NEW MATERIALS

CORROSION IN MEDIA

AND CORROSION CONTROL

RESISTANCE FOR

OF

PRODUCTION

CONSTRUCTION OF ACETIC

ACID

MATERIALS FROM

HYDROCARBONS T.

E.

Kil'chevskaya

and

T.

P.

Anokhina

UDC 669.018.29:620.193:661.731

A unit f o r production of acetic acid by liquid-phase oxidation of light naphtha is in operation at the N a i r i t E r e v a n I n d u s t r i a l Corporation. The method was developed by D i s t i l l e r s Co., Ltd. (England), and the unit was designed by the P o w e r Gas f i r m (England). The p r o c e s s for obtaining acetic acid by this method cons i s t s of the following s t e p s : oxidation of light naphtha by oxygen of a i r , fractionation of the oxidate, and d r y i n g by a z e o t r o p i c distillation. Mainly austenitic c h r o m i u m - n i c k e l - m o l y b d e n u m s t e e l s Adeholm 624 (Sweden) of type Kh17N14M3B and BS 1501-845 (England) of type Khl7N13M2B and also h i g h - p u r i t y c o p p e r BS 1172/1964 (England) w e r e used to m a n u f a c t u r e the unit. A f t e r five y e a r s of operation of the unit, its equipment was examined. c o r r o d e d equipment.

B a s i c attention was given to

The r e a c t o r f o r oxidation of light naphtha, made of the Khl7N14M3B-type steel, o p e r a t e s at 18ffC. In its u p p e r p a r t , welded joints of flanges of the c o v e r to the unit's n e c k underwent c o r r o s i o n . B l i s t e r s and pits with depths of 2-3 m m w e r e o b s e r v e d on the cover. Insignificant general c o r r o s i o n was o b s e r v e d on the s u r f a c e s of the circulation tube and d r o p r e p e l l e r . C o r r o s i o n of welded joints was o b s e r v e d in units (also made of Khl7N14M3B-type steel) following the oxidation r e a c t o r which a r e intended f o r cooling and condensation of the gaseous r e a c t i o n products. The l i q uid product, the oxidate, goes f r o m the l o w e r p a r t of the r e a c t o r to the fractionating column for p r i m a r y d i s tillation of the highly volatile fraction. F r o m the c o r r o s i o n standpoint, the m o s t vulnerable place in this column, m a d e of KhlTN13M2B-type s t e e l , is the still p a r t because of the i n c r e a s e d f o r m i c acid content in the working m e d i u m and the t e m p e r a t u r e of 115~ B e c a u s e of intensive general c o r r o s i o n , the r e b o i l e r of the f r a c t i o n a t i n g column, made of the s a m e s t e e l , was r e p l a c e d with a s p a r e one made of the s a m e s t e e l a f t e r t h r e e y e a r s of operation. During the next two y e a r s of o p e r a t i o n , this r e b o l l e r a l s o b r o k e down and was r e placed with a new one made of s t e e l 10Kh17N13M2T. A f t e r two o r t h r e e y e a r s of o p e r a t i o n , annular s e c t i o n s and circulation tubes broke down in the f r a c tionating columns f o r distillation of heavy f r a c t i o n s , f o r distillation of light f r a c t i o n s , and f o r a z e o t r o p i c d r y i n g of acids (the columns w e r e m a d e of h i g h - p u r i t y copper). They w e r e r e p l a c e d with new ones made of s t e e l 10Kh17N13M2T, which w e r e in s a t i s f a c t o r y condition at the t i m e of examination. Some cooling c o n d e n s e r s of t h e s e columns w e r e a l s o r e p l a c e d with new ones made of s t e e l 10Kh17N13M2T. In the s y s t e m of the column for obtaining c o m m e r c i a l f o r m i c a c i d , all the equipment was made of Kh17N13MB-type steel. A f t e r four y e a r s of o p e r a t i o n , the tube bundle of this c o l u m n ' s r e b o i l e r was r e placed with a new one m a d e of s t e e l 10Khl7N13M2T. All the equipment of the s y s t e m of the column f o r obtaining c o m m e r c i a l propionic acid was made of Kh17N13M2B-type steel. B e c a u s e of c o r r o s i o n of the t u b e s , the tube bundle of this c o l u m n ' s h e a t e r w a s r e placed with a new one m a d e of s t e e l 10Khl7N13M2T a f t e r five y e a r s of operation. The r e m a i n i n g equipment w a s in s a t i s f a c t o r y condition. During five y e a r s of o p e r a t i o n , the tubes made of h i g h - p u r i t y c o p p e r w e r e completely r e p l a c e d with new ones made of s t e e l s 10Khl7N13M2T and 12Kh18N10T. An a n a l y s i s of the r e s u l t s of e x a m i n a t i o n of the equipment of this unit showed that the units and tubes made of copper BS 1172/1964 should o p e r a t e in an a t m o s p h e r e of o x y g e n - f r e e nitrogen. Since c o p p e r was obs e r v e d in s o m e units m a d e of s t a i n l e s s s t e e l , the oxygen was r e m o v e d insufficiently thoroughly f r o m the nitrogen, and the copper w a s corroded. C o r r o s i o n of welded joints was o b s e r v e d in the units made of s t a i n l e s s steels. A f t e r two to four y e a r s of o p e r a t i o n (in r e l a t i o n to the c o r r o s i v e n e s s of the o p e r a t i n g conditions), T r a n s l a t e d f r o m K h i m i c h e s k o e i Neftyanoe M a s h i n o s t r o e n i e , No. 11, pp. 24-26, N o v e m b e r , 1979.

852

0009-2355/79/1112-0852507.50

9 1981 Plenum Publishing C o r p o r a t i o n

TABLE

~

I

Rate of corrosion~

P

alloys

Medium composition

0 0 ~:~

08Kh21N6M 10KhlqN13M2T 10KhlTN13M3T

d~ Z8

87~oacetic acid, S~opropionic] 120 acid, 0.5#oformicacid, and 7.5~ water

2

of variousmaterials

steels

8~,acetic acid. l~o~opionic acid,5~ formic aczd, and ~f~ water

120

140 160

0, I3

oT~ 0,01

0,24

180

o,,Viv,,.o

!08KhlqN15M3T 06KbN28MDT KlaN [

0,06 0,03--0,36 0,56

0,03 0,03--0,21 0,50

0,04 0,01--0,18 0,39

0,04 0,01--0,17

0,38

0~

0,0b. 0,10 0,21 0,38

0,0l 0,07 0,15 0,23

0,00 0,05 0,II 0,15

0,00 0,03 0,09 0,14

0~0 0,01

0,03

" Titaniun

0~0

0,005

0,06

0~05

o7~5 0,06

o~o 0,002

3 60#.acetic acid,4a.formic acid,and 36~ water

120 140 160 180

0,04 0,11 0,49

0,03 0,09 0,45 0,56

0,02 0,07 0~28 0,45

0,06

0,01 0,23

0,41

0,01 0,05 0,19 0,33

4

120 140 160 180

0,28 0,70

o~7

058 0,25

o5, 0,18

o50 0,18 0,40

0~0 0,01

0,00 ~0'003

I /

0,21 0,28 0,36 0,47

0,08 0,05--0,23 0,32

0,07 0,05--0,20 0,23

0,00 0,01

0,04 0,27 0,38

0,41

0,04 0,26 0,30 0,38

0,09 0,19

0,08 0,17

5

55z~acetic acid and 45#0 propionic acid 66aoacetic acid, 24~.formic acid, and 10#.water

120

140 160 180

44~oaceticacid,q~,propionic acid'3Zoformicacid'2OoL methyl ethyl ketone.2 lao wateqand 5%n-bu~rl alcoho 16ol.acetic acid, 13~propioni~ acid, 50z,succideic acid, and| 21aAsoamyl acetate / 8

9

99. la.acetic acid, 0.6a. proplonic acid, O.O5~ofor-

l

0,31

0,65 0,36

0,49

0,24

0,31 0,42

0,54

120 140 160 180

0,09 0,32 0,47

120 140 100 180

o~9 0,13 0,64

0,05 0,32 0,40 0,49

G8

' O,I i 0,20

0,48

0,40

0,36

120 140 160 180

0,003 0,03

o,oo3 0,02

o,oo 0,004

mic acid, and O. 2F~o water

0,23_

0,21~

0,18~176

o,oo 0,003 0,14~176

water 76of; formic acid and 24o~.

90 I1O

0,48 --

0,08-0,40 0,59

0,06--0,34 0,39

0,05--0,25 0,38

-

o~o

I

0,00 0,00

l

0,03

0,05

0,01 0,00--0,22 I

0,04 0,19 0,24 0,30

0~! 0,02 0,02--0,27

0,00 0,00 0,0O4 0,006

l I I 1

0~

o~o

0,30

0,07 0,16

0,00

0~0

0,005

1

o~o --

0~0

'

0,006

o,oo 0,003 0,11~176

0,008

0,03 0,15

0,01 0,06

0,001

0,005 ] 0,03-3,16 I

the tube bundles of the e v a p o r a t o r s , r e b o i l e r s , and heaters were replaced with new ones. A pilot-plant unit for obtaining acetic acid by liquid-phase oxidation of butane, developed by the Institute of Chemical P h y s i c s of the Academy of Sciences of the USSR, is in operation at the Moscow Petroleum R e finery. The p r o c e s s for obtaining acetic acid by this method c o n s i s t s of oxidation of butane and fractionation of the oxidate. The equipment of the unit was made of stainless steels 10Kh17N13M3T,10Kh17N13M2T, and 12KhlSN10T and also of bilayer steels with a plating layer of steel 10Kh17N13M2T. The equipment was examined after three y e a r s of operation. The reactor for oxidation of butane, made of steel 10Kh17N13M3T, w a s corroded mainly at the places of the welded joints. The operatingtemperature of the reactor is 165~ In a heater made of the same steel as the reactor which was installed in the middle part of the reactor, corrosion was observed at the places where the tubes were welded to the grid. On cooling condensers (made of steel 10Khl7N13M2T and a bilayer steel with a plating layer of steel 10KhlTN13M2T) intended for condensation of acid gas leaving the reactor, c o r r o s i o n of welded joints and pitting c o r r o s i o n of the plating layer w e r e observed. In the column for debutanation of the oxidate, made of steel 10KhI7N13M2T, c o r r o s i o n was observed on the surfacing of the sealing surface on the flanges, which was made with NZh-13 electrodes using 0 4 K h l 9 N l l M 3 wire. Corrosion at the places where the tubes were welded to the tube grid was observed in this column's reboiler, also made of steel 10Khl7N13M2T, and corrosion of the plating layer was observed on the flanges made of bilayer steel St3 + 10KhlTN13M2T. In the s y s t e m of the column for distillation of the highly volatile fraction, made of steel 10Khl7N13M2T, the welded joints of the column itself and of the reboilers were intensively corroded. After one year of o p e r a tion, the fractionating section of this column, made of bilayer steel 20 + 10KhlTN13M2T, was replaced with a new one made of steel 10Khl7N13M2T because of strong c o r r o s i o n of the casing. 853

TABLE 2 Rate of corrosion(mm/yr) of variousmater. steels

Column

TernF ~

alloys

O,1 v.4

o

For distill, of highly volatile fraction

100

0,~0

0,000

0,003

0,003

0,000

For drying of crude acetic acid

I15 130 63 I10

0,019 0,005

0,113 0.023

0,091 0,007

0,101 0,020

0~057 0~010 0~000 0 . 0 0 4 0,050 0,000

For removal of resins from crude acetic acid For separation of formic acid from crude acetic acid ! For removal of water from crude acetic acid For production of glacial acetic acid

135

0.000

0,000

o;o03 o;o15 0;007 o;o2o o:o13 o:ooI o;ooo O,045 0 io0 o,o~7 o.102 0,072 o.on o.ooo 0,034 0,019 o;o23] O:OlS o;ooo o;ooo 0,046

The fractionating sections of all the other columns w e r e also replaced. At the same time of e x a m i n a tion, the new fractionating sections made of steel 10Khl7N13M2T were in s a t i s f a c t o r y condition. A number of v e s s e l s of the unit w e r e made of bilayer steel VSt3sp + 10Kh17N13M2T. operation, they were replaced with new ones made of steel 10Khl7N13M2T.

After a y e a r of

An analysis of the r e s u l t s of examination of the equipment of this unit showed that the bilayer steel used for manufacturing some units is insufficiently c o r r o s i o n - r e s i s t a n t , during the f i r s t y e a r of operation, the units were c o r r o d e d at the places of the welded joints because of mixing of the metals of the base and plating l a y e r s . The plating l a y e r was also c o r r o d e d because of its nonuniform thickness. It is obvious that for the m a n u f a c ture of equipment operating under such c o r r o s i v e conditions as o c c u r mainly in the production of acetic acid, we should r e c o m m e n d a monometal or bilayer steel with a p l a t i n g - l a y e r thickness of not less than 3 mm. The tube bundles of the r e b o i l e r s of the fractionating columns operate under v e r y s e v e r e conditions: heating with s t e a m at 151-179~ T h e r e f o r e , the c o r r o s i o n r e s i s t a n c e of a s e r i e s of steels and alloys was studied under l a b o r a t o r y and industrial conditions. F o r the l a b o r a t o r y t e s t s , we selected nine media, whose compositions are given in Table 1. The test conditions were taken close to the operating conditions of the h e a t - t r a n s f e r equipment (the m o s t corrosive). Steels and alloys having h i g h c o r r o s i o n r e s i s t a n c e in f o r m i c acid acetic acids [1-9] were investigated. M o r e o v e r , taking into account the need to conserve nickel, we studied the possibility of using steel 08Kh21N6M2T and titanium VT1-0. The chemical compositions of the investigated m a t e r i a l s corresponded to the standard ones. All the e x p e r i m e n t s were c a r r i e d out in autoclaves in the p r e s e n c e of nitrogen (to avoid oxidation and resinification of the media). On the a v e r a g e , the duration of the l a b o r a t o r y t e s t s was 100 h. The c o r r o sion r e s i s t a n c e of the m a t e r i a l s was d e t e r m i n e d a c c o r d i n g to the weight loss of the sample. The test results are given in Table 1. As is evident, alloy KbN65MV (of Hastalloy C type) was the most stable in all the investigated media with the exception of the medium of composition No. 6 at 180~ in which this alloy was in an unstable a c t i v e - p a s s i v e state. Another m a t e r i a l which showed high c o r r o s i o n r e s i s t a n c e in m o s t of the investigated media was titanium VT1-0. Only in the media of compositions Nos. 5 and 9 at 180 and 110~ r e s p e c t i v e l y , was the titanium in an unstable a c t i v e - p a s s i v e state, apparently because of the high f o r m i c acid content in these media. The r e m a i n i n g investigated m a t e r i a l s can be a r r a n g e d in the following o r d e r of d e c r e a s e of c o r r o s i o n r e s i s t a n c e . 06KhN28MDT, 08Khl7N15M3T, 10Kh17N13M3T, 10KhlTN13M2T, and 08Kh21N6M2T. It should be noted that in general the c o r r o s i o n was nearly uniform in nature. Samples of the same m a t e r i a l s w e r e tested at the Moscow P e t r o l e u m Refinery as under l a b o r a t o r y conditions in units of the pilot plant for production of acetic acid. Chains of the s a m p l e s were mounted in the middle part of six columns of the oxidate-fractionation d e partment. The tests lasted 4320 h. Unfortunately, it was p r a c t i c a l l y impossible to mount the samples in the r o l l e r s of these columns, although it is p r e c i s e l y the tube bundles of these units which operate under the m o s t s e v e r e conditions.

854

The r e s u l t s of the industrial t e s t s a r e given in T a b l e 2. As is evident, titanium V T 1 - 0 and alloy Kh65MV had high c o r r o s i o n r e s i s t a n c e , and all the r e m a i n i n g investigated m a t e r i a l s had an acceptable c o r r o s i o n r a t e . The r e s u l t s of l a b o r a t o r y and industrial t e s t s at identical t e m p e r a t u r e s w e r e in good a g r e e m e n t . The r e s u l t s of the t e s t of welded joints of the s t a i n l e s s s t e e l s under l a b o r a t o r y conditions showed that in high-quality welding the weld m e t a l w a s close to the base m e t a l , c o r r o s i o n - r e s i s t a n t under the given conditions. On the b a s i s of the r e s u l t s of the e x a m i n a t i o n and a l s o of c o r r o s i o n t e s t s , we developed r e c o m m e n d a t i o n s f o r the m a t e r i a l design of the equipment of the p r o c e s s f o r production of a c e t i c acid f r o m butane. The oxidation r e a c t o r and the f r a c t i o n a t i n g columns should be made of s t e e l 10Kh17N13M3T (monometal), the h e a t t r a n s f e r equipment should be made of alloys 06KhN28MDT and KhN65MV and titanium V T 1 - 0 in relation to the a v e r a g e t e m p e r a t u r e of the tube wall and the f o r m i c acid content in the working m e d i u m , the c o n d e n s a tion equipment should be made of s t e e l 10Kh17N13M2T, and the v e s s e l s should be made of s t e e l 08Kh22N6T or 08Kh21N6M2T or of carbon s t e e l with an e n a m e l coating. As c o n c e r n s the use of copper in design of the p r o c e s s equipment, this m a t e r i a l r e q u i r e s that highly o x y g e n - f r e e nitrogen be fed to the units. O p e r a t i n g e x p e r i e n c e has shown that in m o s t c a s e s copper is intensively c o r r o d e d . The r e a s o n for this is apparently oxygen, in whose p r e s e n c e the copper is in an active state. LITERATURE 1.

2. 3. 4. 5.

6. 7.

CITED

I . A . Levin and T. E. K i l ' c h e v s k a y a , " E f f e c t of oxygen p r e s s u r e on the rate of c o r r o s i o n of m e t a l s in a solution containing a c e t i c (50%) and f o r m i c (4%) a c i d s , " T r . Gos. Nauchno-Issled. Proektn. Inst. N e f t . M a s h i n o s t r . , No. 2, 41-44 (1964). I . A . Levin and T. E. K i l ' c h e v s k a y a , " C o r r o s i o n r e s i s t a n c e of titanium V T - 1 and its alloy V T - 5 in fatty a c i d s , " Ibid., 64-66 (1964). T . E . K W c h e v s k a y a , " E f f e c t of t e m p e r a t u r e and concentration on the c o r r o s i o n of m e t a l s in fatty a c i d s , " Zh. PriM. Khim., 43, No. 5, 1062-1068 (1970). T . E . K i l ' c h e v s k a y a and A. V. S h r e i d e r , " E l e c t r o c h e m i c a l behaviour of s t a i n l e s s s t e e l s in aqueous solutions of l o w - m o l e c u l a r - w e i g h t fatty a c i d s , " Zh. Prikl. Khim., ~ No. 10, 2341-2344 (1972). T . E . K i l ' c h e v s k a y a , " E f f e c t of f o r m i c acid solutions on the c o r r o s i o n activity of fatty a c i d s , " in: M a t e r i a l s . C o r r o s i o n . Welding (A collection of A r t i c l e s of the All-Union S c i e n t i f i c - R e s e a r c h Institute for P e t r o l e u m - M a c h i n e r y Construction) [in R u s s i a n ] , M a s h i n o s t r o e n i e , Moscow (1975), 145-151. P . I . Anuchin, A. I. F i r s o v , and G. F. Mikhalyuk, " C o r r o s i o n r e s i s t a n c e of v a r i o u s g r a d e s of copper in a c e t i c acid s o l u t i o n s , " Gidroliz. Lesokhim. P r o m - s t . , No. 2, 12-14 (1965). I. Ya. Klinov and M. A. V o r o b ' e v a , " C o r r o s i o n r e s i s t a n c e of some alloyed s t e e l s and titanium under conditions f o r production of synthetic a c e t i c a c i d , " Vestn. T e k h . Ekon. Inform. N I I T E k h i m a , No. 5,

41-44 (1962). 8. 9.

A . M . Sukhotin (editor), C o r r o s i o n and P r o t e c t i o n of Chemical Equipment. Handbook [in R u s s i a n ] , Vol. 5, Khimiya, Leningrad (1971); Vol. 9, Khimiya, Leningrad (1974). A . A . Sharnin, T. A. P e n z e v a , V. S. Glushchenko, et al., C o r r o s i o n R e s i s t a n c e of Construction M a t e r i a l s in P r o c e s s e s f o r Synthetic Fatty Acids and Alcohols. Review. " O p e r a t i o n , Modernization, and R e p a i r of Equipment" Series [in R u s s i a n ] , T s N I I T E n e f t e k h i m , Moscow (1974).

855