Propylene Oxide Production Research Articles

Silylated Pd/Ti-MCM-41 catalyst for the selective production of propylene oxide from the oxidation of propylene with cumene hydroperoxide

Titanium-containing mesoporous molecular sieves with regular pore structure, high specific surface area, tunable pore size and suitable active sites have attracted great attention in the epoxidation of alkenes. Herein, we report the silylated Pd/Ti-MCM-41 (PdTM-ZS) catalysts prepared by treating the series Ti-MCM-41 samples (Si/Ti molar ratio = 10, 15, 20, 25 and 30) with palladium loading followed by surface silylation with trimethylchlorosilane. Reaction results show that the PdTM-ZS catalysts can be applied as efficient catalysts for the selective production of propylene oxide from the oxidation of propylene with cumene hydroperoxide as the oxidant. The PdTM-20S catalyst exhibits an excellent catalytic performance with the selectivity of propylene oxide approaching 100%, which can be attributed to the synergistic effect of abundant active sites, palladium loading and surface silylation.

Low-waste Technology of Obtaining Epoxy Compounds. Part 2. The Technology of Propylene Oxide Production by Peroxide Method

The proposed technological process of manufacturing propylene oxide, calculated on the production capacity of 50 thousand ton per year to create the raw materials base for synthesis of polyols, polyurethanes, polyether resins. On the basis of the research trial of the process by liquid-phase epoxidation of propylene the optimal parameters of the process are determined. The conversion of hydrogen peroxide is more than 99 %, the yield of the propylene oxide is 94 %. The process includes three main stages: (1) raw materials preparation, (2) liquid-phase epoxidation of propylene, (3) distillation of the target product. The scheme provided for recirculation of unreacted propylene and the solvent – methanol.

Effects of TiO2 in Low Temperature Propylene Epoxidation Using Gold Catalysts

Propylene epoxidation with molecular oxygen has been proposed as a green and alternative process to produce propylene oxide (PO). In order to develop catalysts with high selectivity, high conversion, and long stability for the direct propylene epoxidation with molecular oxygen, understanding of catalyst structure and reactivity relationships is needed. Here, we combined atomic layer deposition and deposition precipitation to synthesize series of well-defined Au-based catalysts to study the catalyst structure and reactivity relationships for propylene epoxidation at 373 K. We showed that by decorating TiO2 on gold surface the inverse TiO2/Au/SiO2 catalysts maintained ∼90% selectivity to PO regardless of the weight loading of the TiO2. The inverse TiO2/Au/SiO2 catalysts exhibited improved regeneration compared to Au/TiO2/SiO2. The inverse TiO2/Au/SiO2 catalysts can be regenerated in 10% oxygen at 373 K, while the Au/TiO2/SiO2 catalysts failed to regenerate at as high as 473 K. Combined characterizations of ...

A density functional theory study of propylene epoxidation mechanism on Ag2O(001) surface.

Propylene oxide (PO) is one of the 50 most produced chemicals according to the production volume. Environmental and economic drawbacks of conventional PO production processes necessitate new production methods. Among the new production alternatives, direct epoxidation of propylene to propylene oxide by molecular oxygen is a highly desired method and seen as the holy grail of propylene epoxidation studies. In this study, the propylene epoxidation mechanism on an Ag2O(001) surface is investigated computationally by means of density functional theory (DFT) calculations using the Vienna Ab-initio Simulation Package (VASP). A perfect Ag2O(001) surface and a surface with one O vacancy are utilized for this purpose. It is found that propylene oxide can be directly formed on an Ag2O(001) surface whether there is an oxygen vacancy or not. The rate controlling step is PO desorption from both surfaces. PO isomers, i.e. acetone and propanal, can also be formed on these surfaces. However, activation barriers do exist for these molecules. Direct allyl formation on the Ag2O(001) surface is found to be unfavorable unlike what is proposed in the literature. On the other hand, it is observed that an allyl radical can be formed either via an oxametallocycle path or after the formation of propylene oxide. In fact, the discovered allyl radical formation pathway from propylene oxide is found as the most probable successive reaction pathway because of the high desorption barrier of PO.

Analysis of the propylene epoxidation mechanism on supported gold nanoparticles

The direct propylene epoxidation reaction has been investigated experimentally in the past by several different groups, and gold-based catalysts tend to provide high selectivity for propylene oxide, but the conversion is relatively low. Models that can connect the atomistic catalytic details to the observed experimental data are desired, in order to identify new catalyst structures and formulations. While electronic structure calculations have been used to quantify some of the key reaction steps in the direct propylene epoxidation reaction, atomistic models for translating this information into more experimentally-relevant data are needed. Here, kinetic Monte Carlo (KMC) simulations are used to bridge this gap in the modeling hierarchy. Relevant data from previous experiments and electronic structure calculations are used to parameterize a KMC model for predicting propylene oxide production from an Au/TiO2/SiO2 catalyst. The model connects the H2/O2-related reactions occurring on the Au sites with the epoxidation step on the isolated Ti surface sites. In addition, the composition in the bulk gas phase is synchronized with the dynamic reaction events occurring on the surface. The KMC model is able to adequately reproduce the experimental trends with respect to temperature and different reactant partial pressures. However, this is only achieved by considering the re-adsorption of trace amounts of the oxidant (H2O2) from the gas phase, versus merely assuming that desorbed species are immediately swept away in the gas stream.

Microporous inert membrane packed-bed reactor for propylene epoxidation with hydrogen and oxygen: Modelling and simulation

United mathematical models for four reactors, two microporous inert membrane reactors as O2 (MR-O) or H2 (MR-H) distributor and two traditional reactors (i.e., three-stage reactor (TSR) and packed-bed reactor (PBR)) with different feeding strategies, are developed to describe direct propylene epoxidation with H2 and O2 to produce propylene oxide (PO). Effects of the feeding strategies on reactor performances (i.e., C3H6 conversion, PO selectivity, PO yield and H2 efficiency) are studied under both isothermal and non-isothermal conditions by using gPROMS. Significantly different reactor performances along the catalyst length are observed and then explained by the reactants and products concentration profiles and/or the temperature distributions. Then, effects of the catalyst lengths of the four reactors are further investigated. It is found that the MR-O gives rise to the outlet C3H6 conversion of 11.3%, which exceeds the previously estimated value (i.e., 10%) with a commercial potential. Finally, an attempt is made to probe whether increasing the H2 and C3H6 feed concentrations in the MR-O without the explosion risk further improves the reactor performance. All the results indicate the potential of the MR-O for the commercial production of PO by direct propylene epoxidation with H2 and O2.

Biosynthesis of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) by bacterial community from propylene oxide saponification wastewater residual sludge

The saponification wastewater from the process of propylene oxide (PO) production is contaminated with high chemical oxygen demand (COD) and chlorine contents. Although the activated sludge process could treat the PO saponification wastewater effectively, the residual sludge was difficult to be disposed properly. In this research, microbes in PO saponification wastewater residual sludge were acclimated to produce poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) from volatile fatty acids. Through Miseq Illumina highthroughput sequencing, the bacterial community discrepancy between the original and the acclimated sludge samples were analyzed. The proportions of Bacillus, Acinetobacter, Brevundimonas and Pseudomonas, the potential PHBV-producers in the residual sludge, were all obviously increased. In the batch fermentation, the production of PHBV could achieve 4.262g/L at 300min, with the content increased from 0.04% to 23.67% of mixed liquor suspended solid (MLSS) in the acclimated sludge, and the COD of the PO saponification wastewater was also decreased in the fermentation. This work would provide an effective solution for the utilization of PO saponification wastewater residual sludge.

Significant enhancement of the selectivity of propylene epoxidation for propylene oxide: a molecular oxygen mechanism.

As an attractive and environmentally friendly process for propylene oxide (PO) production, direct epoxidation of propylene (DEP) with molecular oxygen catalyzed by metal-based catalysts such as Ag and Cu has drawn much attention, but remains one of the biggest challenges in chemistry. In this work, the crucial competitive reactions of propylene α-H stripping (AHS) versus the oxametallacycle formation (OMMP formation) using adsorbed atomic oxygen (O*) or adsorbed molecular oxygen (O2*) as an oxidant are extensively compared on IB group metal surfaces (Cu, Ag and Au) with varied electronic and structural effects in order to explore the possibility to enhance the PO selectivity by virtue of first-principles calculations. The determining factor for the PO selectivity is quantitatively revealed: it is found that with atomic O*, the AHS pathway was preferred, indicating the reason for low PO selectivity with current catalysts. By contrast, the undissociated molecular O2* species is found to prefer to electrophilically attack the C[double bond, length as m-dash]C double bond of propylene and form a special oxametallacycle intermediate (OOMMP) rather than nucleophilically abstracting the α-H. This OOMMP can readily cleave the O-O bond and transform into OMMP. These results demonstrate that the presence of undissociated O2* can efficiently promote the PO selectivity. Furthermore, the merit of such a molecular O2* mechanism can be rationalized by our quantitative barrier decomposition analyses, which reveal that the lower hydrogen affinity (ΔEH) of the O2* species dominantly contributes to the limited AHS reaction, and boosts the OMMP selectivity. Therefore, ΔEH can be applied as a selectivity descriptor. An efficient strategy to promote PO formation is presented. The insight obtained could pave the way for further development of catalysts for propylene epoxidation.

Direct Propylene Epoxidation over RuO2–CuO–NaCl–TeO2–MnOx/SiO2 Catalysts: Optimized Operating Conditions and Catalyst Characterization

Multimetallic catalysts of RuO2–CuO–NaCl–TeO2–MnOx supported on SiO2 were investigated for the direct-gas-phase epoxidation of propylene to propylene oxide (PO) using molecular oxygen under atmospheric pressure. Four operating variables (reactor temperature, O2 to propylene feed gas volume ratio, reactants to carrier gas volume ratio, and total feed gas flow rate) were studied using the Box–Behnken design, which enabled the achievement of a relatively high PO formation rate at 1507 gPO h–1 kgcat–1 with PO selectivity of 25.3% and propylene conversion of 5.9% at 1 h of time on stream. The optimized conditions were a reactor temperature of 297 °C, a O2/C3H6 ratio of 11.95, a (O2 + C3H6)/He ratio of 0.24, and a total feed gas flow rate of 36 cm3 min–1. The physical and chemical properties were characterized using various techniques that revealed that the crystallinity of RuO2 and CuO, the close proximity of RuO2 and CuO, and the surface’s acidity are crucial for PO production. NaCl plays a key role in reducing CO2 combustion. TeO2 and MnOx enhanced the active sites that facilitate PO production.

Propylene epoxidation with hydrogen peroxide in acidic conditions

In the present work, the epoxidation of propylene with hydrogen peroxide in the presence of acids and halides is studied. The presence of acids and halides is indispensable for increasing the selectivity of the direct synthesis of hydrogen peroxide, the first step of the direct propylene oxide production from hydrogen, oxygen and propylene. Therefore, we focus on the systematic study of the effect of these compounds on the epoxidation of propylene with hydrogen peroxide in prospective of its future integration with hydrogen peroxide in-situ formed. Indeed, the epoxidation of propylene with hydrogen peroxide is the second step of the direct PO synthesis from hydrogen, oxygen and propylene. The acid concentration and type were shown to have an effect on the PO selectivity. Sulphuric and hydrochloric acids, typical compounds used to stabilize the hydrogen peroxide, are not suitable for the direct propylene oxide due to their fast dissociation in the solution. This leads to a fast ring opening reaction of the epoxide. Phosphoric acid was shown to have a much milder effect on the propylene oxide selectivity, therefore being an option for the direct propylene oxide synthesis. Also, the amount of halides (NaBr) needed to stabilize the hydrogen peroxide, does not have an effect on the epoxidation step. Therefore phosphoric acid and NaBr can be implemented in the direct propylene oxide synthesis from hydrogen, oxygen and propylene.

Theoretical mechanistic insights into propylene epoxidation on Au-based catalysts: Surface O versus OOH as oxidizing agents

Propylene oxide (PO) is an important bulk chemical used for synthesis of many value-added products. Much effort has been devoted to finding a simple and “green” process for PO production. Promising results in terms of activity and selectivity have been achieved for propylene oxidation on supported gold catalysts with a mixture of O2 and H2 or with O2 and H2O. In this work a detailed transformation network of competitive reaction pathways following the initial steps of oxidation has been studied theoretically using density functional theory (DFT). The results of calculations question some of the earlier assumptions regarding the mechanism of PO formation. Surface hydroperoxo species (OOH) formed in situ are shown to be responsible for the high selectivity of propylene epoxidation with O2 on gold-based catalysts using hydrogen or water as co-reactants.

One-pot two-step process for direct propylene oxide production catalyzed by bi-functional Pd(Au)@TS-1 materials

Different bi-functional materials (Pd(Au)@TS-1) based on metallic nanoparticles supported onto active nanocrystalline titanium silicalite (TS-1) zeolites were synthesized, characterized and used as recyclable heterogeneous catalysts for direct propylene oxide production from hydrogen, oxygen and propylene through one-pot two-step consecutive process. These catalysts allowed carrying out the combined reaction where metallic nanoparticles catalyzed the formation of in situ H2O2 that was the necessary intermediate for propylene epoxidation catalyzed by active TS-1 nanocrystalline support. Several variables were considered such as use of supercritical CO2 conditions, modifiable content of metallic species, and presence of additional co-solvents, surface acidity inhibitors and H2O2 stabilizers. Reusability and stability of the bi-functional catalyst was showed through consecutive catalytic cycles.

Kinetic modeling of 1,2‐dichloropropane (PDC) free‐radical chlorination

Recent government mandates have lowered the permissible global warming potential (GWP) for refrigerants in mobile air conditioning substantially below that of the hydrofluorocarbon products that are used currently. Potential replacements, hydrofluoro‐olefins (HFO), have a reduced impact on the ozone layer and lower GWP. Many desirable HFO compounds, such as HFO‐1234yf, can be produced utilizing chlorocarbons as feedstocks such as the preferred 1,1,2,3‐tetrachloropropene (TCPE). TCPE can be produced by several routes; however, producing TCPE from 1,2‐dichloropropane (PDC) is potentially more desirable environmentally and economically since PDC is a byproduct of propylene oxide and allyl chloride production. One process option is to convert PDC to pentachloropropane (PCP) intermediates by chlorination, followed by dehydrochlorination of the PCPs to produce TCPE. In this work, we show that PCPs can be produced through the chlorination of PDC in a free‐radical liquid phase reaction and have developed a kinetic model for PDC chlorination based on the relevant free radical elementary reactions. Thermodynamic properties including standard heats of formation, standard entropies of formation, and heat capacities for the radical and non‐radical species were estimated by using ab initio and COSMOtherm calculations and validated against available experimental data. The reaction equilibrium constants were determined from the Gibb's free energies of the reactants and products. Phase equilibria were calculated by means of a consistent set of thermodynamic properties of the species. In addition, physical properties such as the vapor pressure of pure components involved in the reaction network were also estimated. Ab initio transition state calculations were employed to estimate the rate parameters including pre‐exponential factors and activation energies for the relevant reactions. The activation energies of some key reactions were then adjusted to match experimental data. The resulting kinetic model provided a basis for process yield optimization and scale up. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1174–1191, 2016

Synergetic photo-epoxidation of propylene over V[sbnd]Ti/MCM-41 mesoporous photocatalysts

The photo-epoxidation of propylene has gained preference among many alternative processes because the current processes for propylene oxide (PO) production are neither economical nor environmentally sustainable. We synthesized various single and binary metal oxides (Ti and V) constructed within the MCM-41 framework and demonstrated their favorable efficiency for the photo-epoxidation of propylene. The results indicated that highly dispersed tetrahedral coordination states played a role in photo-epoxidation. The maximum PO formation rate was 634±17 (μmolg−1h−1) on V0.2Ti0.3/MCM-41 under UV-light irradiation of 0.3mWcm−2 at 323K. The Delplot method revealed two pathways to produce PO. One is indirectly from propionaldehyde via either V or Ti oxides, and the other is directly from a C3H6 reactant via Ti oxides. This paper clearly illustrates how V and Ti oxides affect the photo-epoxidation pathways. Furthermore, a possible photo-epoxidation mechanism via the metal oxide active site is proposed to elucidate the synergetic photoactivity.

A density functional theory study of partial oxidation of propylene on Cu2O(0 0 1) and CuO(0 0 1) surfaces

This work theoretically investigates propylene epoxidation reaction on Cu2O(001) and CuO(001) surfaces using periodical DFT method to determine the active copper species within the reaction mechanism. The transition states and energy profiles are calculated for the formation of surface intermediates such as oxametallopropylene (OMP) over Cu2O(001) and oxygen bridging (OB) over CuO(001) and allylic H-stripping reaction (AHS) over both surfaces as well as for formation of products. Propylene oxide (PO) and acetone are obtained through OMP and OB surface intermediates and acrolein generation is observed through allylic H-stripping reaction (AHS). The calculations revealed that the corresponding surface intermediates for epoxidation reaction need to overcome an activation barrier of 13kcal/mol over CuO surface whereas they occur without an energy barrier over Cu2O surface indicating the higher activity of Cu+ species. Acrolein is also found to be a thermodynamically more favorable product for both surfaces especially over CuO surface due to the presence of more surface oxygen atoms on which the basicity has been evaluated by the adsorption of sulfur dioxide. This indicates that the lattice oxygen inherent in both surface types does not participate in PO production.

Direct Oxidation of Propylene to Propylene Oxide with Molecular Oxygen: A Review

The direct oxidation of propylene to propylene oxide (PO) using molecular oxygen has many advantages over existing chlorohydrin and hydroperoxide process, which produce side products and require complex purification schemes. Recent advances in liquid-phase and gas-phase catalytic oxidation of propylene in the presence of only molecular oxygen as oxidant and in absence of reducing agents are summarized. Liquid-phase PO processes involving soluble or insoluble Mo, W, or V catalysts have been reported which provide moderate conversions and selectivities, but these likely involve autoxidation by homogeneous chain reactions. Gas-phase PO catalysts have been mostly Ag-, Cu-, or TiO2-based substances, although other compositions such as Au-, MoO3-, Bi-based catalysts and photocatalysts have also been suggested as possibilities. The Ag catalysts differ from those used for ethylene oxide production in having high Ag contents and numerous additives. The additives are solid-phase alkali metals, alkaline earth metals, and halogens, with the most common substances being NaCl and CaCO3. Nitrogen oxides in the form of gas-phase species or nitrates have also been found to be effective in enhancing PO production. Direct epoxidation by surface nitrates is a possibility. Titania catalysts supported on silicates have also been reported. These have higher PO selectivities at high conversion than silver catalysts.

Full-scale bioreactor pretreatment of highly toxic wastewater from styrene and propylene oxide production

The wastewater originating from simultaneous production of styrene and propylene oxide (SPO) is classified as highly polluted with chemical oxygen demand level in the range 5965 to 9137mgL−1—as well as highly toxic. The dilution factor providing for a 10 percent toxic effect of wastewater samples in a test with Paramecium caudatum was 8.0–9.5. Biological approach for pretreatment and detoxification of the wastewater under full-scale bioreactor conditions was investigated. The number of suspended microorganisms and the clean up efficiency were increased up to 5.5–6.58×108CFUmL−1 and 88 percent, respectively during the bioreactor’s operation. Isolates in the Citrobacter, Burkholderia, Pseudomonas, and Paracoccus genera were dominant in the mature suspended, as well as the immobilized microbial community of the bioreactor. The most dominant representatives were tested for their ability to biodegrade the major components of the SPO wastewater and evidence of their role in the treatment process was demonstrated. The investigated pretreatment process allowed the wastewater to be detoxified for conventional treatment with activated sludge and was closely related to the maturation of the bioreactor’s microbial community.

Selective Oxidation of Propylene to Propylene Oxide over Silver-Supported Tungsten Oxide Nanostructure with Molecular Oxygen

Propylene oxide (PO) is a versatile chemical intermediate, and by volume it is among the top 50 chemicals produced in the world. The catalytic conversion of propylene to PO by molecular oxygen with minimum waste production is of high significance from an academic as well as an industrial point of view. We have developed a new synthesis strategy to prepare 2–5 nm metallic silver nanoparticles (AgNPs) supported on tungsten oxide (WO3) nanorods with diameters between 30 and 40 nm, in the presence of cationic surfactant (cetyltrimethylammonium bromide: CTAB), capping agent (polyvinylpyrrolidone: PVP), and hydrazine. The synergy between the surface AgNPs and WO3 nanorods facilitates the dissociation of molecular oxygen on the metallic Ag surface to produce silver oxide, which then transfers its oxygen to the propylene to form PO selectively. The catalyst exhibits a PO production rate of 6.1 × 10–2 mol gcat–1 h–1, which is almost comparable with the industrial ethylene-to-ethylene oxide production rate.

Crystal‐Plane‐Controlled Selectivity of Cu2O Catalysts in Propylene Oxidation with Molecular Oxygen

The selective oxidation of propylene with O2 to propylene oxide and acrolein is of great interest and importance. We report the crystal-plane-controlled selectivity of uniform capping-ligand-free Cu2 O octahedra, cubes, and rhombic dodecahedra in catalyzing propylene oxidation with O2 : Cu2 O octahedra exposing {111} crystal planes are most selective for acrolein; Cu2 O cubes exposing {100} crystal planes are most selective for CO2 ; Cu2 O rhombic dodecahedra exposing {110} crystal planes are most selective for propylene oxide. One-coordinated Cu on Cu2 O(111), three-coordinated O on Cu2 O(110), and two-coordinated O on Cu2 O(100) were identified as the catalytically active sites for the production of acrolein, propylene oxide, and CO2 , respectively. These results reveal that crystal-plane engineering of oxide catalysts could be a useful strategy for developing selective catalysts and for gaining fundamental understanding of complex heterogeneous catalytic reactions at the molecular level.

Crystal‐Plane‐Controlled Selectivity of Cu2O Catalysts in Propylene Oxidation with Molecular Oxygen

AbstractThe selective oxidation of propylene with O2 to propylene oxide and acrolein is of great interest and importance. We report the crystal‐plane‐controlled selectivity of uniform capping‐ligand‐free Cu2O octahedra, cubes, and rhombic dodecahedra in catalyzing propylene oxidation with O2: Cu2O octahedra exposing {111} crystal planes are most selective for acrolein; Cu2O cubes exposing {100} crystal planes are most selective for CO2; Cu2O rhombic dodecahedra exposing {110} crystal planes are most selective for propylene oxide. One‐coordinated Cu on Cu2O(111), three‐coordinated O on Cu2O(110), and two‐coordinated O on Cu2O(100) were identified as the catalytically active sites for the production of acrolein, propylene oxide, and CO2, respectively. These results reveal that crystal‐plane engineering of oxide catalysts could be a useful strategy for developing selective catalysts and for gaining fundamental understanding of complex heterogeneous catalytic reactions at the molecular level.