US 3753653 A
Method and apparatus for gas analysis by chemical reaction in the gas phase, and determination of the components by chromatographic detecting means, comprising the steps of injecting a sample into a gaseous carrier stream, dividing the sample-carrying gaseous carrier stream into at least two parts for being conveyed through independent supply branches, passing at least one of the branched streams through a chemical reactor for selectively modifying the composition of the sample, adjusting the residence of the parts in the branches to different times, and conveying the branched parts or streams into a passage leading to the detecting means, so that they will arrive there separately and without interference.
Description (OCR text may contain errors)
United States Patent [191 Brieva et al.
[ Aug. 21, 1973  Inventors: Antonio Mario Brieva, Vicente Lopez; Nestor Luis Soulages, LaPlata, both of Argentina  Filed: Mar. 1, 1971 [211 App]. No.: 119,681
 US. Cl. 23/230 R, 23/230 M, 223/232 C, 23/253 R, 23/253 PC, 23/254 R, 23/254 EF,
73/23.1 51] Int. Cl. 00111 31/08, 00111 31/12  Field of Search 23/232 C, 253, 254, 7 23/230 R; 73/211 ["56] References Cited UNITED STATES PATENTS 3,096,157 7/1963 Brown et al 23/230 C 3,235,70 11/1966 Robertson 23/232 c 3,304,159 2/1967 Hinsvark 23/232 c 3,460,909 8/1969 Gayle 23/232 c 3,518,059 6/1970 Levy 23/230 PC X 3,607,073 9/1971 Stamm... ..23/232c Primary Examiner-Morris O. Wolk Assistant Examiner-R. E. Serwin Attorney-Tab T. Thein  ABSTRACT Method and apparatus for gas analysis by chemical reaction in the gas phase, and determination of the components by chromatographic detecting means, comprising the steps of injecting a sample into a gaseous carrier stream, dividing the sample-carrying gaseous carrier stream into at least two parts for being conveyed through independent supply branches, passing at least one of the branched streams through a chemical reactor for selectively modifying the composition of the sample, adjusting the residence of the parts in the branches to different times, and conveyingthe branched parts or streams into a passage leading to the detecting means, so that they will arrive there separately and without interference.
The invention also relates to an apparatus for carrying out the method, for analyzing the gases by chemical reaction and determination of the components by chromatographic detecting means.
18 Claims, 3 Drawing Figures METHOD AND APPARATUS FOR GASEOUS-PHASE CHEMICAL REACTION ANALYSIS The present invention relates to a system for analysis of components in a gaseous stream by selective chemical absorption, and determination of the components by chromatographic detecting means.
The reactivity of certain components in the gaseous phase has been applied in numerous processes as a means of isolating or removing a given compound from a mixture, the best known and most classical example being one where several liquid solutions are employed which are absorbers for the several gaseous compounds to be analyzed. In the last decade, the major developments in analytical methods, in which chemical reactions in the gaseous phase are employed, have taken place in the technique called Gaseous-Phase Chromatography" or, more specifically within this technique, in the so-called Gaseous-Phase Chromatography with Chemical Reaction.
The combination of gaseous-phase chromatography with a chemical reaction results in a new analytical method offering broader possibilities than the two techniques taken separately. Very specific methods have been developed on the basis of this technique, such as elementary analysis, substractive analysis, pyrolytic analysis, and the like.
In the process of the present invention no chromatographic column is employed but only chemical absorb ers or reactors are used. The injected sample or specimen is transported by a carrier gas and is separated into two or more portions, each of them being passed through chemical absorbers or reactors, where the several components react selectively. Each of the portions into which the sample has been divided passes through a corresponding number of independent branches which subsequently are joined in a common outlet leading to a single chromatographic detecting means. In order to cause that the sample streams passing through the branches, and which include also compounds that have not disappeared by reaction, reach said single detecting means in succession and without any interference, it is necessary to control the residence or passage times through the branches. The above constitutes another feature of the invention and is achieved by controlling the rate of the carrier gas flow in each of the branches and/or by adding dead volumes of different capacities in each or some of the branches.
Accordingly, the main object of the present invention is a gas analysis method by chemical reaction in the gas phase, which comprises the following steps: injecting a sample into a gaseous carrier introduced in the analysis system; dividing the carrier stream into at least two portions; passing eachof the portions through independent branches, at least one of which is provided with a chemical reactor capable of selectively modifying the chemical composition of the sample; adjusting the residence of the sample in each of the branches to a different time; and conveying. the portions to a single detector to which the sample components from the different branches arrive in succession and without any interference.
It is also an object of the present invention to provide separate and independent branches, at least one of which includes receptacles for chemicals capable of selective modification of the sample stream passing through the particular branch; the branches being connected to a common conduit which leads to a singel detector of the components; in at least one of the branches, a dead volume and flow-controlling means are arranged, whereby the sample flowing through each of the branches will reach the detector separately and without interference.
In order that the present invention may be clearly and readily understood it will be described with reference to several examples of uses of the process, and a preferred embodiment of the apparatus, but it should be understood that such description is given only by way of illustration, and that the invention is not limited to such uses and/or embodiment but will include all modifications.
In the drawings:
FIG. 1 shows schematically a preferred embodiment of the apparatus adapted for practising the process of the present invention, in combination with a chromatograph;
FIG. 2shows a chromatogram obtained in the analysis of a given type of sample; and
FIG. 3 illustrates a further chromatogram obtained in analysis of a different type of sample.
Referring now to FIG. 1 of the drawings, an inlet for the carrier gas is shown by numeral 1, an optional carrier-gas conditioner by 2. The conditioner may be a humidifier, a purifier, or the like. A sample injector 3 is next in line, associated with a flow divider 4 which is needed when very small amounts of gas are to be analyzed. The gas is then passed through a connector A which may be a three-way, four-way or multiple connector depending on how the apparatus is to be used.
The function of connector A, is to divide the sample into two, three or more portions. Further provided are restrictors B B and B which may becapillaries or any other type of fixed or variable restrictors, having the functin of controlling the flow in each of the branch lines; containers C and C are arranged in the branch lines in whichthe chemical absorbents or reagents are placed and which may be heated independently or simultaneously in accordance with the working conditions of the reactants (by heating means not shown). Independent heating means are provided whenit isdesired. to operate at different temperatures in the branches, otherwise a single heater can be provided.
D and D are empty tubes of known volumes forintroducing an additional so-called dead volume into each of the branches in which they are placed. A isa.
three-, fouror multiple-way connector, adjustable to the number of branches usedin aspecific embodiment of the apparatus, where all branches meet in-a common outlet communicating with a. single detector 5..
In accordance with. FIG. I, the part of the apparatus enclosed within brokenlines defines the basic features of the invention, since the other elements arecommon to a gaseous-phase chromatograph of conventional design. This means that the apparatus may constitute a complete unit, as indicated in FIG. I, or may. form a partial'unit, i.e. the part enclosed within the dottedor broken lines, which is inserted inca chromatograph in the place normally occupied by the chromatographic column.
For a clearer understanding of the process, the apparatus will be described for some specific uses, one of them being the analysis of types of hydrocarbons saturated, aromatic and olefinic as they are present in gasolines and petroleum distillates boiling up to 220C. Such analyses are very frequent in the oil and petrochemical industries since they allow control of product quality, control of the process, control of mixing (blending) operations, and the like.
In recent years, several techniques have been developed employing this type of analysis, by gaseous-phase chromatography with chemical reaction, wherein chromatographic separation is combined with chemical absorption, the analysis taking about 30 to 40 minutes to perform. With the use of the method and apparatus according to the invention, the time is cut down to 3 to minutes.
To carry out this analysis in accordance with the present invention, the apparatus is employed as illustrated in FIG. 1, i.e. havingthree branches. In branch 1, a receptacle C is placed, containing as absorbents perchloric acid and mercury perchlorate impregnated in an inert and porous support, and a receptacle C containing as absorbents sulfuric acid and mercury sulfate impregnated in a similar support as above, is placed in branch 3. The quantities of samples injected are those normally used in gaseous-phase chromatography. As detector the use of a known flame-ionization detector is preferred, the features of sensitivity and response of which show excellent adaptability.
Aromatic hydrocarbons and olefins are quantitatively absorbed in receptacle C,, while saturated hydrocarbons pass unmodified; in receptacle C only olefins are absorbed, the saturated and aromatic hydrocarbons being allowed to pass through. Since there are no absorbers in branch 2, the entire sample passes through.
Before being admitted into the apparatus, the carrier gas is wetted in conditioner 2, which in this case acts as a humidifier, so that the gas will have a water-vapor pressure equal to the vapor pressure in receptacles C C this is to prevent modification in the original concentration of the acids from taking place, which would occur if a dry carrier gas, or one having a water content different from that corresponding to the vapor pressure in the absorbent containers were employed. For the above use, the working temperatures of the apparatus is 70 i 5C.
FIG. 2 illustrates the chromatogram obtained, in which peak S corresponds to the saturated hydrocarbons, peak T to the total sample and peak S+A to the saturated plus aromatic hydrocarbons. The olefin percents are obtained by deducting the saturated as well as the aromatic values from the total sample percentage.
Before the quantitative computation is effected, it is necessary to calibrate the instrument to determine the amount of sample which will pass through each branch and which exclusively depends on the carrier gas flow in each of the branches, and therefore on the restrictors B,, B, and B which are being employed.
This calibration is carried out by injecting a saturated hydrocarbon which passes unaltered through the three branches and by relating the areas of the three peaks produced by this saturated hydrocarbon. Once the calibration factors f are known, computation of the FIG. 2 chromatogram is effected in accordance with the following equations:
% saturated hydrocarbons (f, X area S)/(f, X area aromatic hydrocarbons [f X area (S+A) f,
Xarea Sl/U: X area T) 5 olefins f, X area T fl, X area (S+A)]/(f, X
area T) Analysis time is five minutes and results thereof are given in Table I which also includes the deviation. The commercial gasoline appearing in this Table was also analyzed for purpose of comparison, according to ASTM Test D-l3l9 6lT. As the method herein described expressed the results in weight percent, while the ASTM method expresses the results in volume percent, it was necessary to convert the latter into weight percent, assuming for the aromatic fraction a density of 0.87, and for the saturated and olefin fractions a density of 0.68. In the same Table a synthetic gasoline is also included the composition of which is known by Obtained according-to ASTM method D-l3l9 6lT Composition given by manufacturer Other examples for the use of this rapid analytical technique is for the analysis of olefins and saturated hydrocarbons in gaseous samples, i.e., the composition of butane and butene feeds in an alkylation plant; or the saturated fraction content in high-purity olefins employed in petrochemical processes.
In such cases, the apparatus can be simplified by removal of one of the branches, and the analysis can be performed with two branches only, one of them including the olefin absorber consisting of mercuric perchlorate-perchloric acid as described above, with no absorber in the other branch.
FIG. 3 shows the chromatogram representing the analysis of high-purity propylene. Operative conditions for this use may be the same as in the previous one described, although for this case it is not necessary to humidify the carrier gas, and the temperature in the apparatus may range from ambient to about 70C. Analysis time is three minutes and the results obtained in the analysis of a high-purity propylene and a sample of butanes and butenes, as well as standard deviations, are shown in Table I above.
Analysis of inorganic compounds is another possible use for the method of the invention, such as the analysis of a mixture of carbon dioxide, water and nitrogen. This analysis is carried out up to now in equpment for elementary analysis by gaseous-phase chromatography with chemical reaction in which the carbon, hydrogen and nitrogen content in a substance are known after their combuston and transformation into carbon dioxide, water and nitrogen, respectively.
Depending on the equipment employed for determining these three compounds, it is first necessary to separate them in a chromatographic column and then detect them separately or else have them absorbed in succession and then detected by means of multiple detectors.
With the apparatus described in the present invention such measurements can be effected without using a chromatographic column or multiple detectors.
Finally, due to the high speed of the method of the invention, which takes between 3 and 5 minutes, as shown in FIGS. 2 and 3, its use is of great interest in the control of processes by means of semi-continuous analysis of the feeds or of the process products. As examples of these last uses the following are mentioned: control of gases in a cracking process, control of aromatic hydrocarbons produced in a catalytic transformation process, control of a solvent distillation or extraction plant, control of a synthesis gas with hydrogen, carbon monoxide, carbon dioxide and methane, and the like.
What we claim is:
1. A method for gas analysis by chemical reaction in the gas phase and determination of the components by chromatographic detecting means, comprising the steps of injecting a sample into a gaseous carrier stream, dividing the sample-carrying gaseous carrier stream into at least two parts for being conveyed through independent supply branches, passing at least one of the branched streams through a chemical reactor for selectively modifying the composition of the sample, adjusting the residence of the parts in the branches to different times, and conveying the branched parts into a passage leading to the detecting means, so that they will arrive there separately and without interference.
2. The method as defined in claim 1, further comprising the step of adjusting the quantity of the sample introduced into each branch by the rate of the carrier gas flow.
3. The method as defined in claim 1, wherein the chemical reactors are filled with different chemicals in each branch for selectively reacting with the different types of gas components contained in the sample.
4. The method as defined in claim 3, wherein the chemicals for selectively reacting with different gas components are absorbents.
5. The method as defined in claim 1, further comprising the step of adjusting the residence time of the carrier gas in each branch by flow restricting means.
6. The method as defined in claim 1, further comprising the step of adjusting the residence time of the carrier gas in at least one branch by adding a dead volume.
7. The method as defined in claim 1, further comprising the step of adjusting the residence time of the carrier gas in at least one branch by inserting a capillary.
8. The method as defined in claim 1, wherein the temperature in each branch is different.
9. The method as defined in claim 1, wherein the temperature in each branch is the same.
10. The method as defined in claim 1, further comprising the step of moistening the carrier gas stream before injecting the sample into the gaseous carrier stream so as to maintain unchanged the concentration of the chemicals in the reactors.
11. The method as defined in claim 1, for analysis of gasoline containing saturated aromatic and olefinic hydrocarbons, comprising the steps of feeding through a first branch line part of the sample, in a gaseous carrier stream, over an absorbent mixture of perchloric acid and mercury perchlorate, thereby absorbing aromatic and olefinic hydrocarbons, while saturated hydrocarbons pass unmodified, feeding through a second branch line part of the sample without arrangement of absorbers, so that the entire sample leaves unmodified, and feeding through a third branch line part of the sample over an absorbent mixture of sulfuric acid and mercury sulfate, thereby absorbing olefins and allowing saturates and aromatics to pass through unmodified, and successively admitting the parts from the branch lines to the detecting means and thereby determining the percentage of each component ofthe sample, the operating' temperature being 79C and the entire time of the analysis amounting to about five minutes.
12. An apparatus for gas analysis by chemical reaction in the gas phase and determination of the components by chromatographic detecting means, comprising means for injecting a sample into a gaseous carrier stream, a gas-supply conduit, gas-flow dividing means in said conduit, at least two supply branch lines being fed through said dividing means, means in at least one branch line for causing chemical modification in the components of the sample, a common outlet conduit for all branch lines with connecting means thereof to the detecting means, and flow controlling means in said branch lines, whereby the flow from each line will reach the detecting means separately and without mutual interference.
13. The apparatus as defined :in claim 12, wherein said means for chemical modification is constituted by a chemical absorber.
14. The apparatus as defined in claim 12, wherein said means for chemical modification is constituted by a chemical reactor.
15. The apparatus as defined in claim 12, wherein said flow controlling means is in the form of a flow restrictor.
16. The apparatus as defined in claim 12, wherein said flow controlling means is in the form of a dead volume in at least one branch line.
17. The apparatus as defined in claim 12, wherein said flow controlling means is in the form of a capillary in at least one branch line.
18. The apparatus as defined in claim 12, further comprising means for moistening the carrier gas stream before the sample is injected into the gaseous carrier stream.
Patent No. 5,755,655 Dated August 21,
Intentofls) A; N. Brieva et al.
It is certified that: error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
In column 4, Table I, in the heading thereof (lines 241/25), the designations for the four vertical columns should read 8.8: follows (the first numerals in each column being added for the l Method of the sake of clarity) (Composition invention v01. wt. Wt. Std. Dev.
also, in lines 52 and 5%, the footnote indicators should read (2) as in the heading of the Table (or, the par entheses should be omitted around "1", also reproduced hereinabove for completeness) g Signed and sealed this 20th day of November 1973.
EDWARD M.FLETCHER,JR. v RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents FORM Po-mso (10-59 USCOMWDC 6037mm)? if} i v; as. eovanuupu mun"; arms: um o-ass-au