Four-vessel Suprex extraction system

Figure 2. Schematic representation of four-vessel suprex extraction system.

Modifier Pump. The first feature in our adapted design is the introduction of a liquid pump via an instrument controlled VALCO (Model E04, Valeo Instruments, Houston, TX), four position selection valve. We have used an LKB Model 2150, dual piston pump for pumping modifier and entrainer fluids (LKB-Produkter AB, Bromma, Sweden). However, any suitable liquid pump could be substituted. Only pure fluids such as carbon dioxide have been introduced with the Suprex system syringe pump. With the addition of this second pump to deliver liquids, modifier is introduced directly into the extraction vessel. A wide range of alternative fluids and fluid mixtures can be rapidly selected with this dual pumping option. The criteria for selection of a modifier pump include the ability of the pump heads to withstand pressures in the range of 100 to 300 atm and interfacing capabilities, i.e. the ability to be turned on and off by the Suprex contact closure controls. 

With this system, two extract delivery lines are required, one for each of the vessels as well as two delivery nozzles. The advantages of this mechanism are its simplicity, ease of operation, and its capacity. The mechanism is also compatible with the method-chaining program in the SUPREX. Since the extraction vessels are treated as pairs,when the program asks for a count number on the columns, an entry of six, which is the maximum allowable, will result in twelve extractions, i.e. 2N. An entry of four will result in eight extractions, etc. However, because at each actuation of the solenoids, a pair of columns is selected, this mechanism does not allow room for independent method use between the extraction vessel pairs. 

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