GB2097281A - Degassing liquids - Google Patents

Abstract

A method of and apparatus for degassing liquids, the liquid to be degassed being transferred into a synthetic resin container, the side thereof distant from the liquid being exposed to a vacuum for effecting the degassing of the liquid. The synthetic resin container, preferably composed of a fluoride resin, eg. PTFE, may be of box form, or it may be in tubular form, or a portion of the container may be in the form of a thin membrane. For example, as shown, liquid to be degassed enters via inlet 4 into synthetic resin tube 1 and exits at 5; closed container 2 is evacuated through outlet 3. <IMAGE>

Description

SPECIFICATION A method of and apparatus for deairing dissolved gases in liquids This invention relates to a method of and apparatus for the deairing of gases (dissolved gases) which have dissolved and remained in liquids.

Some liquids are deemed undesirable when containing dissolved gases, for example, solvents used for liquid chromatography, drugs, or inks and oils for printing. In the case of a solvent used for liquid chromatography, a highly accurated result cannot be obtained unless the dissolved gases are almost completely removed from the liquid, because even extremely small amounts of bubbles (dissolved gases) cause noises in proportion to the increase in the sensitivity of the detector. Also, the deterioration of drugs and oils accelerates proportionately to the amount of dissolved gases which are present.

In order to cope with this problem, a boiling method, a vacuum method or an ultrasonic method is conventionally employed to deair dissolved gases in liquids. However, these conventional methods cannot remove the dissolved gases to a virtually non-existent level, and such methods are prone to various inconveniences and shortcomings. Specifically, the boiling method, which deairs liquids by heating and boiling, is dangerous and not applicable for flammable liquids. In addition, it is not possible to apply the boiling method to liquids such as organic solvents because such solvents change quality or state when heated.

Likewise, the vacuum method, which effects deairing by the use of an aspirator or a decompression device, suffers from the following disadvantages; it requires a water system when an aspirator is used; low boiling point liquids may boil in a vacuum; liquids may incorporate air again after they are relieved from the exposure to a vacuum. The ultrasonic method, which deairs by exposing liquids to ultrasonic waves, is also inconvenient and defective because it not only requires an ultrasonic wave oscillator, but it also must be used jointly with the vacuum method due to its insufficient deairing effect if used alone.

Other disadvantages associated with conventional methods are for example, that these methods cannot be incorporated into an integrated system like liquid chromatography, and consequently, liquids deaired at a different site must be brought into the system. Also, there is a risk that the deairing treatment may become meaningless unless the liquids are handled properly so as to ensure that the liquids do not incorporate air once agin.

In consideration of the above related disadvantages attached to the conventional methods, by installing and housing a synthetic resin container in a deairing closed vessel which is connected by piping to a decompression device, and by transferring a liquid into this synthetic resin container for deairing of the gases dissolved in the liquid, the present invention seeks to provide a deairing method for gases dissolved in liquids, which is safe and applicable to flammable liquids or liquids with a low boiling point, which can remove the dissolved gases almost completely, and which at the same time can be incorporated easily into an integrated system such as liquid chromatography.

According to one aspect of the present invention, there is provided a deairing method for dissolved gases in liquids wherein a liquid is transferred into a synthetic resin container and the said synthetic resin container is exposed to a vacuum state for deairing of dissolved gases in the liquid.

According to a second aspect of the present invention, there is provided deairing apparatus for dissolved gases in liquids comprising a synthetic resin container for receiving a liquid to be deaired and into which a liquid is transferred, said container being installed and housed in a closed deairing vessel which is connected by piping to a decompression device.

In order that the invention may be more readily understood, embodiments thereof will now be described, by way of example, reference being made to the accompanying drawings, wherein:~ Figure 1 is a sectional elevation of apparatus according to a first embodiment of the present invention; Figure 2 is a horizontal sectional plan view of the apparatus of Fig. 1; Figures 3 to 5 are sectional elevations showing alternative embodiments of apparatus according to the present invention; Figure 6 is a flow diagram illustrative of a case where apparatus of the present invention is incorporated into an integrated system; Figure 7(a) is a graph indicating the liquid chromatography differential refractometer test results of a liquid which is deaired by the method of the present invention; Figure 7(b) is a graph indicating the test results of a liquid which is deaired by a conventional method; and Figure 7(c) is a graph indicating the test results of a liquid which is not deaired at all.

In the drawings, there is shown a synthetic resin container 1, a deairing closed vessel 2, a liquid a to be deaired, a deaired liquid b, deairing apparatus A of the present invention, a differential refractometer B, a recorder C and a vessel D.

In the following, an actual example of the present invention will be explained.

When putting this invention into effect, synthetic resin container 1 shall meet the following conditions only. Specifically, it shall not be penetrated by liquid a to be deaired or it shall not elute into liquid a. Any synthetic resin material may be used provided it does not permit penetration by liquid a. Accordingly, the material for container 1 can be expediently selected depending upon liquid a to be deaired. However, among the presently known synthetic resins, fluorine resin, and particularly ethylene tetrafluoride, is desirable as a selection because it is the best resin from the aspects of chemical resistance, temperature resistance and intensity resistance.Likewise, the shape of this container 1 can be a flexible tube as indicated in Fig. 1, Fig. 2 and Fig. 3, or it can be an open or closed box as indicated in Fig. 4, or it can be partially a thin membrane as indicated in Fig. 5, as long as the container can expose liquid a to be deaired to the vacuum for deairing.

Deairing closed vessel 2 is shaped as a closed box (Fig. 1, 2 and 4) or as a tube (Fig.

3), using a synthetic resin material or a metal, and is connected by a pipe 3 at a desired location to a compression device (not shown in the drawings) for evacuating the interior. At the same time, synthetic resin container 1 is installed and housed in this vessel.

With the above design characteristics, when deairing a liquid using tube shaped synthetic resin container 1 of Figs. 1 to 3, this operation can be performed continuously by passing liquid a to be deaired through tubular container 1. Precisely, in the examples of Fig.

1 and Fig. 2, liquid a in tubular container 1 will be almost completely deaired and become free of dissolved gases during the period of time which it enters through inlet 4 and exits through outlet 5. Also, when deairing using a box shaped (Fig. 4) or partially thin membrane shaped (Fig. 5) synthetic resin container 1, the deairing is performed by storing liquid a to be deaired in container 1. In this case, as will be understood, the deairing efficiency improves by heating or agitating liquid a to be deaired.

When the synthetic resin container 1 is shaped into a tube, the inner diameter, thickness and length of the tube may vary depending upon the properties and flow rate of liquid a to be deaired, the degree of vacuum, or the quality and the correlation of the inner diameter, thickness and length of the synthetic resin material that composes tubular container 1. However, it will be understood that the inner diameter must be narrow, the thickness must be as little as possible and the length must be adequate since liquid a is deaired during its passage through tubular container 1. As an example of applications, when this invention was used for liquid chromatography, the test results indicated that an inner diameter of 0.2 to 12 m/m and a thickness of 0.2 to 1.0 m/m were desirable.In regard to the length, a length of 1 Om obtained a near perfect deairing result when the inner diameter and the thickness of tubular container 1 moulded of ethylene tetrafluoride resin material, were 1.8 m/m and 0.2 m/m respectively when 3 cc/min distilled water used as liquid a to be deaired, was exposed to a vacuum of 700-mmHg. Also, in another actual example, when the inner diameter and the thickness of the tubular container moulded of polyethylene resin material were 0.2 m/m and 0.2 m/m respectively, and 3 cc/mln methanol used as liquid a to be deaired, was exposed to a vacuum of 700mmHg, a tube length of 20m was best suited to deair the liquid almost completely.

Liquid b deaired by the method and the apparatus of the present invention was tested using a detector (liquid chromatography differential refractometer), and the results are shown in Fig. 7(a). Fig. 7(b) presents the test results of a liquid which was deaired by a conventional method, whilst Fig. 7(c) presents the test results of a liquid which was not deaired at all. As indicated by these test results, the liquid treated by the method and apparatus of the present invention was almost completely deaired. All the test cases were carried out under the same conditions using distilled water.

An explanation will now be given to a case, referring now to Fig. 6, where the apparatus of the present invention was incorporated into an integrated system of liquid chromatography differential refractometer. In the drawings, a is a liquid (authentic liquid) to be deaired, A is a deairing device according to the present invention, B is a differential refractometer, and C is a recorder. An inlet pipe that introduces liquid a into the optical cell of differential refractometer B is formed using a synthetic resin material, and the said inlet pipe is housed and installed in the deairing closed vessel. Thus, whilst passing liquid a through the inlet pipe, the dissolved gases in the liquid are deaired, and the deaired liquid is continuously and directly introduced to the optical cell.In short, this inlet pipe is equivalent to the above described synthetic resin tubular container 1. In Fig. 3, reference D indicates a vessel that receives deaired liquid b when the deaired liquid is let out from the system of differential refractometer.

As explained above, the present invention is designated to deair dissolved gases in a liquid by transferring liquid a to be deaired into synthetic resin container 1 which is installed and housed in deairing closed vessel 2 which is connected by piping to a decompression device. Therefore, deaired liquid b can be, as shown in Fig. 6, let out into separate vessel D, or can be easily incorporated into an integrated system such as liquid chromatography differential refractometer.

Furthermore, due to the fact that heat and pressure are not applied directly to the liquid to be deaired, the invention can be safely applied to flammable liquids or liquids with a low boiling point. In accordance with the above merit, it does not require an elaborate equipment, but can remove dissolved gases almost completely using a simple device.

In addition, the synthetic resin container and the deairing closed vessel can be moulded as desired depending upon the purpose of the use. A box shaped synthetic resin container can deair a large amount of liquid all at once while a tube shaped synthetic resin container can deair the liquid continuously.

Also, utilisation of the present invention makes it possible to perform vapour-liquid separation of the liquids that are susceptible to gasification and to separate a very small amount of gases dissolved in liquids.

Claims (8)

1. A deairing method for dissolved gases in liquids wherein a liquid is transferred into a synthetic resin container and the said synthetic resin container is exposed to a vacuum state for deairing of dissolved gases in the liquid.

2. Deairing apparatus for dissolved gases in liquids comprising a synthetic resin container for receiving a liquid to be deaired and into which a liquid is transferred, said container being installed and housed in a closed deairing vessel which is connected by piping to a decompression device.

3. Deairing apparatus according to claim 2, wherein the synthetic resin container is shaped like a box.

4. Deairing apparatus according to claim 2, wherein the synthetic resin container is shaped like a tube.

5. Dearing apparatus according to claim 2, wherein a portion of the synthetic resin container is shaped like a thin membrane.

6. Deairing apparatus according to any of claims 2 to 5, wherein the synthetic resin container is made of a fluoride resin.

7. Dearing apparatus substantially as herein described with reference to and as illustrated in Figs. 1 and 2, or Fig. 3, or Fig.

4, or Fig. 5 of the accompanying drawings.

8. A deairing method for dissolved gases in liquids substantially as herein described.