November 15, 1942
ANALYTICAL EDITION
TABLEIV. DETERMINATION OF UNSATURATIOK OF FIYECARBOX-ATOM HYDROCARBOXS AND MIXTURESTHEREOF BY HYDROGENATION Substance
%aoa
Found Corrected Synthesis M o l e Per Cent Cnsaturation b 202 0 199 6 200 0
Isoorene. nure 1.4217 Miiture ' 37.0% trimethylethylene 1.3871 28.0% piperylenes 1.4311 35.0% isoprene 1.4217 165 0 163 2 163 0 Xixture 46.4% n-pentane 1.3577 1 6 . 5 7 trimethylethylene 1.3869 37.1 piperylenes 1.4305 90.7 90.3 90.7 a Best literature valuea: isoprene, 1.4216; mixrd piperylmez. 1 4309: trimethylethylene, 1.3869: n-pentane, 1.3578 6 On basis of hydrocarbon content.
%
gen are carried out at constant volume, the pressure being measured. The liquid hydrocarbon is vaporized into a previously evacuated vessel until a pressure of 250 mm. is attained. Hydrogen gas is then admitted until the total pressure rises to 750 mm. The partial pressure of the hydrocarbon in the blend is well below the saturation pressure under the conditions of measurement. The blending operation is readily adapted to the ordinary Podbielniak distillation apparatus. It has been found convenient in this laboratory to prepare all blends of the pentane-pentene fractions a t these pressures and use a single correction factor (+0.5 mole per cent) for the composition of the blend. There are obviously many other ways in which the blending can be done, but the addi-
883
tive correction factor applies only to blends made up in the exact manner described. The corrections for the hydrogenation method when applied to a 33.8 mole per cent blend of pentane-amylene fraction in hydrogen have been calculated and the resulting corrections are plotted in Figure 6. These corrections are based on the use of equal volumes of additional hydrogen and blend in the analysis. To check the method, a series of pure five-carbon-atom hydrocarbons, and mixtures thereof, n-ere prepared, blended with hydrogen, and the unsaturation determined by hydrogenation. The results, presented in Table IV, offer very good confirmatory evidence for the validity of the method and the corrections.
-4cltnowledgmeiit The authors wish to thank H. K. Wiese for obtaining experimental data, IT. J. Troeller, Jr., and D. RI. Mason for some independent work on the corrections for Cd fraction, and the Standard Oil Development Company for permission to publish.
Literature Cited Batuecas, T., J. chim. phys., 31, 165-83 (1934). (2) International Critical Tables, Vol. 111, p. 3, New York, McGrawHill Book Co. (3) Jessen, F. W., and Lightfoot, J. H., IND.ENG.CHEM., 30, 312(1)
14 (1938).
(4)
Leendertse, J. J., and Scheffer, F. E. C., Rec. t
~ w chirn., . 59, 3-13
(1940).
(5)
McMillan, W. A., Cole, H. d.,and Ritchie, A. V., IND. ENQ. CHEM., ANAL.ED.,8, 105-7 (1938).
(6) Roper, E . E . , .J. Phuvs. C'hern.. 44. 83.5-37 f l R 1 0 ) .
Contact Sulfuric Acid Manufacture Evaluation of the Reich Test GERRIT DRAGT AND K. W. GREEXYAN (;rasselli Chemicals Dept., E. I. du Pont de Nemours & C o . , Inc., Cleveland, Ohio
T
HE Reich test for sulfur dioxide is commonly used in the determination of gas strength in sulfuric acid manufacture. I t s flexibility, ease of operation, and simplicity make it a desirable method for the routine testing of gas strengths in different parts of the gas purification or conversion system. Various modifications of the original test proposed by Reich (11) both as t o apparatus (2, 3, 4,7 ) and to the nature of the absorbing solution (6, IO), have been described, but so far as could be determined, no study of the accuracy and precision of which the test is capable has been reported. The present work evaluates the factors that influence the accuracy and precision of the test as used in brimstone-burning contact sulfuric acid plants. The test as described is applicable to chamber burner gases, but must be modified for use with chamber gases containing oxides of nitrogen.
Apparatus and iMaterials Keich test apparatus (Figure 1). Woulff bottle, 4-liter capacity, equipped with thermometer, inlet, and siphon tubes. In operation, this bottle is filled with water to the mark shown. Reich bottle, 350-ml. capacity, equipped with a 2-mm. bore glass tube with attached stopcock. Ga8 pressure bottle, 350-ml. capacity, equipped with T and vent tubes. Graduate, 125-ml. caparity, graduated in 0.5-ml. units. Oisat gas analysis apparatus, Bureau of Mines type. Sulfur dioxide gas mixture, 12 per cent sulfur dioxide, balance nitrogen. This gas mixture was stored in a regulation size cyl-
inder and kept above 21.11" C. (70" F.) to prevent liquefaction of sulfur dioxide. Barometer, mercurial. Chromic acid solution, 50 per cent aqueous. 0.1 N iodine solution, prepared from c. P. iodine crystals and potassium iodide (20 grams per liter). This solution was standardized against Bureau of Standards arsenic trioxide. Starch solution, 2 per cent.
Procedure After flushing the sampling line up to the tip of the inlet tube of the Reich bottle with the gas t o be tested, the stopcock was closed and the gas was analyzed according to the following procedure: Ten milliliters of 0.1 N iodine were added to the Reich bottle containing 175 ml. of distilled water, 5 ml. of starch solution, and sufficient iodine to give a light blue color. The Reich bottle was replaced in the Reich assembly, the clamp of the siphon tube removed (the siphon having previously been set), and the water from the Woulff bottle permitted to run to waste. When the flow of water had stopped, the graduate was placed under the siphon tip and the stopcock of the Reich bottle opened. The Reich bottle was shaken during the course of the absorption and the gas permitted to pass until the solution in the Reich bottle again assumed its original light blue color. As the end point vias approached, the stopcock was closed, and then momentarily opened to permit the passage of additional small volumes of gas by a rapid turn through a 180" angle. The clamp was again replaced on the siphon tube, after the system had reached its original pressure state as indicated by the cessation of water flon, and the volume of water was read to the nearest 0.5 mi. This volume of water represented the volume of gas analyzed with the
884
Vol. 14, No. 11
INDUSTRIAL AND ENGINEERING CHEMISTRY
THCRFlOfiETER
WOULFT
BOTTLE
REICH
BOTTLE
0.09 per cent in 12 per cent gas strength. Although a 2' change is a rather large variation, i t seems desirable to pass the gas through a U-tube immersed in the water of the Woulff bottle (Figure 1) in order that the gas may assume the temperature of the water. This also permits taking the -water temperature as the gas temperature. ACCURACYOB VOLUME MEASUREMENTS. Calculations indicate that a 1-ml. difference in the volume of aspirated water obtained whenever a 10-ml. portion of 0.1 N iodine is decolorized with 12 per cent sulfur dioxide gas results in a 0.14 per cent difference in strength. This indicates the desirability of PRESSURE measuring the water volume to the nearest 0.5 mi. This was accomplished by the use of BOTTLE _. the special graduated cylinder. RATEOF GAS FLOW.Experimental tests indicate that it is difficult to obtain satisfactory end points when the rate of gas flow is too rapid. The rate of gas flow is controlled by the size of glass tip in Reich bottle, water head in J170ulff bottle, and size of tip from which water is discharged from the Woulff bottle. I n the apparatus that was used, these factors were controlled by using a glass tip in the Reich bottle of such size as just to permit the passage of a piece of No. 26 gage wire, cutting the siphon tube to such a length as to provide a 12.5cm. (5.5-inch) water head and using a n exit tip of about 1.5mm. diameter. This necessarily lengthens the time required for making a Reich test by approximately one minute (over-all time for complete test 4 to 5 minutes); this is not, however, considered excessive. Loss OF IODINE OR INCOMPLETE ABSORPTIONOF SULFUR DIOXIDEIN REICHBOTTLE. Obviously the loss of iodine or sulfur dioxide from the Reich bottle would result in erroneous results. ~
FIGURE 1. REICHTESTAPPARATUS
exception of the sulfur dioxide which had been absorbed. The temperature of the water in the Woulff bottle and the barometric pressure were noted and the volume of gas as indicated by the volume of water was corrected to standard conditions of temerature and pressure by the application of the familiar gas hws. t h e per cent of sulfur dioxide was determined by dividing the volume of sulfur dioxide equivalent to the 10 ml. of 0.1 N iodine by the total volume of gas (sum of corrected volume and volume of sulfur dioxide equivalent to 0.1 N iodine volume used).
Factors Influencing Accuracy and Precision of Reich Test
A careful study of the method indicates that the following factors have a direct bearing on the accuracy and reproducibility of the test: (1) pressure of the gas within the system, (2) temperature of the gas within the system, (3) accuracy of volume measurement, (4)rate of gas flow, (5) loss of iodine or incomplete absorption of sulfur dioxide in Reich bottle, and (6) value of gram molecular volume used for sulfur dioxide. PRESSURE OF GAS WITHIN THE SYSTEM. The pressure of the gas within the system after the cessation of mater flow, following the decolorization of the iodine solution, is dependent upon the barometric pressure, the water head of the Wou@ bottle, and the degree of saturation with regard to moisture content. The first of these factors is obvious. Calculation will show that a difference of 10 mm. in pressure results in a difference of 0.15 per cent in the calculation of the strength of a 12 per cent sulfur dioxide gas. The second pressure factor to be observed is the height of the water head in the Woulff bottle. When a bottle of 4-liter capacity is used, the difference between water head at start and finish of a test is not significant; its absolute value is, however, important, since a 32.5-cm. (13-inch) head, for example, results in a negative pressure of approximately 11 mm. of mercury. This is a large correction and should be taken into account. The third pressure factor is the degree of water saturation of the gas within the Woulff bottle. A study of the sample calculation shown below indicates the water vapor correction and the importance of this factor. Experimental data to determine a possible state of unsaturation were obtained by placing a water trap between the Reich bottle and the Roulff bottle. Yo change in result was indicated and the conclusion was reached that this error, if present, was not significant in the present Reich test apparatus. Apparently the gas becomes saturated with water vapor by its passage through the Reich bottle. TEMPERATURE OF GAS WITHIN THE SYSTEM. Calculations show that a 2" C. difference in temperature of the residual gas collected in the Woulff bottle represents a difference of
TABLEI. Loss
OF
IODISE FROM REICHBOTTLEAT ELEVATED TEMPERATURES
(Rate of H20 Temp. O
F. 85 95
100 120 120 a
Asplrated
gag
flow, 100 ml. in 70 seconds)
KI Added
Remarke
Grams
250 400 104 400 460
0.0 0.0 0.0 5.0 3.0
No iodine lost No iodine lost Iodine lost No iodine lost Slight amount of It losto
Color of starch-iodine was dispelled by 1 drop of 0.01 N NazSzOa
The possibility of the loss of sulfur dioxide due to rapid passage and incomplete absorption in the Reich bottle was tested by inserting a trap into the line between the Reich bottle and the Woulff bottle. This consisted of a 20-cm. (&inch) test tube closed by a two-hole rubber stopper equipped with inlet down through
the solution and outlet to Woulff bottle. A light blue starchiodine solution was placed in the trap, but in spite of frequent runs was not decolorized. Failure to decolorize in spite of rapid passage of high strength gas through the Reich bottle indicated no loss of sulfur dioxide. A similar experiment in which the starchiodine solution was replaced by a colorless starch solution (previously adjusted to show no capacity for absorbing iodine without change in color) indicated that no loss of iodine was experienced from this dilution-10 ml. of 0.1 N iodine per 180 ml. of solution when treated by gas stream as above at room temperature (25; C.). Additional tests to determine the volatility of the iodine solution were made at higher temperatures, using a 4-liter Woulff bottle, a test tube trap as above, and the Reich bottle with the special glass tip previously described. The solution in the Reich bottle consisted of 10 ml. of 0.1 N iodine and 180 ml. of water,
ANALYTICAL EDITION
November 15, 1942
containing 5 ml. of starch solution. The trap contained 1 gram of potassium iodide dissolved in 5 ml. of water plus 3 ml. of starch solution. In these tests, the inlet of the Reich bottle was opened to the air instead of being connected to the gas cylinder. The results indicated that iodine was lost from the Reich bottle at temperatures of 37.78: C. (100' F.) Or abpve. This loss may be corrected by the addition of potassium iodide to the Reich bottle. Under these conditions, the test may be made at 48.89' C. (120' F.) without serious loss of iodine. The results obtained are shown in Table I. These results indicate that no iodine is lost from the Reich bottle during a normal determination a t room temperature. When tests are made a t 37.78" C. (100" F.) or above, the addition of potassium iodide is necessary to prevent iodine losses. GRAM-MOLECULAR VOLUMEOF SULFURDIOXIDH.The gram-molecular volume of the ideal gas has been determined as 22.4 liters. Fairlie (1) and Lunge (6) have based their Reich test tables on this value for sulfur dioxide. The grammolecular volume of sulfur dioxide as based on experimentally determined values of density (8) is 21.89 liters. Obviously, the use of the one or the other results in a 0.2 per cent discrepancy. Since the 22.4 value rests upon theoretical considerations of the perfect gas and 21.89 rests upon values experimentally determined, it is sound to adopt the latter value. This procedure is also the one followed by Lunge-Berl ( 7 ) ,Miles (9) and Sullivan (12). Using this latter value 10 ml. of 0.1 iL' iodine are equivalent to 10.95 ml. of sulfur dioxide measured a t standard conditions of temperature and pres-Lire.
Normality of 12, 0.1. (lo ml. of 0.1 N 11 = 10.95 ml. of SO2 under standard conditions) Negative pressure 4 . 0 mm. Temperature correction on barometer 3 . 4 mm. Vapor pressure correction 22.4
29.8 Corrected barometer 757.1 - 29.8 89.5
OBTAIXED BY REICHTEST TABLE11. RESULTS
AV.
Series 2 12.15 12.20 12.15
12.19-
12.17-
Series 3 12.17 12.15 12.23 12.21 12.19-
Av. of allruns, 12.197" SOz
Additional determinations of equal precision were made, but the above are typical and indicate that the reproducibility of the test is within *O.l per cent. A sample calculation using proper corrections is shown. SLVPLECALCULATION Water volume, 89.5 ml. Temperature of Woulff bottle, 24" C. Barometer, 757.1 mm. at 26" C.
__ 727'3 X
760
273 297
=
=
727.3 mm.
78.72 ml. occupied by residual gas 10.95 ml. occuDied bv" so,__ 89.67 ml. total volume of gas 89.67
12.21% SO%
The absolute accuracy of the Reich test was shown by comparison with results obtained on a n Orsat apparatus (Bureau of Mines model) using mercury as the confining liquid and chromium oxide as the gas absorbent. The results obtained on the same gas mixture as above are shown in Table 111. Results of a confirmatory nature were obtained by absorbing known volumes of the cylinder gas in a 1 per cent solution of sodium hydroxide, oxidizing to sulfate with sodium peroxide, and precipitating as barium sulfate. When analyzed in this manner the values of 12.26 and 12.28 per cent were obtained. These results as determined by the above t1.i.o methods indicate that the accuracy of the Reich test when properly conducted is n-ithin 0.1 per cent. Reich and Orsat techniques both give results on a dry basis.
TABLE111. GASANALYSISBY ORS.4T
K i t h the above factors in mind, a series of tests was made on the sulfur dioxide-nitrogen mixture obtained from cylinder source. This particular strength (12 per cent) was chosen because the obtainment of satisfactory results with this gas of high sulfur dioxide concentration would automatically indicate the suitability of the method for gases of lower strength. Apart from sulfur dioxide percentage, the prepared gas mixture differed from normal contact gas produced from brimstone only in oxygen and nitrogen content, since other impurities present in the gas are removed in the purification train and small amounts of sulfur trioxide are removed by inserting a 98 per cent sulfuric acid absorber between the sampling point and the Reich test apparatus. The variation in oxygen and nitrogen content is of no significance, since both are inert with respect to the iodine absorbent. The results that were obtained are sholm in Table 11.
12.19 12.23 12.17
x
- =
Precision and Accuracy of Test
Series 1
885
1st pass
2nd pass 3rd pass 4th pass
5%
sora
(CrOa ahsorbent) Run 1 Run 2 88.30 88.40 87.90 87.98 87.90 87.90 87.90 87.88 12.15 12.17
APPARATUS
Run 3 88,40 88.00 87.90 87.90 12.15
A,. 12 16% 0
Corrected according t o gas buret calibration.
Summary The various factors involved in the accurate analysis of sulfur dioxide gases by Reich test procedure are (1) pressure, (2) temperat'ure, (3) accuracy of volume measurement, (4) rate of gas flow,(5) completeness of sulfur dioxide absorption and loss of iodine, and (6) sulfur dioxide gram-molecular volume value. Experimental data which include comparisons made by accepted Orsat technique, as well as gravimetric sulfate determinations, indicate that the Reich test when properly conducted is capable of an accuracy and precision of *O,l per cent on 12 per cent sulfur dioxide gas strength.
Literature Cited (1) Fairlie, "Sulfuric Acid Manufacture", p. 276. New York, Reinhold Publishing Corp., 1936. (2) Grounds, Ind. Chemist, 8, 189 (1932) (3) Hewson, Ibid., 8,224 (1932). (4) Ljungh, Chem.-Ztg., 33, 143 (1903). (5) Lofert, Z . angm. Chem., 52, 219 (1939~. (6) Lunge, "Manufacture of Sulfuric Acid and Alkali", Vol. 1, Pt. 1, p. 571, New York, D. Van Nostrand Co., 1913. (7) Lunge-Berl, "Chemisch-technische Untersuchungsmethoden", Vol. I, p. 366, Berlin, Julius Springer, 1910. (8) Mellor,. "Comprehensive Treatise on Inorganic and Theoretical Chemistry", p. 190, New York, Longmans, Green and Co.. 1936. (9) Miles, "Lunge's and Cumming's Manufacture of Sulphuric Acid", p. 184, New York, D. Van Nostrand Co., 1925. (10) Raschig, Z . angew. Chem., 22, 1182 (1909). (11) Reich, Berg- u. hiittenmtinn. Ztg. (1858). (12) Sullivan, "Sulfuric Acid Handbook", p . 109, New York, M c Graw-Hill Book Co., 1918.
