ENGINEERING AND PROCESS DEVELOPMENT (7) Hiester, N. K., and Vermeulen, T., J . Chem. Phys., 16, 1087 (1 948). ( 8 ) Kahn, H., Nucleonics, 6 , S o . 5, 27; No. 6, 60 (1950). (9) King, G . W., IND.ENG.CHEM.,43, 2475 (1951).
(lo) Kunin, R., and Myers, R. J., “Ion Exchange Resins,” New York,
John Wiley & Sons, 1950. (11) Lapidus, N., and Amundson, N. R., J . Phys. Chem., 56, 373 (1952). (12) Lombardo, R. J., Ph.D. thesis, Pennsylvania State College, 1951. (13) Mayer, S. W., and Tompkins, E. R., J . Am. Chem. SOC., 69,2866 (1947). (14) IMetropolis, N., and TSlam, S., J . Amer. Stat. Assoc., 44, 335 (1949). (15) Kaohod, F. C., “Ion Exchange,” New York, Academic Press, 1949. (16) Natl. Bur. Standards, A p p l i e d Mathematics Series 12.
(17) Rose, A., Lombardo, R. J., and Williams, T. J., IND. ENG. CHEM.,43, 2454 (1951). (18) Rosen, J. B., and Winsche, W. E., J . Chem. Phys., 18, 1578 (1950). (19) Salner, H. E., Natl. Bur. Standards, Applied Mathematics Series
16. (20) (21) (22) 123)
Selke, W. A., and Bliss, H., Chem. Eng. Progr., 46, 509 (1950). Thomas, H. C., Ann. AT. Y . Acad. Sci., 49, 161 (1948). Thomas, H. C., J. Am. Chem. Soc., 66, 1664 (1944). Trueblood, K. N., and Malmberg, E. W., J . Am. Chem. SOC.,72,
4027 (1950). (24) Vermeulen, T., and Hiester, N. K., IND. ENG.CHEM.,44, 636 (1952). (25) Walter, J. E., J . Chem. Phys., 13, 229 (1945). (26) Wasow, W., J . Research Natl. Bur. Standards, 46, 65 (1951). RECEIVED for review November 28, 1952.
ACCEPTEDJ u l y 17, 1953.
I
Evaluation of Packed Distillation Columns T. J, WALSH’, G. H. SUGIMURA2,AND T. W. REYNOLDS lewis Flighf Propulsion loborofory, Nofional Advisory Cornmiffee for Aeronautics, Cleveland, Ohio
T
HE National Advisory Committee for Aeronautics, Lewis Flight Propulsion Laboratory, has been engaged in the preparation of pure hydrocarbons for several years in order to obtain correlations of molecular structure with engine performance and with other physical and chemical properties of the compounds. In the purification process to obtain these hydrocarbons, distillation is extremely important. Distillation to obtain maximum purity of a compound often requires the greater part of the total 1
Present address, Case Institute of Technology, Cleveland, Ohio.
* Present address, Loa Angeles, Calif.
Operations of Glass and Steel Packed Columns are Observed at Atmospheric and Reduced Pressures
VENT WATER ROTAMETER
0 CONDENSER COOLING WATE
ERMOCOUPLE
PRODUCT RECEIVER LE TRANSFORMER
220 VOLT A.C.
THERMOCOUPLES EN PACKING SUPPORT CON FILLER HOLE
THERMOCOUPLE
Figure 1.
December 1953
time required for the complete synthesis of the compound. Purification of commercial starting materials also requires considerable time. Consequently, it is important to know the operating characteristics of the distillation equipment, not only a t atmospheric pressure but also a t reduced pressures, in order to obtain the most efficient performance for any required separation. I n order to determine separating ability, pressure drop, and throughput relations of the various distillation columns and the characteristics of the packings used a t this laboratory, this investigation was conducted under the various operating conditions commonly used.
Stainless Steel Distillation Column
Stainless Steel Columns. A typical diagram of the stainless steel stills is shown in Figure 1. All of the columns are basically the same but differ in the type of packing used and in the diameter of the column. The stills are housed in an air-conditioned constant temperature room. The still pots have capacities of 10 or 20 gallons. Each still has an over-all height of 37 feet with a packed height of 30 feet. Heat is supplied to the still pots by three resistance elements wound concentrically beneath the pot and connected so as to give continuous control of from 0 to 5 kw. input. The column of each still is enclosed in a thin metal jacket which is wound with three sections of asbestos- and glass-covered resistance wire. Each section is controlled by a separate variable transformer and has a capacity of 2 kw. Thermocouples are located on the metal jacket a t the center of each section of winding. Packing in each column is supported a t the pot flange by a sieve cone with a perforated area equal to the cross-sectional area of the column. Throughput is calculated from the heat pickup of the condenser water. For this purpose, the water rate is metered with a rotameter and the temperature of the water into and out of the condenser is measured. From these data and the latent heat of the test mixture the throughput may be calculated. Pressure drop is determined by measuring the pressure in the still pot vapor space, the top of the column being open to the a b mosphere. The manometer lines are flushed with nitrogen to prevent condensation in the line. Glass Columns. A typical glass column used in the Lewis Flight Propulsion Laboratory is shown in Figure 2. The height
INDUSTRIAL AND ENGINEERING CHEMISTRY
2629
ENGINEERING AND PROCESS DEVELOPMENT of the glass columns is either 9 or 10 feet, depending on the height of the packed section, which is either 6 or 7 feet. Column diameters, packed height, and packing are indicated in Table I11 (deposited with the American Documentation Institute). The Podbielniak column is insulated with a metal reflectorshielded vacuum jacket. The helix-packed columns were wound with nichrome heating wire in two sections-each of 500-watt capacity-controlled by variable voltage transformers. Still pots are attached t o the column by a standard taper ground-glass joint and heated by heating mantles. A variable voltage transformer controls the heat input to each pot.
CONTROLLED
TAKE-OFF VAL
VACUUM PUMP
RECEIVER
-
-TUBING JACKET
MANOMETER SIEVE-CONE PAC MANTLE 0 POT SUPPORI
110 VOLT A.C. I
VARIABLE TRANSFORMER
Figure 2.
this system by Gelus et al. (8). The best curve through their data may be fitted with the equation a: = 1.04774
(1)
where z is the mole fraction 2,2,4-trimethylpentane in the mixture. Synthetic mixtures of these components were prepared to cover the range of compositions with 21 samples differing by 0.05 mole fraction and the refractive index measured for each sample with an Abbe precision refractometer. The refractive index of any ianiple may he expressed by n n o - 1.4231 - 003762 0.006122 (2)
+
\\.ith this mixture the number of theoretical plates in a column operating a t atmospheric pressure were determined from a plot of theoretical plates versus refractive index. This plot was prepared by making a plate-to-plate calculation a t total reflux for the separation between 0.01 and 0.99 mole fraction 2,2,4-trimethylpentane. Values of the relative volatility, a, a t each plate were determined for the corresponding mole fraction from Equation l. The refractive index v a s also calculated for each mole fraction and a large plot permitting use of the refractive index to the fourth decimal place was prepared. Data to be used in duplicating this plot are presented in Table I. This plot, in reduced size, is shown Figure 3. The refractive index of the sample from the head and from the pot of the still was read to five decimal places and is used to four places a t all points except for concentrations rich in 2,2,4-trimethylpentane. Over a majority of compositions an error of 0.0001 in the refractive index corresponds to 0.2 theoretical plates. At high 2,2,Ptrimethylpentane concentrations (ivhere relative volatility is most constant) an error of 0.0001 in refractive index corresponds to betv, een four and six theoretical plates and the fifth decimal place in the refractive index was desirable in the calculation. A t low 2,2,4-trimethylpentane concentrations an error of 0.0001 in the refractive index corresponds to an error of four theoretical plates, but in this region the value of the relative volatility is subject to question and refining the calculation of theoretical plates for greater accuracy is not justified.
Glass Distillation Column Table I.
The condenser unit is described in detail by Diehl and Hart (6). To measure reflux rates an adapter was inserted between the condenser and the column. Liquid reflux was collected for 15 seconds only, in order not t o disturb the column equilibrium. Curves were prepared on reflux rate versus pot heater setting. As the room is maintained a t constant temperature, pot heater settings could be used to lix the reflux rate. The columns are set up for operation a t atmospheric pressure or a t reduced pressure. Pressures below atmospheric are maintained within h 0 . 2 mm. of mercury by a metal Cartesian diver type of manostat mounted between a 30-cubic-foot-per-minute vacuum pump and a 4-cubic-foot surge tank. In practice, a bank of several columns operating a t the same pressure is connected t o a common surge tank. All column controls are assembled into a single control panel. Deviations from Constant Relative Volatility Are Determined for Each Test Mixture
The mixture that is preferred for the experiments a t atmospheric pressure consists of methylcyolohexane and 2,2,4trimethylpentane. This was originally chosen as i t was reported to be an ideal mixture 15-ith a relative volatility, 01, of 1.049 (14). Early work indicated that the mixture deviated considerably from the constant relative volatility a t low 2,2,4trimethylpentane concentrations. This deviation from ideality was confirmed by data reported for
Methylcyclohexane-2,2,4-Trimethylpentane.
2630
f 0.06126 (0.00313)2
Refractive Index versus Theoretical Plates at Total Reflux
(2,2,4-Trimethylpentane-methylc~~clohexane a t 760 mm. Hg. sbs. pressure) N o . of Mole Fraction 2,2,4-Trimethylpentane Refractive Theoretical in Liquid, z Index, n2,0 Plates 0.0100 0.0243 0.0557 0.1132 0.2000 0.3096 0.4320 0,5556 0.6694 0.7650 0.8327 0,8930 0.9302 0.9551 11.9715 0.9820 0.9886 0.9901
1.4226 1.4221 1,4209 1,4188 1.4157 1.4120 1.4079 1.4040 1.4005 1,3978 1 ,3957 1 3943 1 3933 1.3927 1.3923 1.3920 1 3918 1.3918
n
10 2n 30 40 50 60 70 80 90 100 110
120
130 140 150
160 163
-1feir samples contained slightly more than 0.99 mole fraction 2,2,4-trimethylpentane. The curve was extended for these Samples using the Fenske equation (6) with a constant relative volatility of 1.049 as long as the extrapolation did not amount to more than 30 theoretical plates. Composition was determined from the refractive index using the data from a blend of the star& ing materials. This is believed justified as the conditions under which this equation applies are met almost exactly by the system a t this point, Further extrapolation was rejected as the accuracy
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 12
ENGINEERING A N D PROCESS DEVELOPMENT of the analysis does not justify extending the data further in this direction. No data are used for runs in which the pot sample contained less than 0.01 mole fraction 2,2,4-trimethylpentane because of the uncertainty of a beyond this point.
about 20 mm. of mercury. The relative volatility at the top of the column will be found a t 20 mm. and that at .the still pot at 40 mm. This change in pressure will affect the calculated number of theoretical plates by as much as 20%. Neglect of this correction leads to low values for the measured efficiency of the column.
200
Extended Toluene-Methylcyclohexane Equilibria Data Improve HETP Correlations
*
,.
i
01
1390
I
1.394
I
1.398
I
1.402
I
1.406
REFRACTIVE
I
1.410
I
1.414
I
1.418
h
1.422
I
1426
INDEX, nD20
Figure 3. Correlation of Refractive Index with Theoretical Plates for 2,2,4-TrimethyIpentane-Methylcyclohexane at Atmospheric Pressure
The toluene-methylcyclohexane system has been reported as nonideal and nonazeotropic (3, 11, I S ) . The equilibria data for this system have been extended to include data a t 80 and 200 mm. of mercury pressure. The relative volatility as a function of the mole fractions methylcyclohexane in the liquid phase for this system is shown in Figure 4. The data of 760 mm. of mercury pressure determined in this study show a relative volatility somewhat greater than the earlier work ( 2 1 ) . It is believed that the new data improve the agreement in the height of equivalent theoretical plate ( H E T P ) values for columns determined with this and other systems (9). A series of eight runs in the equilibrium still indicate that an azeotrope having a composition very close to pure methylcyclohexane and R boiling point differing from t h a t of methylcyclohexane by a fraction of a degree may exist in this system.
Somc runs extended beyond the curve in both directions. While t8hese data indicate highly satisfactory separation efficiency for the column being tested, they are commented upon in the discussion of the proper column without being reported with quantitative numbers for the number of theoretical plates.
2*2[ 00
a DATA OF OUtGGLE AND
0 THIS
FENSKE (11)
INVESTIGATION
2 , o k
Relative Volatility of n-Heptane-Methylcyclohexane
Is Constant at Atmospheric Pressure Another useful system for testing distillation columns a t atmospheric pressure is n-heptane-methylcyclohexane. This system was shown to be ideal by Beatty and Calingaert (g), and equilibria data a t atmospheric pressure are given by Ward ( I S ) . The relative volatility is constant a t 1.074 a t 760 mm. of mercury for all compositions. D a t a obtained with this test mixture are not reported in this paper as they agreed completely with the data obtained with the system methylcyclohexane-2,2,4-trimethylpentane. This system appears to be ideal a t all pressures. However, the vapor pressure curves of the pure components approach each other as the pressure is reduced (1.2). The relative volatility of the system decreases as the distillation pressure is reduced below 1 atmosphere. At 62 mm. of mercury pressure the two materials have a common boiling point of 31.4"C. Below this pressure the relative volatility increases with methylcyclohexane as the more volatile component. This is not an azeotrope even though mixtures of these components cannot be separated by distillation a t 62 mm. of mercury, as the behavior is not a function of the composition of the mixture. II
Average Relative Volatility over Composition Range i s Used for Cyclohexyleyclopentane-Dodecane
The system cyclohexylcyclopentane-dodecaneis the preferred system for vacuum operation. D a t a for this system are presented by Feldman et al. (6). The system isnearly ideal a t all pressures. Caution should be exercised, however, not t o use the average relative volatility of the mixture at a given pressure in evaluating column efficiency. Rather, the average relative volatility for the range of composition used in the particular distillation must be evaluated. In using the system at high vacuums, the relative volatility should be evaluated using the pressure and composition corresponding to the conditions at each point of the column. At high vapor velocities, the column pressure may be 20 mm. of mercury and the pressure drop through the column also
December 1953
-
a tu
d
1.0
0
MOLE
Figure 4.
.2 .4 .6 .8 10 . FRACTION METHYLCYCLOHEXANE IN TOLUENE
Relative Volatility of Methylcyclohexane-Toluene
This system is useful if the efficiency of the column to be tested is not expected to exceed 30 theoretical plates. The refractive index is a convenient method of analysis ( I I ) , and a plot of refractive index veraus number of theoretical plates was prepared for use with this system at 760 mm. of mercury pressure (Figure 5). The number of theoretical plates was calculated from composition using a plate-to-plate calculation with the appropriate value of relative volatility as read from Figure 4. The cross plot against refractive index was then prepared. Data for reproducing this plot are given in Table 11. As the columns reported here are all more efficient than 30 plates, this system gave confirming data but was insensitive to changes in number of theoretical plates with vapor velocity. The data obtained with this test mixture are not included in this report. Separating Efficiency Depends o n Type of Packing and Relative Volatility of Mixture
Procedure. The still t o be teated was charged with an ap-
INDUSTRIAL AND ENGINEERING CHEMISTRY
2631
ENGINEERING AND PROCESS DEVELOPMENT
REFRACTIVE
INDEX,
"02'
Figure 5. Correlation of Refractive Index with Theoretical Plates for Methylcyclohexane-Toluene at Atmospheric Pressure
200r _.
0
L 2i 3
-2
80.
-
I
-
-
d
- 4 +
W
m
fz
-
0.01 02 103 .05
LL
height equivalent to a theoretical plate for this packing is between 2.0 and 3.6 inches. The best efficiency of these columns compares with the H E T P of 2.3 inches found by Fenske, Lawroski, and Tongberg ( 7 ) for a column 10 feet long by 5.1 cm. in diameter. Thus the superficial vapor velocity seems to produce greater variation iri the efficiency of the packing than does the height of the packed bed. Other variations may be observed in the efficiency of the packing as tested in this laboratorr. The data indicate that an improved separation occurs when small concentrations of 2,2,4trimethylpentane exist in the still pot. Composition data were determined to 0.00002 units with a Bausch and Lomb precision refractometer. An error of 0.00005 corresponds t o 0.0013 mole fraction. Relative volatility data in the region below 5% 2,2,4-trimeth~-lpentaneare not certain, but errors in relative volatility data cannot explain the trend of the efficiency results, as any correction will shift all points in the same direction. These results are opposite in direction to those found in such systems as ethj-1 alcohol-water in bubble plate columns where the efficiency of the trays seems to decrease rather than increase as the pure components are approached (IO). The 1/8-inch helices give results in the 1-inch diameter column that are about 18% better than the same helices in the 2-inch diameter column. This may be interpreted as due to better reflux distribution in the smaller column, where the size of the packing and column are in bettcr balance.
I
-
- 6 - 8 -10
OPEN POINTS FOR 2" COLUMN SOLID POINTS FOR I" COLUMN
0
118'' STAINLESS-STEEL HELICES 114'' PORCELAIN B E A L SADDLES
o
318'' PORCELAIN RASCHIG RINGS
A
200r
a
NO PACKING
-I
n
SUPERFICIAL VAPOR
Figure 6.
VELOCITY,
f tJsec.
Performance of 30-Foot Helix-Packed Columns a t Atmospheric Pressure
2,2,4-Trimethylpentane-methylcyclohexane
$
uc
100-1 I
:
I
LL
2632
I
W
test mixture
propriate quantity of test mixture (about 5 gallons for the stainless steel stills and 600 ml. for the glass stills). The still pot and column heaters were turned on and heat was applied until material was refluxing a t the top of the column. The colunin heaters were then adjusted until the jacket temperature and the corresponding column temperature were approximately the same. Where necessary, the inside temperatures n ere estimated from the vapor temperature a t the top and bottom of the column. The still pot heat was incieased until flooding occurieci a t the top of the column The heat was then slightlv decreased, the flood alloxed to subside, and the column allowed to reflux undei these conditions until equilibrium, as indicated by constant p o t and reflux composition, was attained. This required from 24 to 72 houis, depending on the column being tested. When successive samples from both the still pot and still head had the Eame composition, the heat t o the still pot was decieased to give a loir el throughput. Equilibrium would normally be re-established in 24 hours, and samples were taken during the morning and afternoon. After successive samples became constant in composition. the heat was again decreased and the process repeated until R minimum throughput was reached. Vacuum operation was identical, esccpt that the still was connected to the proper vacuum surge tank. The stainless steel columns were operated a t atmospheric pressure only. The data for these columns are shown in Figures 6 and 7. (Full data on all columns are given in tables which may be obtained from the American Documentation Institute.) The behavior of '/*-inch, single-turn, stainless steel helices i n the 2- and 1-inch diameter columns is shown in Figure 6. The
150-
0
I
50:
cc 'D
W
2 2
Z
la.-
-
.5
O
.o
I
S U P E R F I C I A L VAPOR VELOCITY,
Figure
ftlsec.
7. Performance of 30-Foot Packed Height Steel Columns a t Atmospheric Pressure
2,2,4-Trimethylpentane-methylcyclohexane test mixture
Table II.
Refractive Index versus Theoretical Plates a t Total Reflux
(Toluene-methyloyolohexane at 760 mm. Hg abs. pressure)
3Iole Fraction 3Iethylcyolohexane in Liquid, 2
Refractive Index, 1.4958 1.4933 1.4880 1 ,4780 1.4648 1.4530 1.4444 1.4380 1.4345 1.4318 1 4302 1.4290 1.4284 1.4278 1.4270 1.4266
~ N D U S T R I A LA N D E N G I N E E R I N G C H E M I S T R Y
No. of
TlieoreticaZ Plates 0
2 4
6 8 10
12 14 16
18 20 22 24 26 28 30
Vol. 45, No. 12
ENGINEERING AND PROCESS DEVELOPMENT The efficiencies of 2-inch diameter columns packed with ‘/ainch stainless steel helices, with ljcinch porcelain Berl saddles, with 3/8-inch porcelain Raschig rings and without packing are shown in Figure 7 . The packings are less efficient in the order named. The ‘/dnch Berl saddles have HETP’s varying from 4.2 to 5.2 inches. This agrees with the lowest values reported in the literature, since they are below the values reported by Fenske et a2. (7) and on the low side of the values reported by Aston et al. (1). The Raschig rings show HETP’s varying from 5.5 to 8.2 inches. Agreement is good with the data of Fenske et al. (7) for both carbon and glass Raschig rings. However, these data indicate a capacity of 3 times that shown by Fenske before flooding occurs. The rings maintain their separating efficiency over the entire range of operation.
ciencies are not maintained as the vapor rate is increased nor were they obtained a t low vapor rates a t low pressures. Under the latter condition, the liquid rate was very low and it is possible that the packing is not perfectly wetted. Data for the Podbielniak packing are shown in Figure 9. HETP values vary from 0.5 to 2.0 inches.
(E)
72 84 72
4.0
2 0 1b012009’670 o v n a 0
0
A
A
9
v
P
n
E 3.0 LL I-
%
HEAD PRESSURE (rnrn. Hg)
.G
I .oo
2
Figure 9.
a“
IW
X
2.0
I
0
Figure 8.
0.5
1.0 1.5 2.0 2.5 SUPERFICIAL VAPOR VELOCITY, ft/sec.
3.0
Performance of Podbielniak Heligrid Packing
All packings show evidence of typical curves. Efficiency curves may be expected to start a t the origin when the packing is not wetted with reflux and rise rapidly to a maximum. This part of the curve was observed only for the 1/8-inch helices. The efficiency of separation then decreases as the load is increased until a minimum efficiency is reached. The efficiency again increases as the flooding point is approached. All data apply to preflooding packings only. Efficiency is improved by preflooding. Nonpreflooded packings give varying and nonreproducible efficiencies. The glass columns were tested as atmospheric pressure and under reduced pressures. Results are summarized in Figures 8 and 9. Pressure affects the efficiency of the random packings less than the variation between runs a t the same pressure. Thus, it appears that the efficiency of random packings is independent of pressure over the range of 200 to 760 mm. of mercury pressure. The allowable superficialvapor velocitybefore flooding is increased by reducing tho pressure. However, the maximum throughput, as measured by liquid rate, remains about the same and is independent of the operating pressure. The Podbielniak Heligrid packing does not behave the same as a random packing in that very high efficiencies can be obtained at low vapor rates at atmospheric pressure. These high effi-
I I 1.0 20 SUPERFICIAL VAPOR VEI OCITY,
I
3.0
4.0
ft/seC.
Performance of 3/16-lnch Glass Helix Packing
The S/le-inch diameter glass helices show H E T P values ranging more or less randomly between 1.7 and 3 inches. These data are summarized in Figure 9. Within the range investigated, neither varying height nor diameter appears to change the HETP. Literature Cited (1) Aston, J. G., Lobo, W. E., and Williams, B., I N D .ENG CHEM., 3 9 , 7 1 8 (1947). (2) Beatty, H. A., and Calingaert, G., Ibid., 26, 904 (1934). (3) Chu, J. C., “Distillation Equilibrium Data,” New York. Reinhold Publishing Corp., 1950. (4) Diehl, J. M.,and Hart, I . , Anal. Chem., 2 1 , 5 3 0 (1947). ( 5 ) Feldman, J., Myles, M., Wender, I., and Orchin, hl.,I V D .ENC. CHEM.,41, 1032 (1949). (6) Fenske, NI. R., Zbid., 24, 482 (1932). (7) Fenske, M. R., Lawroski, S., and Tongberg, C. O., I b z d , 30, 297 (1938). (8) Gelus, E., Marple, S., Jr., and Miller, M. C., Ibid., 41, 1757 (1949). (9) Griswold, J., Zbid., 35, 247 (1943). (IO) Keyes, D. B., and Byman, L., Univ. Illinois Bull., 37 (May 6, 1941). (11) Quiggle, D., and Fenske, AI. R., J . Am. Chem. Soc., 59, 1829 (1937). (12) Stull, D. R., IND.ENQ.CHEM.,3 9 , 5 1 7 (1947). (13) Ward, C. C., U . 8.Bur. Mines, Tech. Paper 600 (1937). (14) Willingham, C. B., and Rossini, R . D., J . Research Nut. Bur. Standards, 37, 15 (1946). RDCEIVBD for review August 4, 1951. ACCEPTED August 29, 1953 Material supplementary to this article bas been deposited as Document No. 4078 with the AD1 Auxiliary Publications Project Photoduplication Service, Library of Congress, Washington 25, D. C. A copy may be secured by citing the document number and by remitting $2.50 for photoprinta or $1.75 for 35-mm. microfilm. Advance payment is required. Make checks or money orders payable to Chief, Photoduplication Service, Library of Congress.
t
December 1953
INDUSTRIAL A N D ENGINEERING CHEMISTRY
2633
