Chemistry: analytical and immunological testing – Measurement of electrical or magnetic property or thermal...
Patent
1992-12-17
1995-07-25
Warden, Robert J.
Chemistry: analytical and immunological testing
Measurement of electrical or magnetic property or thermal...
422 90, 422 95, G01N 2518, G01N 2718
Patent
active
054361656
DESCRIPTION:
BRIEF SUMMARY
SPECIFICATIONS
The invention relates generally to an apparatus and method for measuring the amount of gas adsorbed on or desorbed from a solid. More particularly, the invention relates to an apparatus and method that will also provide a governing of the reactions of a gas with a solid by pressure and by temperature and by rate of flow in a broad range of those parameters. Most particularly, the invention provides an apparatus and method for very accurate and rapid measurement of the amount of gas adsorbed on or desorbed from a solid and means to govern the reaction of a gas with a solid at pressures ranging from substantially below one atmosphere to substantially above One atmosphere.
BACKGROUND OF THE INVENTION
It is estimated that solid catalysts account for about 90% of manufactured chemicals, and thus are extremely important to the chemical industry. It is well known that the performance of a catalyst can be greatly altered by small changes in its properties. Therefore, measuring the rate and products of chemical reactions between gases and catalysts and the characterization of catalysts ,are important endeavors. The most common and important methods of characterizing a solid catalyst involve the measurement of the adsorption of a gas on and the desorption of a gas from a catalyst.
It is also important to characterize many other types of noncatalytic solids by measuring their interaction with a gas. One such method is to determine the pore structure of a solid by measuring the physical adsorption of a gas near its boiling point, this frequently being done with N.sub.2 (g) near 77K. For example, the weathering of concrete is influenced by it pore structure. Another example is to determine the strength or quantity of acidic sites on the surface of a solid polymer by measuring the adsorption of a base, such as NH.sub.3 (g).
Reactivity measurements of a catalyst are almost always done at pressures at or above 1 atm, and it is common for such measurements to be done at pressures exceeding 10 atm. In contrast, some of the most important methods of characterizing a solid require measuring the adsorption and desorption of a gas at pressures substantially below 1 atm. One of the most accurate and important of these techniques is termed the volumetric method and requires high vacuum capability (P<5.times.10.sup.-5 torr, 760 torr=1 atm) and a highly accurate pressure transducer for the range of about 0 to 760 torr.
The measurement of reactivity typically involves exposing a catalyst to a reaction mixture and measuring the amount and type of products formed. This data yields the activity and product distribution of a catalyst at the given reaction conditions. It is normally desirable to control the rate of flow, temperature, and pressure of reactants in a reactor. By varying these parameters, information can also be obtained on the kinetics of a reaction including the rate constant, activation energy, and orders of the reaction.
Reactors operable at high pressure are made of metal. Since metal is strong, virtually all such reactorrs are rated at >1000 psia (14.7 psia=1 atm). Pressurized containers pose an explosion hazard. They are not combined with good vacuum capability and the volume of the reactor is usually not critical. Virtually all manufactured laboratory scale reactors usuable at high pressure have a volume in the range of 100 mL to 10 L.
A high pressure reaction system will have a high pressure gauge. Since such an apparatus is not designed for measuring the adsorption and desorption of a gas with a solid by the volumetric method, there is no need for also having a highly accurate low pressure gauge. The most accurate high pressure gauges have an accuracy of about 0.1% of full scale, but in the lower end of their range are much less accurate due to noise and drift. Therefore, such a gauge with a range of 1000 psia can measure a pressure to an accuracy of only about 53 torr. Assuming a very small reaction volume of 100 mL and a temperature of 20.degree. C., this corresponds to an error in measur
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Carpenter Robert
Warden Robert J.
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