E X C H A N G E OF EXPERIENCE.

PRODUCTION CONTROL

DURABILITY OF RUBBER IN MEDIA CONTAINING DIMETHYLACETAMIDE I. D. Doroshenko, T. G. Klimenko, V. A. Kachanov, and D. G. Nikitin

UDC 66.018.8

Tests were carried out with rubbers for the purpose of finding a suitable material for rubber packing of maximum durability in media containing dimethylacetamide ~(DMAA) in chemical equipment. The packing specimens for the tests were produced from various grades of raw rubber, IRP-1225 (SKF-32), IRP-1256 and KB-121 (butyl rubber), 14-RV (SKT), 51-3042 (SK~PT), and 51-1481 (SKEP), and from the rubbers KShch-s, MB-s, and GOST 7338-65. The specimens were tested in pure DMAA and in DMAA-containing liquors at a temperature of 20-I00°C in laboratory conditions and on experimental installations. Investigations were carried out of the resistance of the rubbers to swelling (and solution) and the stability of the mechanical properties of the specimens (hardness according to the TM-2 scale and the elasticity on a UMR instrument) to corrosive media. In these tests note was taken of the surface state of the specimens and of changes in the color of the solutions. The data in Table 1 show that rubbers 51-1481 and 51-3042 based on ethylene propylene raw rubbers are prone to slight swelling in pure DMAA at a temperature of 60-80°C. The hardness of these specimens on the TM-2 scale was 76 and 92 before and 80 and 90 after the tests, and the resilience 40 and 30 conventional units before and 42 and 36 conventional units after the tests. The durability of rubber 51-3042 in a mixture of DMAA with isobutyl alcohol at 60°C was also quite high. After testing for 830 h the weight of the specimens had increased by 2.4% on average while their resilience and hardness c h a n g e d o n l y marginally. Rubber 51-3042 proved to be stable also in a suspension of LiCI in DMAA (i0 +90 wt. %) at 90°C. After testing for 517 h the weight of the specimens had increased by o n l ~ 2.05%. The resilience of the specimens after the test was 34 conventional units while the hardness remained practically unchanged. With 22 wt. % acetic acid added to DMAA the resistance of these rubbers to swelling at 100°C was significantly lower. The specimens were elastic but broke on slight bending. Rubbers IRP-1256 and KB-121 based of butyl rubber swelled slightly at 20°C in media containing DMAA. When the temperature of the suspension DMAA--LiCI--H20 (87.5 +12.0 +0.5 wt. %) was increased to 90°C the resistance of rubber KB-121 remained quite high. Rubber IRP-1256 swelled considerably at 90°C in a suspension of LiCI in DMAA. After 1096 h the weight of the specimen had increased by 16.6% and their surface was tacky. This rubber was destroyed after 500 h in a DMAA solution with CHsCOOH (78 + 22%) at IO0°C. In pure DMAA at 60°C the swelling of rubber IRP-1256 is accompanied by the erosion of the soluble components. After 24 h the weight of the specimens had increased by 4.26% on average and after 830 h by 1.93%. In a mixture of DMAA with isobutyl alcohol at 60°C the stability of this rubber is adequate. After i036 h the degree of swelling of the specimens was only 3.36 wt. %. Their resilience and hardness remained practically unchanged. Rubbers IRP-1225 and 14-RV (based on fluorine rubber SKF-32 and silicone rubber respec-. tively) are destroyed in DMAA-containing liquors at 60°C or over. R u b b e r KShch-s, which is acid and alkali resistant, is adequately stable in a suspension of NH4CI in DMAA at 20°C but is unstable in pure DMAA at 90°C. The oil and gasoline resistant rubber MB-s is unstable in dimethylacetamide-containing media even at 20°C. The results of the laboratory tests were confirmed by the results of the testing of the rubbers on experimental installations (Table 2). Rubbers 51-3042 and 51-1481 proved to be reasonably stable in dimethyl acetamide-containing media at temperature of I0-I15°C, i.e., Translated from Khimicheskie Volokna, cle submitted June 21, 1978.

0015-0541/79/1103-0245507.50

No. 3, pp. 52-54, May-June,

1979.

© 1980 Plenum Publishing Corporation

Original arti-

245

TABLE i. '

Results of the Laboratory Tests on Rubbers 1

Rubber grade

Appearance after the tests

Testing conditions

h-

icomposition of the

~'--~,

medium, wt. %

Swelling of the specimens,wt. % after the stated testing time

of the specimens

of the corrosive medium

~1 KShch-s 51-3042

IDMAA (density 943

increase

k g / m 3) The same

Yellow

e

51-1481 IRP-1256 ~P-1225

I

Faintly colored

in 72 h

The same. Yellowed Turbid

1

Slightly yellowed

n 292 h

The same White turbid

51-3042

DMAA- isobutyl al_ cohol-H20

P,P-1256 14-RV

The same

MB-s

DMAA- LiC1--H20

Orange

I~-121

The same

Slightly yellowed Yellowed

(12,03 + 88,6 ~ 0,37)

KB-121 r.P-1256

(87,5 + 12 0 + 0,5) =,

DMAA- LiC1 ( 9 0 + I0)

51-3042 ~,P-1225

"

The same

ace

The same

l in 95 h

Turbid

14-RV KShch-s 14-RV ~,P-1256 51-3042 51-1481 ~P-1256

The same DMAA-- NHaCI (80 + 20) The same

Orange Unchanged Clear y~llow

DMAA - CHsCOOH

(78 + 22)

The same

~-P-1225

breaks on

Yellowed

tn 500 h

t h e same turbid

in 24 h

rhe same

14=RV

TABLE 2.

Results of the Tests of the Rubbers on Experimental

Rubber.

Testing conditions

grade KShch-s 51-3042 51-1481 KBI21 51-3042 51-1481 KBI21

51-3042 51-1481 KB121

246

apparatus Crystallizer

composition of the medium, wt. % D M A A - LiCI- H2.O (87,5 + 12, 0 + 0,5)

DMAA--water separation column (column vat )

DMAA + H20 (99,35+ 0,65)

Evaporator

DMAA-LiCI-H20 .* before evaporation 55, 0 + 2,7 + 42;_3_, after evaporation 87,4 4 12,1+ 0,5

!.,tempera- :: time, h tute, °C

Installations Average change in Appearance of the weight of | tested specimens specimen, oTd

8--10

360

--4,57

Unchanged

8--10 8--10 8--10 I15 115

0,78 0,42 2,43 1,36 3,01

The same

I15

360 860 360 1060 1060 1060

19,84

85--90 85--90 85--90

122 122 122

0,42 3,05 .0,72

Significant increase in volume Unchanged The same

the weight of specimens of rubbers 51-3042 and 51-1481 had increased after testing for 1060 h in the column vat of a DMAA--water separator by 1.36 and 3.01% while their hardness and resilience remained almost unchanged. Their appearance did not change at all. The durability of DMAA-containing media at temperature up to I15°C is highest therefore %n the case of the ethylene-propylene rubbers 51-3042 and 51-1481. These rubbers were recommended for the manufacture of packing devices for heat exchange apparatus.

SAFETY CAPS FOR THE PROTECTION OF LOW-PRESSURE EQUIPMENT V. T. Poltavskii and I. P. Shelyuk

UDC 621.646.42

Safety caps are a reliable means of protecting chemical equipment in the case of an unforeseen increase in the pressure. Their rapid response, simple design, sealing capacity, and absence of limitations on the transmission capacity renders these devices suitable for the explosion protection of equipment. The efficiency of these caps in actual operating conditions depends on their design. Protection is most difficult in the case of equipment operating at a low pressure (500 kPa or less), especially when the cap diameter must be small (100-150 mm), the reason being that the existing range of thin-rolled sheet metals places a limit on the scope for the manufacture of bursting caps with the required parameters. The operating pressure of safety caps is lowered by various methods, one of which consists of machining grooves into the exposed surface (Fig. I). Tests carried out at the AllUnion Scientific-Research Institute of Safety in the Chemical Industry showed that the operating pressure of these caps depends on the depth, configuration, and method of production of the grooves. Grooved caps have not come into extensive use, however, because of the considerable variance of their operating pressure, 50-60%. The depth of the groove is the principal parameter for regulating the operating pressure. The stability of the pressure at which the cap operates depends on the dimensional precision of the groove[l]. The known methods of producing the grooves (etching, pressing, etc.) are unsuited for the m a n u f a c t u r e o f safety caps with an operating pressure of the necessary stability. The stability of the operating pressure of the cap can be increased by grading, i.e., by testing the caps in the manufacturing process at a pressure equal to their operating pressure in the apparatus. Some of the caps will be destroyed in the tests but the stability of the remainder of the batch will be higher. Even then, however, the variance of the bursting pressure will be i0-15%.

Fig. i. Safety caps With intersecting grooves (a) and a circular groove (b). Translated from Khimicheskie Volokna, No. 3, pp. 54-56, May-June, 1979. cle submitted August 14, 1978.

0015-0541/79/1103-024.7507.50

© 1980 Plenum Publishing Corporation

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247