H₂S Loss through Nalophan™ Bags: Contributions of Adsorption and Diffusion

Abstract

Hydrogen-sulfide (H2S) is a molecule of small dimensions typically present in the odor emissions from different plants. The European Standard EN 13725:2003 set a maximum storage time allowed of 30 hours, during which the sampling bag has to maintain the mixture of odorants with minimal changes. This study investigates the H2S losses through Nalophan bags and it shows that nonnegligible losses of H2S can be observed. The percent H2S loss after 30 hrs with respect to the initial concentration is equal to 33% ± 3% at a relative humidity of 20% and equal to 22% ± 1% at a relative humidity of 60%. The average quantity of adsorbed H2S at 30 h is equal to 2.17 105 gH2S/gNalophan at a storage humidity of 20% and equal to 1.79 105 gH2S/gNalophan at a storage humidity of 60%. The diffusion coefficients of H2S through Nalophan, for these two humidity conditions tested, are comparable (i.e., 7.5 10−12 m2/sec at 20% humidity and 6.6 10−12 m2/sec at 60% humidity).

Evaluation of the Efficacy of SIFT-MS for Speciation of Wastewater Treatment Plant Odors in Parallel with Human Sensory Analysis

“…In addition, the surface area of Nalophan to gas sample was increased with the smaller SIFT-MS samples. As per the experiments of Eusebio et al [36], the increased surface area may have contributed to the adsorption of hydrogen sulfide and other gases when compared to the olfactometry sample gas composition. The increase in gas volume of the samples used for olfactometry, may have assisted in keeping the chemical composition more stable.…”

“…A study of hydrogen sulfide retention in Nalophan bags [36] suggested that Nalophan itself not only allowed the release of hydrogen sulfide over a 30-hr retention period, the Nalophan may have also absorbed some of the hydrogen sulfide. This was demonstrated by inserting additional Nalophan material into the bag to increase the surface area [36]. The bags used for olfactometry were long sausage shaped bags that contained between 30 to 40 L of gas.…”

Physical Confounding Factors Affecting Gas Sensors Response: A Review on Effects and Compensation Strategies for Electronic Nose Applications

“…One of the easiest and most intuitive methods to control the RH level of analyzed samples relies on the permeability of the materials where the gas is collected and stored before the analysis. For example, Nalophan TM , which is the most common material used for the storage of samples to be analyzed via dynamic olfactometry (according to EN 13725:2022 [197]), is highly prone to diffusion of small hydrophilic molecules (e.g., water, ammonia, or hydrogen sulfide) [85,198]. Bax et al [199] used its permeability to humidity to reduce the moisture content of exhaled breath samples analyzed for detecting respiratory failures in patients affected by SARS-CoV-2.…”

“…Moreover, if polymeric bags are used for storage [196,222], they can be left in a controlled environment and exploit the bag's material permeability to regulate the sample temperature and humidity to a desired level. One of the main challenges of this material-based control is related to the potential interactions of such materials with the target gases, which may lead to a loss of volatile compounds that could be of interest to the study's goal [85,198]. In this scenario, materials such as polyvinyl fluoride (PVF, Tedlar ® ) and polyethylene terephthalate (PET, Nalophan NA TM ) are pointed out as appropriate containers for e-nose analyses because they are inert (i.e., they do not react with the target gas) and odorless [222].…”

Chemical characterization of odorous emissions: A comparative performance study of different sampling methods

“…These three methods differ in portability, applicability, sampling volumes and storage of samples. Focusing on storage time, canisters and tubes allow maintenance for longer times (up to 30 days), while bags can be stored for a shorter period, mainly due to the diffusion phenomena [36][37][38][39]. Although, canisters are voluminous, heavy and high operative costs are correlated with the cleaning procedures [40].…”