Vinyl Acetate Synthesis Research Articles

Enhanced metal-support interaction over Pd-Au/TiO2 catalysts for vinyl acetate synthesis

The reaction of ethylene and acetic acid to produce vinyl acetate (VAM) was investigated on Pd-Au nanoparticles (NPs) supported on TiO2. Compared with the commercial catalyst Pd-Au/SiO2, Pd-Au/TiO2 exhibited a higher turnover frequency (TOF), likely due to the formation of smaller Pd-Au NPs (∼1.9 nm) and metal support interactions (MSI) between TiO2 with Pd-Au NPs. We found that the oxygen vacancies (OVs) of the TiO2 were regulated by adjusting the reduction temperature, facilitating electron transfer from TiO2 to the Pd-Au NPs, leading to enhanced MSI. In situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTs) and density functional theory (DFT) calculations indicated that the electron-rich Pd-Au NPs of Pd-Au/TiO2 catalyst enhanced O2 activation for increased TOF, and also promoted AcOH dehydrogenation and the key reaction of ethylene and acetate coupling. Our findings demonstrated that reducible supports could effectively influence the electronic properties of Pd-Au NPs through the construction of MSI, thereby enhancing catalytic activity.

Mechanistic Insights on Coverage-Dependent Selectivity Limitations in Vinyl Acetate Synthesis.

Developing improved catalysts for sustainable chemical processes often involves understanding atomistic origins of catalytic activity, selectivity, and stability. Using density functional theory and steady-state kinetic analyses, we probe the elementary steps that form decomposition products that limit selectivity in vinyl acetate (VA) synthesis on Pd surfaces covered with acetate species. Acetate formation and coupling with ethylene control the VA formation catalytic cycle and steady-state coverage, but acetate and ethylene can separately decompose to form CO2. Both decompositions involve initial C-H activations at acetate vacancies, followed by additional C-H activations and eventual C-O formations and C-C cleavages involving reactions with molecular oxygen. Acetate decomposition paths with non-oxidative kinetically-relevant steps exhibit similar free energy barriers to oxidative paths. In contrast, the non-oxidative ethylene path involving an ethylidyne intermediate exhibits a much lower barrier than paths with oxidative kinetically-relevant steps. Ethylene decomposition is very facile at low coverages but is more coverage-sensitive, leading to similar decomposition and VA formation barriers at coverages accessible at steady state, which is consistent with moderate VA selectivity in measurements and ethylene vs. acetate decomposition contributions assessed from regressed kinetic parameters. These insights provide a detailed framework for describing VA synthesis rates and selectivity on metallic catalyst surfaces.

Mechanistic insights into ethylene catalytic combustion and CO2 formation in vinyl acetate synthesis

Vinyl acetate is a crucial monomer for the production of polyvinyl alcohol and polyvinyl acetate, with extensive applications in the photovoltaic and pharmaceutical industries. CO2 is the primary by-product in the synthesis of vinyl acetate, significantly burdening the separation process and impacting the ecological environment. Reducing CO2 generation at the source is an effective solution. In the vinyl acetate synthesis process, CO2 is primarily produced through the catalytic combustion of ethylene. However, the reaction mechanism of ethylene catalytic combustion on Pd-based catalysts in vinyl acetate synthesis remains incomplete, with existing mechanisms presenting certain limitations. Therefore, further investigation into the reaction mechanism of ethylene catalytic combustion leading to CO2 formation on Pd-based catalysts is necessary.This study employs density functional theory to calculate the reaction mechanism of ethylene catalytic combustion on the Pd(100) surface, obtaining elementary reaction kinetics data. Based on these data, the kinetic Monte Carlo method was used to investigate the reaction process of ethylene catalytic combustion, revealing the predominant pathway for CO2 formation. This research provides targeted strategies for catalyst modification. It aims to improve the understanding of the reaction mechanism of ethylene catalytic combustion in vinyl acetate synthesis, reduce the consumption of ethylene in by-product formation, enhance vinyl acetate yield and ethylene utilization, and ultimately decrease CO2 production, thereby lowering carbon emissions.

Single-Atom Alloy Formation via Reaction-Driven Catalyst Restructuring.

We demonstrate that single-atom alloy catalysts can be made by exposing physical mixtures of monometallic supported Cu and Pd catalysts to vinyl acetate (VA) synthesis reaction conditions. This reaction induces the formation of mobile clusters of metal diacetate species that drive extensive metal nanoparticle restructuring, leading to atomic dispersion of the precious metal, smaller nanoparticle sizes than the parent catalysts, and high activity and selectivity for both VA synthesis and ethanol dehydrogenation reactions. This approach is scalable and appears to be generalizable to other alloy catalysts.

Mechanistic aspects of Pd-catalyzed ethylene decomposition in vinyl acetate synthesis

Vinyl acetate has a broad range of applications in the market. However, the side reactions of ethylene decomposition and CO2 formation have a significant effect on the selectivity of vinyl acetate synthesis. In this study, a comprehensive reaction network was calculated by the density functional theory (DFT) method to understand the mechanism of the side reactions. The DFT results indicated that the C-H bond is easier to break than C-C bond except for CCH species during ethylene decomposition on the Pd (100) surface. The introduction of Au on the alloy surface inhibits the decomposition of ethylene, which improves the selectivity of the reaction. The adsorbed O atom inhibits the first three dehydrogenation of ethylene but promotes the CCH species dehydrogenation. The pathway for the decomposition of ethylene is: CH2CH2 → CHCH2 → CHCH → CCH → C+CH, and the C-C bond cleavage of CCH is identified as the rate-determining step. The rate-determining step for CO2 formation is the combination of carbon and oxygen atoms to produce CO, and the alloy surface presents a high energy barrier, hindering CO2 production. This study presents a further mechanistic insight into ethylene decomposition and CO2 formation, which has implications for the control of side reactions in vinyl acetate synthesis.

A combination of DFT and kMC to study on the formation mechanism of ethyl acetate during the gas-phase synthesis of vinyl acetate from ethylene on PdAu(100) surface

Vinyl acetate (VAc) is an important chemical raw material for the production of polyvinyl alcohol and polyvinyl acetate, among others. The preparation of vinyl acetate over PdAu catalysts using ethylene, oxygen and acetic acid as raw materials is one of the mainstream processes for the production of vinyl acetate in the world. The by-product ethyl acetate in this process is more difficult to be completely removed, and it is an impurity component in vinyl acetate products that needs to be strictly controlled in content. However, studies on the mechanism of ethyl acetate generation have not been reported, which limits the improvement of the purity of vinyl acetate products and the optimization of the ethyl acetate separation process. In this paper, the mechanism of ethyl acetate generation during ethylene vinyl acetate reaction on PdAu catalysts was systematically investigated using a combination of density functional theory (DFT) and kinetic Monte Carlo (kMC) simulations.The results show that the species tend to adsorb to the Pd-Au bridge sites, diagonal Pd-Pd vacancies, and diagonal Pd-Au vacancies of PdAu(100), and the Pd on the catalyst surface interacts more strongly with the adsorbed species. The dominant pathway for the generation of ethyl acetate on PdAu(100) is CH2CH2* + O*→ CH2CH* + H* → CH3CH* + CH3COO* → CH3COOCHCH3* + H* → CH3COOCH2CH3*, where the hydrogenation of CH2CH* to CH3CH* is the rate-control step in the dominant pathway for the generation of ethyl acetate. This step has an energy barrier of 1.09 eV and a reaction heat of 0.90 eV. The study of the generation mechanism of the by-product ethyl acetate in this paper is hoped to provide more targeted guidance and suggestions for the modification of Pd-Au catalysts, so as to reduce the generation of ethyl acetate as a by-product, to reduce the energy consumption required for the separation, and to enhance the purity of vinyl acetate products.

Promotional Role of Acid Sites on Aluminosilicate-Supported PdAu for Vinyl Acetate Synthesis

Promotional Role of Acid Sites on Aluminosilicate-Supported PdAu for Vinyl Acetate Synthesis

Optimization of Autoclave Reactors to Improve Bearing Life Using the Taguchi Method and the Response Surface Methodology

Plastic pervasiveness in daily life has increased in tandem with population growth. Ethylene–vinyl acetate (EVA) is emerging as a popular compound for manufacturing plastic, which is obtained from ethylene and vinyl acetate synthesis. EVA is produced using autoclave reactors, which often encounter bearing damage under specific operating conditions. This research aims to optimize the parameters in autoclave reactors to enhance bearing life. The study focuses on two crucial factors: the number of impellers and the temperature, with bearing life as the response variable. Simulations using finite-element analysis were conducted to obtain the fatigue life of bearings and validated using real-time company data stating the damage of bearings within 80 days. The optimization process employed the Taguchi method (TM) and the response surface methodology (RSM). A comparison of these techniques revealed that temperature had the most significant influence on the response. Interestingly, both methods yielded the same optimal parameters: seven impellers and a temperature of 150 °C. The simulation results using these optimized parameters demonstrated a noteworthy 3.095% increase in bearing life compared to the initial design. The RSM outperformed the Taguchi method in accurately predicting response values with minimum prediction error under optimal conditions.

Theoretical insights into the dissociation and oxidation of ethylene during vinyl acetate synthesis

Gas phase synthesis of vinyl acetate from ethylene over Pd-Au catalyst is one of the mainstream processes. During the synthesis of vinyl acetate, the surface C generated by the dissociation of ethylene can be doped into the lattice of Au to form interstitial C. The synergistic effect of interstitial C and Au can promote the production of vinyl acetate. However, the formation mechanism of surface C is not clear. In addition, CO2 is formed during the dissociation and oxidation of ethylene. In order to reduce carbon emissions, it is also necessary to clarify the formation mechanism of CO2. In this study, the reaction mechanism for the dissociation and oxidation of ethylene on the PdAu(100) surface was investigated by density functional theory and kinetic Monte Carlo, and the formation pathways of surface C and CO2 were clarified.The results show that the generation pathway of surface C is CH2CH2→ CH2CH→ CHCH→ CHC→ CC→ CCO→ C+CO. The rate control step is CCO→C + CO with energy barrier of 1.39 eV and reaction heat of 0.52 eV. The generation pathway of CO2 is C → COH → CO → CO2. The rate control step is C+OH→COH with energy barrier of 0.71 eV and reaction heat of -1.12 eV. Clarification of the reaction mechanism for dissociation and oxidation of ethylene on the PdAu(100) surface and the formation pathways of surface C and CO2 can more specifically reduce the consumption of ethylene for by-products, better construct the synergism of surface C and Au, and reduce the emission of CO2 in the process of catalyst improvement and optimization.

A DFT study on the mechanism of acetaldehyde generation during vinyl acetate synthesis from gas-phase ethylene acetoxylation on Pd/Au (100) surface

Acetaldehyde (CH3CHO) is an important by-product in the reaction of ethylene to vinyl acetate (VAC). However, the mechanism of the generation of CH3CHO has been little studied. In this paper, we designed a reaction network for the possible generation of acetaldehyde from intermediate species on Pd/Au catalysts, including three reaction paths. Stable adsorption configurations of the species involved in each elementary reaction were identified by Density Functional Theory (DFT) calculations and the charge changes on the catalyst surface during the adsorption process as well as the structural parameter changes of the adsorption configurations were compared. Based on this, we calculated the kinetic parameters on three reaction paths and combined with Kinetic Monte Carlo (KMC) simulations to found the dominant path and rate-determining step to help understand the mechanism of acetaldehyde generation on the surface of Pd/Au (100). Results suggest that species involved in the reactions are adsorbed mainly on Pd-Au bridge sites, Pd top sites, and Pd-Pd intermediate vacancies and species structure changes after adsorption. CHCH, CH2CH, and CH3CH could all generate CHxCHO by reacting with O species or OH species, and the energy barrier for reactions with O species are all lower than those for reactions with OH species. The dominant pathway for acetaldehyde generation on Pd/Au (100) surface is CH2CH2 → CH2CH→ CH2CHO → CH3CHO and the ethylene dehydrogenation elementary reaction is the rate-determining step.

Oxygen effect on the synthesis of vinyl acetate on Pd (100) and Pd/Au (100) surfaces: A periodic DFT study

Vinyl acetate is mainly produced by oxidative acetoxylation of ethylene over the Pd/Au bimetallic heterogeneous catalyst. This process requires the involvement of oxygen, but the role of oxygen has not been well studied. The oxygen effect on the synthesis of vinyl acetate is of considerable economic benefit, as the process conditions can be better optimized. In this study, the O2 adsorption and dissociation on the Pd (100) and Pd/Au (100) surfaces, the effect of the co-adsorbed O atom on the C2H4, CH3COOH and CH3COO adsorptions, and the reaction mechanism have been investigated using ab initio density functional theory (DFT) method. The calculated results suggest that the O adatoms are detrimental to the adsorption of C2H4 and CH3COO, but favorable for CH3COOH. For the reaction, the O adatoms reduce the energy barrier of CH3COOH dehydrogenation and VA formation, and increase the reaction enthalpy (more exothermic). This study provides further mechanistic insight into VA synthesis on the Pd-based catalysts.

Synthesis of Vinyl Acetate Monomer Over PdCu Alloys: The Role of Surface Oxygenation in the Reaction Path

AbstractThis work uses sol–gel and sonochemical methods to prepare bimetallic PdCu catalysts supported on modified ZrO2 with Ti and Al. The catalysts are tested for vinyl acetate synthesis from ethylene, acetic acid, and oxygen, varying the reaction temperature for two catalysts prepared, which show higher activity. Catalysts characterization results show bimetallic species and distort alloys with a dispersed distribution of active metal onto the support. The in situ reaction by DRIFT‐MS identifies the surface formation of main intermediates like palladium acetate monomers and mono and bidentate intermediates, associated to vinyl acetate formation, like vinyl hydrogenated species over PdCu. Finally, this behavior will be attributed to the bimetallic distortions of PdCu samples, provided by interaction effects between PdCu and supports, indicating a more exposition of PdCu species suitable for the reaction, according to high‐resolution transmission microscopy electron microscopy results for PdCu/ZrTi sample. Thus, this sample exhibits a minimal formation of sub‐products and catalytic stability for 18 hh. These results evidence the participation of hydroxyls and oxygen vacancies of the catalyst in the catalytic reaction measured in situ, monitoring the products formed at the reactor outlet. Finally, it is proposed a reaction pathway as a function of reaction conditions.

Molecular insights into the effects of N-doping on synthesis of vinyl acetate over carbon-supported zinc acetate

This work provides a mechanistic insight into the effects of different type of N-doped carbon-supported catalysts on the synthesis of VAc by the acetylene method. The introduction of N-doping can enhance the adsorption of acetylene and acetic acid molecules onto the catalyst supports. The N6–3 surface which with three pyridinic-N shows the most adsorption stability for both acetylene and acetic acid molecules, and facilitates the synthesis of VAc efficiently. While the N6 surface which with the pyridinic-N is obstructive to the VAc formation.

Theoretical study on the synthesis of vinyl acetate from acetylene and acetic acid over nonmetallic catalysts with different carbon-nitrogen ratios

At present, the acetylene acetic acid reaction catalysts studied are metal catalysts. Whether there are non-metallic materials that can catalyze the reaction is very worth exploring. In this study, we used density functional theory (DFT) to calculate the feasibility of preparing vinyl acetate (VAc) on four CN non-metallic materials (C2N, C3N, C4N and C5N) under the reaction conditions of 1 atm, 393.15–493.15 K at B3LYP/6-31G(d, p) level. It is found that after considering the reaction temperature, only C2N and C3N show good adsorption capacity for acetylene and acetic acid, and C3N has stronger adsorption capacity for reactants. After that, we calculated and simulated the reaction process of acetylene acetic acid reaction catalyzed by four CN materials. It is found that among the four CN materials, the energy barrier of the reaction rate control step of C3N is the lowest (the free energy barrier of the rate control step is only 30.57 kcal/mol at 393.15 K), and the interior of CN non-metallic materials has higher activity than the boundary of hydrogen sealing. We also found that the reaction process on CN non-metallic material is consistent with the acid catalysis mechanism, which shows that the non-metallic catalyst is theoretically feasible for catalyzing the acetic acid acidification of acetylene, and the two-dimensional C3N material is likely to be a potential non-metallic catalyst for the preparation of vinyl acetate by acetylene gas phase method.

A density functional theory study on the effect of acetylene on vinyl acetate synthesis from acetoxylation of ethylene over Pd-Au catalysts

In this work, the reaction network of acetylene on Pd-Au catalyst was constructed firstly, and the single adsorption configurations and adsorption energies and electronic properties of key species in the reaction network were calculated with Density Functional Theory (DFT). It was found that most of the species tend to be adsorbed on the sites around Pd atoms and acetylene does not occupy the active site of ethylene. Then the energy barrier and reaction energy of the related reaction of acetylene on the Pd-Au surface and the geometric configuration of the transition state were calculated through DFT. Acetylene is highly reactive and oxidation, hydrogenation and polymerization were easy to occur. Among all the reactions, the oxidation reaction had the most competitive advantage. CO2 was the most in the final product, followed by the intermediate product C2H3. CO2 and C2H3 have no adverse effect on the reaction system, so the trace of acetylene in the raw material ethylene had a very weak effect on the vinyl acetate reaction system.

Molecular Insights into the Effects of N-Doping on Synthesis of Vinyl Acetate Over Carbon-Supported Zinc Acetate

Molecular Insights into the Effects of N-Doping on Synthesis of Vinyl Acetate Over Carbon-Supported Zinc Acetate

Performance Study of Zn-Co-Ni/AC Catalyst in Acetylene Acetylation

Zinc acetate (Zn(OAc)2) loaded on activated carbon (AC) is the most commonly used catalyst for the industrial synthesis of vinyl acetate (VAc) using the acetylene method. The aim of this study is to optimize the Zn(OAc)2/AC catalyst by adding co-catalysts to improve its activity and stability. Ternary catalysts were synthesized by adding Co and Ni to the Zn(OAc)2/AC catalyst (Zn-Co-Ni/AC). Due to the strong synergistic effect among promoter Co, Ni, and the active component of Zn(OAc)2, the resulting catalyst is capable to absorb more acetic acid and less acetylene. The stability and activity of Zn-Co-Ni/AC catalyst have been improved through electron transfer to alter the electron cloud density around the Zn element. Under the same reaction conditions, the activity of Zn-Co-Ni/AC catalyst was enhanced by 83% compared to that of Zn(OAc)2/AC, and the activity was still as high as 30.1% after 120 h of testing.

Molecular insights into the vinyl acetate synthesis on Pd/Au (1 1 1) Surface: Effects of potassium ion

The surface structure of bimetallic Pd/Au catalyst, accompanied by the presence of potassium acetate (KOAc) are critical for synthesis of vinyl acetate (VAc). In this study, different configurations of the Pd/Au (111) surface were constructed. The density functional theory (DFT) was used to investigate the adsorption of ethylene and acetate on the Pd/Au (111) surface. The reaction mechanism of VAc formation was studied by following the Samanos pathway. The existence of potassium ion (K+) enhanced the adsorption of ethylene and acetate on the Pd/Au (111) surface, and promoted the dehydrogenation of acetic acid. The Pd/Au (111) surface configuration, with two adjacent palladium atoms embedded on the gold surface, is the most favorable surface structure for VAc synthesis. The introduction of K+ was obstructive to the formation of ethyl acetate-like intermediates, but facilitated β-H elimination during the formation of VAc. This work provides a deeper mechanistic understanding of VAc synthesis on the Pd/Au (111) surface, which could shed some light on the catalysts design and the industrial control of VAc synthesis.

Influence of the Nature of the Retainer (Carrier) on the Catalytic Activity of the Catalyst in the Gas-Phase Synthesis of Vinyl Acetate from Ethylene

The article examines the effect of γ-Аl2О3, high-silicon zeolite (HSZ), bentonite, expanded clay, the nature of bentonites, their porous structure, methods of preparation and modes on the activity of the catalyst consisting of palladium, copper and potassium acetate for the vapour phase synthesis of ethylene-vinyl acetate. IR spectra of the synthesized samples were recorded in the reflection mode in the range 400–4000 cm–1 using a Nexus Nicolet Fourier transform IR spectrometer (Thermo Scientific). Thermal studies (TG/DTG-DTA) were carried out on an STA-1500H thermal balance. The specific surface area was determined by the method of low-temperature nitrogen adsorption using a Quantachrome Autosorb-6B instrument. X-ray structural analysis (XRD) was investigated in the range 5–80° 2θ on a DRON 3M diffractometer using a CuKα (λ=1,54178 A) radiation source. X-ray photoelectron spectra were recorded on a SERIES 800XPS Kratos photoelectron spectrometer. Transmission electron microscopy (TEM) photomicrographs were obtained using a JEM100CX-II electron microscope.The specific surface area was determined by low-temperature argon adsorption on a Crystallux-4000M gas chromatograph. The size and radius of the pores were determined using mercury porometry directly on the amount of mercury compressed in them in a mercury porometric device that allows the measurement of the size of the pores. Vinyl acetate synthesis in a pilot device on a catalyst containing 0,4%Рd+4%Cu+7%CH3COOK/HSZ for 2000 hours at a temperature of 165 ℃, a pressure of 0.1 MPa, a vapour-gas mixture at a volumetric rate of 2000 h-1 and the amount of oxygen in the mixture with ethylene Performed when 7 vol.%. During 2000 hours of operation, the catalyst activity was 95-97% selectivity at 370-350 g of vinyl acetate/l. cat. hours.

Влияние количества активных компонентов катализатора на выход продукта при синтезе винилацетата из этилена и уксусной кислоты

The development of active and selective catalysts for the synthesis of vinyl acetate from ethylene and acetic acid, the effect of the amount and ratio of individual components of the catalyst to control the catalytic properties of the introduced components were studied. In vinyl acetate synthesis, the effects of each component were studied to describe the effect of catalyst constituents on its properties, and empirical one-factor mathematical dependencies were obtained. Their generalized mathematical relationships of the activities of the catalysts, defined as the rates of the reactions of the formation of vinyl acetate and CO2, have been proposed. As a result of the research, a mathematical model was proposed to select the most optimal composition of the catalyst. The activity of the catalyst containing 0.4%Pd+4%Cu+7%CH3COOK/HSZ averaged 700 g VA/(l×cat×h) at 93–97% selectivity of ethylene-vinyl acetate formation.