Hard Coke Research Articles

Effect of Mesoporosity, Acidity and Crystal Size of Zeolite ZSM‐5 on Catalytic Performance during the Ex‐situ Catalytic Fast Pyrolysis of Biomass

AbstractThe catalytic performance of a set of technical, zeolite ZSM‐5 extruded materials have been studied in a bench scale unit for the ex‐situ Catalytic Fast Pyrolysis (CFP) of lignocellulosic biomass. The set of catalysts include micro‐ and mesoporous materials, with and without ZrO2‐promotion, with different Si/Al ratios and with micro‐ and nanosized zeolite crystals. Mesoporosity, acidity and crystal size play a key role on the overall catalytic performances in terms of activity and selectivity (i. e., in their ability to obtain the highest bio‐oil fraction with the lowest oxygen content), and also importantly, stability. Detailed post‐mortem bulk and micro‐spectroscopic studies of the solid catalysts complement the catalytic testing. The obtained results point towards coke deposits as the main cause for catalyst deactivation. Details of the nature, formation and evolution of these coke deposits revealed essential insights, which serve to evaluate the design of catalysts for the ex‐situ CFP of biomass. In particular the mesoporous catalysts are overall better preserved with increasing time‐on‐stream and deactivate later than their microporous counterparts, which suffer from pore blockage. Likewise, it was seen that ZrO2‐promotion contributed positively in the prevention against deactivation by hard coke spreading, thanks to its enhanced Lewis acidity. The zeolite's crystal size is another important characteristic to combine the different components within catalyst bodies, ensuring the proper interaction between zeolite, promoter and binder. This is illustrated by the nanocrystalline ZrO2/n‐ZSM‐5‐ATP material, which shows the best catalytic performance.

Simultaneous pretreatment and catalytic conversion of polyolefins into hydrocarbon fuels over acidic zeolite catalysts

The effect of pre-degradation treatment in catalytic pyrolysis of polymer was assessed using thermogravimetric analysis (TGA) and pyrolysis reactor experiments of different polymers on various catalysts. Intimate contact between the polymer and catalyst was achieved using physical, mechanical and thermal treatments. The results from the TGA analysis show that pre-degradation treatment has greatly improved the performance of the catalyst attaining maximum degradation at lower temperature. Pre-degradation treatment had increased the liquid yield and lowered the coke yield at various extents depending on the catalyst structure and acidity. The ZSM-5 catalyst with high Si/Al ratio showed maximum amount of (C5–C9) and ZSM-5 with lower Si/Al ratio has maximum percentage of (C14–C20). Based on the performance of the pre-degradation treatment methods, normal mixing produced the maximum amount of lighter fractions and therefore pre-degradation treatment can serve to enhance the gasoline fraction while the diesel fraction can be optimised using the co-pressing method, where polymer and catalyst particles were thoroughly mixed and co-pressed together into mixed particles. Coke characterisation showed coke formed by linear low density polyethylene contained more volatile coke components while polypropylene coke had higher percentage of hard coke. ZSM-5 had lower retention of coke components with volatile coke precursors. The volatility of the coke increases while coke concentration and decreases as the catalyst amount decreases. Pre-degradation treatment facilitated the formation of soft coke components that are easy to remove in inert atmosphere.

Study on the deactivation process of dimethyl ether carbonylation reaction over Mordenite catalyst

The deactivation of Mordenite (MOR) catalyst in dimethyl ether (DME) carbonylation reaction was systematically studied. The influence of coke deposition on the structure, morphology and acid sites were characterized and the transformation of coke deposition was investigated. Characterization results revealed that coke deposition had little effect on the structure and morphology of the catalyst. Soft and hard coke could be identified on the catalysts throughout the reaction process. The acid sites decreased more rapidly in the induction period of carbonylation reaction due to the formation of reaction intermediates and soft coke while the hard coke mainly accumulated in the deactivation period. C2H4 generated in the desorption process of DME and methyl acetate (MA) molecules were speculated as an important source of coke deposition. The soft coke was mostly formed via degradation of DME molecules at first half of reaction period, which gradually transformed into hard coke by releasing CH4 and H2. The hard coke mainly derived from MA molecules and transformation of soft coke.

Producing gasoline-like hydrocarbons by cracking crude soybean oil: tuning the NaZSM-5 zeolite’s acidity for increasing the catalyst lifetime

This work investigates the effect of NaZSM-5 zeolite’s acid properties on the catalytic cracking of crude soybean to produce gasoline-like hydrocarbons. We modified both the acid concentration and the acid strength of the NaZSM-5(60) zeolite (where 60 denotes the SiO2/Al2O3 molar ratio) either by varying the SiO2/Al2O3 ratio (i.e., 30, and 90) or by exchanging the compensation cation (i.e., from Na+ to H+). Given the ammonia temperature-programmed desorption and temperature-programmed oxidation tests, we observed that the acid strength of the catalyst is associated not only with the distribution of the cracking products, but also with the nature of the carbonaceous deposits formed during the reaction. Weak, medium, and strong acidity were associated with the formation of heavy hydrocarbon species, soft, and hard coke, respectively. The NaZSM-5 zeolites exhibited weak and medium acidity, while the HZSM-5(60) zeolite exhibited weak and strong acidity. Although both NaZSM-5(30) and HZSM-5(60) zeolites delivered higher gasoline yield than the NaZSM-5(60) zeolite due to its higher acid concentration, the HZSM-5(60) zeolite formed carbonaceous deposits with lower reactivity (i.e., hard coke). Therefore, low values of SiO2/Al2O3 ratio in the NaZSM-5 zeolite drive the reaction products towards gasoline-like hydrocarbons and favor the catalyst reactivation through the formation of more reactive carbonaceous deposits.

Studying the Characteristics of a Waste Industrial Со-Мо/Al2O3 Catalyst for the Deep Hydrotreatment of Diesel Fuel

The physicochemical properties of a waste industrial Со-Мо/Al2O3 catalyst for the deep hydrotreating of diesel fuel are studied. IR spectroscopy, thermogravimetry (TG), differential thermal analysis (DTA), and scanning electron microscopy (SEM) are used to establish that the catalyst surface is uniformly coated with a coke film. This soft coke is mostly a mixture of saturated hydrocarbons with a low degree of branching in their structure. The coke is oxidized at temperatures of 190–375°C (soft coke) and 375–525°C (hard coke); its quantitative removal is achieved by means of oxidative calcination in air for 3 h at 550°C. X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption, and chemical analysis are used to show that the waste catalyst undergoes considerable structural transformation with a 7.7% drop in the Mo content and the accumulation of Fe, Ha, and V impurities. As a result of sintering, its specific surface area and total pore volume are reduced by 31.5 and 28.4%, respectively. The obtained data are needed to develop a scheme for its recycling.

Characterization of the spent industrial catalyst Co-Mo/Al2O3 for fine hydrotreatment of diesel fuel

Physicochemical properties of the spent industrial catalyst Co-Mo/Al2O3for hydrotreatment of diesel fuel were studied. IR, TG, DTA and SEM techniques were used to establish that the catalyst surface is covered uniformly by a coke film; the soft coke consists predominantly of a mixture of slightly branched saturated hydrocarbons. Coke is oxidized at 190–375 °C (soft coke) and 375–525 °C (hard coke) and was removed quantitatively by calcining in air at 550 °C for 3 hours. XRD and SEM techniques, low temperature nitrogen adsorption, and chemical analysis were used to demonstrate considerable changes in the structure of the spent catalyst (phases Co3O4, CoCO3and CoSO4·6H2O); the Mo content decreased by 7.7 %; Fe, Na and V impurities were accumulated; sintering resulted in a decrease in the specific surface area and total pore volume by 31.5 and 28.4 %, respectively. The data obtained are necessary for developing methods for the catalyst utilization.

High efficiency of phenol oxidation in a structured fixed bed over Cu-ZSM-5/PSSF prepared by ion-exchanged method

Cu-ZSM-5 zeolite membrane catalysts coating on paper-like sintered stainless fibers (PSSF) were prepared by ion-exchanged method for the catalytic wet peroxide oxidation (CWPO) of phenol in a structured fixed bed reactor. Firstly, two types of Cu-ZSM-5/PSSF catalysts were synthesized by ion-exchanged and impregnation methods. Then, the structures and properties of the catalysts were characterized by SEM, EDS mapping, BET, FT-IR, UV–vis, H2-TPR and XPS, respectively. The SEM results showed that the continuous and compact ZSM-5 membrane (about 5 μm in average thickness) was coated well over the PSSF surface. The XPS results indicated that the catalyst prepared by ion exchanged method had more amount of Cu+ species and more lattice oxygen than that of the catalyst prepared by impregnation. In addition, the CWPO performance of phenol was independently conducted in the structured fixed bed composed of the two Cu-ZSM-5/PSSF catalysts. The experimental results showed that the phenol was entirely eliminated, and high TOC conversion (80%), CO2 selectivity (around 80%) as well as low total copper leaching rate (about 23%) were obtained over the catalyst prepared by ion-exchanged method, while TOC conversion of 51%, CO2 selectivity of 52% and high total copper leaching rate (about 60%) were achieved over the catalyst prepared by impregnation method. Finally, good durability with low Cu leaching concentration (only about 17 ppm) and complete phenol conversion were obtained after continuously operating 11 h. Meanwhile, the loss of Cu+ active component and hard coke formations over the catalysts prepared by ion-exchanged method were primary reason for the deactivation.

Underground mining slurry transportation viability

Underground mining requires lot of water pumping to surface which increases cost. Because of safety, support, ventilation and environment costs underground mines are closing down gradually all over the world. This innovative paper is based on method studies by computer programming with realistic data. With development of electronic control systems, coal water slurry mix can be remote controlled for transport to surface Separator-bunker. Main consumers need powdered coal/mineral like thermal power stations, for feeding to Fuel Burners of boilers, generating power or in steel plants for feeding into coke ovens to make hard coke for charging into Blast Furnaces for making pig iron. Feed for coal washeries also require crushed coal and output of washed coal as slurry can be sent to coke ovens of steel plants directly. Production from mine faces should be taken through lump-breaker and conveyed to a mixing chamber, near panel sump, from where adequate capacity slurry pump will propel up to pit-top. The projected financial benefit can be several millions of Rupees per year, as compared to road, rail conveyor or winders is shown, by run of a computer program in Java, with realistic cost figures from mines.

Product distribution of the thermal and catalytic fast pyrolysis of karanja (Pongamia pinnata) fruit hulls over a reusable silica-alumina catalyst

The conversion of karanja fruit hulls by fast pyrolysis was investigated using a drop-type two-stage reactor. The ex-situ catalytic fast pyrolysis of karanja fruit hulls over a silica-alumina catalyst was performed at 500 °C and at a catalyst loading of 0.1 g. The obtained bio-oil yield was 41.09 wt%. The bio-oil contained 84.38% carbonyls. The silica-alumina catalyst reduced the liquid yield to 39.73 wt%. The production of aromatics and hydrocarbons in bio-oil was enhanced, whereas the yield of carbonyls was reduced from 84.38% (non-catalytic) to 7.83% (catalytic). After catalyst regeneration, the aromatic yield was increased from 30.08% (1st run) to 52.18% (5th run), and the deoxygenation degree was increased from 35.15% (1st run) to 57.13% (5th run), thereby demonstrating that the silica-alumina catalyst had satisfactory reusability. The amount of catalytic coke was reduced after catalyst regeneration, because less hard coke was formed.

Catalytic degradation of linear low-density polyethylene over HY-zeolite via pre-degradation method

The catalytic degradation of linear low-density (lldPE) polyethylene over HY-zeolite catalyst was studied in a semi-batch reactor. One of the important problems encountered during catalytic pyrolysis of macromolecules is the contact with the catalyst, which is known to affect the product distribution and the quality of the coke formed. A pre-degradation procedure was introduced to achieve efficient contact between the LLDPE macromolecules and the catalyst. The influence of the pre-degradation to the reaction conditions including holding time, temperature, polymer to catalyst ratio and flow rate of carrier gas was examined. Moreover, the pre-degradation results were compared with the results obtained using normal mixing procedure. The results obtained showed that, pre-degradation promotes the liquid fraction by a factor of more than one-fold increase at the expense of the gas fraction and the coke yield. The optimal liquid fraction with pre-degradation was obtained at low reaction temperature and catalyst amount respectively, i.e. high polymer to catalyst ratio, making it economically viable method for the degradation of lldPE.The coke content was analysed using TGA in nitrogen atmosphere to remove the soft coke and then in air isothermally at the final temperature to burn the hard coke. The TGA results of the coked sample show less concentration of coke components on the catalyst using the pre-degradation method as compared to the normal mixing which shows high concentration of coke components especially at low reaction temperature. Moreover, the majority of the coke components produced using the pre-degradation method were soft coke, making it more efficient for the re-usability of the catalyst.The liquid samples collected were analysed using gas chromatography and the products distribution were presented in the form of boiling point distribution curves. The bulk of the liquid products produced were lighter fractions with a peak around the gasoline range.

Investigating the Coke Formation Mechanism of H-ZSM-5 during Methanol Dehydration Using Operando UV–Raman Spectroscopy

Methanol dehydration on solid acid catalysts is a fundamental step in many industrial chemical processes, such as methanol to dimethyl ether (MTD) and methanol to olefin (MTO). The performance of catalysts often encounters the detrimental effect of coke deposition. However, the heterogeneous distribution of feedstock and product in a fixed-bed reactor usually brings in difficulties in the study of the coking mechanism. In this work, the coking progress of H-ZSM-5 in a fixed-bed reactor under MTD conditions is investigated using operando UV-Raman spectroscopy. Methylbenzenium carbenium ions (MB+), a key precursor for coke formation, was identified by UV resonance Raman spectroscopy and isotope exchange experiments. At higher temperature (473 K), MB+ rapidly transforms into “hard coke” at the beginning of the catalyst bed. The relative intensity of the 1605 cm–1 peak can serve as an indicator for the catalyst deactivation. Moreover, water formed during MTD can suppress the transformation of MB+ into “hard c...

One-step aldol condensation reaction of dimethoxymethane and methyl acetate over supported Cs/ZSM-35 zeolite catalysts

This study was performed for the development of a green and promising approach for the synthesis of methyl acrylate and acrylic acid by a one-step aldol condensation reaction of dimethoxymethane and methyl acetate over cesium oxide-supported on ZSM-35 zeolite catalysts; the effect of base sites as well as acid sites on the aldol condensation reaction was studied in detail. It was found that base sites were harmful for aldol condensation due to their failure in catalyzing the decomposition of dimethoxymethane precursor into formaldehyde, whereas the acid site was indispensable for the reaction to proceed. This reaction cannot take place without an acid site. Although acid sites in H-form of the zeolite (HZSM-35) are indispensable for the aldol condensation reaction, not all of them tend to favor this reaction. A strong acid catalyzes methanol-to-olefin-like reactions resulting in hydrocarbon byproducts, which are finally transferred to hard coke. Medium strong acids and weak acids are great candidates for the target aldol condensation reaction with high activity and selectivity. A γ-Al2O3 sample with abundant weak-strength Lewis acid sites, together with a few medium-strong-strength acid sites, performs well with a high activity and considerable stability during the synthesis of methyl acrylate and acrylic acid.

Synergistic effects of Nb2O5 promoter on Ru/Al2O3 for an aqueous-phase hydrodeoxygenation of glycerol to hydrocarbons

Synergistic effects of niobium oxide (Nb2O5) on the Ru/Al2O3, where the alumina had boehmite phases prepared by sol-gel method with subsequent co-impregnation of bimetallic Ru-Nb, were investigated for an aqueous-phase hydrodeoxygenation (APH) as well as aqueous-phase reforming (APR) reaction of glycerol to form gaseous hydrocarbons and hydrogen with useful liquid-phase glycols such as ethylene and propylene glycols. The promoting effects of the Nb2O5 on the prototype Ru/Al2O3 were mainly attributed to the stabilized boehmite structures with the help of an incorporation of niobium oxides, which largely increased the catalytic activity and stability through less aggregations of smaller Ru nanoparticles. At an optimal Nb/Ru molar ratio of ∼1, the much smaller Ru nanoparticles were highly dispersed on the Nb-incorporated alumina matrices on the hexa-coordinated Al3+ sites selectively even after hydrothermal aqueous-phase reactions. The highly dispersed Ru nanoparticles on the Lewis acid sites of the boehmite phase of Al2O3 surfaces showed a facile reducibility and larger metallic Ru surface area with less formations of inactive hard coke precursors. It was mainly originated from the preferential presence of the reduced metallic Ru nanoparticles on the surfaces of the acidic Nb2O5-modified boehmite, which can strongly anchor the active Ru metals with their smaller sizes.

Behaviors of coking and stable radicals of a heavy oil during thermal reaction in sealed capillaries

This work studies thermal reaction of a heavy oil at temperatures of 250–500°C in sealed capillaries. The samples are extracted by chlorobenzene and toluene, and the insoluble matters are quantified in mass and in radical concentration. It is found that the chlorobenzene insolubles (CI) forms at temperatures of and higher than 440°C while the toluene insolubles (TI) forms at temperatures higher than 350°C. Both of these insoluble matters increase with time and temperature, and approach to similar asymptotic values. The CI formation can be fitted with a combination of the second-order and autocatalytic kinetics while the TI formation can be fitted with the second-order kinetics. Both CI and TI contain stable radicals measurable by electron spin resonance (ESR), and the radical concentration in CI is higher than that in TI. The kinetics of stable radical concentration in CI and TI are different from that in mass, except that of TI at a low temperature range (350–440°C). The changes in ESR line width of CI and TI are also studied. The above data are also discussed in terms of hard coke (CI insoluble matters) and soft coke (the difference between TI and CI), and in activation energy.

Carbon Deposition and Sintering Characteristics on Iron-Based Oxygen Carriers in the Catalytic Cracking Process of Coal Tar

Experiments on carbon black production from coal tar via chemical looping pyrolysis were performed in a fluidized bed reactor using natural hematite, hematite/γ-Al2O3 (Fe/Al), and hematite/NiO (Fe/Ni) composites as oxygen carriers (OCs). After 3 redox cycles, thermogravimetric analysis combined with differential scanning calorimetry results show that, in comparison to natural hematite, the oxidation rate of the Fe/Al OC became faster above 700 °C; however, the oxidation performance of the Fe/Ni OC was always poor. The addition of γ-Al2O3 could effectively inhibit carbon deposition; nonetheless, NiO exhibited the opposite effect. On the basis of the burning temperature, the carbon deposition on reduced OCs was mainly hard coke. The X-ray diffraction analysis showed that NiO was not only more effective than γ-Al2O3 to promote the reduction of Fe2O3 in compound OCs but also increased the sintering trend. The scanning electron microscopy analysis indicated the melting of original grains at the surface of the ...

Investigation on Coking Performance with Sulfur / Phosphorous-containing Additive and Anti-coking SiO2/S Coating during Thermal Cracking of Light Naphtha

Coke deposits during thermal cracking of light naphtha in the presence of the sulfur/phosphorous-containing additive and the anti-coking SiO2/S coating were investigated. The structure of the coke layer was studied. The results show that the coke is more amorphous with the additive mass concentration of 200μg.g-1. The additive has altered the microstructure of the coke layer by effecting the dehydrogenation reaction during coke formation. Coke deposits on the SiO2/S coating prepared by atmosphere pressure chemical vapor deposition (APCVD) method are mainly composed of coke granules. The TGA results show that the coke deposits are mainly composed of a small amount of volatile coke and a large amount of hard coke. The results of the low H/C ratios show the highly condensed structure of the coke deposits. When additive is added, inorganic sulfur is mainly formed in the cokes based on the analysis of XPS spectra. Phosphorus in the cokes is in the form of PO43- and phosphide species. The analyses of Raman spectra indicate that the coke deposits formed during thermal cracking are mainly composed of amorphous carbon. Cokes deposited on the SiO2/S coating are more disordered, which may make the decoking operation facilitated.

Coking and deactivation behavior of ZSM-5 during the isomerization of styrene oxide to phenylacetaldehyde

Coking and deactivation behavior of ZSM-5 in the isomerization of styrene oxide to phenylacetaldehyde were investigated under gas-phase free of solvents. More soft coke was firstly formed on HZSM-5 and then partly converted to hard coke with the reaction carried through. The soft coke, which can be removed via desorption at 200–400°C, had little effect on the catalyst activity and selectivity. While the hard coke, which had a certain degree of crystallization and must be completely removed via combustion with oxygen, would cause major catalyst deactivation. By confirmed, pore blocking was the predominant mode leading to deactivation of catalyst.

Biomass Pyrolysis in Sealed Vessels. Fixed-Carbon Yields from Avicel Cellulose That Realize the Theoretical Limit

In agreement with prior experimental work, thermodynamics predicts differences in the outcome of biomass pyrolysis conducted in sealed, constant-volume systems as opposed to constant-pressure systems. In particular, much higher values of the fixed-carbon yield can be expected in constant-volume systems. Avicel cellulose is known to give very low char and fixed-carbon yields; thus, char and fixed-carbon yields from cellulose have been given primary attention in this work. Our tubing bomb results reveal (i) fixed-carbon yields that realize the theoretical “limiting” values when the vessel is pre-pressurized to a modest pressure with N2 gas, and (ii) a gas product composed of steam (water) and CO2, with traces of CO and virtually no tars. Above a small range of modest temperatures and pressures, the char endures a molten phase and becomes a hard coke. The ash content of the char/coke reflects the composition of the glass wool and kao wool materials used to hold the Avicel powder in place.

Activation of Mo/HZSM-5 for methane aromatization

The effect of Mo/HZSM-5 pretreatment at 973 K in inert (He), oxidizing (artificial air), and carburizing (CH4/He mixture) atmospheres on its performance in non-oxidative methane dehydroaromatization (MDA) was investigated. The effect of post-synthesis silylation on deactivation of external acid sites was also studied. Precarburization resulted in increased aromatic selectivity and improved catalyst stability. The benzene selectivity was the highest for the silylated Mo/HZSM-5 catalyst (benzene + naphthalene selectivity after 1 h on stream was close to 100%). The deactivation of precarburized zeolites was less pronounced than that of zeolites heated in air or He. During heating in air or He, larger fractions of the molybdenum oxide species diffused into the micropores than during heating in methane. Carburization of the molybdenum oxide species in the micropores during MDA resulted in the formation of molybdenum carbide particles, and these contributed to pore blocking, making the Brønsted acid sites inaccessible. The formation of molybdenum carbides during heating in methane resulted in a less mobile Mo phase. It is argued that the presence of molybdenum carbide particles in the micropores contributes to rapid catalyst deactivation, in addition to the formation of hard coke on the external surface.

Coke Deposition on Ni/HZSM-5 in Bio-oil Hydrodeoxygenation Processing

The deactivation of bifunctional Ni/HZSM-5 catalysts is essentially due to the formation of heavy secondary products (i.e., coke) in the hydrodeoxygenation (HDO) of bio-oil. Coke deposited on the Ni/HZSM-5 catalyst was characterized using analytical techniques, including Fourier transform infrared spectroscopy (FTIR), thermogravimetric (TG) analysis, and transmission electron microscopy (TEM). The type and quantitative distribution of the deposited coke on the Ni/HZSM-5 catalyst were determined by the dissolution of the aluminum–silicate matrix in a hydrofluoric acid solution. The composition of soluble coke was obtained by gas chromatography–mass spectrometry (GC–MS) measurements. It is found that coke can be divided into soft coke, hard coke, and graphite at different reaction temperatures. Organic reactants can be transformed into soft coke and hard coke by different chemical reactions, such as alkylation, aromatization, hydrogen transfer, and dehydrogenation. The quantitative distribution between solu...