Silicone rubber capillary

It is convenient to have some means, e.g. a gate clip on a section of Tygon or silicone rubber capillary tubing, to stop the flow of buffer at the bottom of the column. These ideas are shown diagram-matically in Fig. 4.7. 

Earlier papers on the continuous membrane column (28,29) have discussed the separation of CO2-N2, CO2-O2 and O2-N2 (air) mixtures in stripper, enricher and total column units composed of 35 silicone rubber capillaries. A characterization of the membrane column using a membrane unit concept (analogous to transfer unit concept — HTU, NTU) has also been presented. The purpose of this paper is to present some new data and discussions on the extended study of continuous membrane column. Specifically, the topics of multicomponent separations, Inherent simulation difficulties, composition minima in the enriching section, variation of experimental parameters, and local HMU variation along the column will be covered. 

Figure 2.2.3. Gas separation by permeation throu silicone rubber capillaries. Reprinted from Chem. Eng. Sd., 3fi(7), 751 (1975), J.M. Thorman, S. RhimandS.T. Hwang Gas separationby diffusion dirough silicone rubber capillaries." Copyri (1975), with permission from Elsevier.

Example 2.2.4 (a) Thorman et al. (1975) investigated the separation of oxygen from air by preferential permeation of oxygen through silicone rubber capillaries kept in a perme-ator. Air contairung 20.9 mole percent of oxygen was... 

When the experiment has been completed, clean the capillary as described above and then store it by inserting through a bored cork (or silicone rubber bung — normal rubber bungs which contain sulphur must be avoided) which is then placed in a test-tube containing a little pure mercury. Lower the mercury reservoir until drops no longer issue from the capillary, then push the end of the capillary into the mercury pool. 

Equation (52) allows us to estimate the impact of viscoelastic braking on the capillary flow rate. As an example, we will consider that the liquid is tricresyl phosphate (TCP, 7 = 50 mN-m t = 0.07 Pa-s). The viscoelastic material is assumed to have elastic and viscoelastic properties similar to RTV 615 (General Electric, silicone rubber), i.e., a shear modulus of 0.7 MPa (E = 2.1 MPa), a cutoff length of 20 nm, and a characteristic speed, Uo, of 0.8 mm-s [30]. TCP has a contact angle at equilibrium of 47° on this rubber. 

Oil drops of 2-5 /iL were introduced into 0.4 cm i.d. capillary tubes containing the aqueous phase. The more viscous heavy oils were heated for a short period to facilitate this addition. The tubes were then sealed with a tightly fitting silicon-rubber septum. A teflon screw was used to apply pressure on the septum after the capillary tube was inserted into the shaft of the tensiometer. In this manner, temperatures up to 200°C were achieved without loss of liquid. 

Figure 2. Flow cell (excluding pump and titration cell). Left Front view. Right Cross section along center line. I. Perspex cover. 2. Outlet tube (back to titration cell). 3. Flow channel. 4. Counter electrode (platinum). 5. Metal plate with cut edge exposed in the channel. 6. Seal of molded silicone rubber. 7. Piston for removal of air fix>m reference electrode compartment. 8. Reference electrode compartment. 9. Capillary holes connecting 8 to 3.10. Inlet tube (from titration cell). II. Reference electrode (Ag/AgCI, sat. KCI). (Reprinted from Ref. 3, with kind permission from Elsevier Science Ltd., Kidlington, Oxford, UK.)...

Figure 5.8 — Probe-type sensor based on continuous circulation of a stream containing an acid-base indicator for the batch determination of COj in sea water, (a) Reagent delivery capillary, (d) Reagent exit capillary, (c) Optical fibre from source, (d) Optical fibre to detector, (e) White silicone rubber membrane. (/) White silicone sealant, (g) Epoxy resin, (/i) 0-ring. (/) Sensor housing. (/) Optical cable. (Reproduced from [12] with permission of the American Chemical Society).

Bessarabov s devices use composite membranes consisting of a thin silicone rubber polymer layer coated onto a microporous poly(vinylidene fluoride) support layer. These membranes have high fluxes and minimal selectivities for the hydrocarbon gases, but the dense silicone layer provides a more positive barrier to bleed-through of liquid than do capillary effects with simple micro-porous membranes. 

Installation of Capillary Columns Glass columns, whidi are coiled when purdiased, must have straight ends to allow than to fit into imions at the injector and detector. A device is commercially available to straightoi capillary ends, but it is more usual to use a small butane flame. The column is suspended on a clamp stand and a supply of csilicone rubber tubing to produce a flow of about 0.5 ml/ min. A cool, small butane flame is used to apply... 

Figure 5. Cross section of concentric capillary gap cell. A, cathode and B2, anode support Cj, outlet C2, inlet D, anode E, silicon rubber seal. (From Ref. 53.)...

A number of different stationary phases have been used, mostly on a solid support impregnated with potassium hydroxide from very polar ones, such as polyglycols, to non-polar ones, such as silicone rubber. Packed columns have mostly been used, but good separations have also been achieved with capillary columns. 

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