Partial Oxidation Of Light Hydrocarbons Research Articles

Thermodynamic analysis of in-situ hydrogen from hot compressed water for heavy oil upgrading

Due to many benefits of heavy oil upgrading in the green medium of hot compressed water (HCW), the present study considers the thermodynamic analysis of in-situ hydrogen created by partial oxidation of light hydrocarbons (HC) in HCW. The aim is seeking the upgrading condition where light hydrocarbons create hydrogen (H2) and carbon monoxide (CO) assisted by partial oxidation of light hydrocarbons. The formed CO collaborates in in-situ active hydrogen through water gas shift reaction (CO+H2O↔H2+CO2) which is more effective than external hydrogen for hydrogenation of heavy oil in HCW. Applying the powerful capability of Aspen Plus®, i.e., sensitivity analysis, the effect of significant parameters, such as temperature, pressure (water density), water to oil ratio, and oxygen (O2) to oil ratio are studied comprehensively in order to maximize the amount of active hydrogen. The results indicate that higher temperatures and the amount of water (H2O/heavy oil) are two favorable factors to increase the contribution of active hydrogen, while the pressure is not a determinant factor at supercritical condition (P ≥ 25 MPa). The formation of methane is also decreased at high temperature which is desired for upgrading system. The higher amount of water implies more quantity of O2 since partial oxidation affords the enthalpy of auto-thermal reforming of HO. Hence there should be a compromise in the selected ratios of H2O/HC and O2/HC in HCW upgrading system. A set of experiments are conducted in order to compare the simulation and experimental results. Although the experimental results are established on kinetic data which also reflect the physical effect of HCW during HO upgrading, however, the thermodynamic study provides valued information, in agreement with experiments, that improves our understanding of HO upgrading in HCW with less coke.

Status of CO<sub>2</sub>-stable dual-phase mixed conductor oxygen permeable membrane materials

Dense ceramic mixed ionic-electronic conducting membranes (MIECMs) are renowned for their rich and varied properties as admirable candidates in energy industries, such as oxygen separation from air, cathode materials for solid fuel oxide cells (SOFCs) or membrane reactors for partial oxidation of light hydrocarbons. Especially, the MIECMs integrated oxy-fuel combustion is considered to be a promising cost-effective and efficient method for CO2 capture and sequestration. During the oxy-fuel process, high purity oxygen production has been put forward to use OTMs technology instead of the conventional cryogenic technique, which can benefit from low costs and energy consumption and high efficiency. According to the phase numbers, the OTMs can be classified into single phase and composite OTMs. Extensive research activities have been directed towards the single phase perovskite-type oxides due to their high oxygen permeability. However, their industrial practical application was limited since they suffer from deactivation in the presence of CO2 due to alkaline earth carbonates forming on their surfaces. In order to overcome these issues, focus has shifted to the development of dual-phase membranes consisting of an oxygen ion conducting phase and an electron ion conducting phase, which benefit from the contribution of each phase and overcome the limitations of perovskite materials. Dual-phase OTM typically composed of an oxygen conducting phase (OCP) and an electronic conducting phase (ECP), which displays a better structural and mechanical stability comparing with the single phase OTM under reducing atmosphere due to the incorporation of fluorite phase. The first generation dual-phase OTMs are usually made from the fluorite oxides and noble metals, where fluorite oxides are used as the OCP and noble metals are adopted as the ECP. However, the noble metal-containing dual-phase OTM is too expensive. In order to lower the costs, researchers have developd the second generation dual-phase OTMs, which are consisted of fluorite oxides and perovskite oxides. Although the costs have been reduced, reactions between two phases were usually observed in the second generation dual-phase OTMs. Based on the previous findings and driven by the demands for oxy-fuel combustion for CO2 capture, research put forwards to the new CO2-stable dual-phase OTMs without noble metals and alkaline earth elements. Until now, already a large number of CO2-stable dual-phase membrane materials have been explored. However, their CO2 stabilities have been enhanced, but most of their oxygen permeabilities are too low for practical applications. Therefore, continues research efforts have to be made since most of available OTMs materials can′t satisfy the practical applications. In order to enhance the oxygen permeability and/or improve material thermochemical stability of dual-phase OTMs, the large majority of studies focused on tuning the composition through doping, synthesized temperatures, modified the membrane surfaces with coating or development of new synthesis methods. Meanwhile, considerable theoretical efforts have been put into the dual-phase OTMs, a number of models for permeation process such as Bouwmeester model, Xu-Thomson model, and Zhu model et al. are proposed. Up to now, countless publications has been produced in this field. In order to give the guidelines for the development of the dual-phase OTM materials and promote the process of industrialization of the OTMs technology in the oxy-fuel process, we summarize the status of CO2-stable dual-phase mixed conductor oxygen permeable membrane materials. In this review, the oxygen permeability mechanism and research progress of the dual-phase OTM materials are briefly introduced firstly. Subsequently, the influence of the preparation methods, sintering temperatures, ratios of two phases and the composition of the two phases on the oxygen permeability and stability are analyzed systematically. Next, the applications of dual phase MIECM reactor in partial oxidation of methane to syngas (POM), coupling reactions, water decomposition and oxy-fuel combustion are introduced and analyzed. Finally, the existing scientific problems and the possible research directions have been pointed out.

Re-evaluation of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ perovskite as oxygen semi-permeable membrane

Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCF), a mixed oxygen ionic and electronic conducting ceramic derived from SrCo 0.8Fe 0.2O 3− δ (SCF), was re-evaluated for its possible application as an oxygen semi-permeable membrane and membrane reactor for partial oxidation of light hydrocarbons. The partial substitution of Sr 2+ with Ba 2+ in SCF led to an increase in the phase stability of the cubic perovskite structure. Both BSCF and SCF were found to have high oxygen nonstoichiometry. However, BSCF possessed a higher oxygen nonstoichiometry than SCF at room temperature, but a similar value at high temperatures. This resulted in the lower chemical expansion for BSCF than SCF. The doping of Ba 2+ in SCF led to the decrease of the electronic conductivity, but an increase in the oxygen ionic conductivity. The oxygen permeation study of the BSCF membrane demonstrated that the permeation rate was mainly rate-determined by the slow surface exchange kinetics at the oxygen lean side (or reaction side) membrane surface. The high ionic conductivity and the slow surface exchange kinetics resulted in the surface oxygen partial pressure at the reaction side membrane surface to be much higher than the surrounded atmosphere, therefore protecting the BSCF membrane from reduction.

Defect formation and transport in SrFe1-xAlxO3-δ

Perovskite-related phases derived from SrFeO3-δ are among known mixed conductors with highest oxygen permeability and are thus of interest as the ceramic membrane materials for oxygen separation and partial oxidation of light hydrocarbons. Dense ceramics of SrFe1-xAlxO3-δ (x=0.1–0.5) were prepared via the glycine-nitrate process. The cubic solid solution formation was found to occur in the concentration range x=0–0.35. Increasing aluminum content leads to decreasing thermal expansion coefficients (TECs), relative fraction of Fe4+ under oxidizing conditions, and also the total conductivity, predominantly p-type electronic at oxygen pressures close to atmospheric. The TECs vary in the range (13.5–16.4)×10−6 K−1 at 373–923 K and increase up to (18.6–31.9)×10−6 K−1 at 923–1273 K. The oxygen permeation fluxes decrease moderately with aluminum additions. The Mossbauer spectroscopy data and p(O2) dependencies of electrical properties indicate a small-polaron mechanism of electronic transport in SrFe1-xAlxO3-δ. Reducing oxygen partial pressure results in transition from dominant p- to n-type electronic conduction. The low-p(O2) stability limit of SrFe1-xAlxO3-δ perovskites lies between that of LaFeO3-δ and Fe/Fe1-γO boundary.

Partial oxidation of light paraffins to synthesis gas in short contact-time reactors

The reaction pathways of ethane and propane partial oxidation to synthesis gas were investigated over a Pt/γ-Al 2O 3 and a Rh/α-Al 2O 3 catalyst. An annular reactor was used for this purpose at high space velocities and at temperatures below 700 °C in order to avoid homogeneous reactions. Under fuel-rich conditions, the Pt-based catalyst produced CO and H 2 at high temperatures (>550 °C), while CO 2 and H 2O were the only reaction products at lower temperatures. The formation of CO and H 2 was consistent with direct oxidation reactions, since contact time had no effect on the product distribution, and secondary reactions (steam and dry reforming) showed negligible activity. The Rh/Al 2O 3 catalyst was also active and selective in the partial oxidation of light hydrocarbons, but in this case the production of hydrogen and CO was strongly dependent on contact time, and steam reforming was important even at short contact times. It was concluded that, over rhodium, both direct and indirect routes were probably involved in the formation of CO and H 2. The main difference between the two noble metals thus seemed to be that Pt mainly produced CO and H 2 by means of O 2 (direct routes), while over Rh the light paraffins were converted to CO and H 2 by means of O 2 and H 2O (direct+indirect routes). This could explain the remarkably different behavior of the two systems when tested in high temperature autothermal reactors ( T>700 °C). Under adiabatic conditions, the partial oxidation of light paraffins led to large amounts of gas-phase olefinic products over Pt, whereas high selectivities to synthesis gas were found over Rh. The mechanistic results suggest that this different behavior could be due to the varying capability of Pt and Rh surface reactions to compete with homogeneous reactions.

99/02755 High temperature gas cleaning using honeycomb barrier filter on a coal-fired circulating fluidized bed combustor

Support effects on the production of synthesis gas and olefins by the partial oxidation of light hydrocarbons has been examined on noble metal catalysts at contact times of ∼5 ms. We consider the effect of the following parameters on selectivities and conversions: adding a washcoat, varying pore size, ceramic support material, and loading of noble metal. In oxidation of methane on rhodium-coated monoliths, maximum hydrogen selectivity improves from 89 to 95% on the addition of a washcoat. It is also a strong function of the catalyst pore size, changing from 83% on a catalyst with 20 ppi (pores per inch) to 93% on a catalyst with 80 ppi. It varies from 86 to 91% on different ceramic supports with ZrO2giving the best results. Usingn-butane as the fuel, the hydrogen selectivity improves from 70 to 95% on adding a washcoat and changes from 70 to 95% on changing the pore size. In the oxidation of ethane on platinum-coated monoliths, the addition of a washcoat reduces ethylene selectivity from 63 to 35%, while changing the pore size results in minor variations. On different ceramic supports, the ethylene selectivity varies from 60 to 64% with mullite giving the best results. We find that washcoat addition, decreasing pore size, and replacement of zirconia for alumina as the support material increase syngas selectivity and reduce olefin selectivity irrespective of the fuel, catalyst, or amount of diluent used. Most of these results can be explained on the basis of differences in mass transfer rates to the catalytic site between catalysts of different support geometries. It is argued that homogeneous reactions play a minor role in these short contact time processes.

99/02752 Evaluation of ceramic fiber filterbags in commercial hot gas environments

Support effects on the production of synthesis gas and olefins by the partial oxidation of light hydrocarbons has been examined on noble metal catalysts at contact times of ∼5 ms. We consider the effect of the following parameters on selectivities and conversions: adding a washcoat, varying pore size, ceramic support material, and loading of noble metal. In oxidation of methane on rhodium-coated monoliths, maximum hydrogen selectivity improves from 89 to 95% on the addition of a washcoat. It is also a strong function of the catalyst pore size, changing from 83% on a catalyst with 20 ppi (pores per inch) to 93% on a catalyst with 80 ppi. It varies from 86 to 91% on different ceramic supports with ZrO2giving the best results. Usingn-butane as the fuel, the hydrogen selectivity improves from 70 to 95% on adding a washcoat and changes from 70 to 95% on changing the pore size. In the oxidation of ethane on platinum-coated monoliths, the addition of a washcoat reduces ethylene selectivity from 63 to 35%, while changing the pore size results in minor variations. On different ceramic supports, the ethylene selectivity varies from 60 to 64% with mullite giving the best results. We find that washcoat addition, decreasing pore size, and replacement of zirconia for alumina as the support material increase syngas selectivity and reduce olefin selectivity irrespective of the fuel, catalyst, or amount of diluent used. Most of these results can be explained on the basis of differences in mass transfer rates to the catalytic site between catalysts of different support geometries. It is argued that homogeneous reactions play a minor role in these short contact time processes.

The Effect of Ceramic Supports on Partial Oxidation of Hydrocarbons over Noble Metal Coated Monoliths

Support effects on the production of synthesis gas and olefins by the partial oxidation of light hydrocarbons has been examined on noble metal catalysts at contact times of ∼5 ms. We consider the effect of the following parameters on selectivities and conversions: adding a washcoat, varying pore size, ceramic support material, and loading of noble metal. In oxidation of methane on rhodium-coated monoliths, maximum hydrogen selectivity improves from 89 to 95% on the addition of a washcoat. It is also a strong function of the catalyst pore size, changing from 83% on a catalyst with 20 ppi (pores per inch) to 93% on a catalyst with 80 ppi. It varies from 86 to 91% on different ceramic supports with ZrO2giving the best results. Usingn-butane as the fuel, the hydrogen selectivity improves from 70 to 95% on adding a washcoat and changes from 70 to 95% on changing the pore size. In the oxidation of ethane on platinum-coated monoliths, the addition of a washcoat reduces ethylene selectivity from 63 to 35%, while changing the pore size results in minor variations. On different ceramic supports, the ethylene selectivity varies from 60 to 64% with mullite giving the best results. We find that washcoat addition, decreasing pore size, and replacement of zirconia for alumina as the support material increase syngas selectivity and reduce olefin selectivity irrespective of the fuel, catalyst, or amount of diluent used. Most of these results can be explained on the basis of differences in mass transfer rates to the catalytic site between catalysts of different support geometries. It is argued that homogeneous reactions play a minor role in these short contact time processes.

Preparation and characterization of CaTiO3-based perovskitic oxides as catalysts for partial oxidation of light hydrocarbons

A series of perovskites of the formula Ca1−xSrxTi1−yMyO3−δ, M=Fe, Co, Cr or Ni,x = 0−1,y = 0−0.6, has been synthesized by a modified sol-gel method using citrate. Several of these materials were proved to be stable under operating conditions in reducing atmospheres of air and hydrocarbons. An outline of the synthesis procedure is given, together with the results of XRD, SEM, BET, TG, DTA and IR characterization before and after catalytic testing. The solubility of Ni and Cr in this perovskite was very limited, and the solubility of Co decreased abruptly above 1173 K. The solubility range of Ca and Sr on alkaline earth sites is 100%.

Partial Oxidation of Light Hydrocarbons. 1. Major Differences Noted in Various Tubular Reactors

Partial Oxidation of Light Hydrocarbons. 1. Major Differences Noted in Various Tubular Reactors

Partial Oxidation of Light Hydrocarbons. 2. New Techniques for Investigating Surface Reactions

Partial Oxidation of Light Hydrocarbons. 2. New Techniques for Investigating Surface Reactions

Partial Oxidation of Light Hydrocarbons. 3. Mechanism Incorporating Key Surface Reactions with Gas-Phase Steps

Partial Oxidation of Light Hydrocarbons. 3. Mechanism Incorporating Key Surface Reactions with Gas-Phase Steps