Carbon traps offer a solution for the removal of undesirable gaseous and vapour contaminants in glove boxes. The unique physical absorptive properties of activated carbon make this an ideal, and economical, consumable product for the removal of solvents. Impregnated activated carbons function by the combined effect of chemical reaction and adsorption to remove contaminants that are not readily adsorbed by activated carbon alone.

Carbon traps can be installed in the outlet vents of gas purged (open loop) glove boxes, and in line prior to the gas purifier in gas recirculated (closed loop) glove boxes. Carbon traps should not be used in place of a particulate filter but in conjunction with one, as each has a dedicated design and operational function.

Gas purifiers are particularly vulnerable to being de-activated (poisoned) by sulphur and sulphur compounds, halides, chlorides, halogen, alcohols, hydrazine, phosphene, arsine, arsenate, mercury and other metallic compounds. Solvents have an adverse effect on the moisture reactant.

Carbon traps need to be carefully selected to the design parameters of the glove box gas flow velocity and volume for effective operation. Additionally, the carbon capacity needs to reflect the amount of contaminant and recharge time scale if saturation, and contaminant bypass, is to be avoided.

In practical terms it is difficult to predict the life or monitor the condition of a carbon filter in glove box applications. Activated carbon has a variable weight of absorbed contaminant to weight of carbon, with ratios of 1% up to 50% for differing chemicals. As a consequence of this a cautious over-design approach should be taken.

Glove Box Technology Ltd offers three basic designs, with carbon capacities of 1 litre, 5 litres and 8 litres. The 1 litre unit is for small glove boxes with low gas flow rates and small quantities of contaminants. The 5-litre unit is designed for general use in gas purged (open loop) or gas recirculated (closed loop) glove boxes with moderate quantities of contaminant. And the 8-litre unit is designed for harsh conditions in gas recirculated (closed loop) glove boxes.

The 1 litre unit is available in stainless steel, as an in-line trap with ½" BSP connections to either end, or in "open" ended design for connection to either a ½" BSP or NW16 outlet. The carbon charge is not included but can be supplied under separate instruction to customer requirements.

The 5-litre unit is available in stainless steel as an in-box trap and features an integrated inline HEPA filter. Connection to the glove box gas outlet (open loop) or gas recirculation system (closed loop) is through a NW40 outlet to the side of the carbon trap. Designed for removal through the glove box antechamber, the carbon trap should first be double bagged (PVC) and sealed with a cable tie prior to transfer to a fume cabinet for recharge. Recharge carbon must be oven dried prior to refill and must be dust free granular quality. The carbon charge is not included but can be supplied under separate instruction to customer requirements.

The 8-litre unit is available in stainless steel, as a self-contained floor mounted unit and is designed as a "break in" trap for fitting prior to the gas purifier using NW40 connections. Features an arrangement of 5 full bore stainless steel ball valves, three for permanent installation in the gas recirculation line to provide a gas bypass facility, and two permanently with the carbon trap, for isolating prior to removal to a fume cupboard for a carbon recharge. Additionally equipped with a compound gauge, and double valve quick disconnect for pluming into the vacuum line to remove air and trace moisture from the recharged and installed carbon trap. Recharge carbon must be oven dried prior to refill and must be dust free granular quality. The carbon charge is not included but can be supplied under separate instruction to customer requirements.

All carbon traps are designed on typical glove box gas flow velocity and volume rates to provide dwell times consistent with the removal of contaminants from our recommended carbon granule size with low gas pressure drop. Carbon capacity is based upon our experience of average duty requirements, and an annual service recharge to optimise filter efficiency and replacement economy.

Custom designed carbon traps can be of an integrated design or stand-alone units for installation into existing glove boxes. Large carbon traps are supplied with carbon filter racks equipped with safe change facilities.

© GLOVE BOX TECHNOLOGY LTD January 2004

Treatable Contaminants

Substances suffixed by a * require special treatment

This list is not exhaustive and if a particular compound does not appear, please contact our technical sales department for further advice.

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