Reactor Feed Research Articles

Co-pyrolysis of biomass woodchips with Ca-rich oil shale fuel in a continuous feed reactor

Co-pyrolysis of biomass woodchips with Ca-rich oil shale fuel in a continuous feed reactor

Artificial Intelligence for Hybrid Modeling in Fluid Catalytic Cracking (FCC)

This study reports a novel hybrid model for the prediction of six critical process variables of importance in an industrial-scale FCC (fluid catalytic cracking) riser reactor: vacuum gas oil (VGO) conversion, outlet riser temperature, light cycle oil (LCO), gasoline, light gases, and coke yields. The proposed model is developed via the integration of a computational particle-fluid dynamics (CPFD) methodology with artificial intelligence (AI). The adopted methodology solves the first principle model (FPM) equations numerically using the CPFD Barracuda Virtual Reactor 22.0® software. Based on 216 of these CPFD simulations, the performance of an industrial-scale FCC riser reactor unit was assessed using VGO catalytic cracking kinetics developed at CREC-UWO. The dataset obtained with CPFD is employed for the training and testing of a machine learning (ML) algorithm. This algorithm is based on a multiple output feedforward neural network (FNN) selected to allow one to establish correlations between the riser reactor feeding conditions and its outcoming parameters, with a 0.83 averaged regression coefficient and an overall RMSE of 1.93 being obtained. This research underscores the value of integrating CPFD simulations with ML to optimize industrial processes and enhance their predictive accuracy, offering significant advancements in FCC riser reactor unit operations.

Effect of reactor temperature and feeding ratio on fed-batch composting of household food waste and green wastes

Currently, most regions of China still treat household food waste (HFW) in a centralized way, which increases the cost of collection and transportation. Therefore, it is necessary to develop a novel technology to treat HFW on site. In this study, a fed-batch reactor was designed to investigate the effect of reactor temperature and feeding ratio on the co-composting of HFW and green wastes (GW). The results showed that an increase in reactor temperature could promote composting efficiency and compost end-product maturity. When the reactor temperature was 50 °C, the moisture (4.1%), weight loss rate (87.3%), organic matter (OM) content (66.1%), and seed germination index (74.1%) of the compost reached the optimum. When the feeding ratio was 2:1, the decomposition rate of OM was the fastest, and the weight loss rate, OM content, and C/N ratio of the compost were 89.3%, 63.1%, and 12.6, respectively. According to the first-order kinetics, it was found that the reactor temperature had a greater impact on fed-batch composting than the feeding ratio. This study suggested that fed-batch composting is a promising technique for the utilization of HFW and GW and provided guidance for the scale-up application of bed-batch reactors.

Study on the process of producing crotonaldehyde from acetaldehyde catalyzed by Zr-β zeolite

As an essential raw material of chemical industry, crotonaldehyde is mainly used to produce sorbic acid, which is a kind of safe food preservative. The nowadays production process of crotonaldehyde adopts sodium hydroxide solution and acetic acid in series as catalysis, which cause serious problems such as salinity waste water and equipment corrosion. Therefore, Zr-β zeolite was developed to catalyze the production of crotonaldehyde from acetaldehyde gas–solid reaction process in our group. This catalyst showed the potential of industrial application for its 94 % selectivity and stability. This paper aims to develop a technological process to produce crotonaldehyde from acetaldehyde based on the newely-researched-out Zr-β zeolite catalyst. According to experimental results of reaction condition and product distribution, a technological process consisting of (1) aldol condensation reaction and raw material recovery section, (2) crotonaldehyde concentration and refinement section, (3) 2-methyl-2-cyclopenten-1-one (MCP) and acidic impurity removal section was established. Mechanical supercharging was employed in section (1) to elevate the heat grade of reactor effluent to heat the reactor feed. Pre-concentration followed by azeotropic distillation was proposed to purify croton aldehyde product. The removal of little MCP in the re-used water was accomplished by evaporating MCP at the top of the column based on our previous finding that MCP-water could form minimum azeotrope. As a result, the purity of crotonaldehyde reached 99.92 wt% and water content reduced below 10 ppm in product, which is much better than the product standard required crotonaldehyde purity 99.5 % and water content 2000 ppm. Based on optimum process, heat exchange network was further optimized with pitch point method, and at last the required heat load was 2.25 Gcal per ton of crotonaldehyde product. The problem of generating salinity waste water in the traditional process was solved thoroughly, which meant that this is a more environmentally friendly process to produce crotonaldehyde.

Simultaneous design and part-load optimization of an industrial ammonia synthesis reactor

Power-to-Ammonia is widely discussed as a way to store and transport renewable energy. Conventional design methods in which only one operating point is considered can be inadequate to design such plants. This work carries out an optimization over two plant models at maximum and minimum load, respectively, for an integrated assessment of the optimum design and operating strategy. We obtain Pareto fronts for several sets of degrees of freedom representing the trade-off between load flexibility and plant cost. At the same time, the optimization provides suitable operating points for both load cases for each design. We found that the minimum achievable load can be reduced from 22 to 10% with an additional reactor cost of only 3 to 7% caused mainly by an increase in the heat exchanger area of the integrated feed-effluent heat exchanger. Increasing the ammonia fraction in the reactor feed is favorable if loads below 13% are targeted. The Pareto front was improved significantly by adding a split option to the reactor and additionally allowing the solver to increase the ammonia fraction in the reactor feed.

Kinetics of silica-assisted pyro-hydrolysis of CaCl2 waste for the recovery of hydrochloric acid (HCl): Effect of interaction between CaCl2 and SiO2

Pyro-hydrolysis of CaCl2 waste for HCl acid regeneration is a circular process enabling the sustainable development of the critical energy mineral extraction industry. However, the lack of detailed kinetic information has posed challenges in implementing this technology. An acidic additive such as silica (i.e., SiO2) is essential to make this reaction thermodynamically available, yet its reaction kinetics are still unknown. This study aims to reveal the detailed reaction kinetics of the SiO2-assisted pyro-hydrolysis of CaCl2 under two typical industrial settings for the feeding of reactants, physical mixing of powders and spray feeding where CaCl2 solution is expected to initially undertake drying and subsequently deposit onto the solid silica powders for a close contact. The isothermal experiment results revealed that the HCl release rate is strongly temperature-dependent. Comparatively, the CaCl2-deposited silica demonstrated a significantly faster release of HCl than the physically mixed sample, achieving 92% HCl release within 30 min at 800 °C. SEM analysis confirmed a closer inter-particle contact for the CaCl2-deposited sample, which is responsive to the accelerated HCl release. In addition, the experimental results were successfully fitted by a variable activation energy model which discovered a steady increase of the activation energy with the progression of the HCl release for both feedstock modes. This is primarily due to the continuous change on the formation of intermediates. The model also confirmed a lower activation energy for the CaCl2-deposited sample than its physically mixed counterpart at any given conversion extent of CaCl2. In contrast, for the physically mixed sample, the loose inter-particle contact led to the formation of a stable intermediate, Ca(OH)Cl, which can readily reverse to CaCl2, thereby slowing down the overall HCl release rate.

Bayesian optimization of HDPE copolymerization process based on polymer product-process integration

A framework for finding an optimal operating point of HDPE with the target properties is proposed. A bimodal high-density polyethylene (HDPE) copolymerization process is established to calculate molecular weights, dispersity, and predict properties. The process incorporates a probability-based description method with reactivity ratio to describe the content of monomer A/B and sequence distribution. A properties prediction model is established to predict glass transition temperature, melt temperature, melt index, and density. Bayesian optimization algorithm is utilized to optimize the process. This algorithm combines Gaussian process regression and an expectation improvement model to determine the optimal mass flow of feed and temperature of reactors. The objective function is modified using a penalty function to incorporate property constraints. The optimization goal is to maximize profits by identifying the optimal composition of feed and reactor temperature. Optimized bimodal HDPE copolymerization process leads to a significant increase in profit, with a 21.8 % improvement compared to the original process. The effect of melt index, is considered in determining the optimal operation range and maximizing profit. This provides valuable guidance for producing new grades of HDPE.

Dynamic modelling of cross-flow printed circuit heat exchangers for multistage reactor intercooling

A reduced-order dynamic model of a cross-flow printed circuit heat exchanger was developed to study both steady-state and transient performance under conditions that would be encountered in multistage catalytic combustion reactors to better understand how they can be used to minimize fluctuations in heat-integrated reactors and intensified processes. Previous transient models for cross-flow heat exchangers rely on an initial steady state and apply only for changes in inlet temperature, but this work presents a model that can be applied to intermediate states or multiple concurrent upstream process changes. Steady-state simulations showed that larger channels reduce volumetric heat transfer performance and effectiveness due to convective resistance. Furthermore, larger channel spacing increases effectiveness but also reduces compactness. Operating temperature was found to have a minimal effect on the overall heat transfer coefficient and effectiveness within the range of conditions studied, and operating pressure was found to have no effect on heat transfer. Transient analyses showed that the response to a unit step in temperature matches closely with an analytical infinite gas velocity model, both for time constants and the overall thermal response, with initial variations in outlet temperatures from ideal-case models below 3.8 % of unit step magnitudes, and average differences below 0.75 %. Transient analyses also show the effects of a finite fluid velocity which is critical in the transient response of large heat exchangers. The presented numerical model can also be more easily extended to complex configurations and can be applied to other changes in inlet conditions such as changing composition and flow rates as are found in combustion applications. A three-fluid thermal management system for a multistage packed-bed microreactor using printed circuit heat exchangers is proposed and modelled to provide a method for temperature regulation and pre-heating of fresh reactor feed.

Nanosized Silica-Supported 12-Tungstophosphoric Acid: A Highly Active and Stable Catalyst for the Alkylation of p-Cresol with tert-Butanol

12-Tungstophosphoric acid supported on nanosilica (TPA/SiO2) was employed as a catalyst for the tertiary butylation of p-cresol using tertiary butanol as an alkylating agent. The TPA/SiO2 catalyst was synthesized using the wet impregnation method followed by steaming at 150 °C for 6 h. The catalysts were characterized by means of X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) analysis. The surface acidity of the untreated and steamed catalysts was characterized via FTIR and DSC thermal analysis using pyridine as a probe molecule. The fresh and spent catalysts were characterized via TGA analysis. The catalytic activity studies showed that the steamed catalyst displayed higher activity, with a higher desired yield of 2-tert-butyl cresol (2-TBC) compared to the untreated catalyst, and that this activity was related to the presence of stronger Brønsted acid sites in the steamed catalyst. A detailed analysis of the TPA/SiO2 steamed catalyst was performed to study the effects of reactant time-on-stream, reactant feed rate, reaction temperature, and the molar ratio of tert-butanol to p-cresol. The optimum reaction temperature, tert-butanol/p-cresol molar ratio, feed rate, and time-on-stream were 413 K, a molar ratio of 2:1, 6 mL/min, and 2 h, respectively. The present study demonstrates that the TPA/SiO2 catalyst exhibits high activity in terms of % conversion and high % selectivity of 2-TBC under the optimized conditions. The characterization of fresh and spent catalysts confirmed the occurrence of coke deposition after the catalytic reaction. The catalyst was regenerated via heat treatment at 400 °C for 5 h. The regenerated catalyst was reused for subsequent runs for three cycles without showing a loss in its activity.

Simulated 13C chemical shifts used to investigate zeolite catalysis

Zeolites have been successfully applied on a wide range of reaction processes (Methanol to Hydrocarbons, Fluid Catalytic Cracking, etc) and continue to attract academic and industrial investigations. Understanding of the reaction mechanisms involved in zeolite catalysis has been a long standing issue due to the wide range of intermediates and products involved, which has hindered the industrial implementation of these materials. Thus, in order to determine and discriminate between each type of compound involved in the complex reaction mixture, computational simulations have been applied to analyse the 13C chemical shifts of a wide range of known or proposed intermediates and products. The first part of this study focuses on calculating the 13C chemical shifts of C1-C3 compounds commonly part of the reactant feed, comparing the results of mobile versus immobile states and determining which compounds could have their 13C chemical shifts superimposed over others. The second part focuses on C4-C6 olefins, analysing the differences stemming from: position of double bond, ramified structure, mobile and chemical state. Finally, the third part translates the same approach from the olefins study on aromatic derivatives.

Autothermal Reforming of Methane: A Thermodynamic Study on the Use of Air and Pure Oxygen as Oxidizing Agents in Isothermal and Adiabatic Systems

In this paper, we analyze the autothermal reforming (ATR) of methane through Gibbs energy minimization and entropy maximization methods to analyze isothermic and adiabatic systems, respectively. The software GAMS® 23.9 and the CONOPT3 solver were used to conduct the simulations and thermodynamic analyses in order to determine the equilibrium compositions and equilibrium temperatures of this system. Simulations were performed covering different pressures in the range of 1 to 10 atm, temperatures between 873 and 1073 K, steam/methane ratio was varied in the range of 1.0/1.0 and 2.0/1.0 and oxygen/methane ratios in the feed stream, in the range of 0.5/1.0 to 2.0/1.0. The effect of using pure oxygen or air as oxidizer agent to perform the reaction was also studied. The simulations were carried out in order to maintain the same molar proportions of oxygen as in the simulated cases considering pure oxygen in the reactor feed. The results showed that the formation of hydrogen and synthesis gas increased with temperature, average composition of 71.9% and 56.0% using air and O2, respectively. These results are observed at low molar oxygen ratios (O2/CH4 = 0.5) in the feed. Higher pressures reduced the production of hydrogen and synthesis gas produced during ATR of methane. In general, reductions on the order of 19.7% using O2 and 14.0% using air were observed. It was also verified that the process has autothermicity in all conditions tested and the use of air in relation to pure oxygen favored the compounds of interest, mainly in conditions of higher pressure (10 atm). The mean reductions with increasing temperature in the percentage increase of H2 and syngas using air under 1.5 and 10 atm, at the different O2/CH4 ratios, were 5.3%, 13.8% and 16.5%, respectively. In the same order, these values with the increase of oxygen were 3.6%, 6.4% and 9.1%. The better conditions for the reaction include high temperatures, low pressures and low O2/CH4 ratios, a region in which there is no swelling in terms of the oxygen source used. In addition, with the introduction of air, the final temperature of the system was reduced by 5%, which can help to reduce the negative impacts of high temperatures in reactors during ATR reactions.

Experimental and modeling studies of intermediate pyrolysis of wood in a laboratory-scale continuous feed retort reactor

Experiments and simulations in Aspen Plus® were performed to study the intermediate pyrolysis of wood in a continuous-feed retort reactor. The experiments were conducted at temperatures of 450, 500, and 650 °C, wood particle sizes of <1.4 mm, and reactor feeding rate of 0.15 kg/h. The experiment recorded a maximum liquid yield of 44.2 wt% at a pyrolysis temperature of 450 °C, while the simulation predicted a maximum yield of 49.1 wt% at 415 °C. Similar results were also reported in other studies. The ultimate analysis of the biochar produced was determined experimentally and by simulation. Results obtained from the experiment and the model were in good agreement. The model's ability to predict the composition of bio-oil was demonstrated through a comparison of its predicted distribution with literature. Furthermore, the study revealed that prolonged char presence in the retort improved biochar quality instead of increasing volatile yields.

Using guaiacol as a capping agent in the hydrothermal depolymerisation of kraft lignin

Abstract The depolymerisation of softwood kraft lignin was investigated, under hydrothermal conditions at 290 °C and 250 bar, with guaiacol in the reactor feed to evaluate its impact on the formation of char and on the molecular weights of the products. The effect of residence time was investigated in the time span 1–12 min. Lignin is depolymerised during the process and guaiacol is both formed and consumed during the reaction, with clearly noticeable changes as early as in the first minute of reaction. Although the addition of guaiacol in the reactor feed causes a reduction in the weight average molecular weight of the products, the yield of char increases. Longer residence times result in repolymerisation of the reaction products as well as a further increase in the yield of monoaromatic components and char.

A wireless, battery-free device enables oxygen generation and immune protection of therapeutic xenotransplants in vivo

The immune isolation of cells within devices has the potential to enable long-term protein replacement and functional cures for a range of diseases, without requiring immune suppressive therapy. However, a lack of vasculature and the formation of fibrotic capsules around cell immune-isolating devices limits oxygen availability, leading to hypoxia and cell death in vivo. This is particularly problematic for pancreatic islet cells that have high O2 requirements. Here, we combine bioelectronics with encapsulated cell therapies to develop the first wireless, battery-free oxygen-generating immune-isolating device (O2-Macrodevice) for the oxygenation and immune isolation of cells in vivo. The system relies on electrochemical water splitting based on a water-vapor reactant feed, sustained by wireless power harvesting based on a flexible resonant inductive coupling circuit. As such, the device does not require pumping, refilling, or ports for recharging and does not generate potentially toxic side products. Through systematic in vitro studies with primary cell lines and cell lines engineered to secrete protein, we demonstrate device performance in preventing hypoxia in ambient oxygen concentrations as low as 0.5%. Importantly, this device has shown the potential to enable subcutaneous (SC) survival of encapsulated islet cells, in vivo in awake, freely moving, immune-competent animals. Islet transplantation in Type I Diabetes represents an important application space, and 1-mo studies in immune-competent animals with SC implants show that the O2-Macrodevice allows for survival and function of islets at high densities (~1,000 islets/cm2) in vivo without immune suppression and induces normoglycemia in diabetic animals.

Effect of phosphorus limitation on the anammox process under different nitrogen concentrations

The effect of phosphorus limitation on the nitrogen removal performance of the anammox process was investigated using continuous feeding reactors. When the phosphorus supply was stopped under an influent nitrogen concentration of 256 mg-N L−1, a high nitrogen conversion rate of 1.88 kg-N m−3 d−1 was maintained for 17 days. However, during the next 25 days, the nitrogen conversion rate decreased by 16.5%. Subsequently, nitrogen removal activity was recovered entirely by re-adding 0.1 mg-P L−1 of phosphorus. Similar tests were performed at different influent nitrogen concentrations. The results showed that the minimum phosphorus concentrations (MPC) in the influent required to maintain anammox activity at influent nitrogen concentrations of 379 and 502 mg-N L−1 were 0.2 and 0.3 mg L−1, respectively. These results indicate that the MPC increased with N concentration, with an MPC/N of 0.0005. A microbial community analysis based on the 16S rRNA gene amplicon sequencing revealed that two genera of anammox bacteria (Candidatus Kuenenia and Candidatus Jettenia) were presented. The dominant anammox bacteria changed from Candidatus Kuenenia to Candidatus Jettenia after the phosphorus-limitation tests.

The impact of semi-continuous and alternating microbial feeding patterns on methane yield from UASB reactors

Feeding strategy represents one of the most important bioreactor operation parameters, however, how different feeding patterns impact reactor microbiome development and treatment performance in up-flow anaerobic sludge blanket (UASB) reactors has not been systematically investigated. In the present study, three feeding strategies, including continuous feeding, semi-continuous feeding (with starvation-feast cycles), and alternate feeding (with high loading-low loading cycles) were assessed and compared using three laboratory-scale UASB reactors. It was observed that both long and short starvation-feast cycles provided by a semi-continuous feeding strategy failed to sustain stable anaerobic digestion under the conditions examined in the present study, while alternate feeding with high and low loading cycles supported microbial development. This feeding pattern resulted in an average methane yield of 74 ± 8.5% and an effluent COD removal efficiency of 89 ± 2.8%, which is comparable to the reactor operated under a continuous feeding pattern (Methane yield of 72 ± 2.4% and a COD removal efficiency of 87 ± 7.7%). Interestingly, as compared to continuous operation, reactors experienced starvation/feast stress (i.e., semi-continuous feeding) developed significantly higher methanogenic activities once continuous feeding was presumed, with dominant methanogens shifted from Methanosaeta in continuous feeding UASB to Methanosarcina in reactors undergone semi-continuous feeding. It was concluded that reactor feeding strategies can significantly impact microbiome communities in UASB, and an alternate feeding pattern is preferred, as compared to semi-continuous operation when reactor feeding cannot be continuously supplied.

Granular biomass technology for providing drinking water: microbial versatility and nitrate performance in response to carbon source

The aerobic granular biomass technology was optimized for treating nitrate-polluted groundwater based on the biological denitrification processes in order to provide drinking water. Reactors inoculated with granular biomass were operated at progressively lower C/N rate using acetate and methanol to encourage heterotrophic denitrification, in order to meet the recommended requirements described by European Drinking Water Framework Directive. The granulation and long-term stability of granular biomass under low C/N were successful for all stages, demonstrated compactness of granules and absence of filamentous microorganisms. The nitrate removal was similar in methanol- and acetate-fed reactors, occurring in both cases nitrate removal ratios > 80%, and fact allows the selection of one of both depending groundwater polluted case. Also, feeding reactors with 2 C/N ratio showed nitrate removal values of ≥ 95%, treating highly polluted groundwater (100 mg·L−1). The microbial diversity was higher in the methanol-fed reactor with representative phylotypes as Flavobacterium, Cytophagaceae, NS9 marine group, while species richness was higher in the acetate-fed reactor, which was mainly represented by Flavobacterium genus. Statistical analyses revealed the higher resilience of bacterial population on granules fed with acetate, showing more resistance under drop C/N ratio. Oscillating pollution in groundwater during seasonal periods should be treated using acetate as carbon source for denitrification carried out by granular biomass, while stable pollution concentrations over time allow the use of methanol as a carbon source since the greater microbial diversity allows the elimination of other contaminants present in groundwater.

Pyrolysis of mixed plastic fractions – Development of predictive models for yield and oil quality

Pyrolysis of plastic mixtures has shown to form complex mixtures of oil, which is difficult to predict. Interaction effects between plastics have shown to affect both the oil composition and the yield distribution of oil, char, and gas. This work aims to generate models for the prediction of oil and char yield, acid number, and viscosity based on the feed composition. Besides the oil composition based on the reactor feed was mapped. Pyrolysis was performed in a batch reactor with a mixture of PP, PE, EVA, PET, PS and PA, where the content of PET, PS and PA were varied from 0% to 15%. The developed models showed a decrease in oil yield of 10% when 15% PS was interchanged with PET. Char content, acid number, and viscosity were shown to increase with the content of PET and lowered with the content of PS. PA caused an increase in char yield and viscosity, while it did not affect the acid number. The models R2-values varied from 0.87 to 0.96, showing that most of the variation in the responses can be explained by the differences in feed composition. The oil composition was found to mainly consist of hydrocarbons (C10 +), naphta and aromatics with only a small precense of alcohol and acid. The content of aromatic hydrocarbons is increased by the presence of PS, due to formation of styrene and toluene while the acid content increases with the PET content.

Experimental and numerical investigation of the reaction of 2,4‐thiazolidinedione and p‐methoxybenzaldehyde in microreactors for the production of drugs for diabetes mellitus type 2 treatment

AbstractThe use of microreactors (MRs) in chemical and pharmaceutical industries allows for a series of advantages due to their reduced sizes regarding conventional batch reactors. In the present paper, the transposition of the reaction between 2,4‐thiazolidinedione (TZD) with p‐methoxybenzaldehyde from batch to a continuous capillary MR was carried out. The microdevice performance was evaluated experimentally and numerically by computational fluid dynamics (CFD). The batch process yielded 92% in 480 min using piperidine for equimolar reactant feed, while the pyrrolidine promoted a 100% yield in a 50 min, both using solvent ethanol. Kinetic and thermodynamic parameters of the synthesis using piperidine and pyrrolidine were also obtained from experimental data. In the transposition to flow chemistry, ethanol was also used as solvent and a product yield of 100% (140°C, pyrrolidine) was obtained for a residence time of 20 min, representing a reduction of 24 times in the reaction time. In the numerical simulations by CFD, two mathematical models were elaborated: a transient batch and a steady‐state continuous flow. Both models exhibited good agreement with experimental data. The average relative deviations of TZD conversion and the reaction yields in MRs were, respectively, 0.23% and −7.1% (78°C) and 1.7% and 1.2% (140°C).

Chemical Titration of Promoted Ag/α‐Al2O3 Ethylene Epoxidation Catalysts

AbstractWe enumerate the active site density for a promoted Ag/α‐Al2O3 ethylene epoxidation catalyst (35 wt.% Ag) by using trifluoroethanol as a chemical titrant. Trifluoroethanol, when introduced into the reactant stream, deprotonates to deposit stable trifluoroethoxy or trifluoromethyl groups on the Ag surface and inhibits ethylene oxide (EO) rates, thus enabling us to assess catalytic site densities. Active site densities vary between 52 and 69 μmolTFE gcat−1 across different chlorine coverages (0–0.4 monolayers) and different oxygen concentrations (2.5–7.7 mol%) in the reactor feed. Site densities measured by in situ trifluoroethanol chemical titration are distinct compared to those evaluated using ex‐situ N2O decomposition (12.3 μmolN2O gcat−1) suggesting that dynamic restructuring of the Ag surface under reaction conditions may render pre‐reaction chemisorption measurements insufficient to accurately enumerate the active sites relevant for ethylene epoxidation.