Trapping systems

Schematic diagram of a purge-and-trap system. Anaiyte is coiiected in the primary adsorption trap. The secondary adsorption trap is monitored for evidence of breakthrough.

We have also tried the trapping reactor system, in which ammonia is trapped on the catalyst/adsorbent and microwave is irradiated intermittently. However, due to the small specific surface area and the small ammonia adsorption capacity on the employed CuO, the trapping system was not effective compared to the continuous irradiation. Further study should be made to develop a material having high ammonia adsorption capacity and high efficiency for microwave absorption. Supported CuO on high surface area material or preparation of high surface area CuO can be effective. 

IDENTIFICATION OF THE REACTION NETWORKS OF THE NO STORAGE/REDUCTION IN LEAN NO TRAP SYSTEMS... 

Nova, I., Castoldi, L., Lietti, L. et al. (2006) A Low Temperature Pathway Operating the Reduction of Stored Nitrates in Pt-Ba/Al203 Lean NOr Trap Systems, SAE Technical Paper, 2006-01-1368. 

The system provides a very sensitive means of detection levels of 10 picograms absolute are measurable with the continuous (permanent) trapping system. A further advantage is that the software calculates the analytical results directly in concentration in the unit volume of sample introduced. However, it should he stressed that the level of mercury measured is an absolute quantity and while the detection Hmit is of the order of 10 picograms, this quantity can be contained in any volume of gas. In addition, the fact that the mercury both absorbs and fluoresces to provide a measurement which can be measured with a specific retention time provides more positive evidence of the presence of mercury. 

To extend the levels of detection for mercury stiU lower, several workers, especially in this area of atomic absorption techniques, have chosen to collect the mercury on gold or other noble metal trapping systems prior to revaporizing the mercury into the measurement technique. Figure 7.14 shows the configuration of a specific system to concentrate mercury onto an amalgam preconcentrator prior to analysis. 

Use of some type of gas purging and adsorbent trapping system that would eliminate solvent interferences and permit a high degree of concentration. 

As a result, water traps are usually placed ahead of the cryotrap (e.g., see Goldan et al., 1995). Alternatively, a two-trap system is used in which water and the organics are trapped in the first trap, which is then slowly warmed to desorb organics, but not most of the water, into a second trap (e.g., Greenberg et al., 1996). 

Table III also presents our data for the extraction of Group 4 phenols from aqueous solutions. The o-bromophenol was added as an internal standard when some initial recovery problems were noted for the 2,6-di-terf-butyl-4-methylphenol results for its extraction are also reported here. The three phenols show good recoveries in the traps and overall good mass recoveries. One experiment was conducted under liquid C02 extraction conditions (temperature = 30 °C and pressure = 1500 lb/in.2) in an attempt to compare the relative efficiencies of the two states of CO2 for phenol extraction. Unfortunately, the phenols showed evidence of substantial breakthrough from the trapping system. The experiment does, however, demonstrate that liquid CO2 is also a good extractant for phenols present in water at parts-per-billion concentration levels.

Trapping Device Experiments. The system used to collect the organic compounds extracted from the aqueous stream was, in most cases, a series of glass U-tubes held at —76 °C. That temperature represented a practical lowest limit to prevent deposition of solid carbon dioxide. During the course of this program, it became evident that, for many compounds, complete mass balances were not being achieved. The trapping system appeared to be a likely source of such losses because many of the compounds studied had a finite vapor pressure at —76 °C. An effluent C02 stream saturated with these... 

The collection of the total CO2 effluent as a solid or liquid and subsequent isolation of the entrained organic compounds. Such a trapping system would minimize losses of organic substances due to the effects of poor thermal transfer possible in the other trap systems. In addition, if the effluent could be collected as liquid CO2 (e.g., at 900 lb/in.2 and 20 °C), several additional benefits were deemed possible. For example, minimal loss of the organic compounds should occur because their concentration in the gas distilled off is... 

The operation of a trap at 900 lb/in.2 would also facilitate the use of a recycling system for the CO2. Several experiments designed to perform a preliminary evaluation of this type of trapping system were also promising. 

---