Determination of water content in various systems
The work leading to the invention described herein was done under a government contract. 
    
    
     CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of application Ser. No. 24,233, filed Mar. 26, 1979, now U.S. Pat. No. 4,198,207. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for determining water in a variety of systems. More particularly, it is concerned with determining water in such systems employing an adsorbing solid. 
     2. Discussion of the Prior Art 
     Current methods for water determination are time-consuming, difficult to run and expensive. One method that has been used for many years is the Karl Fischer method, described in one of its aspects in ASTM D1744-64(1968). Basically, this procedure involves the titration of a liquid petroleum product to be analyzed with Karl Fischer reagent, as described in D1744. 
     Other methods include distillation and the use of, for example, anhydrous sodium sulfate or concentrated sulfuric acid. The determination of water content with the latter two reagents is made by measuring the temperature rise due to heat of solution. While the same principle is found with the solids used in this invention, i.e. measurement of temperature rise as a function of the amount of water present, it is believed that the use of adsorbing solids for the purpose is unobvious. The method is extremely accurate and selective, permitting rapid determination of water in systems wherein the amount of water occurs over a wide range. 
     U.S. Pat. Nos. 3,528,775 and 4,089,652 disclose methods for determining water in oils. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention there is provided a method for determining the amount of water in a given system which comprises adding an adsorbing solid to a sample to be tested and determining the amount of water as a function of the rise in temperature produced. 
    
    
     THE FIGURE 
     The FIGURE is a schematic of the apparatus used in determining water content in fluid systems. 
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENTS 
     The invention described herein is applicable to many systems containing water. Although the present invention will be described and illustrated with reference to water and oil systems, it is not limited thereto. For example, the present method can be used to determine water in biological samples, such as in blood or in tissue. It is also useful in finding the water content of foods, such as juice concentrates, meats, cereals and the like, or of the products or by-products of industry, such as the water content of chemicals, liquid hydrocarbon fuels, filter cakes and the like. A complete listing of areas to which the method is applicable and of specific things within these areas is not believed to be necessary. Suffice it to say that the method can be employed to determine the amount of free water in any system that does not interfere with such method by causing, for example, an artifically higher or lower temperature change. It is contemplated that the method will be operative in systems containing from about 0.2% to about 99.0% by weight of water. 
     The range of 0.2 to 99% is approximate and refers to the range within which one practicing the method in the field can expect acceptably accurate results. It is contemplated, however, that in a laboratory, where more sophisticated equipment can be set up, accurate determination can be made on samples containing as little as about 0.01% by weight of water. 
     One specific area of applicability is the lubricating system of a marine diesel engine, the circulating lubricant of which generally becomes contaminated with water. The effective working life of a marine lubricant is limited by the accumulation of water, which, apart from altering the lubricant properties of the oil, may have a deleterious effect on the metal being lubricated. Similar considerations arise with other uses of oils. 
     In order to determine whether an oil is suitable for further use or for regeneration, or for rejection, it is frequently necessary to know whether water is present therein in excess of a predetermined tolerable proportion. Such a proportion might be in the range of from less than 1% to 5 percent or more by weight of wet lubricant, but substantially higher water contents can be encountered, and the present method can be used with oils containing water within the ranges normally encountered. 
     Devices are known by means of which the water content of an oil or other material can be determined. For instance, a measured amount of a water-containing sample may be confined in a closed vessel incorporating a pressure gauge together with a substance which reacts with water to produce gas. The amount of water present in the oil (which, for the present invention, includes liquid hydrocarbon fuel oils) is then determined according to the pressure rise shown on the gauge. The oil may also be contacted in a vessel with a water-reactive substance and a carrier. The amount of gas produced may then be measured by means of a separate manometer U-tube equipped with another manometric liquid and connected to the vessel, measuring the internal pressure developed. 
     Further, in the maintenance of Diesel engines, such as those used on railroad locomotives, it is generally recognized that the water content of the lubricating oil should be kept below about 0.45% to 0.5% by weight to minimize damage to the moving parts of the engine. Trace quantities of dispersed water in aviation fuels can have serious consequence as such water may accumulate in the float bowl of the carburetor and result in engine failure particularly at high altitudes and low temperatures where carburetor icing may occur. Water that is present in aviation jet fuels freezes to form ice crystals at the low temperatures encountered in high altitude operations. Such ice crystals may block the fuel lines and fuel jets. Transformer oil is another petroleum product, the performance of which is adversely effected by the presence of trace amounts of moisture. 
     Also, there are numerous applications for water-in-oil or oil-in-water emulsions. Notable among such applications are the hydraulic oils. In view of the wide use of hydraulic oils, as for instance in automobiles, airplanes and various industrial areas, such as mining, there is a serious need for an accurate, selective and rapid analytical method for determining water. 
     Many methods have been developed for the quantitative determination of water, but such procedures, in general, must be carried out in well-equipped laboratories, using sophisticated equipment. If one requires immediate, on the spot, information with respect to the water content of a particular petroleum product, there is not sufficient time to transmit samples to a distant laboratory and wait for a report from a chemical analyst. The present invention eliminates this time consuming analysis by allowing a simple apparatus to be set up at the desired site for essentially instantaneous determinations of water. 
     In the present invention, the adsorbing solid can be used alone, i.e. without solvent, or it can be used with a solvent to aid in the moderation of the heat of adsorption and in preventing the adsorbing solid from adsorbing water from the air, when mixed with a solvent. The mixture may contain from about 0.1 part to about 5 parts of adsorbent per part of solvent. From about 0.1 part to about 10 parts of fluid to be tested per part of total mixture of solvent and adsorbent are injected into the mixture which is sealed in a vial inside a vacuum flask (Dewar-type). 
     The adsorbent solids useful in this invention must (1) adsorb water, (2) be selective toward the water in the system and (3) should give off heat of adsorption that is easily measured. The preferred adsorbent having these prerequisites is a zeolite. Generally, any zeolite having a low SiO 2  /Al 2  O 3  molar ratio, i.e. from about 2 to about 10, will suffice. Among these, the most preferred zeolite is zeolite 4A because of its large exotherm on adsorption of water. However, other zeolites may be used. Among them are included zeolites 3A, 4A 5A, 10X and 13X. The amount of heat generated and the rate at which this heat is generated will vary from zeolite to zeolite. 
     Solvents are used to permit good contact between the test emulsion and solid reactant and, as mentioned hereinabove, to limit the temperature rise to reasonable and safe levels, i.e. the rise should not exceed about 130° F. Among the useful solvents are Stoddard Solvent (a mixed aromatic fluid) and isooctane. These solvents are for use with oil-miscible emulsions. However, the method applies to other fluids such as water-glycols systems or to soluble oils. In these cases the &#34;solvent&#34; should be water-miscible, including alcohols, ketones and the like. Large-pore zeolites are not recommended for water-miscible systems; they should be restricted to 3A, 4A and other small-pore zeolites. 
     The apparatus for detecting water in the oil by this method consists of a vacuum flask and presealed glass disposable reaction tube with a septum lid, an injection syringe and an electrical instrument (analyzer) comprising a thermistor probe for insertion into the reaction tube to measure the increase in temperature. 
     The electrical instrument used herein was calibrated so as to read directly in percent water as a function of temperature by inserting the thermistor probe of the analyzer into a heated water bath and then scaling accordingly. 
     Many oils are compatible with the method of the present invention. These oils include petroleum products, including liquid fuels and oils of lubricating viscosity as well as synthetic fluids. The latter class embraces synthetic ester lubricants, such as those formed from monohydric alcohol and dicarboxylic acids, from glycols or glycerols and monocarboxylic acids, and from pentaerythritols and carboxylic acids, including alcohols having from about 4 to 20 carbons, and monocarboxylic acids having from about 2 to about 18 carbon atoms. The class also include synthetic esters made from various mixtures of alcohols and carboxylic acids, such as, for example, an ester made from a mixture of alcohols and an acid or from a mixture of acids and an alcohol. Examples of some useful ester fluids include 2-ethylhexyl sebacate, trimethylolpropane trioctanoate, and especially pentaerythritol esters of valeric acid, isovaleric acid, caproic acid, caprylic acid, pelargonic acid, capric acid, and the like. Of special interest is a mixed pentaerythritol ester of an equimolar proportion of commercial valeric acid (containing isovaleric acid) and pelargonic acid. Other synthetic fluids include liquid polyolefins, alkylene oxide fluids, silicone fluids, polyacetals, and simple hydrocarbons of stable fluid viscosities. 
     Having disclosed the invention in general, the following will illustrate it. It will be understood that the Examples that follow are illustrative only and are not meant to limit the scope of the invention. 
     EXAMPLE 1 
     The numbers in this Example refer to the FIGURE. 
     Five grams of zeolite 4A and 10 grams of isooctane were premixed in a small 24 ml. capacity reaction tube with a septum lid (1). A thermistor (2) from the water analyzer (3) was inserted into the reaction tube which had been placed inside an insulated chamber (a Dewar-type flask) (4). 2 ml. of a water-in-oil emulsion containing 43% by weight of water was injected into the tube with a syringe (5). The entire assembly was shaken for 30 seconds and the percent water determined as amount of temperature rise above ambient. 
     It was determined that the sample contained 43±1% by weight of water. 
     Prior to making the determination of this Example (and of those that follow), the meter was calibrated at 43% water by running a sample known to contain that amount of water. The zero adjust knob (6) was used to zero the meter for the fluid ambient temperature before adding the sample. 
     EXAMPLE 2 
     This example is a comparison of the results obtained using this method with those obtained using Karl Fischer reagent. 
     Using substantially the procedure of Example 1, 11 grams of Stoddard Solvent and 11 grams of zeolite 4A were mixed and placed in the reaction tube and three ml. of emulsion was injected into the tube. After shaking for 30 seconds, the results shown in Table 1 were obtained. 
     The same emulsion was tested for water by the standard Karl Fischer method. The results are also shown in Table 1. 
     
                       TABLE 1                                                     
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        Wt. Percent Water                                                 
Emulsion  This Invention  Karl Fischer                                    
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A         43.0            43.0                                            
B         32.0            31.4                                            
C         42.8            42.5                                            
D         43.0            43.0                                            
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 Emulsions A, B and C  Commercially available emulsions                   
 Emulsion D  a hydraulic fluid comprising 100&#34; paraffinic neutral mineral 
 oil, water, ethylene glycol and an additive package.