Valeo valves

The equipment used in this application included two Waters M-45 pumps, a Waters 481 UV detector with microbore cell, an air-actuated Rheodyne 7413 injection valve with a 1-pl injection loop, an air-actuated Valeo four-port sampling valve (A2CI4UW2) with no groove in the injection entry ports, an air-actuated Valeo three-port switching valve (AC3W), and a Digital Equipment LSI-11/23 microcomputer. The LC system was located in a purged cabinet suitable for use in Class I, division 2 areas. The cabinet was in a heated room about 40 feet from the reactor column. The two Valeo valves were mounted next to the reactor column, while the microcomputer was located in the control room. 

Normally the Valeo valve was in the inject position. In this position, the reactor feed was blocked from entry, since the valve rotor had no grooves. To sample the reactor, the valve was switched for 1.2 seconds to the load position, using the 750-psi reactor pressure to fill a 2-pl slot in the valve rotor from the sample collected in the cup in the reactor. Upon switching back to... 

It is often observed, however, that the actual injection profiles are far from the Dirac model, as illustrated in Figure 2.3b, which compares a rectangular pulse injection of 100 fiL (solid line) and the injection profile recorded with a six-port Valeo valve (Houston, TX) fitted with a 100- L loop [42]. The Dirac injection is an acceptable model only if the width of the experimental injection is small compared to the standard deviation of the band profile under linear conditions. Usually, the experimental injection profile has a sharp front followed by a tailing decay (Figure 2.3b). This profile is also typical of those encoxmtered in preparative chromatography, except that they include a concentration plateau lasting for a certain period of time (see Figure 2.3). 

The methanol conversion reaction was carried out over these H-silicalite/honeycomb samples in a reactor set up as shown in Figure 1. Absolute methanol was injected into an evaporator at the rate of 0.49 ml/hour. Dry helium, a diluent gas, was passed into the evaporator at a rate of 45 ml/minute. Gaseous products were directly passed via a heated line through a six port Valeo valve with a 0.25 ml sample loop. The products were analyzed by a Varian 6000 GC with a Chromosorb-102 column. For each sample, reaction runs were made for at least 50 hours and steady state conversion data were collected. Methanol conversion was monitored at different catalytic reaction temperatures 100°C, 150°C, and 250°C. However, percent methanol conversions were calculated only for the 100°C and 150°C runs. Methanol conversion, calculated per gram of zeolite in the washcoat, was plotted (Figure 2) vs. percentage binder content. 

The reactor feed or effluent was analyzed using a Varian 3300 gas chromatograph using a seven foot 0.19% picric acid on Graphpac packed column (Alltech) and a FID detector. The column was held at 50°C for four minutes and then heated at a rate of 25°C/min to a final temperature of 100°C and maintained until all C5 species were eluted. A sixteen port Valeo valve rotated by an electric motor was used to collect samples at short intervals immediately following introduction of the feed to the reactor. 

When pyrolysis temperatures are reached, the six-port Valeo valve is switched and the 34-port Valeo valve automatically takes 15 samples of the gas stream for later analysis in the Hewlett-Packard 5834a Gas Chromatograph (HPGC). Unsampled gas is collected in a Teflon bag for later analysis. 

Rates of gas production can be measured using the reactor in either a differential or an integral mode. The differential mode employs the Valeo valve system to obtain fifteen 0.6-ml samples of gas evolved during the course of the experiment. With Ar tracer gas injected at a measured rate, the dilution of the tracer gas sample can be directly related to the "instantaneous" rate of volatile gas production in the reactor. For example, with a tracer gas flow of 5 ml per min, a dilution of 50% in the gas sample would correspond to an "instantaneous" volatile gas production rate of 5 ml per... 

Figure 1.10 shows a switching valve module produced by Sciware Systems (Sciware Systems S.L., Palma de Mallorca, Spain) implementing a VICI Valeo valve, which allows the number of lateral ports to be programmed. This imphes that only the valve cover needs to be changed according to the selected number of lateral ports, e.g. 6, 8, or 10 positions. 

Packing 100/120 HayeSepDB Cat. No. custom Column 30 x 1/8" stainless steel Oven 120°C Carrier helium, 30mL/min Del P.E.900T.C.,300ma Inj. 250mL Valeo valve, 120°C... 

Det. P.E.900T.C.,225ma, 140°C Inj. lOOmL, Valeo valve, ambient... 

A further extension of the SPME technique is coupling to HPLC (or HPLC-MS), which extends the method to (usually polar) compounds that are not amenable for GC analysis. This is also performed by DI sampling. After extraction, compounds bound to the fiber are extracted by a strong solvent. Note that the much simpler thermal desorption cannot be used, as the compounds to be studied are not volatile. This extraction takes place in a special extraction chamber, connected to a modified Rheodyne or Valeo valve of an HPLC system. To facilitate HPLC analysis, a special, so-called in-tube SPME device has been developed. With this technique, organic compounds in aqueous samples are directly extracted from the sample into the internally coated stationary phase of a capillary column and then desorbed by introducing a moving stream of mobile phase. 

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