Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

be used to reduce corrosion in the reaction area. In the data shown, conditions in the vapor line from the reactor are even more corrosive than those encountered in the kettle liquid. This situation may or may not occur in a similar unit, depending on the mode of operation. The coils, or other heating apparatus used on the kettle, will again experience the greatest corrosion. For this reason, a major effort should be made to identify the optimum material of construction for this service. Graph- ite construction is sometimes used for this specific area. As for the other ester preparations, Type 304 stainless steel is adequate for many of the recovery stages following the reaction. If wash waters are used in the process, the possibility of stress-corrosion cracking from chlorides in the water should be considered. Otherwise, the stainless steels will provide product of a good quality at a minimum cost. Duplex structured stainless steel such as Type 329 or alloys containing higher nickel contents such as Alloys 600 and 800 are resistant to chloride stress-corrosion cracking in this service. The higher acrylate esters (four carbon and higher) are produced in a manner comparable to the ethyl acrylate process. However, the temperatures are higher and the attendant corrosion is increased. Here the reaction condi- tions are extremely severe, as noted in Table LXXX. Extensive corrosion testing should be conducted to iden- tify the desired materials of construction for the reactor

wide range of resinous products. The esters are best known as the starting material for the preparation of latex paints. Previous comments given in the sections on acrylic acid and the acetic esters are pertinent to the production of the acrylates. It was pointed out in the discussion of the acrylic acid that a simultaneous production of the ester can be achieved starting with propylene. If the process produces only acrylic acid, the acid is reacted in a manner analogous to that used for the acetic esters. 27 Ethyl acrylate is produced in a continuous system by the addition of sulfuric acid, or a similar catalyst, to the acid in alcohol. As in the case of the acetic esters, the conditions in the reactor are most aggressive. Type 316L stainless steel can usually be used for all equipment following the reaction step, and Type 304 stainless steel can be used for many of the recovery areas. On the other hand, the conditions in the kettle can be so severe that alloy materials higher than the austenitic stainless steels are required. Table LXXIX shows typical data from the exposure of coupons in an ethyl acrylate synthesis. Note the extreme corrosion of Type 316 stainless steel which occurred. As in the case of acetic esters, combinations of nickel-copper Alloy 400, nickel-chromium Alloy 600, copper alloys and the nickel-base molybdenum-chromium-iron alloys may

TABLE LXXVII Corrosion Generated in Phthalic Anhydride Esterifications

Exposure 1–Octyl phthalate batch preparation using 0.15% H 2 SO 4 with trace chloride present in some batches. Exposure of 83 days on 84 rpm agitator shaft in kettle liquid at average of 149 ºC (300 ºF). Exposure 2–Higher alcohols and phthalic anhydride plus 0.5% toluene sulfonic acid and 0.25% H 2 SO 4 at 140 ºC (284 ºF) average for 135 days in kettle liquid. Exposure 3–Toluene sulfonic acid catalyzed reaction of phthalic anhydride and higher alcohols at 174 ºC (345 ºF) for 10 days in glass laboratory kettle.

Corrosion Rate

1

2

3

Alloy

mm/y

mpy

mm/y

mpy

mm/y

mpy

.25 .30 .15 .08 .03

10 12

>1.27

>50

.05

2 – 2

Type 304 Stainless Steel Type 202 Stainless Steel Type 316 Stainless Steel Type 317 Stainless Steel CARPENTER alloy 20

–

–

–

6 3 1

1.60 1.04

63 41

.05

– – – – – –

– – – 1 – – – 5 – – 7 –

.03

1 – –

ACI CN-7M Casting HASTELLOY alloy C HASTELLLOY alloy B INCOLOY alloy 825 INCONEL alloy 600 MONEL alloy 400 Nickel 200 Ni-Resist Type2 Copper Titanium

<.03

< 1

– –

.03* .08*

1* 3*

.03

<.03

<1

.03 .10

1 4 – 7 – –

.03 .33 .08 .20 .15

1

13

–

3 8 6 – –

.13

.18

– –

– –

– –

.18

.08*

3*

–

*No Pitting. All other alloys pitted to some extent.

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