Removal of Low-Concentration Formaldehyde by a Fiber Optic Illuminated Honeycomb Monolith Photocatalytic Reactor

Abstract

In this study, we systematically investigated the removal of low-concentration formaldehyde by the fiber optic illuminated honeycomb monolith photocatalytic reactor and the influential factors including formaldehyde concentration (0.8-2.0 ppm), relative humidity (RH30-70%), and air flow rate (800-1600 mL/min). The experimental results of various formaldehyde concentrations indicate the kinetic fits the Langmuir-Hinshelwood model, and the rate constants (k) under RH30%, 50% and 70% are 1.09, 1.37, and 1.68 μ-mole/m 2 /s, respectively. The Langmuir adsorption constants of formaldehyde under RH30%, 50% and 70% are 4.10 × 10 -3 , 2.98 × 10 -3 and 2.14 × 10 -3 ppm -1 , respectively. Increasing relative humidity has a positive effect on the rate constant of photocatalytic oxidation k, which is relevant to the enhancement effect of relative humidity on the formation of hydroxyl radicals. On the other hand, the formaldehyde conversion and Langmuir adsorption constant of formaldehyde decrease with the increase of relative humidity, which may be associated with the competition between formaldehyde and water molecules for the adsorption sites on the surface of TiO 2 photocatalyst. Because the air flow rate was low (≤ 1600 mL/min), the gas retention time (≥ 7.7 sec) was long enough for the reactor to achieve a high formaldehyde conversion (≥ 92%), but the breakthrough of formaldehyde might occur when air flow rate > 4200 mL/min.

Investigation of A Potted Plant (Hedera helix) with Photo-Regulation to Remove Volatile Formaldehyde for Improving Indoor Air Quality

“…Current performance assessment of the air cleaning primarily has been occurred in laboratories, often using high challenge concentrations of chemicals, low airflow rates, and single contaminant species in a controlled environment (Yu et al, 2015). In generation, a performance of air cleaning was determined by two ways including a direct upstream versus downstream measurement and empirical determination with a single zone mass balance model (Thunyasirinon et al, 2015;Ciuzas et al, 2016).…”

Using Box Modeling to Determine Photodegradation Coefficients Describing the Removal of Gaseous Formaldehyde from Indoor Air

“…Because of the initial rapid adsorption of HCHO onto the TiO 2 photoreactor, the gaseous HCHO concentration jumps to the fixed value and the kinetic reaction is presumed as a first-order reaction (Langmuir isotherm). However, the results of data driven observation in most studies present an approximate zero-order reaction except for low concentration of HCHO (Lo et al, 2015;Yu et al, 2015). We suggest that the measurement uncertainties of rate-dependency are trade-off the accuracies of processing contributions in quantitation.…”

“…Therefore, the aerosol term of HCHO is emphasized in our model to reflect the effect of water molecules in the photochemical reactions. Based on other studies (Han et al, 2012;Lo et al, 2015;Yu et al, 2015), three air conditions of temperature, relative humidity and wind speed are considered as the principal factors on the removal of gaseous VOCs indoors.…”

Indoor Air Pollution Levels in Decorated Residences and Public Places over Xi’an, China

“…The health effects of VOCs were shown detailed in Qian and Dai (2013). Formaldehyde is the most ubiquitous and typical indoor air pollutant, and was proved to be the carcinogen (Tao et al, 2015;Yu et al, 2015;Ling et al, 2016), which can irritate the skin and the respiratory tract, leading to the occurrence of dysosmia, allergy, and immune dysfunction.…”