On the Adsorption of Formaldehyde at High Temperatures and Zero Surface Coverage

Abstract

The adsorption of formaldehyde (HCHO) at very low vapor concentration (zero surface coverage) is studied on several carbon materials by using inverse gas−solid chromatography (IGC). The adsorption process is carried out in the Henry's law region. Therefore, the specific retention volumes, V s, allow the determination of the standard enthalpy of adsorption, ΔH o A, using the linear relationship between ln V s vs 1/T. Nevertheless two linear plots are obtained for the adsorption of HCHO on these carbon materials. Several experiments have been designed in order to determine the physical meaning of these linear plots. The general conclusion is that they are produced by a temperature-dependent mechanism which allows the adsorption to occur in smaller pores at lower temperatures and in larger ones at higher temperatures.

A Study of Acetaldehyde Adsorption on Activated Carbons

“…On the porous materials they are expected to be twice greater reaching about 30 kJ/mol for ethane and 70 kJ/mol for acetone (32). On the other hand, the heat of formaldehyde adsorption on various activated carbons was found to be between 15 and 33 kJ/mol (10). Following this, and Avgul and Kiselev's evaluation of the heat of one CH 3 moiety on nonporous carbon black equal to 9 kJ/mol (30), the heat of acetaldehyde obtained on microporous carbons should be in the range of 33-51 kJ/mol.…”

“…It also must be able to retain the sorbed odoriferous compound at even close to saturation conditions. Adsorption of formaldehyde on activated carbons was studied by Domingo-Garcia et al (10). They found that formaldehyde is strongly adsorbed with isosteric heat between 15 and 33 kJ/mol.…”

Microemulsion‐Assisted Preparation of a Mesoporous Ferrihydrite/SiO2 Composite for the Efficient Removal of Formaldehyde from Air

“…2 In this sense, the maximum concentration of HCHO in residential dwellings and workplaces has been strictly regulated. Many technologies have been used to address the removal of HCHO from air, both in laboratories and in fields,3 including plant absorption,4, 5 plasma technology,6 physical adsorption,7, 8 photocatalysis,9–11 and catalytic oxidation 12. 13 Among these technologies, physical adsorption has advantages in terms of its low cost and easy operation.…”

Effect of Some Oxidation Treatments on the Textural Characteristics and Surface Chemical Nature of an Activated Carbon

“…Although the adsorption capacity depends mainly on the textural characteristics, i.e., porous structure and pore volume, the surface nature can condition in many cases (1, 2) the adsorption behavior in solution, in the gas phase, and also the activity as catalyst and catalyst support (3,4). This means that the adsorption behavior of the activated carbons cannot be easily explained only on the basis of textural characteristics (surface area and pore size distribution); the chemical surface nature must also be taken into account.…”

“…pends on the treatment to which they are submitted. For instance, acidic groups are produced when activated carbons are treated in solution with different oxidizing agents such as HNO 3 , KClO 3 , and H 2 O 2 , or in the gas phase with O 2 , CO 2 , or steam. However, these treatments, in most cases, produce a modification of the textural characteristics of the original activated carbon, which can be a drawback in carbon materials with a narrow microporosity or a well-defined porosity.…”