C2 Yield Research Articles

Methyl Radical Reactivity on the Basal Plane of Graphite

The reaction of submonolayer Li atoms with CH3Cl at 100 K on a highly oriented pyrolytic graphite (HOPG) surface has been studied under ultrahigh vacuum. We exploit the low defect density of the high quality HOPG used here (∼109 defects cm–2) to eliminate the effects of step edges and defects on the graphite surface chemistry. Li causes C–Cl bond scission in CH3Cl, liberating CH3 radicals below 130 K. Ordinarily, two CH3 species would couple to form products such as C2H6, but in the presence of graphite, CH3 preferentially adsorbs on the flat basal plane of Li-treated graphite. A C–CH3 bond of 1.2 eV is formed, which is enhanced relative to CH3 binding to clean graphite (0.52 eV) due to donation of electrons from Li into the graphite and back-donation from graphite to CH3. A low yield of C1, C2, and C3 hydrocarbon products above 330 K is found along with a low yield of H2. The low yield of these products indicates that the majority of the CH3 groups are irreversibly bound to the basal plane of graphite, a...

Experimental Study on Pyrolysis Behaviors of Coal in a Countercurrent Downer Reactor

Experiments on pyrolysis of Chinese Fugu coal were carried out with a downer reactor, and the effects of temperature and coal feeding rate on product distribution were investigated. It was found that the gas yield increases with increasing temperature, and the yield of tar increases with increasing coal feeding rate. When temperature is 650 °C with coal feeding rate of 12 kg/h, the yield of tar reaches the highest value of 10.29 wt % (dry coal basis). Compared to cocurrent downer reactor, the countercurrent downer reactor favors higher yields of C2 + C3 and tar.

Modeling of diffusion and reaction in monolithic catalysts for the methanol-to-propylene process

The present paper gives an insight into the methanol conversion to propylene (MTP) performance in a monolith reactor by means of a two-dimensional adiabatic heterogeneous reactor model accounting for interfacial and intra-particle gradients. Interactions of mass and heat transfer and chemical reactions were taken into account within monolith channels and inside the channel walls. Concentration and temperature profiles in both radial and axial direction were calculated for a multiple-stage monolithic reactor simulating the MTP process with special focus to influence of monolith channel geometries on selectivity of propylene. Calculated results showed that the total yield of light C2–C4 olefins can be achieved high up to 71%, with that of propylene up to 49% by a selected monolith structure of 400 cells per square inch with a 0.2mm catalytic wall thickness. Thus, the monolithic catalyst with high cell density and thin walls is recommended for the MTP process.

Particle/metal-based monolithic catalysts dual-bed reactor with beds-interspace supplementary oxygen: Construction and performance for oxidative coupling of methane

A novel particle/metal-based monolithic catalysts dual-bed reactor with beds-interspace supplementary oxygen is constructed comprising of the upper-layer 5 wt%Na2WO4-2 wt%Mn/SiO2 particle catalyst and the under-layer 3 wt%Ce-5 wt%Na2WO4-2 wt%Mn/SBA-15/Al2O3/FeCrAl metal-based monolithic catalyst as well as a side tube in the interspaces of two layers for supplementing O2. The reaction performance of oxidative coupling of methane (OCM) in the dual-bed reactor system is evaluated. The effects of the reaction parameters such as feed CH4/O2 ratio, reaction temperature and side tube feed O2 flowrate on the catalytic performance are investigated. The results indicate that the suggested mode of dual-bed reactor exhibits an excellent performance for OCM. CH4 conversion of 33.2%, C2H4 selectivity of 46.5% and C2 yield of 22.5% could be obtained, which have been increased by 6.4%, 4.1% and 5.5%, respectively, as compared with 5 wt%Na2WO4-2 wt%Mn/SiO2 particle catalyst in a single-bed reactor and increased by 10.7%, 31.9% and 17.7%, respectively, as compared with 3 wt%Ce-5 wt%Na2WO4-2 wt%Mn/SBA-15/Al2O3/FeCrAl metal-based monolithic catalyst in a single-bed reactor. The effective promotion of OCM performance in the reactor would supply a valuable reference for the industrialization of OCM process.

The Role of Ir in Ternary Rh-Based Catalysts for Syngas Conversion to C2 + Oxygenates

Transition metal modified Rh-catalysts can be used for converting syngas (CO+H2) into C2+ oxygenates. It has been found that Mn has a favorable effect in the selectivity towards oxygenates, while addition of Ir to the binary Rh-Mn catalysts significantly increases the space-time yield of C2+ oxygenates. In this paper, we use quantum mechanical calculations to investigate the distribution of promoter sites within Rh rich nanoparticles and their role in the conversion of syngas towards ethanol. This work was supported by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy Biomass Program. The Pacific Northwest National Laboratory (PNNL) is operated by Battelle for the DOE under Contract DE-AC05-76RL01830. A portion of the research was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national science user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research located at PNNL.

The effect of Fe on the catalytic performance of Rh–Mn–Li/SiO2 catalyst: A DRIFTS study

Different amounts of Fe promoted Rh–Mn–Li/SiO2 catalysts were prepared and investigated for the synthesis of C2 oxygenates from syngas. The results showed that the low amount of Fe (≤ 0.1 wt.%) improved the reactivity and yield of C2+ oxygenates, but an opposite effect appeared at high content of Fe (> 0.1 wt.%). Diffuse reflectance infrared Fourier transform spectroscopy was used to probe the effects of Fe on CO adsorption and hydrogenation, and two opposing effects were evidenced. Moreover, it is proposed that the facile transformation of dicarbonyl Rh+(CO)2 into H–Rh–CO is responsible for high selectivity of C2+ oxygenates.

Catalytic Oxidative Coupling of Methane Assisted by Electric Power over a Semiconductor Catalyst

Abstract Oxidative coupling of methane (OCM) on La2O3 semiconductor catalysts at 423 K external temperature was investigated. DC power supplied from two electrodes in a catalyst bed enabled stable and selective production of C2H6 and C2H4 over Sr–La2O3 (Sr/La = 1/200 and 1/20), but plasma reactions proceeded over other catalysts. The electrical conductivity of the semiconductor catalyst was important for controlling this reaction. A high yield of C2 (49% selectivity, 51.3% O2 conversion) was obtained using 2.7 W of electricity at a lower external temperature (423 K).

Modeling the oxidative coupling of methane using artificial neural network and optimizing of its operational conditions using genetic algorithm

The effect of some operating conditions such as temperature, gas hourly space velocity (GHSV), CH4/O2 ratio and diluents gas (mol% N2) on ethylene production by oxidative coupling of methane (OCM) in a fixed bed reactor at atmospheric pressure was studied over Mn/Na2WO4/SiO2 catalyst. Based on the properties of neural networks, an artificial neural network was used for model developing from experimental data. To prevent network complexity and effective data input to the network, principal component analysis method was used and the number of output parameters was reduced from 4 to 2. A feed-forward back-propagation network was used for simulating the relations between process operating conditions and those aspects of catalytic performance including conversion of methane, C2 products selectivity, C2 yielding and C2H4/C2H6 ratio. Levenberg-Marquardt method is presented to train the network. For the first output, an optimum network with 4-9-1 topology and for the second output, an optimum network with 4-6-1 topology was prepared. After simulating the process as well as using ANNs, the operating conditions were optimized and a genetic algorithm based on maximum yield of C2 was used. The average error in comparing the experimental and simulated values for methane conversion, C2 products selectivity, yield of C2 and C2H4/C2H6 ratio, was estimated as 2.73%, 10.66%, 5.48% and 10.28%, respectively.

Simultaneous overcome of the equilibrium limitations in BSCF oxygen-permeable membrane reactors: Water splitting and methane coupling

The equilibrium limitations of water splitting and the coupling of methane to C2 hydrocarbons (ethane+ethylene) were simultaneously overcome by using a perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) oxygen-permeable membrane reactor. Oxygen produced from thermal water splitting was transported through the BSCF membrane and consumed in the coupling of methane. The BSCF membrane consists of an about 70μm thick dense BSCF layer on an about 0.8mm thick porous BSCF layer as support. By applying the membrane reactor concept instead of a fixed bed reactor without oxygen supply, the methane conversion and C2 yield increased from 3.7% to 26% and 3.1% to 6.5% at 950°C, respectively. In both experiments, the supported 2wt.% Mn–5wt.% Na2WO4 catalyst was used at 950°C. Simultaneously, about 9% of the H2O injected was converted to hydrogen with a production rate of about 3.3cm3min−1cm−2 at 950°C which is higher than 1 m3 (STP) H2 m−2h−1.

Optimization of Fluidized Bed Reactor of Oxidative Coupling of Methane

Optimization of process variables in the oxidative coupling of methane (OCM) over Mn/Na2WO4/SiO2 catalyst in a fluidized bed reactor was carried out. Effects of operating temperature, distribution pattern of oxygen injected to the reactor and the number of injections on the reactor performance on C2 (ethane + ethylene) yield were investigated. Process variables for one, two and three secondary oxygen injections were investigated to obtain the maximum C2 yield by genetic algorithm optimization method. The maximum C2 selectivity and yield of 47.1% and 22.87%, respectively, were achieved for three secondary oxygen injections at operating temperature of 746.05°C. The C2 yield achieved in this study is approximately 4% better than previous works reported in literature while the optimum temperature is lower.

Study on Natural Gas Converted to C<sub>2</sub> Hydrocarbons in Plasma State

This paper presents the methane coupling with a new developed rotary multidentate helix electrode under plasmas at atmospheric pressure and in the presence of hydrogen to investigate the effects of peak voltage input the electric fields and feed flow rate on CH4 conversion and C2 yield and selectivity. The best result without remarkable amount of coke is 69.85% of single pass yield of C2 hydrocarbons with 70.46% of CH4 conversion and 99.14% of selectivity of C2 hydrocarbons. The emission of excited species such as excited radicals and atoms (C,CH,C2,H and H2) were detected in the spectra range of 300 nm～700 nm.

Oxidative coupling of methane using non-stoichiometric lead hydroxyapatite catalyst mixtures

Lead hydroxyapatite (PbxCa10−x(PO4)6(OH)2, 0<x⩽10) is one of the most active catalysts for oxidative coupling of methane (OCM) to produce ethane and ethylene from natural gas (methane). In this study, we investigated how the OCM activity of a precipitated lead hydroxyapatite is associated with its mixture and non-stoichiometric properties. Lead hydroxyapatite was prepared through aqueous precipitation in the presence of chlorine anions and calcination under helium background at 1073K, which resulted in a mixture of non-stoichiometric lead hydroxyapatites, each having a different cationic composition (PbxCa10−x). The mixture could be diversified by extracting the chlorines thermally from the chloro-hydroxyapatites of various chlorine contents. The formation of an apatite structure was confirmed through Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), X-ray fluorescence (XRF) and inductively coupled plasma (ICP) analyses. The non-stoichiometric characters of the prepared hydroxyapatites were analyzed through Raman/FT-Raman spectroscopy. The C2 selectivities of the prepared catalysts were evaluated at 1048K with a fixed CH4 conversion of 35%. Among the tested catalysts, lead hydroxyapatite, which was obtained by removing chlorines from Pb2Ca8(PO4)6(OH)0.5Cl1.5, showed a C2 selectivity of 62%, and achieved a C2 yield of 22% at 1048K. The OCM activity of the catalyst was mainly associated with its surface basicity, which was investigated using CO2-temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) analyses.

The role of gas hourly space velocity and feed composition for catalytic oxidative coupling of methane: Experimental study

A parametric study taking into account gas hourly space velocity (GHSV) and methane to oxygen ratio for the oxidative coupling of methane (OCM) is applied. The GHSV and methane to oxygen ratio are shown to effect the methane conversion and selectivity towards ethane and ethylene. The importance of methane to oxygen ratio on catalytic performance is highlighted. The experiments are carried out in a differential tubular fixed bed reactor, using 0.7–1.5g of titanate perovskite, Sn/BaTiO3, as the reaction catalyst at temperature of 1048K. Different GHSVs (8000–12000 and 17000h−1) and methane to oxygen ratios (1, 2, 3, 4 and 7.5) are selected. An optimum GHSV and methane to oxygen ratio is proposed in order to develop process toward maximization of desirable hydrocarbon product such as ethylene and ethane and minimization of carbon oxides production in isothermal performance of reactor. It is concluded that methane to oxygen ratio of 2 and GHSV of 8000–12000h−1 are optimal conditions for achieving the highest yield of C2.

In Situ Synthesis of SAPO-34 Grown onto Fully Calcined Kaolin Microspheres and Its Catalytic Properties for the MTO Reaction

Rapid deactivation and short lifetime are challenges for SAPO-34 catalysts for the reaction of methanol to olefins (MTO). To overcome these drawbacks, SAPO-34 on fully calcined kaolin microspheres (CKMs) was synthesized in situ by a hydrothermal method with tetraethylammonium hydroxide (TEAOH) and triethylamine (TEA) as templates. To facilitate the growth of SAPO-34, the CKMs were first pretreated by 2–14 wt % NaOH aqueous solution, and the effects of the NaOH concentration on the physicochemical properties of CKMs and the SAPO-34/kaolin microspheres (SCKMs) were characterized by means of XRD, XPS, SEM, low-temperature N2 adsorption, and NH3-TPD. The results showed that NaOH pretreatment has obvious effects on the chemical compositions and morphologies of the CKMs and, thus, the physicochemical properties of the SAPO-34 grown on them. Moreover, the textural and catalytic properties of the SCKMs were found to depend strongly on the concentration of NaOH solution, and the optimal NaOH concentration was determined to be 4 wt %. For the MTO reaction catalyzed by the prepared SCKM catalyst, 100% methanol conversion, 89.8% light olefins selectivity, and a 964-min lifetime (the reaction time during which the yield of C2–C4 olefins exceeded 70%) were obtained at 450 °C, which are much better than the values for free SAPO-34 and SAPO-34 supported on metakaolin microspheres.

Mixed Naphtha/Methanol Feed Used in the Thermal Catalytic/Steam Cracking (TCSC) Process for the Production of Propylene and Ethylene

The addition of some methanol to petroleum light naphtha used as feed in the Thermal Catalytic/Steam Cracking(TCSC) process significantly increases the product yield of C2–C4 olefins, particularly that of ethylene + propylene. However, over 20–25 wt% of methanol content in the naphtha feed, the beneficial effect is attenuated. At relatively high values of contact time, the (Zn–Pd) co-catalyst of the hybrid catalyst exerts noticeably its coke cleaning effect on the zeolite acid sites, particularly when methanol is present in the feed. The product weight ratio (propylene/ethylene) is not affected by such “moderate” addition of methanol and remains higher than 1.3.

Role of pore structure in the deactivation of zeolites (HZSM-5, Hβ and HY) by coke in the pyrolysis of polyethylene in a conical spouted bed reactor

The deactivation of three different catalysts used in the cracking of high density polyethylene (HDPE) has been compared. The catalysts used are HZSM-5, Hβ and HY zeolites agglomerated with bentonite and alumina. The reactions have been carried out in a conical spouted bed reactor at 500°C, and plastic (high density polyethylene) has been fed in continuous mode (1gmin−1) for up to 15h of reaction. The HZSM-5 zeolite catalyst gives way to high yields of C2–C4 olefins (57wt%) and, moreover, it is the one least influenced by deactivation throughout the run, which is explained by the lower deterioration of its physical properties and acidity. The results of temperature program combustion and transmission electron microscopy show that coke growth is hindered in the HZSM-5 zeolite pore structure. The high N2 flow rate used in the conical spouted bed reactor enhances coke precursor circulation towards the outside of the zeolite crystal channels.

Kinetics of Methanol Transformation into Hydrocarbons on a HZSM-5 Zeolite Catalyst at High Temperature (400−550 °C)

A kinetic model of seven lumps has been established which allows the quantification of the product distribution (oxygenates, n-butane, C2−C4 olefins, C2−C4 paraffins (without n-butane), C5−C10 fraction, methane) in the transformation of methanol into hydrocarbons at high temperature (400−550 °C) on a HZSM-5 zeolite catalyst (SiO2/Al2O3 = 30) with high acidic strength (>120 kJ (mol of NH3)−1) and agglomerated with bentonite and alumina. The kinetic model fits well the experimental data obtained in a fixed bed reactor, from small values of space time in which the formation of hydrocarbons is incipient, to a space time of 2.4 (g of catalyst) h (mol CH2) −1 for a complete conversion of methanol. The rise in temperature increases the yield of C2−C4 olefins, so that the maximum value (∼50%) is obtained at the ceiling temperature for the hydrothermal stability of the HZSM-5 (550 °C) and space times between 0.6 and 1 (g of catalyst) h (mol CH2)−1.

Oxidative Coupling of Methane with High C2 Yield by using Chlorinated Perovskite Ba0.5Sr0.5Fe0.2Co0.8O3−δ as Catalyst and N2O as Oxidant

Assess the C2-ation: A novel chlorinated perovskite-type oxide is prepared as catalyst for oxidative coupling of methane in a packed-bed reactor. Chlorine doping significantly improves the selectivity towards C2 species (C2H6 and C2H4). Furthermore, using N2O instead of O2 as oxidant, to some extent, prevented the deep oxidation of C2. As a result, a high C2 yield was acquired.

Oxidative Coupling of Methane in a BCFZ Perovskite Hollow Fiber Membrane Reactor

A membrane reactor that incorporated hollow fiber in combination with an established catalyst was used for the oxidative coupling of methane (OCM). A perovskite membrane of the composition BaCoxFeyZrzO3−δ (BCFZ, x + y + z = 1) allows a controlled oxygen feed into the reactor over its axial length. Using this novel hollow fiber membrane reactor with a 2 wt % Mn/5 wt % Na2WO4 on SiO2 catalyst as a packed bed around the fiber, oxygen separation from air and C2 formation could be established at 800 °C with long-term stability. The highest C2 selectivity of ∼75% was observed at a methane conversion of 6% with a C2H4:C2H6 ratio of 2:1. The highest C2H4:C2H6 ratio of 4:1 and maximum C2 yield of 17% was obtained at 50% C2 selectivity. It is known from the literature that such results can be obtained without a catalyst in a similar membrane reactor only at temperatures 150 °C higher.

Synthesis of ethylene and propylene on a SAPO-34 silica—alumina—phosphate catalyst

A process for the preparation of ethylene and propylene from methanol on a microporous silica—alumina—phosphate SAPO-34 catalyst is described. The influence of the temperature and the nature and concentration of the diluting agent on the catalyst activity, its selectivity with respect to C2=-C4= olefins, and ability to be regenerated were studied. The SAPO-34 catalyst was shown to be highly effective in the selectivity of ethylene and propylene formation; the total yield of C2=-C4= olefins at 350–450°C was 77–84% and methanol conversion was up to 96–99%. In the conversion of methanol under helium at 450°C, the yield of ethylene (∼36%) was higher than at 375°C (∼29%), while the yield of propylene (∼30%) was lower (∼38%). The use of water and helium vapors as a diluent increased the yield of ethylene to ∼36% at 375°C and to ∼50% at 450°C. In the conversion of methanol at 450°C in water vapors without helium, the yield of ethylene reached ∼44–49% and the yield of propylene was 24–29%. The C3= to C2= ratio in the process varied from ∼0.5 to 1.5. The high efficiency of the SAPO-34 catalyst is the consequence of the microporous structure of zeolite and the high content of acid centers of medium strength. In the course of methanol conversion, the catalyst was deactivated due to coking. After regeneration with air at 550°C, the catalyst activity was completely restored, while the crystal structure and the acid properties did not change. The activity of the catalyst in a cycle is prolonged if water vapors are used as a diluent and the catalyst is processed at a high temperature with vapors. The industrial processes for the production of ethylene and propylene from nonpetroleum materials are not used in Russia. The results of this study are comparable to the data obtained from the UOP/Norsk Hydro process on the SAPO-34 catalyst. The catalyst can be recommended for further trials on an FCC type pilot plant with a moving catalyst bed.