Simple Procedure for Washing Solids with Liquified Gases M. Binder, C. W. Walker, Jr., R. J. Mammane, W. L. Wade, Jr., and S. Gilman U S Army. LABCOM. Electronics Technology and Devices Laboratory. Fort Monmouth, NJ 07703 In chemical extractions or wash procedures, the solids to be treated are washed with liquified gases. However, use of gases that are liquid only a t temperatures helow ambient carries experimental problems. Firstly, the low temperatures could allow unwanted moisture to condense and thus orovide additional unwanted contamination. Secondlv, .. I ~.Q uified and especially toxic gases pose safety problems. The f i ~ u r illustrates e a clever cell desim that allows solids to be effectively and safely washed in thelaboratory without fear of moisture contamination or gas leakage. The gas used in this case is Son. The wash procedure is simplified by use of an SO2 gas cylinder that is factory equipped with an eductor tube (a tube extending to the bottom of the gas cylinder so as to allow only the liquid phase of the gases to be removed). When the gas cylinder valve is opened, sulfur dioxide in the liquid form is removed. The cell, used for cleaning, is a highpressure aerosol container (Labcrest Industries) and the Swagelock valves can be made of Teflon or stainless steel. Teflon tubing is used throughout. The sample to he cleaned is placed in the cell and sealed with the screw cap. Quickconnect adapters are then connected to an active vacuum suchasa watkaspiratororpumpequipped with a trap and a liquid SOi source. The atmosphere in the cell as well as all interconn&ng lines are first evacuated by means of the applied vacuum, and then liquid sulfur dioxide is allowed to enter. When the solid to be washed has been sufficiently cleaned, the liquid sulfur dioxide is removed through the vacuum and either vented safely or allowed to react with the water in the aspirator. This process may he safely and rapidly repeated any number of times as desired. Referring to the drawing, the screw cap used to seal the cell is connected by means of Teflon tubing through a union cross to valves A, B, and C. Valve A is a two-way valve that regulates the flow of liquid from the SOz source. When in the open position, valve A allows liquid sulfur dioxide to flow into the cell. Valve B is a h a two-way vaheconnecting thecell valve C. When in the open position, valve H regulates the vacuum heingapplied to the c&.
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Valve C, a three-way valve, is connected to vacuum. In the down nosition i t shunts vacuum to valve B and throueh connecking Teflon tubing. In the up position, valve C shu& vacuum to valve A. This action evacuates the line UP to valve A. In the center position, valve C is closed. In the cleaning process, valve C is first rotated to the upper position to evacuate air or moisture that may he trapped in the line from the sulfur dioxide tank to valve A. When this region is fully evacuated, valve C is rotated downward so that the applied vacuum evacuates the line to valve B. Valve B is then opened to evacuate the cell fully as well. Valves C and B are then closed, and valve A is opened to allow sufficient quantities of liquid sulfur dioxide to enter the cell. The solids to be extracted or cleaned are stirred. Spent sulfur dioxide is then removed by rotating valve C downwards and opening valve B to withdraw liquid through valve C to vacuum. Any solid material can be washed using this method. The procedure works particularly well when washing porous carbon cathodes used in electrochemical cells. In such cases, cathodes are washed to selectively remove discharge products from the cathode following cell discharge.
The apparatus.
