Deacon Process Research Articles

Techno-economic analysis of bromine mediated propane oxidative dehydrogenation to produce propylene

The production of propylene from propane is becoming increasingly important. Catalytic propane dehydrogenation (PDH) is the major on-purpose propylene production process today. The conventional PDH process has a relatively high energy consumption (6.1–9.4 kWh/kg C3H6) which results in high direct CO2 emissions and modest propylene yield (0.8–0.9 kg C3H6/kg C3H8). A bromine-mediated propane oxidative dehydrogenation process (Br-ODH) is evaluated in this techno-economic study which can potentially improve both the process energy efficiency and product yield. To investigate the Br-ODH process feasibility, a heat integrated process model was designed using Aspen Plus® V12 for a 450 kta propylene facility using reaction data from the literature. The partial oxidation of propane under bromine limited conditions selectively produces a propylbromide intermediate which can be readily separated from propane. Propylbromide undergoes dehydrobromination under relatively mild conditions to produce the propylene product in a second step. Bromine is regenerated by conversion of the hydrogen bromide byproduct either thermochemically or electrochemically. Due to the current interest in use of renewable electricity in chemical processes, the electrochemical regeneration process was evaluated in this study. Based on the model, the Br-ODH process can achieve approximately 10% higher propylene yield with 37% lower utilities than conventional PDH. However, the use of high-cost electrolyzers resulted in the capital investment increasing by approximately 11%. Capital cost was also increased due to the requirements of high alloy materials of construction for the potentially corrosive halogen containing equipment. The sensitivity analysis showed that the production cost was most sensitive to the propane price. For the electrolyzer-based regeneration process the capital cost was found to be key parameter that might limit competition with conventional PDH; however, the development of a commercial thermochemical HBr oxidation process analogous to the Deacon process for chlorine would likely bring significant cost savings.

Insight into the effects of calcination temperature on the structure and performance of RuO2/TiO2 in the Deacon process

With an appropriate calcination temperature for preparing a rutile-TiO2 supported RuO2 catalyst, rich surface RuO2 species can be formed on TiO2, leading to its high activity in the oxidation of HCl.

Photocatalytic Deacon Reaction over SrTiO3

AbstractSrTiO3 was prepared by a polymeric precursor method and applied in the photocatalytic aerobic oxidation of HCl in a flat‐plate reactor equipped with a UV LED array (368 nm). Reaction rates up to 240 mmol h−1 m−2 and apparent quantum yields up to 33 % using an illuminated area of 60 cm−2 were achieved with highly crystalline SrTiO3 calcined at 750 °C, outperforming commercially available SrTiO3 by a factor of almost 2. A gradual catalyst deactivation was observed, which was due to the formation of crystalline SrCl2×2 H2O on the surface confirmed by X‐ray diffraction, electron microscopy and X‐ray photoelectron spectroscopy (XPS). Increasing the HCl partial pressure accelerated both Cl2 formation and catalyst deactivation. XP spectra revealed an intrinsic surface segregation of Sr and the presence of several Sr‐ or O‐containing surface species. High Cl2 yields up to 42 % obtained with an illuminated area of 120 cm−2 encourage further research on a photocatalytic Deacon process for improved HCl recycling.

Effects of the Support-Crystal Size on the Catalytic Performance of RuO2/TiO2 in the Deacon Process

RuO2/TiO2 catalysts with different TiO2 crystal sizes were prepared via a dry impregnation method, and these prepared catalysts were applied in the oxidation of HCl. The results show that decreasing the support-crystal size is an effective method to enhance the dispersion of RuO2 on TiO2, which is helpful to increase the catalytic activity significantly.

Insights into the sintering resistance of RuO2/TiO2–SiO2 in the Deacon process: role of SiO2

RuO2 nanoparticles are still formed on the surface of TiO2 to prevent the thermal sintering because of the geometric effects of SiO2 and the resultant RuO2/TiO2–SiO2 catalyst has an improved stability in the Deacon process.

Sustainable utilization of chlorine via converting HCl to Cl2 over a robust copper catalyst

Offering a substantial method to convert HCl to Cl2 over CuCl2/pumice, Deacon process is of great importance in chemical industry. In the process, the difficulty of Cl2 formation/desorption and catalyst re-oxidation have been unanimously recognized as the origin of the instability of CuO-based catalysts. In this work, the stability of the CuO/Al2O3 catalyst was significantly improved by adding Co. The fabricated CuO(12)–CoOx(13)/Al2O3 catalyst showed unprecedented stability with HCl conversion (xHCl) above 80%, lasting for at least 1000 h. The X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and H2-temperature programmed reduction (H2-TPR) characterizations suggested that the addition of Co greatly enhanced the dispersion of CuO on Al2O3 and hindered the reduction of CuO due to their strong interaction. The results of reaction kinetics suggested that the lattice oxygen participated in the reaction and the reaction order on oxygen was estimated to be 0.15, suggesting that the catalyst obeyed the Mars-van Krevelen (M-K) mechanism, while only small amount of oxygen was required to maintain the activity of catalysts compared to CuO/Al2O3. Density functional theory (DFT) calculations proved that the CuO–CoOx/Al2O3 ternary system was more stable than CuO/Al2O3 binary system and easier to be oxidized by O2, which greatly reduced the difficulty of Cl2 associative desorption.

Catalytic Stability Studies Employing Dedicated Model Catalysts.

Long-term stability of heterogeneous catalysts is an omnipresent and pressing concern in industrial processes. Catalysts with high activity and selectivity can be searched for by high-throughput screening methods based maybe on educated guesses provided by ab initio thermodynamics or scaling relations. However, high-throughput screening is not feasible and is hardly able to identify long-term stable catalyst so that a rational and knowledge-driven approach is called for to identify potentially stable and active catalysts. Unfortunately, our current microscopic understanding on stability issues is quite poor. We propose that this gap in knowledge can be at least partly closed by investigating dedicated model catalyst materials with well-defined morphology that allow for a tight link to theory and the application of standard characterization methods. This topic is highly interdisciplinary, combining sophisticated inorganic synthesis with catalysis research, surface chemistry, and powerful theoretical modeling. In this Account, we focus on the stability issues of Deacon catalysts (RuO2 and CeO2-based materials) for recovering Cl2 from HCl by aerobic oxidation and how to deepen our microscopic insight into the underlying processes. The main stability problems under harsh Deacon reaction conditions concomitant with a substantial loss in activity arise from deep chlorination of the catalyst, leaching of volatile chlorides and oxychlorides, and decrease in active surface area by particle sintering. In general, powder materials with undefined particle shape are not well suited for examining catalyst stability, because changes in the morphology are difficult to recognize, for instance, by electron microscopy. Rather, we focus here on model materials with well-defined starting morphologies, including electrospun nanofibers, shape-controlled nanoparticles, and well-defined ultrathin crystalline layers. CeO2 is able to stabilize shape-controlled particles, exposing a single facet orientation so that comparing activity and stability studies can reveal structure sensitive properties. We develop a quasi-steady-state kinetic approach that allows us to model the catalyst chlorination as a function of temperature and gas feed composition. For the case of pure CeO2 nanocubes, this simple approach predicts chlorination to be efficiently suppressed by addition of little amounts of water in the reaction feed or by keeping the catalyst at higher temperature. Both process parameters have great impact on the actual reactor design. Thermal stabilization of CeO2 by intermixing Zr has been known in automotive exhaust catalysis for decades, but this does not necessarily imply also chemical stabilization of CeO2 against bulk-chlorination since Zr can readily form volatile ZrCl4 and may quickly lose its stabilizing effect. Nevertheless, with model experiments the stabilizing effect of Zr in the Deacon process over mixed CexZr1-xO2 nanorods is clearly evidenced. Even higher stability can be accomplished with ultrathin CeO2 coatings on preformed ZrO2 particles, demonstrating the great promise of atomic layer deposition (ALD) in catalysis synthesis.

Exceptional stability and chemical mechanism over spinel ZnCr2O4 catalyst for HCl oxidation to Cl2

Deacon process, one-step catalytic oxidation of HCl to Cl2, is the most effective way to realize the recycling utilization of chlorine element in industry since 1868. However, the stability of non-noble metal catalysts, e.g. Cr-based catalysts, is problematic to be commercialized due to the Cr loss in reaction atmosphere. Herein, we reported a spinel ZnCr2O4 catalyst exhibiting a high activity as well as an unprecedented long-term stability, with a sustainable HCl conversion rate (χHCl) of ˜78% and the space time yield (STY) of 2.25 gCl2 gcat−1 h−1 even after 300 h run at 390 °C and feed O2/HCl (1:1). In addition, we conceived the control experiments and density functional theory (DFT) calculations to deeply understand the chemical mechanisms over spinel CoCr2O4 and ZnCr2O4. The XPS, O2-TPD and H2-TPR characterizations suggested the different surface redox behaviors of both catalysts. DFT calculations indicated that a defect surface of ZnCr2O4 was more active in HCl catalyzed oxidation and HCl preferred to be absorbed on the Zn top site and Cl* coupling to Cl2 was the△G-determining step, which led to the excellent stability of ZnCr2O4 by efficiently avoiding the Cr loss. On the contrary, the higher reaction energy of HCl adsorption on the Co-Cr bridge sites of CoCr2O4 caused the decreasing of activity and stability. Consequently, the different stability performance over CoCr2O4 and ZnCr2O4 was well correlated with the two distinct chemical mechanisms and therefore an outstanding agreement was obtained from the theoretical calculations and experimental behaviors.

Interaction of HCl with a CeO2(111) Layer Supported on Ru(0001): A Theory and Experiment Combined Study

Ultrathin crystalline CeO2(111) films were grown on Ru(0001) in order to study the interaction of HCl with this surface as a first step of the Deacon reaction with experimental techniques, including low energy electron diffraction (LEED), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS) in combination with density functional theory calculations (DFT+U). HCl molecules adsorb dissociatively on CeO2(111), forming a well-ordered (3x3)R30° overlayer structure with one Cl and one H per surface unit cell. DFT calculations indicate that HCl adsorption is exothermic by 1.15 eV and proceeds via an acid–base reaction. The mixed overlayer structure is stabilized by Lewis acid–base pairing (∼0.4 eV). Stoichiometric CeO2(111) films are likely to be not very active in the Deacon process since at 800 K the recombination of adsorbed H* and Cl* to form HCl is far more preferred over Cl* + Cl* recombination to form the desired product Cl2.

The stabilizing effect of water and high reaction temperatures on the CeO2-catalyst in the harsh HCl oxidation reaction

We studied the stability of CeO2 nano-cubes with preferentially (1 0 0)-oriented facets in the HCl oxidation reaction (Deacon process) for various reaction temperatures and the addition of small concentrations of water in the gas feed. For a reaction mixture HCl:O2 = 1:2 we find that CeO2 is substantially chlorinated below 380 °C, revealing a low catalytic activity. At 390 °C both the activity and the chlorination degree change abruptly: activity becomes high and chlorination is not detectable by XRD. The experimental results are rationalized by a kinetic model which allows us to study catalyst chlorination as a function of temperature and gas feed composition. The model predicts that chlorination sets in at the inlet of the catalyst bed and propagates then slowly along the catalyst bed towards the reactor outlet to fully chlorinate the CeO2 catalyst bed. This process has been confirmed by a dedicated experiment employing two separate catalyst layers, where only the first layer is shown to be chlorinated while exposed to the Deacon gas feed. Our model attributes the excessive chlorination at the reactor inlet to the absence of H2O in the gas feed, as the formation of H2O by the reaction of HCl with CeO2 is the prevailing driving force for catalyst chlorination. When running the Deacon process at 375 °C, the chlorination of CeO2 nano-cubes is efficiently suppressed by the addition of 1% water to the reaction mixture. This extrinsic stabilization of oxide catalysts towards chlorination by water is a general concept, which may enable the identification of new oxide materials that have previously been ruled out as Deacon catalysts due to their low stability under reaction conditions.

First‐Principles Computational Screening of Dopants to Improve the Deacon Process over RuO2

AbstractDoping of metal oxides is a promising route to further optimize their catalytic performance. To guide corresponding experimental endeavors, we performed a DFT‐based computational screening study for a wide range of metal dopant atoms in rutile RuO2. With a focus on the Deacon process, that is, the catalytic oxidation of HCl to chlorine and water, we used the rate‐controlling Cl desorption energy as a reactivity descriptor. As stability descriptors, we employed the dopant surface segregation energy and as the dopant thermodynamic stability against precipitation into the metal oxide or bulk oxide grains. In the oxygen‐rich conditions of the Deacon process, particularly the instability against oxide precipitation, represents a strong limitation. In this respect, doping with Cu appears as an optimum compromise between stability and catalytic activity enhancement.

Low-Voltage Gaseous HCl Electrolysis with Iron Redox-Mediated Cathode for Chlorine Regeneration

Chlorine (Cl2) is used to synthesize numerous consumer products and useful intermediates.[ 1 ] Chlorination of alkanes or aromatics is a substitution reaction with hydrogen, for which only one chlorine atom is actually used to produce chloro-organics, while the other is lost as gaseous hydrogen chloride (HCl) by-product, which is either disposed as waste gas or recovered as low-value HCl aqueous solution. Today, HCl by-product totals globally 9.3 million tons per year, when only considered is the synthesis of polyurethane, chloromethane, and polycarbonate. At present, only 15% of this HCl by-product is recycled, leaving an unrealized Cl2 regeneration market of $2.4 billion peryear (based on the current price of Cl2: $315/ton).[2] The need to regenerate Cl2 from HCl has become urgent in recent years as the demand for Cl2 is increasing drastically. Conversion from HCl to Cl2 can be achieved via chemical reactions in the Deacon process using a heterogeneous catalyst, but high temperature (e.g., 250–350 oC) and complex reactor design are needed to mitigate intrinsically low reactivity and yield. Alternatively, an electrochemical process can be used that as a simple modular design and mild operating conditions. [3] To complete the electrolysis process, anodic regeneration of Cl2 from HCl must be balanced by a cathodic reaction. There are two major types of cathodes used in HCl electrolysis process: the hydrogen evolution cathode (HEC) (Eqn. 1), and the oxygen reduction cathode, also commonly known as the oxygen depolarized cathode (ODC) (Eqn. 2). HEC-based electrolysis can produce H2as a valuable by-product but ODC-based electrolysis offers significantly lower standard cell voltage due to its high redox potential (1.23 V vs. SHE) HCl → Cl2 + H2 (1) 4HCl → 2Cl2 + 2H2O (2) Herein, we demonstrate a gaseous HCl electrolyzer with Fe3+/Fe2+ redox-mediated cathode (IRC) for the first time to regenerate Cl2. At the anode, gaseous HCl is oxidized to generate chlorine and protons, at the cathode, Fe3+ is electrochemically reduced to form Fe2+. Subsequently, Fe2+ is chemically oxidized to Fe3+ by oxygen in a reactor external to the electrolytic cell. Regeneration Fe2+ is recycled to the electrolyzer. Due to high standard potential (p o, 0.77 VSHE) and fast kinetics (exchange current density, i0 , of ~10−2 A/cm2 on glassy carbon, no catalyst was required),[4] IRC offers substantial benefits over alternative commercial HEC and ODC cathodes. Taking advantage of IRC, a much lower cell voltage is achieved: 0.67 V vs. 1.16 V (with ODC) and 1.22 V (HEC) at a typical current density of 4 kA/cm2. Compared to the commercial HEC or ODC-based HCl electrolysis processes, it will save 45–50% of energy consumption approximately. Moreover, without the need for a precious metal cathode catalyst and a costly thick membrane, the captital cost can be reduced by 40%–50% (IRC: $2,640/m2 vs. HEC: $4,339/m2 and ODC: $5,034/m2, estimated with 4 kA/m2and current materials prices). [1] J. Perez-Ramirez, C. Mondelli, T. Schmidt, et al, Energy & Environmental Science, 2011, 4, 4786. [2] ThyssenKrupp, HCl electrolysis brochure. [3] I. G. Martinez, T. Vidaković-Koch, R. Kuwertz, et al, Electrochimica Acta, 2014, 123, 387. [4] Y. H. Wen, H. M. Zhang, P. Qian, et al, Electrochimica Acta, 2006, 51, 3769.

Shape-Controlled CeO2 Nanoparticles: Stability and Activity in the Catalyzed HCl Oxidation Reaction

CeO2 is a promising catalyst for the HCl oxidation (Deacon process) in order to recover Cl2. Employing shape-controlled CeO2 nanoparticles (cubes, octahedrons, rods) with facets of preferential orientations ((100), (111), (110)), we studied the activity and stability under two reaction conditions (harsh: Ar:HCl:O2 = 6:2:2 and mild: Ar:HCl:O2 = 7:1:2). It turns out that both activity and stability are structure-sensitive. In terms of space time yield (STY), the rods are the most active particles, followed by the cubes and finally the octahedrons. This very same trend is reconciled with the complete oxygen storage capacity (OSCc), indicating a correlation between the observed activity STY and the OSCc. The apparent activation energies are about 50 kJ/mol for cubes and rods, while the octahedrons reveal an apparent activation energy of 65 kJ/mol. The reaction order in O2 is positive (0.26–0.32). Under mild reaction conditions, all three morphologies are stable, consistent with corresponding studies of CeO2 p...

Mechanism of ethylene oxychlorination over ruthenium oxide

The oxychlorination of ethylene is an industrially relevant process within the manufacture of polyvinyl chloride (PVC). Although RuO2 is the best performing catalyst for the Deacon process (4HCl+O2→2H2O+2Cl2), experiments demonstrate a modest activity in the selective oxychlorination to vinyl chloride, favouring oxidation and polychlorinated saturated products. From the computational modelling three main contributions are found to control the performance: (i) coverage effects that alter the configuration of intermediates; (ii) the monodimensional arrangement of the active sites, in which the reaction of coadsorbed species works on a “first-come, first-served” basis; and (iii) the high reactivity of the oxygen species. Competition between oxidation and chlorination processes results in variable selectivity, depending on the reaction conditions (particularly temperature and reactant partial pressures), which influence the surface composition. From the analysis of the complex reaction network, the essential requirements for a good oxychlorination catalyst are formulated.

Rate-Determining Step or Rate-Determining Configuration? The Deacon Reaction over RuO2(110) Studied by DFT-Based KMC Simulations

Ab initio kinetic Monte Carlo (KMC) is successfully applied to simulate the experimentally observed promoting effect of O2 on the HCl oxidation reaction (Deacon process) catalyzed by RuO2(110). Density functional theory (DFT) calculations provide, in addition to the adsorption energies of reaction intermediates and activation energies, also interaction energies between the adsorbates within the cluster expansion approach. KMC simulations with this extended set of energy parameters were analyzed employing the concept of “degree of rate control”. In contrast to previous propositions, our simulations indicate that neither the dissociative O2 adsorption (the sterically hindered first reaction step) nor the associative desorption of chlorine (the step with the highest activation energy) are rate determining under typical Deacon conditions. Instead, the hydrogen transfer in the water formation determines the rate of the overall reaction. These hydrogen transfer processes are not highly activated but turn out to...

Effects of flue gas components on removal of elemental mercury over Ce–MnOx/Ti-PILCs

The adsorption and oxidation of elemental mercury (Hg0) under various flue gas components were investigated over a series of Ce–MnOx/Ti-PILC catalysts, which were synthesized by an impregnation method. To discuss the mechanism, the catalysts were characterized by various techniques such as N2 adsorption–desorption, scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) analysis and X-ray photoelectron spectroscopy (XPS). The results indicated that the presence of 500ppm SO2 in the flue gas significantly restrained the Hg0 adsorption and oxidation over 6%Ce–6%MnOx/Ti-PILC due to the formation of SO42− species. Hg0 could be oxidized to HgCl2 in the presence of HCl, because the Deacon process occurred. NO would react with active oxygen to form NO2-containing species, which facilitated Hg0 oxidation. While the presence of NO limited the Hg0 adsorption on 6%Ce–6%MnOx/Ti-PILC due to the competitive adsorption of NO with Hg0. The addition of NH3 in the flue gas significantly restrained Hg0 adsorption and oxidation, because the formed NH4+ species covered the active adsorption sites on the surfaces, and further limited Hg0 oxidation. However, when NO and NH3 were simultaneously added into the flue gas, the Hg0 oxidation efficiency of 6%Ce–6%MnOx/Ti-PILC exhibited a relatively high value (72%) at 250°C, which indicated the practicability to use Ce–MnOx/Ti-PILC for Hg0 removal under SCR conditions.

Electrospun ceria-based nanofibers for the facile assessment of catalyst morphological stability under harsh HCl oxidation reaction conditions

Long-term stability is a major issue in the development of new catalysts and in the improvement of existing catalysts. In general, high-surface-area materials in catalysis are not well suited as model materials for testing catalyst stability, because changes in the morphology are difficult to recognize with electron microscopy. Therefore, we developed a new type of model catalyst in the form of nanofibers for assessing structural changes of CeO2-based catalysts under highly corrosive Deacon reaction conditions. In the Deacon process, chlorine is recycled by heterogeneously catalyzed gas-phase oxidation of HCl, using metal oxide catalysts. The Deacon process generally suffers from degradation of the catalyst due to in-depth chlorination. One-dimensional CeO2-based nanofibers with a well-defined morphology and surface enable direct visualization of structural changes before and after the Deacon reaction, simply employing scanning electron microscopy supported by X-ray diffraction and physisorption measurements. Preparing solid solutions of CeO2 and ZrO2 has shown to improve both the chemical stability and the activity of the catalyst.

An adaptive moving grid method for solving convection dominated transport equations in chemical engineering

Convection dominated processes in chemical engineering are frequently accompanied by steep propagating fronts. Numerical simulation of corresponding models with uniform fixed grids requires an excessive amount of grid points along the expected range of the front movement. In this contribution the implementation of an efficient adaptive grid method is presented and applied to two relevant spatially one-dimensional cases, the chlorination stage of the Deacon process and oxygen storage processes in a three-way catalyst. The algorithm exhibits a high accuracy with a much lower number of grid points and a therefore reduced computational effort as opposed to a fixed grid simulation. The present work demonstrates that the algorithm allows for a robust, simple, and fast implementation of the adaptive grid method in common simulation tools and, together with adequate supplementary material, aims to make the method readily accessible to the interested reader.

Chlorine Evolution Reaction on RuO2(110): Ab initio Atomistic Thermodynamics Study - Pourbaix Diagrams

Constrained ab initio thermodynamics in the form of a Pourbaix diagram can greatly assist kinetic modeling of a particular electrochemical reaction such as the chlorine evolution reaction (CER) over RuO2(110). Pourbaix diagrams reveal stable surface structures, as a function of pH and the potential. The present DFT study indicates that the Pourbaix diagram in the CER potential region above 1.36 V and pH values around zero is dominated by a stable surface structure in which all coordinatively undercoordinated Ru sites (Rucus) are capped by on-top oxygen (Oot). This oxygen saturated RuO2(110) surface is considered to serve as the catalytically active phase in the CER, quite in contrast to the heterogeneously catalyzed HCl oxidation (Deacon process), for which the active RuO2(110) surface is mainly covered by on-top chlorine. The active sites in the CER are suggested to be RucusOot surface complexes, while in the Deacon process both undercoordinated surface Ru and oxygen sites must be available for the activation of HCl molecules.

Stable and Active Mixed Zr–Ce Oxides for Catalyzing the Gas Phase Oxidation of HCl

Electrospun mixed Zr1−x Ce x O2 nanofibers were used to assess both the activity in the Deacon process and the morphological stability of these model catalysts under harsh HCl oxidation conditions. CeO2 nanofibers are morphologically unstable, while Zr doping stabilizes CeO2 nanofibers. Already 30 % of Ce results in high activity of Zr1−x Ce x O2 nanofibers.