Adding 1570 for a safety factor, we Lvould probably use a bed with a volume of approximately 21 cu. feet. This volume c a n be split u p into any reasonable diameter and bed depth combination and still give the desired results. Linear velocities should be kept below 100 feet per minute to prevent abrasion of the desiccant. Other matters to be considered are the allowable pressure drop through the bed. space available for the installation, and economics of construction. A velocity of 50 feet per minute might be assumed. Since 100 cu. feet of dry air per minute are required, cross100 sectional area of bed = = 2 sq. feet SO
Height of bed Diameter of bed
=
=
vol. area
~
dx
=
0.785
21 2
=
=
10.5 feci
4/2.55= 1.6 fect
If the pressure drop through the bed were too large for this design, or if the calculated height \vere too large. a linear velocity of, say. 25 feet per minute could be employed. Cross-sectional area of bed
=
100
- = 4 sq. feet 25
Diameter of bed
=
4 1-' 0.785
=
d j r =2.26 feet
Acknowledgment
The authors ackno\vledge the generous support of this work by Alcoa Research Laboratories. literature Cited (1) De Vault, D.. J . Am. Chem. Soc. 6 5 , 532 (1943). (2) Eagleton, L. C., Bliss, H.. Chem. En,?. Progr. 49, 543 (1953). (3) Getty, R. J., "Drying of Air with Activated Alumina under Adiabatic Conditions," D. Sc. dissertation, it-ashington University, St. Louis. 1955; Microfilm, University Microfilms, 313 N. First St., Ann Arbor, Mich. (4) Jury. S.J., Licht, \V., Jr., Chem. Eng. Progr. 48, 102 (1352). (5) Klotz, I. M., Chem. ReL. 39, 241 (1946). (6) Marshall, \V. R., Pigford, R. L., "Application of Differential Equations to Chemical Engineering Problems," University of Delaware. Newark, Del.. 1947. (7) Thiele, E. \V., Ind. Eng. Chem. 38, 646 (1946). (8) Thomas, H. C., J . Am. Chenz. SOL. 66, 1664 (1944). (9) \Vickr, E., Kolloid 2. 93, 129 (1940). RECEIVED for review April 22, 1360 RESUBMITTED March 11, 1963 .\CCEPTED J u n e 10, 1963
AVIATION GASOLINE CORROSIVENESS CAUSED B Y SULFATE-REDUCING BACTERIA Pveuention
Growth Inhibitovs A L B E R T 0 M. W A C H S , S H I M S H O N B E N T U R , Y E H U D A M E N A H E M B A B I T Z , A N D A L F R E D B. S T E R N
K O T T ,
Technion, Israel Institute of Technology, Haifa, Israel
A sulfate-reducing bacteria, Desulfovibrio desulfuricans, has been found to be responsible for the corrosiveness occasionally occurring in aviation gasoline stored in tanks with small water bottoms, under the climatic conditions prevailing in Israel. In laboratory experiments, gasoline stored on culture media inoculated with D. desulfuricans became corrosive after 1 week of incubation. The diffusion of H2S in gasoline stored on aqueous H2S solutions and its consequent oxidation to free sulfur were determined experimentally. O f the numerous bacterial inhibitors tested initially on Desulfovibrio cultures, methyl violet, a mixture of chloramphenicol and streptomycin, and sodium azide were selected for experimental investigation of their capability of preventing corrosiveness in gasoline stored over inoculated culture media. Under the test conditions, the best results were obtained with methyl violet.
IT
IS a well established fact that aviation gasoline and turbine fuels may become corrosive during storage, the increase in corrosiveness being shown by the copper strip test, ASTM D-130 ( 3 ) ,whereby progressively higher results are obtained. 'I'he development of corrosiveness has been related to the presence of water bottoms and sludge in storage tanks (5.9>73). There seems to be no correlation between the period of storage and the development of corrosiveness: in some instances the gasoline becomes highly corrosive a short time after discharge into a tank. while in other cases it remains noncorrosive after prolonged storage, even when water bottoms are present. -4s previously reported ( 8 ) ,incidence of highly corrosive free sulfur in stored gasoline, in concentrations of u p to 5 mg. per liter, corresponded to a decline in the sulfate content in the water bottoms of the tanks. Other workers have sho\vn that bacteria isolated froin water or sludge found in the bottom of tanks are capable of utilizing sulfates, Ivith production of sulfides (70). In certain cases, petroleum may be highly corrosive to oil
well and oil processing equipment, and its corrosiveness has been related to the presence of sulfate-reducing bacteria in the wells. 'To prevent this type of corrosion, various inhibitors have been tested, among them certain dyestuffs by Rogers ( 7.3)> and chlorophenols by iYilliams (76). The influence of nitrophenols and mercury derivatives on mixed bacteria cultures containing DesulJooibrzo has been studied by Bennet and Bauerle ( 7 ) ,xvhile Bakanauskas (5) and Degray and Killian ( 9 ) have tried to inhibit bacterial growth by using borates. An antibiotic, terramycin, \vas tried by Anderson et al. ( I ) in injection \vel1 flood water. The effect oi quaternary ammonium compounds has also been investigated ( 7 7 ) . Some of the products mentioned have proved effective for the conditions under xvhich they were tested, but there is still considerable interest in finding effective means for preventing the development of corrosiveness in stored gasoline. The objective of the work described here was primarily to determine the causes of the corrosiveness developing in aviation gasoline stored on small water bottoms under Israel's VOL. 3
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65
climatic and storage conditions. Second, when it was found that sulfate-reducing bacteria could be the principal cause, the bacteriological and chemical processes involved were experimentally studied. I n the third stage of the investigation, the possibility of preventing corrosiveness by using substances inhibiting the growth of sulfate-reducing bacteria was investigated and, after preliminary screening tests: a n antibiotic, 3. dyestuff, and a chemical were selected for comparative studies. Results of these investigations are presented here.
Experimental
Identification of Sulfate Reducing Bacteria. A number of storage tanks where aviation gasoline had become corrosive Fvere selected for the study. Cultural investigations of sulfatereducing bacteria were performed in the following types of samples: water from the wells from which water is pumped to the tanks; tank water bottoms above which gasoline had become corrosive; sludge formed at the bottom of the tanks; and samples obtained at the ivater-gasoline interface. For investigating the presence of sulfate-reducing bacteria in samples of the well water supplied to tanks, I-gallon samples ofwater were p m e d through membrane filters (Millipore Filter H.A.). The filters were transferred to anaerobic culture dishes, covered with Allred’s medium agar ( 2 ) , p H 7.2: and incubated a t 23’ C. for 2 weeks. Samples from sludge. water bottoms, and water-gasoline interface from the storage tanks \cere examined by inoculating -4llred’s medium and providing anaerobic conditions as follows : by addition of 1.5% of agar in deep culture tubes, by pyrogallol-alkali plugs in sealed tubes, and by use of anaerobic culture jars. After 2 weeks’ incubation at 25’ C.. black bacterial colonies in the agar tubes and blackening of the bottom of the tubes containing liquid medium \vas observed in those tubes that had been inoculated v i t h ssniples of \vel1 water: tank sludge, and t i n k water bottoms. Negative results were obtained in tubes inoculated with material from the gasoline-\rater interface. Trdnsfers were made from positive tube to deep culture tubes with Allred’s medium agar. The typical black colonies thus obtained were closely surrounded by other bscterial colonies which were found to be of a n .4lkal~genesspecies. Since these interfering bacteria Irere sho\vn to be inhibited by chloramphenicol (Synthomycetine),pure cultures of the sulfatereducing bacteria were obtained by adding chloramphenicol to Allred’s medium agar, in a concentration of 10 pg. per ml.. which \vas selected on the bisis of growth inhibition tests. Single colonies of the purified cultures grown in Allred’s medium agar were transferred several times until good growth was achieved \vithin 4 days of incubation 2t 25’ C. Such cultures were identified as Desulfocibrio desulfuricans using the criteria proposed by Postgate (12). Pure culture checkings were regularly made for each batch used in the experimental work by microscopic obseriration of Gram-stained slides and by inoculations in nutrient agar slants aerobically incubated. The uniform characteristic shape of Gram-negative Desulfovibrio bacteria from black colonies developed in Allred‘s medium and nil growth on nutrient agar slants were considered to be indicators of culture purity. Production of Corrosiveness in Aviation Gasoline. T o confirm that the sulfate-reducing bacteria isolated from the storage tanks were capable of causing gasoline to become corrosive, laboratory experiments were performed in which noncorrosive aviation gasoline, grade 100/130. was kept in 66
I&EC PROCESS D E S I G N A N D DEVELOPMENT
dark bottles over culture media inoculated with the bacteria. Preliminary assays showed that it was possible to produce corrosiveness under those experimental conditions and that the degree of corrosiveness was influenced by the amount of sulfate present in the underlying culture. When gasoline of the same batch was kept under identical experimental conditions on noninoculated media of various sulfate concentrations or on sterile water, no corrosiveness developed. Mrhen sulfates or ferrous iron were excluded in the preparation of the media, no growth of the sulfate reducers could be observed and corrosiveness did not develop in the overlaying gasoline. Desulfovibrio separated by centrifugation from Allred‘s medium, washed with sterile water, and added to water-saturated gasoline did not produce corrosiveness. The influence of sulfate availability on the degree of corrosiveness that could be induced in the gasoline under the conditions described above can be explained by the fact that gasoline corrosiveness. as measured in the ASTM test, is mostly determined by its free sulfur content. Results of the ASThl Test D-130 (3) are expressed, according to the degree of discoloration produced on the standard copper strips, as slight tarnish ( l a , l b ) , moderate tarnish (Za, 2b, 2c, 2d, 2e). dark tarnish (3a, 3b), aiid corrosion (4a, 4b, 4c). To follow changes in the composition and concentration of sulfur compounds resulting from bacterial activity. an experiment \vas carried out using Allred’s medium Lvith various concentrations of IVaZSOA and Mohr’s salt. In some of the bottles, an iron rod or iron rust was added to observe the effect of additional iron sources on the reducing activity of the bacteria. The 1-liter dark bottles containing the inoculated medium and the gasoline in a 9 to 1 ratio were incubated a t 25’ C. for 1 week. The 9 to 1 ratio was used on the basis of preliminary experiments which showed that such high ratios were desirable to induce corrosiveness in a relatively short incubation period of 7 days. At the end of the incubation period the corrosiveness of the gasoline was determined at 2 hours and 100’ C., according to ASTM test D-130 ( 3 ) . Free sulfur and HZS were determined in the gasoline and in the culture medium by colorimetric methods (6>75)! and sulfate was determined gravimetrically in the culture media. Results
Results are summarized in Table I and shov that under the experimental conditions a high degree of corrosiveness. 4a to 4b. could be produced. The highest value. 4b. occurred in the bottle where the iron rod had been added and corresponded to the highest concentration of free sulfur in the gasoline. This indicates that elementary iron may be of importance in terms of electron transfer. a feature previously observed by
Table I. Development of Corrosiveness and Changes in Sulfur Compounds in Gasoline Culture Medium Results aftpr 7 Daw‘ Incubation at 25’ C. Sulfur Components Gasoline .4dded to i n Culture Medium Allred’s Medium, To,-H?S .%./Liter as S. as S , siveness mq./ ( A S T M HzS as S, Free S, Mohr’s mg.1 litpr 0-130) mg./litw mg./lzter lVaZSO4 salt liter 80 22 0 50 4a 67 50 3 0 19 9 9 4a 67 500 0 5 42 4 9 4b 67 50* 8 0 29 4 2’ 4a 67 100 134 50 7 14 4a 1.5 37 a Iron dust added. b Iron rod added.
corro-
~~
Influence of Different Ratios of Gasoline-Culture
Table II.
Medium on Development of Corrosiveness
Incubation time, 1 w e e k a t 25' C.; both samples contained 1 2 0 mg. of NazSOc and 7.5 ,118.of Mohr's salt
Test Compositions, MI. s l t u r e medium bacteria Gasoiine
Corrosiveness ( i l S T M 0-730)
Gasoline H 9 as S, mg./liter
3b-4a 3b-4a
0
~~
+
300 500
600 400
0
Abd-El-Malek and Rizk ( 7 ) and by Starkey (74)and confirmed in the present study. Since the Corrosiveness produced in the described experimental conditions was higher than that usually occurring in storage tanks, similar experiments were carried out using lower volume ratios of culiure media to gasoline. Table I1 shows the results obtained when 1 to 2 and 5 to 4 ratios were used. As in the previous case, the HaS evolved by the bacterial action o n the sulfates was partly oxidized to free sulfur, xvhich caused the gasoline corrosiveness. Relatively high concentrations of iron sulfide lvere found in the culture media; this is in accord with results of examinations carried out on sludge found in tanks where gasoline had become corrosive, lrhich showed the presence of significant amounts of iron sulfide. Table 111, Lchich presents results of the same experiment in terms of sulfur o r sulfur equivalents, shows that the sum of the free sulfur found in the gasoline and that of iron sulfide corresponded, within a small percentage of error, to the sulfur initially present in the sulfates.
Table 111.
Sulfur Balance in Gasoline-Culture Medium System before and after Bacterial Growth
Free and Combined Suljur after 7 Days' Incubation at 2 P C., Mg. ______ vel. Ratio, So40 in Soa-2 Culture Culture remaining Free S Total S 'Lledium to ;tiedium,l in culture an in Gasoline ME. mediuma F?Sa gasoline system 35 12 15 34 1 /2 5 /4 45 17 11 10 38 a Expressed as S. .7
Culture Medium
F r X mg. jliter 25 22
H2S as S,
SOa-2 as S,
mg./liter
mg. /liter
0 0
120 100
FeS calcd. SO 4 - 2 , mg .:'liter 22 33
Diffusion of H2S and Formation of Free Sulfur. It is clear from the results of the experiments described above that the causative agent of corrosiveness was D . desulfuricans. These bacteria produced H2S in the media, which partly diffused through the gasoline phase, being oxidized to free sulfur. Since the solubility of H2S in gasoline is very low, and practically olefin-free gasoline was used in these experiments, it was assumed that H2S not converted to free sulfur or iron sulfide escaped to the atmosphere. T o follolv the progress of the diffusion of HXS and the formation of free sulfur in the gasoline, experiments were carried out in a glass column 200 cm. high and 6.3 cm. in diameter, in which four equally spaced outlets were installed (Figure 1). I n a series of tests carried out with this column, which was protected from light by a black cover, different concentrations of aqueous solution of HZS Fvere placed a t the bottom, and above these solutions, noncorrosive aviation gasoline was carefully introduced u p to the top of the column. To detect any H2S escaping from the gasoline, a strip of lead acetate paper \vas placed above it. The height of the kvater phase \vas 40 cin. and the volume about 1.5 liters; the volume of gasoline \vas about 6 liters. The temperature range was between 15' C. a t night and 25' C. in the daytime. At a concentration of 68 mg. per liter of H2S in the water, the lead acetate paper was blackened after 20 hours. Gasoline samples from taps 1, 2, and 3 showed corrosiveness of degree 3b, and samples from tap 4 a corrosiveness of degree 2c. LVith a concentration of 22 mg. per liter of H*S, the lead acetate paper was blackened after 10 days. Daily observations were made, and samples taken from taps 1, 2, and 3 were examined for H2S and sulfur contents and corrosiveness. No samples
GROUND GLASS
0 TAP 4
x TAPS 2 4 3
0
2
4
8
6
10
R
/4
/G
T i M E , DAYS
Figure 1.
H2S diffusion column
Figure 2. Effect of time on concentration of H2S and free sulfur derived from i t VOL. 3
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T ~ Dais 1 2 4 6 8 10 12 14 16
Table IV. Gasoline Corrosiveness in Relation to HIS Diffusion H2S as S,.Mg/Lzter at T a p JYO. ~Corrosiveness ~ . ( A S T M 0 - 1 3 0 ) at T a p KO. I 2 3 7 2 3 4a lb la 0 0.3 0 4a lb la 1 .o 0 0 lb 4a la 0 0 1 .o 4a lb0 lb 1. o 0 2b 4a lb 1.6 0 0 4a 2b 2b Traces 1. o 0.3 4a 2b 2b Traces 0.5 Traces 3b 2b Traces 2a 0.3 Traces 3b lb0 2a 0 0
Table V.
1Yo. 3 0.6 0.6 0.6 0.6 1 2 2 2 2
Effect of Bacterial Growth Inhibitors in Preventing Gasoline Corrosiveness
Added to Culture Medium
Corrosiveness ( A S T M 0-730)
Gasoline (blank) Antibiotics-gasoline NaNs-gasoline 10 pg./ml. methyl violet-gasoline 1 pg./ml. methyl violet-gasoline
2d-3a lb 1b-2a
Gasoline H2S as S, m,g./liter
0
2b-2c
---
-
S, mg./litu 3.0 0.5
1 0 0 0 1
could be obtained from tap 4 because the gasoline level was lowered as a result of ivithdrawal of samples. Results are summarized in Table IV and Figure 2 which show the progress of diffusion of the H2S and the varying concentration of its oxidation product. free sulfur, which incrersed rapidly a t the beginning and finally remained constant. The progress of diffusion of free sulfur was examined in a separate experiment carried out with the same column. Instead of a n aqueous solution of HgS, a n equal volume of gasoline solution containing 21 mg. per liter of free sulfur was placed a t the bottom of the column and noncorrosive aviation gasoline carefully introduced over it up to the top of the column. Daily observations were made. and samples taken from taps 1 and 2 were examined for sulfur content and corrosiveness. T h e average gasoline temperature was between 15' and 25' C. (daily range). Results are given graphically in Figure 3, which s h o w that the diffusion rate of free sulfur in gasoline is very low. Over a 7-day period, no corrosiveness was observed in samples drawn from the above-mentioned taps. Results of both experi-
1 .o
0.5 1.o
A
S,mg. /lifer
Culture Medium H2S as S, mg./liter
300 375 337 500 337
1 0 0 0
0
15 0 10 0 0
I n a third phase of the study, the prevention of corrosiveness by substances inhibiting the growth of sulfate-reducing bacteria was experimentally investigated. A considerable number of screening tests were carried out to check the growth-inhibiting characteristics of certain chemicals, dyestuffs, and antibiotics o n pure cultures of the bacteria which had been isolated from the storage tanks. O n the basis of the results of those screening tests, which have been reported in detail elsewhere (77), the follolving substances were selected for further investigation : methyl violet, sodium azide, and a mixture of chloramphenicol and streptomycin. The new experiments were performed in a manner Lvhich permitted the results to be expressed in terms of
TAP I
TAP2 CORROSIVENESS
I
Effect of time on diffusion of added sulfur and corrosiveness
l & E C PROCESS D E S I G N A N D D E V E L O P M E N T
FeS. mg./liter
Bacterial Growth Inhibitors
T I M E , DAYS
Figure 3.
SO1-2 as
ments show that the presence of free and corrosive sulfur is mainly due to the diffused H3S and only minute quantities of free sulfur move upward in the gasoline phase. These experiments explain why no H?S and only elemental sulfur could be found in stored gasoline.
SULFUR
3.5-
68
Free S. lMg./Liter at T a p 7 2 4 0.6 6 0.6 8 0.6 10 0.6 10 1 10 2 12 2 12 2 12 2
Table VI.
Effect of Bacterial Growth Inhibitors on Aviation Gasoline Propertiesa
TeJ t Density at 15 ’ C.. gramicc. Distillation range, O C. Initial b.p. 10%; distilled to 50% distilled to 90y0 distilled to Final b.p. Corrosiveness (ASTM I>-130, 2 hr. at 100’ C.) Existent gum, mg./100 ml. Potential gums, m ~ . / 1 0 0ml. Octane number a ‘4ST.If (.?) tests.
Gasolin 5 Blank 0,7220 47
65 100
129 162 la 0.7
3.0 100.0
absence or development of gasoline corrosiveness, rather than degree ofgro\vth inhibition. I n the preliminiry tests mentioned above. it had been found that for those substances the concentration required for complete inhibition of growth in Allred‘s medium were: 10 pg. per ml. for methyl violet; 0.65 mg. per ml. for sodium azide; and for the Entibiotics a mixture of 10 fig. per ml. of chloramphenicol a n d 40 fig. pcr ml. of streptomycin. The same concentrations \vere used in the corrosiveness control tests Jvhich were carried out as folloivs: 600 ml. of gasoline were placed in dark glass battles over 400 ml. of culture media to which the inhibitors hzd been added prior to inoculation. T h e bottles \vere incubzted a t 25” C. for 7 days, after which period the gasoline \vas examined for corrosiveness, HZS, and free sulfur, while the underlying culture medium was analyzed for sulfates. H2S, a n d sulfide ion. Results of these examinations are presented in Table V. T h e results show that methyl violet was effective in preventing the development of corrosiveness in gasoline when its concentration in the underlying aqueous medium was 10 mg. per liter. I n the concentrations used in these experiments, sodium azide and the mixture. of antibiotics were only partially effective in preventing corrosiveness. T h e relatively shorter period o f activity of the antibiotics would be a negative aspect to be considered from the viewpoint of their practical application in storage tanks. I t was deemed important to investigate whether the substances used in the experiments described above would have 24.n)- adverse effect on the properties of aviation gasoline as determined b>- the usual A S T M tests. For this purpose, 200 ml. of the following aqueous solutions were added to flasks containing 800 ml. of aviation gasoline a n d mixed vigorously for 0.5 hour in a shaking machine: methyl violet: 10 pg. per nil.; NaN3. 0.65 mg. per ml.; a n d chloramphenicol, 10 pg. per ml.. and streptomycin, 40 pg. per ml. Results of the tests are shoivn in Table \,’I which indicate that intensive contact
-Va.Va 0.7233
Gasoline Treated mith Solutions of .Wethy1 aioiet Antibiotics 0.7233 0.7229
45 66 100 129 162
45 66 100 129 162
45 66 100 129 163
la
la
la
0.8 5.9 99.8
0.5 3 .O 100.0
1.1 4.0 99 .O
Lvith these substances caused no significant changes in the properties of the gasoline. Considering these results. it is expected that the laboratorv investigations o n growth inhibition desxibed here will be folloived by tests carried out in aviation gasoline storage tanks. literature Cited
(1) Abd-El-Malek, Y . , Rizk? S.G.. .Vature 182, 538 (1958). (2) Allred: R. C., Mills: T. ’4.:Fisher! H. B., ProducPrs .Vfonthlj 19, 31 (1954). (3) Am. Soc. Testing Materials, Philadelphia, Pa., “ASTM Standards on Petroleum Products and Lubricants,” 1960. (4) Anderson, K. E., Lanigan. Regina, Liegey, F., \l?orden, ~ J . , Yackovich, F., Finan, A,, “Science Symposium,” p. 68, St. Bonaventure Univ., St. Bonaventure, N. Y., 1957. (5) Bakanauskas, S., \Tright Air Development Command Tech. Rept. 58-32,March 1958. (6) Bartlett, J. K., Skoog, D. A , ,4nal. Chem. 26, 1008 (1954). (7) Bennet, E. O., Bauerle, R. H.: Australian J . Bzol. Sci. 13, 142 (1960). (8) Bentur, S.: Babitz, M . , ”Aviation Fuel Corrosiveness,“ Technion-Israel Institute of Technology, Haifa, August 1958 (in Hebrew). (9) Degray: R. J., Killian, L. N., Ind. Eng. Chem. 52, No. 12, 74A, (1960). (10) :t. Brit. Dept. Sci. Ind. Research, “Chemistry Research,’‘ p. 93, 1952. (11) Nalco Chemical Corp., Chicago. 111.: Spec. Rept. No. 12, 1959. (12) Postgate, J., “Science Symposium,’‘ p. 44, St. Bonaventure Univ., St. Bonaventure, N. Y . , 1957. (13) Rogers, H. T., J . Soc. Chem. Ind. London 59, 2 (1940). (14) Starkey, R. L., ”Science Symposium,” p. 25, St. Bonaventure Univ.? St. Bonaventure, N. Y . , 1957. (15) Stern, A. B., Babitz. M., Bull. Research Council Israel Sect. C, 8 , NO. 3, 109-16 (1960). (16) IViIliams, 0. B., “Science Symposium,” p. 61, St. Bonaventure Univ., St. Bonaventure, N. Y . , 1957. (17) Technion Research and Development Foundation: “Aviation Gasoline Corrosiveness Caused by Sulfate Reducing Bacteria and its Prevention,” February 1962 (in Hebrew). RECEIVED for review May 14, 1962 RESUBMITTED February 18, 1963 ACCEPTED June 21, 1963
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