Hydrocarbon Formation Rate Research Articles

Study on Pyrolysis-Mechanics-Seepage Behavior of Oil Shale in a Closed System Subject to Real-Time Temperature Variations.

In situ mining is a practical and feasible technology for extracting oil shale. However, the extracted oil shale is subject to formation stress. This study systematically investigates the pyrolysis–mechanics–seepage problems of oil shale exploitation, which are subject to thermomechanical coupling using a thermal simulation experimental device representing a closed system, high-temperature rock mechanics testing system, and high-temperature triaxial permeability testing device. The results reveal the following. (i) The yield of gaseous hydrocarbon in the closed system increases throughout the pyrolysis reaction. Due to secondary cracking, the production of light and heavy hydrocarbon components first increases, and then decreases during the pyrolysis reaction. The parallel first-order reaction kinetic model shows a good fit with the pyrolysis and hydrocarbon generation processes of oil shale. With increasing temperature, the hydrocarbon generation conversion rate gradually increases, and the uniaxial compressive strength of oil shale was found to initially decrease and then increase. The compressive strength was the lowest at 400 °C, and the conversion rate of hydrocarbon formation gradually increased. The transformation of kaolinite into metakaolinite at high temperatures is the primary reason for the increase in compressive strength of oil shale at 400–600 °C. (ii) When the temperature is between 20 and 400 °C, the magnitude of oil shale permeability under stress is small (~10−2 md). When the temperature exceeds 400 °C, the permeability of the oil shale is large, and it decreases approximately linearly with increasing pore pressure, which is attributed to the joint action of the gas slippage effect, adsorption effect, and effective stress. The results of this research provide a basis for high efficiency in situ exploitation of oil shale.

A scanning pulse reaction technique for transient analysis of the methanol-to-hydrocarbons reaction

A method of scanning pulse gas chromatography (SP-GC) suitable for time-resolved analysis of transient response of catalysts to reactant pulses is introduced. Applied to the methanol-to-hydrocarbons reaction over several zeolite-based catalysts (HZSM-5, Ca/ZSM-5 and Ga/ZSM-5), SP-GC provided quantitative information about the transient reactivity and selectivity during methanol conversion. The SP-GC analysis demonstrates substantial differences in the relative rates of hydrocarbon formation between catalysts that favor aromatic or olefin cycles of the dual cycle hydrocarbon pool mechanism. The influence of metal promoters on the main reaction pathways was highlighted with an emphasis on mechanistic aspects.

Formation kinetics of hydrocarbon compounds in the vacuum gas oil oxycracking process

The kinetics of the formation of oxygen-free hydrocarbon compounds obtained during the process of oxidation of vacuum gas oil at 450–550 °C for 2700 s of conducting of the process was studied. It was established that the highest rate of hydrocarbon formation was noted for the C1–C4 fraction starting from the moment the process started and up to 900 s (1.76 × 10−8 – 4.58 × 10−8). For other fractions, reaction rate maximums were noted: for C5–C9—300 s from the start of the process; for C10–C12—in the interval between 300 and 900 s, i.e. at 600 s process duration; for the raw fractions C22–C30, C31–C35 and C36–C40, grew after 1800s. The data on the influence of the process temperature on the rate of hydrocarbon formation allowed us to establish that the oxycracking process is limited by the formation of C10–C16 hydrocarbon fractions. The increase in contact time to a greater extent affects the rate of formation of hydrocarbons C1–C4 and C17–C21. The features of the rate of hydrocarbon production as a function of the amount of oxygen were found out: the rate of formation of hydrocarbons C1–C4 and C17–C21 increases with increasing oxygen content (in the case of C17–C21 it passes through a minimum); C5–C9 and C13–C16—monotonously decreases; C10–C12 passes through a maximum at an oxidation state of 1%, which undoubtedly indicates the role of oxygen in the destructive processes of the formation of hydrocarbons that do not contain oxygen under oxycracking conditions.

Fischer–Tropsch synthesis over Pt/Co/Al2O3 catalyst: Improvement in catalyst stability by activation with diluted CO

Fischer–Tropsch cobalt-based catalyst deactivation is one of the major challenges facing gas-to-liquids processes. Changes in catalyst formulation and pre-treatment methods are among the promising routes to address this challenge. In this study, diluted CO was used to pre-treat a 0.5%Pt/25%Co/Al2O3 catalyst, in comparison to H2, and the resulting effects on catalyst stability, activity and product selectivity were evaluated. The investigation was performed using BET, TEM, TPR, XPS and XRD techniques, combined with catalyst evaluation in a 1 L continuously stirred tank reactor. The results reveal that microporous carbon shells encapsulate Co particles during activation by CO at higher temperatures, resulting in lower activity and higher methane selectivity compared to the H2-reduced catalyst, at early reaction times. However, the CO-activated catalyst displayed superior stability, resulting in better performance at extended time-on-stream compared to a deactivating H2-activated catalyst, which showed an increase in CH4 selectivity and a decline in C5+ hydrocarbon formation rate.

A simple coupled ANNs‐RSM approach in modeling product distribution of Fischer‐Tropsch synthesis using a microchannel reactor with Ru‐promoted Co/Al 2 O 3 catalyst

A simple approach using hybrid artificial neural networks (ANNs)-response surface methodology (RSM) was developed to model the detailed product distribution using Ru-promoted cobalt-based catalyst with Al2O3 as the support in a microchannel reactor for Fischer-Tropsch (FT) synthesis. Using the independent process parameters for training, the established model is capable of predicting hydrocarbon production distributions, ie, paraffin formation rate (C2-C15) and olefin to paraffin ratio (OPR C2-C15) within acceptable uncertainties. The ANNs-RSM model and comprehensive mechanistic model using the Langmuir-Hinshelwood-Hougen-Watson (LHHW) approach were compared to identify a few inherent advantages of the proposed model in modeling complex FT synthesis. The proposed ANNs-RSM model shows its appealing merits, ie, faster converge and higher accuracy (less than ±10% uncertainties was achieved from ANNs-RSM model, while LHHW model achieved less than ±15% uncertainties except a few exceptional high errors uncertainties at certain experimental conditions). The statistical significances to the product distributions and hydrocarbon formation rate during FT synthesis could be easily identified and quantitatively analyzed by the established ANNs-RSM model. The future effective alternative of kinetic study of the complex system such as FT synthesis in the microstructured reactor might follow the methods of using empirical reliable approach for process optimization together with mechanistic kinetic study for detailed reaction pathway discrimination.

Pore diffusion effects on catalyst effectiveness and selectivity of cobalt based Fischer-Tropsch catalyst

Abstract In this study we investigate performance characteristics (catalyst effectiveness, CH4 selectivity, and hydrocarbon product distribution) of with a highly active Co/Re/Al2O3 catalyst particle for Fischer-Tropsch synthesis. In numerical simulations we utilize kinetic parameters for CO consumption rate, CH4 formation rate and hydrocarbon formation rates (C2+ hydrocarbons) determined from experiments with this catalyst to study effects of catalyst activity, catalyst particle shape (sphere, slab, solid and hollow cylinder), size (i.e. diffusion length), catalyst distribution (uniform vs. eggshell type distribution for a spherical particle) and process conditions (temperature, pressure, syngas composition and conversion level) on the catalyst performance. With increase in Thiele modulus (i.e. particle size at a fixed set of process conditions) we observe increasing H2/CO ratio profile towards the center of the particle resulting in increase of local and average CH4 selectivity. The goal is to find conditions which allow one to use sufficiently large particles to reduce pressure drop, while avoiding negative influence of diffusional limitations on selectivity and activity. For each catalyst particle shape we determined values of Thiele modulus, i.e. characteristic length of diffusion, corresponding to the upper limit of the kinetic region, and investigated how it changes with operating conditions. We found that simultaneous increase of pressure and the use of syngas with H2/CO feed ratio of 1.4–1.7 is the best strategy for mitigating the negative impact of intraparticle diffusional limitations on CH4 selectivity. For a spherical particle of 1 mm in diameter, one can achieve CH4 selectivity of 5.6% with catalyst effectiveness factor of 1.07 at the reactor inlet by operating at 50 bar, 473 K and H2/CO = 1.4.

Ultrathin-Film Titania Photocatalyst on Nanocavity for CO2 Reduction with Boosted Catalytic Efficiencies.

Photocatalytic CO2 reduction with water to hydrocarbons represents a viable and sustainable process toward greenhouse gas reduction and fuel/chemical production. Development of more efficient catalysts is the key to mitigate the limits in photocatalytic processes. Here, a novel ultrathin‐film photocatalytic light absorber (UFPLA) with TiO2 films to design efficient photocatalytic CO2 conversion processes is created. The UFPLA structure conquers the intrinsic trade‐off between optical absorption and charge carrier extraction efficiency, that is, a solar absorber should be thick enough to absorb majority of the light allowable by its bandgap but thin enough to allow charge carrier extraction for reactions. The as‐obtained structures significantly improve TiO2 photocatalytic activity and selectivity to oxygenated hydrocarbons than the benchmark photocatalyst (Aeroxide P25). Remarkably, UFPLAs with 2‐nm‐thick TiO2 films result in hydrocarbon formation rates of 0.967 mmol g−1 h−1, corresponding to 1145 times higher activity than Aeroxide P25. This observation is confirmed by femtosecond transient absorption spectroscopic experiments where longer charge carrier lifetimes are recorded for the thinner films. The current work demonstrates a powerful strategy to control light absorption and catalysis in CO2 conversion and, therefore, creates new and transformative ways of converting solar energy and greenhouse gas to alcohol fuels/chemicals.

Influence of crystal size of HZSM-5 on hydrodeoxygenation of eugenol in aqueous phase

Hydrodeoxygenation of eugenol to hydrocarbons in aqueous phase can be catalyzed by the combination of Pd/C and HZSM-5. In this paper, micro-, submicro- and nano-sized HZSM-5 samples were chosen as catalysts to investigate the influence of crystal size of HZSM-5 on the hydrolysis and dehydration. It was found that the formation rates of hydrocarbons were correlated with the total acidic sites of the submicro- and nano-sized HZSM-5 samples; while for the micro-sized sample, a much lower hydrocarbon formation rate was observed. Meanwhile, HZSM-5 with larger crystal size showed a lower hydrocarbon formation rate even with higher acid density.

Fischer–Tropsch Synthesis: Effect of K Loading on the Water–Gas Shift Reaction and Liquid Hydrocarbon Formation Rate over Precipitated Iron Catalysts

The effect of K loading on the water–gas shift (WGS) reaction and hydrocarbon formation rate during Fischer–Tropsch synthesis (FTS) was studied over 100 Fe/5.1 Si/2 Cu/x K (x = 1.25 or 3) precipitated catalysts using a 1-L continuously stirred tank reactor. The catalysts were tested over a wide range of experimental conditions: 260–270 °C, 1.3 MPa, H2/CO = 0.67 and 20–90 % CO conversions. On the low K loading (1.25 % K) Fe catalyst, the H2 deficiency required for the FTS reaction was made up by the WGS reaction only at high CO conversion level, i.e. >70 %; however, increasing potassium loading to 3 % dramatically improved the WGS reaction rate which provided enough hydrogen for the FTS reaction even at low CO conversion level, i.e. 30 %. Kinetic analysis suggests that increasing K loading resulted in significant increases in the WGS rate constant relative to that of FTS, which is a major cause of the high WGS activity on the high K loading catalyst. Both the low and high potassium containing iron catalysts have high liquid oil and solid wax formation rates, i.e. 0.78–0.93 g/g-cat/h at 260 °C, 1.3 MPa, H2/CO = 0.67 and 50 % CO conversion, but increasing potassium loading from 1.25 to 3 % shifted the primary product to wax (70 %) from oil (73.5 %). The wax fraction increased with increasing CO conversion for both iron catalysts. The effect of K loading on initial FTS activity and hydrocarbon distribution/selectivity of the Fe catalysts was also studied. High K loading, i.e. 3 % K, increased the iron carburization rate and significantly shortened the induction period of the FTS reaction. Secondary reactions of olefins were remarkably suppressed and the olefin content was greatly enhanced with increasing K loading from 1.25 to 3 %, consistent with a number of studies in the open literature.

Comparison of staged combustion properties between bituminous coals and a low-rank coal; Fiber-shaped crystallized carbon formation, NOx emission and coal burnout properties at very high temperature

Previously, we developed a new-concept for a drop-tube furnace in order to investigate staged combustion properties for pulverized coals. Two high-temperature electric furnaces were connected in series. Coal was burnt under fuel-rich conditions in the first furnace, then, staged air was supplied at the connection between the two furnaces. In the present study, we investigated influence of burning temperature on NOx emission and combustion efficiency by using the furnace. The influence of the temperature differed between hv-bituminous coals and a sub-bituminous coal. For the hv-bituminous coals, combustion efficiency was improved when burning temperature in the fuel-rich region rose. When combustion efficiency was improved, NOx emission decreased. The NOx reduction reaction in the fuel-rich region was promoted by increasing the burning temperature in this region. On the other hand, NOx emission increased for the sub-bituminous coal when the temperature was higher than 1800K. Usually, combustion efficiency was increased with burning temperature. However, combustion efficiency lowered for the sub-bituminous coal when burning temperature was higher than 1900K. We observed the ash obtained by this temperature condition using Scanning Electron Microscope (SEM) and, Transmission Electron Microscope (TEM) and observed fiber shaped carbon. The difference in NOx properties was derived as a difference of hydrocarbon concentration. For low-rank coals (sub-bituminous or lignite), the hydrocarbon formation rate was smaller than that for hv-bituminous coals. When the hydrocarbon contribution to the NOx reduction reaction was large, NOx emission decreased with increasing burning temperature; however, hydrocarbon content in volatile matter was small for low-rank coals.

Negative Effects of CO2 in the Feed Stream on the Catalytic Performance of Precipitated Iron-Based Catalysts for Fischer–Tropsch Synthesis

Fischer-Tropsch synthesis was carried out over precipitated iron-based catalysts with different amounts of CO2 in the feed stream while maintaining both total reac- tion pressure (1.5 MPa) and partial pressure of H2 ? CO (0.75 MPa) using an inert balance gas, N2. The CO2 in the feed stream decreased the rate of hydrocarbon formation, but it had no significant influence on the carbon number distribution of hydrocarbons. The CO2 in the feed stream also suppressed CO2 formation, decreasing both CO con- version and CO2 selectivity. We attribute the decreased reaction rate to the partial competition in the adsorption behavior between CO and CO2 as revealed in the temper- ature-programmed desorption.

Low-temperature graphene growth using epochal catalyst of PdCo alloy

Palladium-Cobalt alloy as a catalyst was introduced to realize low temperature graphene growth on glass substrate by using remote RF plasma-enhanced chemical vapor deposition. Few layer graphene films were easily formed with high transmittance of 88.8% at temperature as low as 400 °C, in good contrast with Ni catalyst in which no graphitic layer was formed at all at the same conditions. High decomposition rate of hydrocarbon gases and formation of nanosize aggregates giving rise to enhancement of carbon incorporation into PdCo alloy and consequently formation of graphene layers at such low temperatures are further discussed with observed Raman spectroscopy and x-ray diffraction.

Application of nano-sized cobalt on ZSM-5 zeolite as an active catalyst in Fischer–Tropsch synthesis

In this study the catalytic behavior of Co/HZSM-5 in Fischer–Tropsch synthesis (FTS) has been examined in order to optimize the operating conditions for acquiring maximum selectivity. Catalysts consisted of various quantities of cobalt particles supported on HZSM-5 zeolite were prepared by impregnation method. In order to investigate the effects of operating parameters on catalytic performance and to estimate the optimum conditions, experiments were designed using L-16 Taguchi method. All experimental runs were carried out in a fixed bed reactor under isobaric condition (2MPa). According to the Taguchi model and considering the impact of the operating parameters on the process output and performing certain validation tests, the optimum operating conditions for the process were determined as T=513K, space velocity=1.1h−1, Co on HZSM-5=11.6%, H2/CO=1.7.In the next step, a kinetic model for FTS based on carbide mechanism was presented applying the synthesized catalyst under the optimum conditions. This model is a combination of kinetic rates of hydrocarbon formation and the relations for the growth probability and olefin re-adsorption factor.

Evaluation of alumina-supported Mo carbide produced via propane carburization for the Fischer–Tropsch synthesis

CO hydrogenation over alumina-supported Mo carbide catalyst synthesized by temperature-programmed carburization of the impregnated MoO3 utilizing H2/C3H8 feed has been investigated. Samples were prepared following a 23-factorial design with temperature, hydrocarbon composition and reaction time as the carburization factors. Catalysts were characterized using N2 physisorption, NH3 temperature-programmed desorption and solid total organic carbon (TOC) analysis. Solid-state carburization kinetics was studied in a thermogravimetric analyzer at different heating rates. Statistical analysis revealed that carburization temperature was a strong determinant of key physicochemical properties (BET, pore volume, acid site strength and concentration). Increasing the H2:C3H8 ratio in the carburizing gas reduced the acid site strength and concentration but improved overall hydrocarbon synthesis rate, olefin-to-paraffin ratio and specific activity. All catalysts possessed Lewis acid centers. The carburizing temperature was also a statistically significant factor in the determination of the FT reaction metrics. A two-stage process involving the transformation of Mo oxide to the MoC1−x carbide via an intermediate oxycarbide phase was observed. The solid-state kinetics was captured by a contracting volume model and Arrhenius treatment implicated the occurrence of a ‘compensation effect’ for the carbothermal synthesis. Although the rate-composition envelope exhibited qualitatively similar features for the entire Mo carbide class, the optimum feed composition for maximum hydrocarbon formation rate varied between 0.67 and 0.75 depending on the catalyst preparation conditions and the carbon number. The olefin-to-paraffin ratio has a reciprocal relationship to the H2 partial pressure but experienced an exponential decay with carbon number. Catalyst with 15wt.% Mo loading produced the highest hydrocarbon synthesis rate and chain growth probability.

Staged combustion properties for pulverized coals at high temperature

Staged combustion properties for pulverized coals have been investigated by using a new-concept drop-tube furnace. Two high-temperature electric furnaces were connected in series. Coal was burnt under fuel-rich conditions in the first furnace, then, staged air was supplied at the connection between the two furnaces. Reaction temperature (1800–2100 K) and time (1–2 s) were similar to those used in actual boilers. When coal was burnt at the same stoichiometric ratio as in actual boilers, similar combustion performance values as for actual boilers were obtained regarding NO x emission and carbon in ash. The most important factor for low NO x combustion was to raise the combustion temperature above the present range (1800–2100 K) in the fuel-rich zone. The NO x emission was significantly increased with decrease of burning temperature in the fuel-rich zone when the temperature was lower than 1800 K. But, NO x emission was cut to around 100–150 ppm, for sub-bituminous coal and hv-bituminous coal, in the latest commercial plants by forming this high-temperature fuel-rich region in the boilers. If the temperature and stoichiometric ratio could be set to the most suitable conditions, and, burning gas and air were mixed well, it would be possible to lower NO x emission to 30–60 ppm (6% O 2). The most important NO x reduction reaction in the fuel-rich zone was the NO x reduction by hydrocarbons. The hydrocarbon formation rate in the flame was varied with coal properties and combustion conditions. The NO x was easily reduced when coals which easily formed hydrocarbons were used, or, when burning conditions which easily formed hydrocarbons were chosen. Effects of burning temperature and stoichiometric ratio on NO x emission were reproduced by the previously proposed reaction model. When solid fuel was used, plant performance values varied with fuel properties. The proposed drop-tube furnace system was also found to be a useful analysis technique to evaluate the difference in combustion performance due to the fuel properties.

Pyrolysis of polymer materials in the presence of metal chlorides of the iron subgroup

Catalytic activity of metal chlorides of the iron subgroup is studied during pyrolysis of polymer cord obtained during processing of worn automobile tires by mechanical grinding. It is established that use of metal chlorides of the iron subgroup increases the rate of hydrocarbon formation by about a factor of four to five. It is established that in order to obtain gaseous pyrolysis products with a high heat of combustion and hydrocarbon content the most suitable catalytic system is CoCl 2 (2% of substrate weight) at 450°C.

Effect of co-feeding carbon dioxide on Fischer–Tropsch synthesis over an iron–manganese catalyst in a spinning basket reactor

The effect of co-feeding CO 2 on the catalytic properties of an Fe–Mn catalyst during Fischer–Tropsch synthesis (FTS) was investigated in a spinning basket reactor by varying added CO 2 partial pressure in the feed gas. It was found that co-feeding CO 2 to syngas did not decrease the activity of the catalyst, on the contrary, a dramatic increase of the activity and an increase of methane selectivity were observed over the catalyst after removal of CO 2 from the feed gas. The addition of CO 2 led to an increase in olefin/paraffin ratios of low carbon hydrocarbons and a slight decrease in C 19 + selectivity. It also slightly decreased CO 2 formation rate on the catalyst by increasing the rate of reverse step of the water–gas shift (WGS) reaction and pushing the reaction towards equilibrium, and did not remarkably influence the hydrocarbon formation rate. However, the co-feeding CO 2 can significantly increase the water formation rate and the overall oxygenate formation rate under these reaction conditions.

Chemical Structures of Coprecipitated Fe−Ce Mixed Oxides

Two series of Fe−Ce catalysts were prepared following two different methods: coprecipitation from Fe and Ce nitrate solutions and physical mixing of pure Fe and Ce precursors. Evidence of the presence of a chemical interaction between Fe and Ce was found in the calcined state of the coprecipitated catalysts. Such evidence was obtained with different techniques. The Fe−Ce interaction occurs through the formation of hematite-like and cubic ceria-like solid solutions. In the hematite-like solid solution, Ce cations are dissolved in the hematite structure, whereas in the cubic ceria-like solid solution Fe cations are dissolved in the ceria structure. Such interactions were absent in the samples prepared by the physical mixing. It is suggested that the Fe−Ce interaction present in the calcined state results in a strong Fe−Ce interaction in the final catalyst that defines their better catalytic properties. When tested in the Fischer−Tropsch synthesis of hydrocarbons from CO + H2 gas mixtures, the coprecipitation method series showed higher CO conversion rates, higher hydrocarbon formation rates, and a higher degree of olefinicity than the pure Fe catalyst sample and the Fe−Ce samples prepared by physical mixing.

Low-energy tritium ion erosion of graphite

Chemical erosion of pyrolytic graphite was measured over the temperature range 300–950K, using a mass-analyzed tritium ion beam. The T2+ beam was produced by cycling 10 Ci (1mg) of T2 gas through the ion source from source getter to pumping getter and back. The T2+ beam current was up to 0.66μA (∼1018T+/m2s) at energies of 50–500eV/T+. Hydrocarbon formation rates were measured in the residual gas using quadrupole mass spectroscopy. CxTy hydrocarbon formation yields were similar to those obtained for H+ and D+ (0.002–0.1). As with H+ and D+, the T+-induced yields at 200–250eV/T+ tend to peak at about 700–800K, with a shift to lower temperature and flatter distributions at lower ion energies.

Anti-ASF Distribution of Fischer–Tropsch Hydrocarbons in Supercritical-Phase Reactions

Direct wax synthesis from syngas was implemented by supercritical-phase Fischer–Tropsch synthesis (FTS) reaction. By introducing supercritical-phase n-pentane into the reaction, waxy hydrocarbon formation rate was increased significantly while light hydrocarbon formation rate was suppressed effectively. Anti-Anderson–Schultz–Flory distribution of FTS hydrocarbons was realized at lower temperatures, such as 473 K. The intermediate, olefins, readily readsorbed onto the catalyst surface and significantly stimulated the carbon chain-growth process.