Initial Formaldehyde Concentration Research Articles

A New Method for Determining the Initial Mobile Formaldehyde Concentrations, Partition Coefficients, and Diffusion Coefficients of Dry Building Materials

The initial mobile formaldehyde concentration, C m,o; the partition coefficient, K; and the diffusion coefficient, D, of a dry building material are key parameters to characterize formaldehyde emissions from the building material. The solvent extraction method and direct thermal desorption method can overestimate C m,o because of high temperature. A new method has been developed to determine C m,o under similar conditions to common indoor environment, together with K and D. In the proposed method, the tested materials are placed in an airtight environmental chamber for which the temperature can be controlled by a water bath, then the materials undergo a multisorption/emission process and the instantaneous formalde-hyde concentration in the chamber is recorded. The K and C m,o are determined from the equilibrium concentrations after every sorption by means of the linear least-square regression, and D is obtained by fitting the concentration at the emission stage into a mass-transfer-based model in the literature. Four kinds of wooden medium-density boards are tested. The C m,o measured using this method is the mobile formaldehyde concentration in the material, which differs significantly from the total formaldehyde concentration in the material measured by using the traditional method recommended by the Chinese standard (GB/T 17657-1999) extraction method. This means that the mobile formaldehyde takes only a small portion of the total quantity in the tested material. The K, D, and C m,o values measured using this new method are used to predict formaldehyde concentrations for sorption processes. The results agree well with experimental data. In addition, some factors influencing the accuracy are analyzed.

Laboratory light-scattering measurements with Titan's aerosols analogues produced by a dusty plasma

The chemistry leading to the formation of solid aerosols (tholins) in Titan's atmosphere is simulated by a capacitively coupled plasma in a N 2–CH 4 gas mixture. The solid grains are produced in volume directly in the gas phase and studied ex-situ by SEM imaging and by light scattering on clouds of particles. The scattered light properties depend on the physical properties of the particles (morphologies, size distribution), as well as on the phase angle and the wavelength of the light. The particles may be aggregated or agglomerated grains. The grains size distribution is studied as a function of plasma parameters such as initial methane concentration introduced into the discharge, gas flow, absorbed RF power and plasma duration. The average grain size increases when the amount of CH 4 increases, when the gas flow decreases, and when the plasma duration increases up to a limit for each production condition. For all the samples, the absorption decreases with increasing wavelength in the visible domain. As usually found for irregular particles, the polarization phase curves have a bell-shaped positive branch and a shallow negative branch. The maximum of polarization ( P max) increases when the average grain size decreases (sub-μm-sized grains). To obtain P max values within the range of those measured in Titan's atmosphere; the average grains diameter has to be smaller than 100 nm, in agreement with the space observations results. In the light-scattering experiment, the size of the agglomerates in the clouds is in the 40–80 μm range in equivalent diameter. As a consequence P max increases with decreasing wavelength due to the increasing absorption, in agreement with observations of Titan from outside the atmosphere.

Degradation of formaldehyde in anaerobic sequencing batch biofilm reactor (ASBBR)

The present study evaluated the degradation of formaldehyde in a bench-scale anaerobic sequencing batch reactor, which contained biomass immobilized in polyurethane foam matrices. The reactor was operated for 212 days at 35 °C with 8 h sequential cycles, under different affluent formaldehyde concentrations ranging from 31.6 to 1104.4 mg/L (formaldehyde loading rates from 0.08 to 2.78 kg/m 3 day). The results indicate excellent reactor stability and over 99% efficiency in formaldehyde removal, with average effluent formaldehyde concentration of 3.6 ± 1.7 mg/L. Formaldehyde degradation rates increased from 204.9 to 698.3 mg/L h as the initial concentration of formaldehyde was increased from around 100 to around 1100 mg/L. However, accumulation of organic matter was observed in the effluent (chemical oxygen demand (COD) values above 500 mg/L) due to the presence of non-degraded organic acids, especially acetic and propionic acids. This observation poses an important question regarding the anaerobic route of formaldehyde degradation, which might differ substantially from that reported in the literature. The anaerobic degradation pathway can be associated with the formation of long-chain oligomers from formaldehyde. Such long- or short-chain polymers are probably the precursors of organic acid formation by means of acidogenic anaerobic microorganisms.

A model for late Quaternary methane ice core signals: Wetlands versus a shallow marine source

[1] A three-reservoir model with first order kinetics for methane records in the Vostok (Antarctica) and GISP2 (Greenland) ice cores reproduces the sawtooth pattern and the maximum and minimum concentrations. The model also returns an atmospheric methane relaxation time of ∼10 years for both cores, which is the same as current estimates. The characteristics of the source reservoirs are long relaxation times (33.3 and 100 ky) and high initial methane concentrations (2500 and 7000 ppm) for GISP2 and Vostok, respectively. These characteristics are consistent with gas hydrate sources in shallow marine sediments, but not with wetland sources which have insufficient storage capacity and low source strength.

FORMALDEHYDE BIODEGRADATION AND ITS EFFECT ON THE DENITRIFICATION PROCESS

Simultaneous formaldehyde biodegradation and denitrification in batch assays and in a continuous lab-scale reactor were studied. In batch assays, initial biodegradation rates between 0.7 and 3.3 g CH2O g VSS-1 d-1 were obtained at formaldehyde concentrations between 300 and 2150 mg l-1. The denitrification process was affected by the presence of formaldehyde. The nitrite accumulation increased with the initial formaldehyde concentration. In the continuous reactor, removal efficiencies above 98.5% were obtained at formaldehyde loading rates between 0.37 and 2.96 kg COD m-3 d-1 (625 - 5000 mg CH2O l-1). Formaldehyde removal led to the appearance of methanol and formic acid in the medium. Denitrification process was almost complete (around 99.7%) at nitrogen loading rates up to 0.44 kg N-NO3 - m-3 d-1. Nitrite occasionally appeared in the effluent at concentrations less than 2.9 mg l-1. The composition of the biogas indicated that denitrification and methanogenesis occurred simultaneously in the same unit.

Formaldehyde degradation by UV/TiO 2/O 3 process using continuous flow mode

The degradation of formaldehyde gas was studied using UV/TiO 2/O 3 process under the condition of continuous flow mode. The effects of humidity, initial formaldehyde concentration, residence time and ozone adding amount on degradation of formaldehyde gas were investigated. The experimental results indicated that the combination of ozonation with photocatalytic oxidation on the degradation of formaldehyde showed a synergetic action, e.g., it could considerably increase decomposing of formaldehyde. The degradation efficiency of formaldehyde was between 73.6% and 79.4% while the initial concentration in the range of 1.84–24 mg/m 3 by O 3/TiO 2/UV process. The optimal humidity was about 50% in UV/TiO 2/O 3 processs and degradation of formaldehyde increases from 39.0% to 94.1% when the ozone content increased from 0 to 141 mg/m 3. Furthermore, the kinetics of formaldehyde degradation reaction could be described by Langmuir-Hinshelwood model. The rate constant k of 46.72 mg/(m 3-min) and Langmuir adsorption coefficient K of 0.0268 m 3/mg were obtained.

Oxygen and methane depletion in soil affected by leakage of natural gas

SummaryAs part of a study to simulate plant responses to leaks from pipelines, we injected natural gas into soil at a depth of 1 m in plots of grass, wheat and beans. Measurements of oxygen and methane in soil exposed to gas show that oxygen is depleted significantly to values less than would be caused by simple displacement by natural gas, indicating consumption within the soil by methanotrophic bacteria. Gas concentrations were clustered into two groups: 18% of the oxygen values were less than 1% by volume and 52% of the methane values were less than 5% by volume, indicating a tendency towards either oxygen‐limiting or methane‐limiting conditions. Oxygen depletion was significantly greater in summer. Depletion rates were greatest under grass, and least under wheat. In grass, 36% of the variation in depletion is explained by soil temperature at 10 cm with Q10 = 2.0 over the 0–20°C range. We developed a model that accounts for three gas exchange mechanisms: soil‐air displacement by the injected gas; gas consumption by bacteria; and re‐infusion of the soil atmosphere to account for a net loss of gas volume by consumption. Using this model, we calculate that an average of 37% of the methane was consumed. At initial methane concentrations less than 10% by volume, as much as 100% of the gas was consumed, but consumption efficiency decreased rapidly thereafter. These findings indicate that the soil sink for methane is dynamic and adaptive, acting as a significant constraint on underground methane sources, limited primarily by oxygen availability.

Kinetic investigation of chemical vapor deposition of B4C on tungsten substrate

AbstractProduction of β‐rhombohedral boron carbide (B4C) on a tungsten substrate by the chemical vapor deposition from a BCl3–H2–CH4 gas mixture was achieved. An impinging‐jet reactor was used to minimize the mass‐transfer limitations on the reaction kinetics, which made a detailed kinetic investigation possible. Results of the XRD and XPS analyses showed that the solid product formed on the substrate is a rhombohedral B4C phase. Both dichloroborane and boron carbide formation rates were found to increase with an increase in the inlet molar fraction of BCl3. The formation rate of boron carbide increased with an increase in the inlet molar fraction of CH4. However, no effect on the formation rate of dichloroborane was observed with an increase in the inlet molar fraction of methane. The activation energy of the boron carbide formation reaction was ascertained to be 56.1 ± 4.0 kJ/mol. The boron carbide formation reaction was proportional with the 0.34 ± 0.055 power of the initial boron trichloride concentration and 0.64 ± 0.084 power of the initial methane concentration. © 2006 American Institute of Chemical Engineers AIChE J, 2006

광촉매/광산화를 이용한 VOCs 처리장치 개발

This study introduces a method to eliminate formaldehyde and benzene, toluene from indoor air by means of a photocatalytic oxidation reaction. In the method introduced, for the good performance of the reaction, the effect and interactions of the <TEX>$TiO_2$</TEX> catalyst and ultraviolet in photocatalytic degradation on the reaction area, dosages of catalysts, humidity and light should be precisely examined and controled. Experiments has been carried out under various intensities of UV light and initial concentrations of formaldehyde, benzene and toluene to investigate the removal efficiency of the pollutants. Reactors in the experiments consist of an annular type Pyrex glass flow reactor and an 11W germicidal lamp. Results of the experiments showed reduction of formaldehyde, benzene and toluene in ultraviolet <TEX>$/TiO_2/$</TEX> activated carbon processes (photooxidation-photocatalytic oxidation-adsorption processes), from 98% to 90%, from 98% to 93% and from 99% to 97% respectively. Form the results we can get a conclusion that a ultraviolet/Tio2/activated carbon system used in the method introduced is a powerful one for th treatment of formaldehyde, benzene and toluene of indoor spaces.

Adsorption of Formaldehyde on Treated Activated Carbon and Activated Alumina

Formaldehyde is extensively used for disinfection and antisepsis in medical facilities and especially in textile and paint industries as a solvent. Owing to the higher concentration of formaldehyde, both in waste effluents and local environment of medical facilities and industries, it has been reported to cause cancer and as an irritant to eyes and skin. The removal efficiency and the adsorption mechanism of formaldehyde onto the treated activated carbons and activated alumina were studied to analyze the effect of modified surface chemistry of adsorbents. The adsorption capacities of all the selected adsorbents were investigated in batch study at varying contact time and initial concentration of formaldehyde at STP. It was found that commercially implemented activated alumina, treated with effective nucleophile, showed significant formaldehyde adsorption with less variation in adsorption capacity even with decrease in initial concentration of adsorbate. These set of experiments indicate that acidity of formaldehyde can be exploited for its removal from waste effluent and air. The optimization studies were carried out to find out the optimum conditions for this adsorption process with adsorption model fitting and kinetic studies. The investigation results were evaluated on per gram of adsorbent basis to predict feasibility of scaling up at commercial level.

대기내 발생하는 복잡한 광화학반응에 대한 수치실험

In predicting oxidants concentration, the most important fact is to select a suitable photochemical reaction mechanism. Sensitivity analysis of and other important photochemical oxidants concentrations was conducted by using CBM-IV model. The predicted oxidants concentration was considerably related with the initial concentration of formaldehyde, , RH and RCHO. As the initial concentration of formaldehyde increased, concentration of increased. concentration was proportional to the ratio. When the initial concentrations of RH and RCHO were high, photochemical reaction was more reactive, including more rapid conversion of NO to and increased oxidants. Also, the sensitivities of ozone formation to rate constants, in the photolysis were studied.

Formaldehyde biodegradation in the presence of methanol under denitrifying conditions

AbstractSimultaneous formaldehyde and methanol biodegradation and also denitrification were studied in batch assays and in a continuous laboratory‐scale reactor. In batch assays, high formaldehyde concentrations (up to 1360 mg dm−3) were removed under anoxic conditions in the presence of methanol. It was found that formaldehyde biodegradation produced methanol and formic acid as products. The denitrification process was affected by the initial formaldehyde concentration. In the continuous reactor, the biodegradation of different concentrations of formaldehyde (1500–275 mg dm−3) and methanol (153–871 mg dm−3) took place, maintaining the organic loading rate at 0.84 g COD dm−3 d−1 (COD/N 4). However, each increase in the methanol concentration in the influent caused a decrease in the denitrification level. An adaptation period to methanol was necessary before the denitrification percentage could be recovered. In contrast with batch assays, in the continuous reactor methanol and formic acid were not detected in the effluent. Moreover, in the continuous reactor the denitrification percentages were higher and the nitrite accumulation was lower. Copyright © 2005 Society of Chemical Industry

Kinetics and Stability of CH4–CO2 Mixed Gas Hydrates during Formation and Long‐Term Storage

The formation of CH4-CO2 mixed gas hydrates was observed by measuring the change of vapor-phase composition using gas chromatography and Raman spectroscopy. Preferential consumption of carbon dioxide molecules was found during hydrate formation, which agreed well with thermodynamic calculations. Both Raman spectroscopic analysis and the thermodynamic calculation indicated that the kinetics of this mixed gas hydrate system was controlled by the competition of both molecules to be enclathrated into the hydrate cages. However, the methane molecules were preferentially crystallized in the early stages of hydrate formation when the initial methane concentration was much less than that of carbon dioxide. According to the Roman spectra, pure methane hydrates first formed under this condition. This unique phenomenon suggested that methane molecules play important roles in the hydrate formation process. These mixed gas hydrates were stored at atmospheric pressure and 190 K for over two months to examine the stability of the encaged gases. During storage, CO2 was preferentially released. According to our thermodynamic analysis, this CO2 release was due to the instability of CO2 in the hydrate structure under the storage conditions.

Complex Behavior in the Formaldehyde−Sulfite Reaction

The formaldehyde-sulfite reaction is an example of an "acid-to-alkali" clock. It displays an induction period, during which the pH varies only slowly in time, followed by a reaction event, during which the pH increases rapidly by several units. When the reaction is performed in a closed (batch) reactor, the clock time is found to increase with a decrease in initial concentrations of formaldehyde and sulfite and an increase in the total initial concentration of S(IV). At long times, following the clock event, there is a slow decrease in pH. In an open (flow) reactor, bistability between a low-pH steady state (pH approximately 6-8) and a high-pH steady state (pH approximately 11) is observed. Additionally, we report the existence of sustained, small-amplitude oscillations in pH in this system. An extended kinetic mechanism reproduces the batch behavior but fails to account for the complex behavior observed in the flow reactor. Possible additional reaction steps are discussed.

Formaldehyde biodegradation and its inhibitory effect on nitrification

AbstractThe simultaneous removal of formaldehyde and ammonium in aerobic cultures and the inhibitory effect of formaldehyde on ammonium oxidation were investigated. The influence of a co‐substrate, methanol, on formaldehyde biodegradation and on the nitrification process was also evaluated. Formaldehyde was completely removed at all concentrations tested (30–3890 mg dm−3) in assays with that compound as the single carbon source and in the presence of methanol as co‐substrate. An initial formaldehyde biodegradation rate of 4.6 g CH2O g−1 VSS d−1 was obtained for 2000 mg CH2O dm−3 as single carbon source compared with a rate of 7.3 g CH2O g−1 VSS d−1 when methanol was added. Formaldehyde was inhibitory to the nitrification process at initial concentrations higher than 350 mg dm−3. Increasing the initial formaldehyde concentration or adding a co‐substrate such as methanol resulted in a longer lag phase before ammonium oxidation and caused a decrease in the degree of nitrification. Nitrification was completely inhibited at initial formaldehyde concentrations higher than 1500 mg dm−3. Copyright © 2004 Society of Chemical Industry

The Effect of Nitrogen Dilution on Nonfuel Hydrocarbons in Laminar Nonpremixed Flames

Centerline and radial profiles of gas temperature and C3 to CI2 hydrocarbon concentrations were measured in nitrogen-diluted methane and ethylene coflowing nonpremixed flames. The methane or ethylene volumetric flowrates were kept constant while the nitrogen flowrate in the fuel mixture was systematically varied. In both series of flames, the lemperatures in the pyrolysis zone were shifted to higher heights in the flame by increases in the overall flame length, and were reduced both by the decrease in the adiabatic flame temperature and by a mechanism that likely involves decreased heat transfer from the flame front to the centerline. The maximum centerline concentrations of every measured non-fuel hydrocarbon monotonically decreased and shifted to higher heights in the flame as dilution was increased. The maximum mole fractions of most linear hydrocarbons were roughly proportional to the hydrocarbon mole fraction in the un reacted fuel mixture, while the maximum mole fractions of aromatic hydrocarbons varied roughly as the square of that quantity. The decrease in the initial methane or ethylene concentration in the fuel appears to be the primary cause of the reductions in the maximum nonfuel hydrocarbon concentrations. For all hydrocarbons the shape of the centerline mole fraction profiles, including the location of the maximum concentration and of the species'disappearance, correlate well with temperature.

The oxidation of formaldehyde on high overvoltage DSA type electrodes

The electrochemical oxidation of formaldehyde is studied on dimensionally stable anodes prepared by thermal decomposition of precursors (the corresponding chlorides). The working electrodes used were: Ti/Ir0.3Ti0.7O2, Ti/Ru0.3Ti0.7O2 and Ti/Ir0.2Ru0.2Ti0.6O2. The electrolyses were performed galvanostatically in a filter press cell with 0.5 mol L-1 H2SO4 solutions with initial formaldehyde concentration equal to 100 mmol L-1. The concentration of formaldehyde decreases fast with the electrolysis time, with the ternary anode (Ir + Ru + Ti) presenting the best performance for this step. The anode containing only Ir, despite presenting the higher superficial charge, is the one with the lowest electrocatalytic activity. For the formic acid oxidation step, the presence of iridium in the anode composition does not promote the process, the anode containing only ruthenium being the most effective for this step.

Kinetics of in situ degradation of formaldehyde with electrogenerated hydrogen peroxide

In the in situ degradation of formaldehyde with electrogenerated hydrogen peroxide, the cathodic reduction of oxygen on the anodization graphite was first order in the concentration of oxygen dissolved in the aqueous phase. The oxidation of formaldehyde with electrogenerated hydrogen peroxide was second order in formaldehyde and first order in hydrogen peroxide. The activation energy was evaluated as 36 kJ/mol. A model calculation of the in situ degradation of formaldehyde with electrogenerated hydrogen peroxide correlated well with experimental results. The effects of temperature and initial concentration of formaldehyde on the induction period of the oxidative degradation of formaldehyde with hydrogen peroxide electrogenerated in situ were explored.

In Situ Oxidative Degradation of Formaldehyde with Electrogenerated Hydrogen Peroxide

The factors affecting the cathodic reduction of oxygen to hydrogen peroxide and the degradation of formaldehyde using in situ generated hydrogen peroxide are presented in this work. The current efficiency for the production of hydrogen peroxide on graphite has been indicated by the experimental results to have been significantly affected by the pH value, the current density, the temperature, and the oxygen sparging rate. The maximum current efficiency for the cathodic reduction of oxygen to hydrogen peroxide was 93.5%. The degradation of formaldehyde by the electrogenerated hydrogen peroxide was primarily governed by the current density, the pH value, and the temperature. The degradation fraction of formaldehyde was more than 99% whenever the initial concentration of formaldehyde was in the range of 250 to 1000 ppm.

Modelling TCE degradation by a mixed culture of methane-oxidizing bacteria

A model describing the growth of bacteria and the degradation of methane and trichloroethylene (TCE) based on the concept of competitive inhibition is proposed. The model has been applied to laboratory batch experiments representing different initial TCE concentrations (50–4300 μg/l) and initial methane concentrations (0.53–3.2 mg/l). The proposed model simulated successfully the data obtained for initial methane concentration (less than 1.8 mg/l), causing constant experimental growth conditions during the experiments. This indicates that the interactions between methane and TCE degradation can be explained as competitive inhibition. The model simulations of the results from the experiments with the highest initial methane concentration of 3.2 mg/l failed, supposedly because the growth conditions changed during the experiments. The proposed model is a useful engineering tool for design of treatment processes and in situ bioremediation schemes for degradation of TCE by methane-oxidizing bacteria.