Formaldehyde Yields Research Articles

The titania-catalyzed oxidative dehydrogenation of methanol to formaldehyde

Formaldehyde is one of the most important intermediates in today’s chemical industry and mainly produced via the silver or Formox process. In this study, we introduce titania as a new catalyst for the oxidative dehydrogenation (ODH) of methanol to formaldehyde. Bulk titania catalysts were tested under methanol ODH conditions and the influence of reaction temperature, residence time and feed composition was investigated. The highest formaldehyde yield exhibited in the titania-catalyzed methanol ODH was around 70 % at 600 °C, 1.6 gCatalyst h molMethanol−1 and 2.0 molMethanol molOxygen−1. Long-term experiments were performed to get insights on the catalyst stability. While catalyst deactivation was observed at 600 °C (90–60 % methanol conversion after 72 h) and 550 °C (90–85 % methanol conversion after 72 h), methanol conversion (85 %) was stable and no deactivation occurred at 500 °C. Characterization of the used catalysts by nitrogen physisorption, powder X-ray diffraction and thermogravimetric analysis revealed deposition of carbon species as the main cause of catalyst deactivation. By alternating reaction and regeneration with oxygen, constant methanol conversions (90 %) and formaldehyde yields (70 %) were achieved at 600 °C.

Cool diffusion flames in a stably stratified stagnation flow

Cool diffusion flames have been a growing research topic since their discovery in 2012. Until now their study has been hindered by the high cost of the experimental systems used to observe them. A method is presented here for observing cool diffusion flames inexpensively using a pool of liquid n-heptane and parallel plates heated so as to produce a stably stratified stagnation flow. The flames were imaged with a color camera and an intensified camera. Measurements included gas phase temperatures, fuel evaporation rates, and formaldehyde yields. These are the first observations of cool flames burning near the surfaces of fuel pools. The measured peak temperatures were between 705 and 760 K and were 70 K above the temperature of the surrounding air. Autoignition first occurred at 550 K.

Carbonyl Yields in Cigars under Three Smoking Regimens Using a Linear Smoking Machine.

This study used standard linear smoking machines and puffing protocols to generate data on carbonyl yields in mainstream smoke from 11 unfiltered sheet-wrapped cigars (SWC), seven leaf-wrapped cigars (LWC), and two Kentucky reference cigarettes (3R4F, 1R6F). Carbonyl yields in cigar and cigarette products were determined using three different smoking regimens: International Organization for Standardization (ISO), Canadian Intense (CI), and Cooperation Centre for Scientific Research Relative to Tobacco (CORESTA) Recommended Method (CRM) No. 64 (CRM64, Routine Analytical Cigar-Smoking Machine─Specifications, Definitions and Standard Conditions). Mainstream tobacco smoke was collected using a smoking machine fitted with an impinger containing 2,4-dinitrophenylhydrazine (DNPH) and carbonyl compounds quantified using liquid chromatography with an ultraviolet detector. Commercial SWC and LWC generated comparable formaldehyde yields (SWC, 9.4-28 μg/cigar [ISO], 8.2-43 μg/cigar [CI], 8.6-13 μg/cigar [CRM64]; LWC, 11-13 μg/cigar [ISO], 11-22 μg/cigar [CI], 16-21 μg/cigar [CRM64]) and acrolein yields; however, LWC generated higher acetaldehyde yields compared to SWC, using CI and CRM64 regimens. Reference cigarettes using standard puffing regimens generated carbonyl yields within reported ranges and 5-10% RSDs, whereas the CRM64 regimen generated lower carbonyl yields and 12-14% RSDs. Reference cigarettes generated higher formaldehyde yields using cigarette smoking regimens (21-28 μg/cigarette under ISO, 76-96 μg/cigarette under CI) but comparable formaldehyde yields under CRM64 (12-14 μg/cigarette). In addition, this study evaluated physical parameters (e.g., tobacco weight, length, diameter, circumference, tobacco rod density) that show the correlation between tobacco weight, tobacco rod density, and acetaldehyde yields under the three smoking regimens. Carbonyl yields in the mainstream smoke of cigar products using the three smoking regimens were highly variable; however, the CI smoking regimen may provide meaningful analytical information regarding cigar smoke constituents, with lower likelihood of self-extinguishment due to the short puffing intervals.

Determination of Formaldehyde Yields in E-Cigarette Aerosols: An Evaluation of the Efficiency of the DNPH Derivatization Method

Recent reports have suggested that (1) formaldehyde levels (measured as a hydrazone derivative using the DNPH derivatization method) in Electronic Nicotine Delivery Systems (ENDS) products were underreported because formaldehyde may react with propylene glycol (PG) and glycerin (Gly) in the aerosol to form hemiacetals; (2) the equilibrium would shift from the hemiacetals to the acetals in the acidic DNPH trapping solution. In both cases, neither the hemiacetal nor the acetal would react with DNPH to form the target formaldehyde hydrazone, due to the lack of the carbonyl functional group, thus underreporting formaldehyde. These reports were studied in our laboratory. Our results showed that the aerosol generated from formaldehyde-fortified e-liquids provided a near-quantitative recovery of formaldehyde in the aerosol, suggesting that if any hemiacetal was formed in the aerosol, it would readily hydrolyze to free formaldehyde and, consequently, form formaldehyde hydrazone in the acidic DNPH trapping solution. We demonstrated that custom-synthesized Gly and PG hemiacetal adducts added to the DNPH trapping solution would readily hydrolyze to form the formaldehyde hydrazone. We demonstrated that acetals of PG and Gly present in e-liquid are almost completely transferred to the aerosol during aerosolization. The study results demonstrate that the DNPH derivatization method allows for an accurate measurement of formaldehyde in vapor products.

Volatile aldehyde emissions from “sub-ohm” vaping devices

“Sub-ohm” atomizers with reduced resistance can deliver more power than conventional electronic cigarettes. Typical battery outputs are 100 W or more. These devices are particularly popular among young users, and can be a significant source of volatile carbonyls in the indoor environment. Emissions from next-generation sub-ohm vaping products were characterized by determining e-liquid consumption and volatile aldehydes emissions for several combinations of popular high-power configurations. Tests explored the effect of dilution air flow (air vent opening), puffing volume, and coil assembly configuration. The mass of liquid consumed per puff increased as the puff volume increased from 50 to 100 mL, then remained relatively constant for larger puff volumes up to 500 mL. This is likely due to mass transfer limitations at the wick and coil assembly, which reduced the vaporization rate at higher puff volumes. Carbonyl emission rates were systematically evaluated using a 0.15 Ω dual coil atomizer as a function of the puffing volume and dilution air flow, adjusted by setting the air vents to either 100% (fully open), 50%, 25%, or 0% (closed). The highest formaldehyde emissions were observed for the lowest puff volume (50 mL) when the vents were closed (48 ng mg−1), opened at 25% (39 ng mg−1) and at 50% (32 ng mg−1). By contrast, 50-mL puffs with 100% open vents, and puff volumes >100 mL for any vent aperture, generated formaldehyde yields of 20 ng mg−1 or lower, suggesting that a significant cooling effect resulted in limited carbonyl formation. Considering the effect of the coil resistance when operated at a voltage of 3.8 V, the amount of liquid evaporated per puff decreased as the resistance increased, in the order of 0.15 Ω > 0.25 Ω > 0.6 Ω, consistent with decreasing aerosol temperatures measured at the mouthpiece. Three different configurations of 0.15 Ω coils (dual, quadruple and octuple) were evaluated, observing significant variability. No clear trend was found between carbonyl emission rates and coil resistance or configuration, with highest emissions corresponding to a 0.25 Ω dual coil atomizer. Carbonyl emission rates were compared with those determined using the same methodology for conventional e-cigarettes (lower power tank systems), observing overall lower yields for the sub-ohm devices.

On the Activity and Selectivity of CoAl and CoAlCe Mixed Oxides in Formaldehyde Production from Pulp Mill Emissions

Contaminated methanol has very good potential for being utilized in formaldehyde production instead of its destructive abatement. The activities, selectivities and stabilities of cobalt–alumina and cobalt–alumina–ceria catalysts prepared by the hydrotalcite-method were investigated in formaldehyde production from emissions of methanol and methanethiol. Catalysts were thoroughly characterized and the relationships between the characterization results and the catalytic performances were drawn. The preparation method used led to the formation of spinel-type structures in the form of Co2AlO4 based on x-ray diffraction (XRD) and Raman spectroscopy. Ceria seems to be present as CeO2, even though interaction with alumina is possible in the fresh catalyst. The same structure is maintained after pelletizing the cobalt–alumina–ceria catalyst. The cobalt–alumina–ceria catalyst was slightly better in formaldehyde production, probably due to lower redox temperatures and higher amounts of acidity and basicity. Methanol conversion is negatively affected by the presence of methanethiol; however, formaldehyde yields are improved. The stability of the pelletized catalyst was promising based on a 16 h experiment. During the experiment, cobalt was oxidized (Co2+ → Co3+), cerium was reduced (Ce4+ → Ce3+) and sulfates were formed, especially on the outer surface of the pellet. These changes affected the low temperature performance of the catalyst; however, the formaldehyde yield was unchanged.

Fast Reactions of Hydroxycarbenes: Tunneling Effect versus Bimolecular Processes

Different uni- and bimolecular reactions of hydroxymethylene, an important intermediate in the photochemistry of formaldehyde, as well as its halogenated derivatives (XCOH, X = H, F, Cl, Br), have been considered using high-level CCSD(T)/CBS quantum chemical methods. The Wentzel-Kramers-Brillouin (WKB) and Eckart approximations were applied to estimate the tunneling rate constant of isomerization of trans-HCOH to H(2)CO, and the WKB procedure was found to perform better in this case. In agreement with recent calculations and experimental observations [Schreiner et al., Nature 2008, 453, 906], the half-life of HCOH at the low temperature limit in the absence of bimolecular processes was found to be very long (approximately 2.1 h). The corresponding half-life at room temperature was also noticeable (approximately 35 min). Bimolecular reactions of trans-hydroxymethylene with parent formaldehyde yield primarily more thermodynamically favorable glycolaldehyde via the specific mechanism involving 5-center transition state. The most preferable reaction of cis-hydroxymethylene with formaldehyde yields carbon monoxide and methanol. Due to very low activation barriers, both processes occur with nearly a collision rate. If the concentration of HCOH (and its halogenated analogues XCOH as well) is high enough, the bimolecular reactions of this species with itself become important, and H(2)CO (or X(H)CO) is then formed with a collision rate. The singlet-triplet energy separation of trans-HCOH is confirmed to be approximately -25 kcal/mol.

New Mo-Fe-O silica supported catalysts for methanol to formaldehyde oxidation

Abstract Silica supported Mo-Fe and Mo-Fe-P mixed oxides (Mo/Fe = 3 atomic ratio) were prepared in the presence of citric acid as chelating agent to obtain a uniform distribution of the active phase. Loading of 23.1% (w/w) of MoO 3 was used exceeding the monolayer content (around 2.2 monolayers of MoO 3 ). The low interaction between the silica and the mixed oxide in addition to the high content of the active phase led to a three-dimensional distribution of the active phase, confirmed by SEM. Several iron (Fe 3+ ) precursors (nitrate, chloride, sulfate, phosphate and pyrophosphate) were used in order to assess their effect on the catalysts performances. Some elements (N, Cl, S and P) from the iron precursors remained in the catalyst. Samples prepared from phosphate and pyrophosphate had phosphorus in their compositions and Mossbauer spectra revealed the presence of iron phosphate. Nevertheless, due to lack of crystallinity, these phases (iron phosphates) are probably inactive. All the prepared catalysts display high activity and selectivity towards formaldehyde, even for low and high methanol conversions. The catalyst prepared from iron pyrophosphate was the most active. The presence of heteropolymolybdates, containing phosphorus, or its Mo rich surface can perhaps explain its enhanced catalytic behavior. For temperatures lower than 625 K this sample (merely 26.2% (w/w) of active phase) presented higher formaldehyde yields than one unsupported industrial catalyst. Such a catalyst prepared from iron pyrophosphate presents promising catalytic performances for use in fluidized bed reactors. The loss of Mo during reaction was observed for all the prepared catalysts. Micrographs for post reaction samples displayed MoO 3 needles (or plates) formed during the redox cycle, which are easily sublimated. Conversely, for the sample prepared from iron pyrophosphate the MoO 3 needles are absent, which is probably indicative of a different reaction mechanism.

Reduced Toxicological Activity of Cigarette Smoke by the Addition of Ammonia Magnesium Phosphate to the Paper of an Electrically Heated Cigarette: Subchronic Inhalation Toxicology

Cigarette smoke is a complex chemical mixture that causes a variety of diseases, such as lung cancer. With the electrically heated cigarette smoking system (EHCSS), temperatures are applied to the tobacco below those found in conventional cigarettes, resulting in less combustion, reduced yields of some smoke constituents, and decreased activity in some standard toxicological tests. The first generation of electrically heated cigarettes (EHC) also resulted in increased formaldehyde yields; therefore, a second generation of EHC was developed with ammonium magnesium phosphate (AMP) in the cigarette paper in part to address this increase. The toxicological activity of mainstream smoke from these two generations of EHC and of a conventional reference cigarette was investigated in two studies in rats: a standard 90-day inhalation toxicity study and a 35-day inhalation study focusing on lung inflammation. Many of the typical smoke exposure-related changes were found to be less pronounced after exposure to smoke from the second-generation EHC with AMP than to smoke from the first-generation EHC or the conventional reference cigarette, when compared on a particulate matter or nicotine basis. Differences between the EHC without AMP and the conventional reference cigarette were not as prominent. Overall, AMP incorporated in the EHC cigarette paper reduced the inhalation toxicity of the EHCSS more than expected based on the observed reduction in aldehyde yields.

Degradation of macrolide antibiotics by ozone: A mechanistic case study with clarithromycin

Macrolide antibiotics are widely used (in the order of 1 g per person per year). They pass the body largely unchanged and are also not degraded in wastewater treatment plants. With not too much effort, they may be eliminated from their effluents by ozonation. The macrolide antibiotics have all a dimethylamino group at one of the carbohydrate residues in common. This functional group is the target of the ozone reaction, and clarithromycin has been selected here for a more detailed study. Since only the free amine reacts with ozone, the rate of reaction is pH dependent (at pH 7: k = 4 × 10 4 M −1 s −1). In analogy to the ozonolysis of trimethylamine, the main reaction is a transfer of an O-atom yielding the N-oxide (identified by HPLC/MS–MS). A minor product (10%, based on formaldehyde yields) is demethylated clarithromycin (identified by HPLC/MS–MS). The dimethylamino group is thought to be essential for the binding of the macrolide antibiotics to their target. As a consequence, chemical changes of this functional group, notably the formation of the N-oxide that is no longer a proton acceptor, inactivates these drugs as assayed by the suppression of the growth of Pseudomonas putida. This is most important for wastewater treatment, as mineralization of clarithromycin by ozone would require 100 times as much ozone.

Modified W/HZSM-5 catalysts: structure and catalytic properties

Conventional aqueous impregnated W/HZSM-5 catalysts have been modified by treatment with an 1 M ammonia aqueous solution prior to the calcination step, obtaining tungsten loading in the range 0.02–0.2 wt.% UV diffuse reflectance spectroscopy (UV DRS), X-ray diffraction (XRD), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (TPDA), surface area measurement, scanning electron microscope (SEM) and TEM were used for the characterization of the samples. The catalysts obtained were almost exclusively constituted of monomeric tungsten species. The characterization findings let us draw a model in which these species are chemically joined to the Brönsted acid sites of the HZSM-5 zeolite and, therefore, well dispersed on the support. These catalysts were tested in the partial oxidation of methane to formaldehyde at atmospheric pressure. The obtained formaldehyde yields were up to three times higher than those of the conventional aqueous impregnated W/HZSM-5 catalysts.

Optimal Control of Catalytic Methanol Conversion to Formaldehyde

An optimal control methodology is applied to find the heat and oxygen flux profiles, distributed along the length of a plug flow reactor, for the conversion of methanol to formaldehyde. The calculations use models for the gas-phase and catalytic [MoO3−Fe2(MoO4)3] reactions. The reactor designs show that a distributed heat flux improves formaldehyde yields, but an oxygen flux does not affect the results. Formaldehyde mass fractions of over 90% have been achieved in the simulations. The solutions obtained, although not proven to be globally optimal, are of very high quality. A fully nonlinear robustness analysis of the formaldehyde production with respect to the catalyst model variables is performed by the use of a high dimensional model representation. This representation is similar to the ANOVA decomposition used in statistics but does not require an increase in the number of data points as the dimensionality of the variable space increases. The most important variables are the catalyst surface area and t...

Reactive uptake of ozone by proxies for organic aerosols: Surface‐bound and gas‐phase products

Gas‐phase and surface‐bound products were determined for the reaction of ozone with self assembled monolayers of alkanes and terminal alkenes serving as proxies for atmospheric organic aerosols. The organic surfaces were characterized using infrared (IR) spectroscopy (direct absorption and attenuated total reflection) as well as contact angle measurements with water before and after the reaction with ozone. The contact angle of the organic surfaces was reduced by ∼20° owing to the reaction. Following the reaction, IR absorption due to the presence of carbonyls and carboxylic acids was observed on the surface. Gas‐phase products were determined using infrared spectroscopy immediately above the reaction surface. Under dry conditions, gas‐phase formaldehyde yields of 0.5±0.1 for organic monolayers of allyltrichlorosilane (C3=) and octenyltrichlorosilane (C8=) terminal alkenes were observed, in good agreement with the yields observed for gas phase ozonolysis of terminal alkenes. Surfaces of n‐octane (C8) as well as processed alkene surfaces were nonreactive toward ozone. The reaction mechanism of ozone with the surface alkenes is discussed. Finally, the possible implications for the chemistry of organic aerosols are discussed and studied using a box model and realistic atmospheric scenarios.

Formaldehyde Yields from Methanol Electrochemical Oxidation on Carbon-Supported Platinum Catalysts

The formation of formaldehyde during methanol electrochemical oxidation on supported Pt and Pt-Ru catalysts was investigated. While on solid platinum electrodes, the formaldehyde yields from methanol oxidation are near 30% at low potentials; the yields fall below 2% for methanol electrochemical oxidation on carbon-supported catalysts in Nafion. The lower formaldehyde yields, which result from more complete methanol oxidation, are believed to arise from the ability of partial oxidation products to be transported to an array of active catalyst sites dispersed within the three-dimensional network of the Nafion film.

Atmospheric chemistry and distribution of formaldehyde and several multioxygenated carbonyl compounds during the 1995 Nashville/Middle Tennessee Ozone Study

Airborne measurements of formaldehyde (FA), glycolaldehyde (GA), glyoxal (GL), methylglyoxal (MG), and pyruvic acid (PD) were made on board instrumented aircraft platforms, the Department of Energy G1 and National Oceanic and Atmospheric Administration P3 (FA only), during the 1995 Nashville/Middle Tennessee Ozone Study. FA data determined on these two aircraft during three intercomparison flights agreed to within ∼10%. The mean and median (in parentheses) concentrations observed within the boundary layer (<2000 m) for FA, GA, GL, MG, and PD were 4.2 (3.9), 0.78 (0.70), 0.07 (0.06), 0.14 (0.10), and 0.24 (0.23), respectively (all in parts per billion by volume (ppbv)). At the observed concentrations, FA accounted for a substantial fraction of the OH reactivity, comparable to isoprene and CO. Further, it served as an important free radical precursor, contributing 25–30% of the radical production during midday and even greater during morning and late afternoon periods. Source attribution of FA was assessed using measured concentrations of hydrocarbons, their reaction kinetics with the OH radicals, and FA yields. The results showed that isoprene was the dominant source of FA, responsible for ∼67%, methane and peroxyacetyl nitrate contributed equally at ∼13% each, and alkanes and alkenes which are largely of anthropogenic origin accounted for only ∼7%. This assessment based on reaction kinetics is consistent with the strong correlations (r > 0.8) observed between FA and two other isoprene products, GA and MG. Further, the magnitudes of the nonzero FA intercept exhibited in these correlation plots are found to qualitatively agree with the fraction of precursors that did not concomitantly produce GA and MG. Inspection of specific flights showed direct evidence of the dominance of isoprene as a precursor for FA, appreciable contribution of FA to CO, and negligible decay of FA overnight. Because of the dominant role isoprene plays as a precursor of FA, FA could be used as a proxy of isoprene for assessing the applicability of various versions of biogenic emission inventory.

Improved Durable-Press Cotton by a Two-Step Poly-Set Process

A crossrinking treatment on scoured, bleached, mercerized, and desized cotton fabric with dimethyloldihydroxyethylene urea (DMDHEU) by a two-step poly-set process is reported. The fabric was also treated with DMDHEU by the conventional pad-dry-cure tecnhique. The resin-finished fabric, along with a control, were studied for various physiochemical properties by standard methods. The number of crosslinks (expressed as CL/GPU) and length of crosslinks were calculated from formaldehyde yields and nitrogen values. The data on resin add-on, CL/GPU, and length of crosslinks of cotton crosslinked with varying concentrations of the resin in the presence of polymerization catalysts is discussed. The add-on values in the case of the sample treated by zinc acetate was much higher compared to the similar sample treated in the presence of magnesium acetate. The number of CL/GPU and length of crosslink increased with the increase of resin concentration. Homopolymerization of resin was evident in step 1. The fabric processed in step 2 showed marked improvement in wrinkle-recovery angle and other properties such as strength, elongation, abrasion, and toughness, compared to the samples treated by the conventional process. The relationship between various properties of the fabric is also dealt with.