Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

general, affords less corrosion of austenitic stainless steel surfaces than does the sulfuric acid. Table LXXV shows data obtained by field exposure of various alloys in a TSA catalyzed reaction during two different runs. Other mate- rials that can be used are benzene sulfonic acid and acetylsulfoacetic acid (ASA). Of these, the ASA is the least corrosive to the austenitic stainless steels but in- creases the rate of attack on copper alloys significantly. Tables IV and XXI show other data relating to the preparation of these esters. Table XXI particularly lists a wide range of alloys evaluated in a synthetic butyl acetate reaction mixture. One of the newer catalysts for use under certain circumstances for esterification reactions is boron tri- fluoride. Table LXXVI shows data generated by condi- tions required for such a reaction. Type 316 or Type 316L stainless steels appear to be adequate for this reaction. However, extensive testing should be conducted before committing an austenitic stainless steel to such a fluoride environment. As indicated, essentially all the corrosion to be experi- enced in the esterification process occurs in the reaction kettle and appurtenant equipment. Distillation of the esters from the kettle is normally conducted in a Type 316L stainless steel still to assure low corrosion rates in this equipment. However, further refining of the ester, or other techniques required for improving the quality of the product, can be conducted in Type 304 stainless steel

equipment. The ester itself is innocuous and can be processed or handled in steel equipment if contamination of the product is not objectionable. Thus, the concern with corrosion in such a process is centered totally in the reaction area of the equipment. B. Phthalate Esters The phthalate esters are prepared directly from the anhy- dride in a manner analogous to the preparation of the acetic esters. The temperatures are higher, but a drier medium is maintained than during acetic ester prepara- tions. Table LXXVII shows typical data generated by three exposures of numerous alloys in phthalic ester preparations. The same general statements as provided for the acetic esters relate to this type of exposure. Phthalate esters prepared from octyl, decyl and other alcohols are important as plasticizers for various plastics. They also have excellent heat stability and can be used for heating mediums for a number of processes. Esterification of the fatty acids to produce soap is not exceptionally corrosive. 28, 32-34 Data shown in Table LXXVIII reveal moderate corrosion of the stainless steels, and very low corrosion rates of the more highly alloyed materials in three different field exposures. As with other esterifications, once the esterification itself is completed, processing of the product becomes much less difficult; Type 304 stainless steel is satisfactory for such a purpose. C. Esterification of Fatty Acids

TABLE LXXV

Corrosion of Alloys in a Typical Acetic Esters Reaction

D. Acrylate Esters The acrylate esters comprise one of the newer, more reactive group of chemicals available for the synthesis of a

Conditions: Batch reactions producing butyl acetate with kettle exposure of alloys in 25-45% acetic acid, 30% acetates, 20% alcohol,

5-8% water and 0.75% toluene sulfonic acid. Test 1 conducted at 107 ºC (225 ºF) for 34 days and Test 2 at 121 ºC (250 ºF) for 29 days.

TABLE LXXVI Comparison of Esterification Catalysts on Corrosion of Alloys Conditions: Preparation of a higher acetic ester in semi-

Corrosion Rate

Test 1

Test 2

Alloy

mm/y mpy mm/y mpy 11.18

works equipment using 1.5 per cent sulfuric acid at 75-110 ºC (167-230 ºF) during 32 days for Test 1 and 0.32 per cent boron

440 10 13 17

8.38 – 1.14 –

330 – 45 –

Type 304 Stainless Steel Type 329 Stainless Steel Type 316 Stainless Steel Type 317 Stainless Steel

.25 .33 .43

trifluoride at 75-85 days in Test 2.

ºC (167-185 ºF) for 5

.36 1.27

14 50 23 8 23 9 20 39 20

– – – – – –

– – – – – –

CARPENTER alloy 20 INCOLOY alloy 825 ILLIUM alloy G HASTELLOY alloy C HASTELLOY alloy B INCONEL alloy 600 MONEL alloy 400 Nickel 200 Copper

Corrosion Rate

Test 1

Test 2

.58 .20 .58 .23 .51 .99 .51

Alloy

mm/y mpy mm/y mpy

.03 .03 .05 .03 Nil .18

1 1 2 1 Nil 7

.43 .05 2.49 .03 Nil .30

17 2 98 1 Nil 12

Type 304 Stainless Steel Type 316 Stainless Steel E-BRITE 26-1 CARPENTER alloy 20Cb-3 HASTELLOY alloy C-276 Copper (C10200)

.18 .43 .18

7 17 7

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