PTFE pumps

These polytetrafulorothylene (PTFE) pumps along with the associated plastic expansion joints were installed, because the sponsors were blinded by the advantages. No one took the time to question their suitability in handling flammable liquids. The plastic pumps are just not fire-safe. They are frail in a fierce hydrocarbon fire. The presence of a containment material, such as plastic, can jeopardize the built-in mechanical integrity of the surrounding equipment. 

The main pump (eluent pump) is a 2- or 3-head membrane (PTFE) pump, able to operate at up to 100 bar, equipped with membrane failure indicators. 

Aqueous hydrogen fluoride of greater than 60% maybe handled in steel up to 38°C, provided velocities are kept low (<0.3 m/s) and iron pickup in the process stream is acceptable. Otherwise, mbber or polytetrafluoroethylene (PTFE) linings are used. For all appHcations, PTFE or PTEE-lined materials are suitable up to the maximum use temperature of 200°C. PTEE is also the material of choice for gasketing. AHoy 20 or Monel is typically used for valve and pump appHcations. Materials unacceptable for use in HE include cast iron, type 400 stainless steel, hardened steels, titanium, glass, and siHcate ceramics. 

Industrial equipment is a continuing area of development for plastics. Pipes, pumps, valves and sight glasses, made from such materials as PVC, PTFE and poly-4-methylpent-l-ene, have become well established on account of their corrosion resistance. The nylons are used for such diverse applications as mine conveyor belts and main drive gears for knitting machines and paper-making equipment. These and other materials are widely used where such features as toughness, abrasion resistance, corrosion resistance, non-stick properties, electrical insulation capability and transparency are of importance. 

Uses of the polyamide-imides include pumps, valves, gear wheels, accessories for refrigeration plant and electronic components. Interesting materials may be made by blending the polymer with graphite and PTFE. This reduces the coefficient of friction from the already low figure of 0.2 (to steel) to as little as 0.02-0.08. 

Fluoroplastic FPs have superior heat and chemical resistance, excellent electrical properties, but only moderate strength. Variations include PTFE, FEP, PFA, CTFE, ECTFE, ETFE, and PVDF. Used for bearings, valves, pumps handling concentrated corrosive chemicals, skillet linings, and as a film over textile webs for inflatables such as pneumatic sheds. Excellent human-tissue compatibility allows its use for medical implants. 

The main domestic use for PTFE is on non-stick utensils such as frying pans. Industrially, the polymer is used for gaskets, pump parts, and laboratory equipment. 

The solvent reservoir is a storage container made of a saterial resistant to chemical attack by the mobile diase. In its simplest fora a glass jug, solvent bottle or Erlenmeyer flask with a cap and a flexible hose connection to the pump is adequate. The PTFE connecting hose is terminated on the solvent side with a 2 micrometer pore size filter to prevent suspended particle matter from reaching the pump. In more sophisticated instruments the solvent reservoir may also be Cjquipped for solvent degassing, as... 

Schematic representation of the experimental setup is shown in Fig 1.1. The electrochemical system is coupled on-line to a Quadrupole Mass Spectrometer (Balzers QMS 311 or QMG 112). Volatile substances diffusing through the PTFE membrane enter into a first chamber where a pressure between 10 1 and 10 2 mbar is maintained by means of a turbomolecular pump. In this chamber most of the gases entering in the MS (mainly solvent molecules) are eliminated, a minor part enters in a second chamber where the analyzer is placed. A second turbo molecular pump evacuates this chamber promptly and the pressure can be controlled by changing the aperture between both chambers. Depending on the type of detector used (see below) pressures in the range 10 4-10 5 mbar, (for Faraday Collector, FC), or 10 7-10 9 mbar (for Secondary Electrton Multiplier, SEM) may be established.

Fig. 2.4p shows three types of post-column reactor. In the open tubular reactor, after the solutes have been separated on the column, reagent is pumped into the column effluent via a suitable mixing tee. The reactor, which may be a coil of stainless steel or ptfe tube, provides the desired holdup time for the reaction. Finally, the combined streams are passed through the detector. This type of reactor is commonly used in cases where the derivatisation reaction is fairly fast. For slower reactions, segmented stream tubular reactors can be used. With this type, gas bubbles are introduced into the stream at fixed time intervals. The object of this is to reduce axial diffusion of solute zones, and thus to reduce extra-column dispersion. For intermediate reactions, packed bed reactors have been used, in which the reactor may be a column packed with small glass beads. 

Any part of the system that is in contact with the mobile phase must be made of materials that are not attacked by any of the solvents that are to be used. The wetted parts are usually made of stainless steel or ptfe although other materials, such as sapphire, ruby, or ceramics are sometimes used. Everything on the high pressure side, ie from the pump outlet to the end of the column, must be strong enough to withstand the pressures involved. 

Figure 3 Schematic diagram of a solid-phase N02 sensor. The sensor consists of a small cell supporting the polymer-coated, glass substrate behind a glass window in full view of a PMT. The CL reagent is immobilized on the hydrogel substrate. The gel is sandwiched between the glass window and a Teflon PTFE membrane. The purpose of the Teflon membrane is to permit the diffusion of N02 from the airstream into the gel while preventing the loss of water from the hydrogel. Inlet and outlet tubes (PTFE) allow a vacuum pump to sample air (2 L/min) directly across the surface of the chemical sensor. (Adapted with permission from Ref. 12.)...

Again, helium degassing as described above is an appropriate way to remove oxygen, especially when combined with heating (40 to 50°C) of the mobile phase. Special care must be taken that oxygen cannot diffuse back into the mobile phase replace PTFE tubing by steel tubing between mobile phase container and pump, and between column and detector. 

Fig. 3.94. Process and instrument flow sheet diagram PI, P2 pumps Wl, heat exchanger Bl, B2, glass reactors FI, F2, membrane cells B3, B4 safety PTFE cells F3, F4, HPLC filter frits. Reprinted with permission from A. Rehorek et al. [155].

Agent same as anolyte circuit. Energetics piping to be PFA-lined carbon steel pumps to be titanium valves to be PFA-lined ductile cast iron agitators to be PTFE-coated stainless steel seals and gaskets to be Kalrez, PTFE, or PTFE-clad. Heat exchangers to be 304L stainless steel. Catholyte evaporator to be Inconel 690/625 hydrocyclones to be titanium. 

Inert material of the sampling device (bags, tubes, valves), no losses by diffusion Preflushing Prediction equipment Volume of the sample Sampling time.pump speed Storage time(<24h) Inert tube material (PTFE. stainless steel, glass) Preflushing Predilution equipment Heated probe jf Dust filters required... 

Yu et al. [139] developed a dry-deposition technique for coating the MPL onto a diffusion layer. This method consisted of forcing a mixture of carbon and PTFE powder through a mesh with the help of a vacuum pump located underneath the DL material. Once the mixture passed through the mesh, it was deposited on the surface of fhe substrate (still with the help of the vacuum pump). After this, the DL, with the MPL, was sintered at 350°C in order to melt the PTFL particles and bind all the particles together. Once the thermal stage was completed, the MPL was subjected to a rolling step in order to adjust the total thickness of the layer (MPL and DL). 

The membranes used are typically composed of cross-linked silicones and are suitable for on-line monitoring of volatile organic and inorganic compounds [93-94]. An alternative material is microporous PTFE, which has more rapid responses as well as lower selectivities and higher fluxes of the mobile phase compared to nonporous silicone membranes. More recently, developments in membrane introduction systems include the use of liquid membranes composed, for example, of a polyphenyl ether diffusion pump fluid [95-96]. This membrane has the advantage that it can take any desirable analyte and the selectivity can be modified using appropriate reagents. 

The sample introduction unit was constructed from inert materials, which minimizes the introduction of metal contamination into the system. The samples or digestion acids make contact only with PTFE, Kel-F, glass, acid-resistant rubber and platinum-iridium (9 + 1) alloy. In addition, the construction materials were Hmited to acid-grade Arborite (ureaformaldehyde laminate). Perspex and stainless-steel. The unit was constructed in three continuous sections a heated sample compartment, a turntable mechanism and heat-exchanger compartment, and a pump compartment. 

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