XRD to analyze the tar cracking mechanism. The results were: (1) PC was prepared at different heating rates, and when the heating rate reached 20 °C/min, the amount of flammable gas was 5.4 L. (2) NiO/PC catalyst was modified with plasma in three background gases withO2 being the best, mainly because of the increase of the oxygen functional groups. (3) PC was modified and calcined with plasma, and when the power reached 40 W, it produced the most combustible gas, and the volume could grow by 94.4%.

Adaptability of Powdered Activated Carbon Production from Ground Catering Waste Pyrolysis Coke

Three mixture of catering waste was pyrolyzed at 650, 725 and 900 °C and the solid residue (coke) was examined for powdered activated carbon production. For this, the carbon content, iodine number, particle size distribution and scanning electron microscopic images were analysed. Based on the carbon content, these cokes are suitable for activated carbon production, which were 60-85 wt.% (depending on the base material and pyrolysis temperature). The studied cokes showed slightly porous structure with smooth surfaces. Because of this, the iodine number was mostly small (13-30). Based on the grinding experiments, 10 minutes of grinding was found to be optimal. After this grinding time, the reached iodine number of powdered activated carbon was 350-610.

Adaptability of Powdered Activated Carbon Production from Ground Catering Waste Pyrolysis Coke

Adaptability of Powdered Activated Carbon Production from Ground Catering Waste Pyrolysis Coke

Modelling coke formation in an industrial ethane‐cracking furnace for ethylene production

AbstractThe development of a model for predicting coke formation in an industrial ethylene cracking furnace is described. Expressions for predicting the rates of catalytic and pyrolytic coke formation are developed and a differential equation is derived to predict changes in coke thickness with time and position. An expression is developed to account for a decline in the rate of catalytic coke formation with increasing thickness of the coke layer. The proposed coke model equations are used to extend a previously developed ethane pyrolysis furnace model that ignored coke. Three model parameters related to coke formation are estimated using industrial data to obtain reliable model predictions. Two of these parameters are coefficients that appear in the catalytic and pyrolytic coke formation rate expressions. The third is a characteristic‐length parameter used to reduce the rate of catalytic coke formation as the coke layer grows. The resulting dynamic model matches the industrial data well and can be used to simulate furnace operation and predict coke thickness profiles over a variety of the operating conditions, thereby helping process engineers who plan the decoking process.