CO2 Assisted Oxidative Dehydrogenation of Propane to Propylene over Fluidizable MoO3/La2O3-γAl2O3 Catalysts

https://doi.org/10.1016/j.jcou.2020.101329Get rights and content

Highlights

  • The La2O3 modified MoO3/La2O3-γAl2O3 catalysts were successfully synthesized.

  • The incorporation of La2O3 controlled the acidity and reducibility of the catalysts.

  • CO2 assisted ODH of propane to propylene are conducted in a CREC Riser Simulator.

  • The La2O3 in the catalysts enhanced propylene selectivity.

  • The presence of CO2 in the feed increased propylene yields.

Abstract

This study investigated the catalytic performance of a novel fluidizable MoO3 supported on La2O3-γAl2O3 composite for oxidative dehydrogenation (ODH) of propane to propylene with and without CO2. The La2O3-γAl2O3 composites were synthesized by a coprecipitation method, while the active MoO3 was deposited by an incipient wetness impregnation approach. The incorporation of La2O3 controlled both the acidity and reducibility of the catalysts, as revealed by NH3-TPD and H2-TPR analysis, respectively. The N2 adsorption/desorption isotherms analysis indicated the mesoporous pore size distribution of the catalysts. The ODH of propane experiments were developed in a fluidized CREC Riser Simulator by feeding propane with or without CO2. The performance of the synthesized catalysts was found to be a function of the La2O3 content of the support. In general, the propane conversion declined slightly, while propylene selectivity increased with the increasing La2O3 content. It was hypothesized that the presence of basic La2O3 reduced the acidity and the non-selective sites of γ-Al2O3, which were responsible for deep oxidation of propylene and propane. Among the studied catalysts, MoO3/La2O3-γAl2O31:2 displayed the highest propylene yield of 28.2 % at 600 ℃ in the absence of CO2. However, a superior yield of 35.2% was achieved over the same catalyst by the introduction of CO2-admixture in the feed at 550 ℃.

Introduction

In recent years, the global demand for light olefins (i.e. ethylene, propylene and butenes) has been increasing significantly. Among the short chain olefins, propylene is the most important feedstock in the petrochemical and chemical industries for the production of polypropylene, acrylonitrile, cumen, phonol, iso-propylic alcohol, propylene oxide and several other variety of propylene derivatives [1][2][3]. The projected annual global propylene demand by the year of 2030 is approximately 160 million metric tons [4][5]. The estimation also shows that there is a gap between propylene demand and supply, which is likely to grow further in the near future [6][7]. Over 80 % of the current world propylene supply is obtained as secondary product of the fluid catalytic cracking (FCC) of vacuum gas oil and steam cracking of naphtha and other hydrocarbons. The remaining 20% of the propylene supply is mainly derived from the on-purpose processes such as dehydrogenation of propane, oxidative dehydrogenation of propane, olefins metathesis and methanol-to-propylene [8][9]. The dynamics of propylene supply from the FCC processes is related to the price of gasoline. As the demand for gasoline decreases, the refineries are forced to cut down production, which affects the propylene supply [10]. Severe coke formation is another issue related to FCC based propylene production. On the other hand, steam cracking is an energy intensive process, which accounts for almost 40% of the total annual energy consumption in the petrochemical industries. The steam cracking process also suffers from coke formation and it significantly contributes to the emission of CO2 into the atmosphere [11][12][13]. In order to address the aftermentioned issues, several innovative technologies have been explored to produce propylene from alternative sources [14].

The dehydrogenation of lighter alkanes, mainly obtained from refinery gas, natural gas, as well as shale gas, which has recently gained much attention as an alternative to produce propylene with higher yields and lower costs than those of the conventional processes [15]. However, the dehydrogenation of the short-chain alkanes is a high temperature process, given the reactions involved are endothermic and limited by the thermodynamic equilibrium. In addition, the process conditions are favorable for thermal cracking of both propane and propylene to undesired lighter hydrocarbons. It also contributes to severe coke formation, which leads to catalyst deactivation and production losses [16][17].

In this regard, oxidative dehydrogenation (ODH) of low molecular weight hydrocarbons is a more promising approach, as the reactions involved are exothermic and occur at relatively lower temperatures. The coke formation is also minimal due to presence of oxygen. There is no issue of thermodynamic equilibrium limitations because of the formation of water as a byproduct [18][19]. However, the control of olefin selectivity in the ODH is challenging due to the possibility of successive oxidation of the feed and the desired products in presence of gas phase oxygen. The high flammability of the hydrocarbons/oxygen mixture is also a major concern for possible runaway reactions [20][21]. To address these limitations, the present research group has been investigating a novel circulating fluidized bed ODH process, which uses lattice oxygen of the metal oxide catalyst (instead of gas phase O2) for oxidative dehydrogenation reactions [22][23]. Fig. 1 shows a schematic diagram of the gas phase O2 free ODH process. In this approach, the lattice oxygen of the catalyst plays a crucial role on hydrogen abstraction from the alkanes by its reduction in oxidation state along with water formation. The reduced catalyst can be regenerated in air by circulating them into another reactor, called catalyst regenerator and recycle back for next the cycle reaction [24][25]. With some encouraging results, this route is also susceptible to the deep oxidation of feed/product into COx, which could be further decreased by using CO2 in the feed as a soft oxidant.

The feeding of CO2 also helps to tackle the formation of undesired COx reaction towards their thermodynamic minima [26][27]. On the other hand, co-feeding of CO2 favors the desired ODH reactions by abstracting H2 through reverse water gas shift reaction, and helps to minimize coke formation via Boudouard reaction [28][29][30]. Furthermore, the high heat capacity of CO2 also contributes to subside the cracking reactions by eliminating hot spots [29][30]. Interestingly, CO2 is a cheap feedstock and its utilization in ODH will contribute to the global efforts on the reduction of greenhouse CO2 gas emission[31][32]. In the light of these merits, oxidative dehydrogenation of short-chain alkane using CO2 as a mild oxidant has been arousing significant research interests [33][34]. However, the major challenge of CO2 utilization arises from its low reactivity due to thermodynamic stability. Only an efficient catalyst and appropriate reaction conditions could activate the CO2 molecule to interact with propane to give high propylene yields [35][36].

Therefore, the development of a suitable catalyst that can contribute to high propane/CO2 conversion with high propylene selectivity/yields is the outstanding challenge. An efficient catalyst should be able to activate the C-H (of hydrocarbons) and O-C-O (CO2) bonds effectively towards the desired products, propylene and water. In the search of feasible catalysts for ODH, several transitional metals oxides such oxides of molybdenum, vanadium, chromium, gallium, indium and some other metals supported on silica, zeolite and mesoporous alumina have been studied [37]. There are two major aspects in development of a selective oxidative catalyst for oxidative dehydrogenation of light alkanes, including, (i) the redox properties - the lattice oxygen of transitional metal oxide catalyst are more effective and selective than molecular oxygen as an oxidizing agent and (ii) isolated active sites – to minimize the successive oxidation of the products [38].

The durability and the activity of a metal oxide catalyst can be enhanced by using a suitable support. Among common support such as Al2O3, SiO2 and TiO2, Al2O3 appears to be more promising due to its mild acidity and favorable textural properties. Although γAl2O3 possesses the desired characteristics as a support material for redox active metals, it is prone to sintering and phase transformation at high temperatures [[39], [40], [41]]. The addition of a second metal oxides such as La, Ce, Zr to γAl2O3 can improve the thermal stability and activity of the catalysts [40,42]. Lanthanum oxide is recognized as one of the outstanding basic material used for most reactions to enhance and improve the basic strength of catalyst [43]. The addition of lanthanum also improves the fluidizability of the catalyst, the surfaces area, thermal stability, the CO2 adsorption capacity, reducibility, dispersion of metal as well as the capability to reduce the acidity of the support [[44], [45], [46], [47]]. Supported vanadium-based catalyst is considered among the most active and studied catalyst for ODH [48,49]. However, they suffer a drawback of poor selectivity due to complete oxidation of reactant/products with high VOx loading. On the other hand, Mo-based catalyst are innocuous, comparatively less expensive, and have therefore received a great deal of attention for oxidative dehydrogenation of hydrocarbons due to its exceptional selectivity towards desired product [50][48][51][52]. The mechanism involves abstraction of hydrogen from the methylene group most probably by the terminal M=O bond to form surface hydroxyl group and an adsorbed iso-propyl. Propylene is generated by hydride elimination from iso-propyl and a second hydroxyl group is formed leading to the reduction of molybdenum oxide and formation of water [53]. The promotional effect of molybdenum was confirmed in the works of Alasiri et al. [54] and Nayak et al. [55]. They found that the increase of the molybdenum content improved the catalyst performances by increasing amount of propane adsorbed which in turn enhances the conversion. There has been a number of research on the utilization of supported molybdenum oxide for the ODH of propane to propylene using gas phase oxygen as oxidizing agent [56][57]. To the best of our knowledge, there is no studies reported in the open literature that investigated the use of CO2 as a mild oxidant in ODH of propane over MoO3/La2O3-γAl2O3 catalysts.

With this background on the desired characteristics of an efficient catalyst, the present study investigated the MoO3/La2O3-γAl2O3 catalysts in oxidative dehydrogenation of propane using CO2 as a mild oxidant. The catalyst support system with varying ratio of La2O3/γAl2O3 was synthesized by the coprecipitation technique. The active MoO3 phase was impregnated on the mixed La2O3/γAl2O3 support by an incipient wetness approach. The CO2 assisted ODH of propane was carried out in a fluidized CREC Riser Simulator at atmospheric pressure and at varying temperature (525-600℃). The stability of the catalyst, effect temperature, effect of CO2, effect of La2O3/γAl2O3 ratios have been investigated.

Section snippets

Catalyst preparation

The La2O3-γAl2O3 composite supports were prepared by a coprecipitation technique, with La2O3/γAl2O3 ratio of 1:3, 1:2 and 1:1. The major steps of the catalyst synthesis are depicted in Fig. 2.

In synthesis, the desired quantity of La(NO3)3.6H2O) and Al(NO3)3.9H2O were dissolved in deionized water and the solution was placed on a hot plate at 40 ℃ with continuous stirring. A buffer solution containing (NH4)2CO3 and NH3.H2O at a pH of 8.5 was added to induce precipitation. The precipitated

X-Ray Diffraction (XRD)

Fig. 4 displays the crystalline structures of the synthesized support (γAl2O3) and the prepared MoO3/La2O3-γAl2O3 catalysts with varying La2O3 to Al2O3 ratios and 10% MoO3. The cubic structured crystalline phases of bare γAl2O3 before MoO3 loading appeared at 2θ angles of 37, 45 and 67°, as suggested by JCPDS card no. 10-0425 [62] [63]. The MoO3/γAl2O3 sample (without La2O3) showed two weak diffraction peaks at 2θ angles of 45° and 67° that were attributed to the presence of crystalline γAl2O3 [

Conclusion

This study employed fluidizable MoO3/La2O3-γ-Al2O3 catalysts with varying La2O3 content for oxidative dehydrogenation of propane in the presence of CO2 as a soft oxidant. It was found that the incorporation of La2O3 moderates the surface acidity of the catalyst sample, improves its reducibility, and enhanced its overall performance on the ODH of propane with or without CO2. In general, propane conversion declined slightly while propylene selectivity increased with increasing La2O3 content. It

CRediT authorship contribution statement

Majid L. Balogun: Methodology, Data curation, Writing - original draft. Sagir Adamu: Methodology, Data curation. Idris A. Bakare: Data curation. Mohammed S. Ba-Shammakh: Supervision, Writing - review & editing. Mohammad M. Hossain: Project administration, Funding acquisition, Supervision, Conceptualization, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The author(s) would like to acknowledge the support provided by the Deanship of Scientific Research (DSR) at King Fahd University of Petroleum & Minerals (KFUPM) for funding this work through project No. DF191028.

References (110)

  • M. Chen et al.

    Supported indium oxide as novel efficient catalysts for dehydrogenation of propane with carbon dioxide

    Appl. Catal. A Gen.

    (2010)
  • Y. Wang et al.

    Boron nitride wash-coated cordierite monolithic catalyst showing high selectivity and productivity for oxidative dehydrogenation of propane

    Catal. Today.

    (2020)
  • M.Y. Khan et al.

    Fluidized bed oxidative dehydrogenation of ethane to ethylene over VOx/Ce-ΓAl2O3 catalysts: Reduction kinetics and catalyst activity

    Mol. Catal.

    (2017)
  • A.A.H. Elbadawi et al.

    VOx-Nb/La-γAl2O3 catalysts for oxidative dehydrogenation of ethane to ethylene

    J. Taiwan Inst. Chem. Eng.

    (2016)
  • A.H. Elbadawi et al.

    A fluidizable VOx/γ–Al2O3–ZrO2 catalyst for the ODH of ethane to ethylene operating in a gas phase oxygen free environment

    Chem. Eng. Sci.

    (2016)
  • J.F.S. de Oliveira et al.

    Effect of CO2 in the oxidative dehydrogenation reaction of propane over Cr/ZrO2 catalysts

    Appl. Catal. A Gen.

    (2018)
  • P. Michorczyk et al.

    Effect of dealumination on the catalytic performance of Cr-containing Beta zeolite in carbon dioxide assisted propane dehydrogenation

    J. CO2 Util.

    (2020)
  • I. Ascoop et al.

    The role of CO2 in the dehydrogenation of propane over WOx–VOx/SiO2

    J. Catal.

    (2016)
  • B.P. Ajayi et al.

    n-Butane dehydrogenation over mono and bimetallic MCM-41 catalysts under oxygen free atmosphere

    Catal. Today.

    (2013)
  • S.-H. Cho et al.

    Synergistic effects of CO2 on ex situ catalytic pyrolysis of lignocellulosic biomass over a Ni/SiO2 catalyst

    J. CO2 Util.

    (2020)
  • M.S. Duyar et al.

    Low-pressure methanol synthesis from CO2 over metal-promoted Ni-Ga intermetallic catalysts

    J. CO2 Util.

    (2020)
  • D. Mukherjee et al.

    CO2 as a soft oxidant for oxidative dehydrogenation reaction: An eco benign process for industry

    J. CO2 Util.

    (2016)
  • K. Takehira et al.

    Behavior of active sites on Cr-MCM-41 catalysts during the dehydrogenation of propane with CO2

    J. Catal.

    (2004)
  • M.A. Atanga et al.

    Oxidative dehydrogenation of propane to propylene with carbon dioxide

    Appl. Catal. B Environ.

    (2018)
  • G. Raju et al.

    CO2 promoted oxidative dehydrogenation of n-butane over VOx/MO2–ZrO2 (M = Ce or Ti) catalysts

    J. CO2 Util.

    (2014)
  • M.A. Adnan et al.

    Ni-Fe bimetallic oxides on La modified Al2O3 as an oxygen carrier for liquid fuel based chemical looping combustion

    Fuel.

    (2020)
  • S. Adamu et al.

    Ni/Ce[sbnd]Al2O3 for optimum hydrogen production from biomass/tar model compounds: Role of support type and ceria modification on desorption kinetics

    Int. J. Hydrogen Energy.

    (2019)
  • T.H. Kim et al.

    Dehydrogenation of propane to propylene with lattice oxygen over CrOy/Al2O3-ZrO2 catalysts

    Mol. Catal.

    (2017)
  • Y.C. Sharma et al.

    Latest developments on application of heterogenous basic catalysts for an efficient and eco friendly synthesis of biodiesel: A review

    Fuel.

    (2011)
  • J. Mazumder et al.

    Fluidizable La2O3 promoted Ni/γ-Al2O3 catalyst for steam gasification of biomass: Effect of catalyst preparation conditions

    Appl. Catal. B Environ.

    (2015)
  • G. Garbarino et al.

    Acido-basicity of lanthana/alumina catalysts and their activity in ethanol conversion

    Appl. Catal. B Environ.

    (2017)
  • A. Barrera et al.

    Structural properties of Al2O3-La2O3 binary oxides prepared by sol-gel

    Mater. Res. Bull.

    (2007)
  • S. Adamu et al.

    Enhancement of glucose gasification by Ni/La2O3-Al2O3 towards the thermodynamic extremum at supercritical water conditions

    Renew. Energy.

    (2017)
  • F. Cavani et al.

    Oxidative dehydrogenation of ethane and propane: How far from commercial implementation?

    Catal. Today.

    (2007)
  • B. Solsona et al.

    Molybdenum-vanadium supported on mesoporous alumina catalysts for the oxidative dehydrogenation of ethane

    Catal. Today.

    (2006)
  • I. Kainthla et al.

    Development of stable MoO3/TiO2-Al2O3 catalyst for oxidative dehydrogenation of ethylbenzene to styrene using CO2 as soft oxidant

    J. CO2 Util.

    (2017)
  • M. Høj et al.

    Structure, activity and kinetics of supported molybdenum oxide and mixed molybdenum–vanadium oxide catalysts prepared by flame spray pyrolysis for propane OHD

    Appl. Catal. A Gen.

    (2014)
  • K. Chen et al.

    Alkali Effects on Molybdenum Oxide Catalysts for the Oxidative Dehydrogenation of Propane

    J. Catal.

    (2000)
  • I.A. Bakare et al.

    Fluidized bed ODH of ethane to ethylene over VOx–MoOx/γ-Al2O3 catalyst: Desorption kinetics and catalytic activity

    Chem. Eng. J.

    (2015)
  • Y. Jiao et al.

    Steam reforming of n-decane for H2 production over Ni modified La-Al2O3 catalysts: Effects of the active component Ni content

    J. Anal. Appl. Pyrolysis.

    (2015)
  • I.A. Bakare et al.

    Steam-assisted catalytic cracking of n-hexane over La-Modified MTT zeolite for selective propylene production

    J. Anal. Appl. Pyrolysis.

    (2015)
  • J. Mazumder et al.

    Steam gasification of a cellulosic biomass surrogate using a Ni/La2O3-γAl2O3 catalyst in a CREC fluidized riser simulator

    Kinetics and model validation, Fuel.

    (2018)
  • L. Katta et al.

    Nanosized Ce1−xLaxO2−δ/Al2O3 solid solutions for CO oxidation: Combined study of structural characteristics and catalytic evaluation

    Catal. Today.

    (2012)
  • Y.F. Zhou et al.

    Enhanced adsorption and photocatalysis properties of molybdenum oxide ultrathin nanobelts

    Mater. Lett.

    (2015)
  • G.E. Buono-Core et al.

    Growth and characterization of molybdenum oxide thin films prepared by photochemical metal–organic deposition (PMOD)

    Polyhedron.

    (2010)
  • K. Chen et al.

    Structure and Properties of Oxidative Dehydrogenation Catalysts Based on MoO3/Al2O3

    J. Catal.

    (2001)
  • H. Bandaru et al.

    The effect of varying the metal ratio in a chromium molybdate catalysts for the oxidative dehydrogenation of n-octane

    Mol. Catal.

    (2018)
  • K. Chen et al.

    Alkali effects on molybdenum oxide catalysts for the oxidative dehydrogenation of propane

    J. Catal.

    (2000)
  • Y. Lou et al.

    SBA-15-supported molybdenum oxides as efficient catalysts for selective oxidation of ethane to formaldehyde and acetaldehyde by oxygen

    J. Catal.

    (2007)
  • E. Heracleous et al.

    Oxidative dehydrogenation of ethane and propane over vanadia and molybdena supported catalysts

    J. Mol. Catal. A Chem.

    (2005)
  • Cited by (0)

    View full text