Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

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D. Fatty Acids

The fatty acids comprise those organic acids exceeding four carbons in length according to some chemical text definitions. However, the term as used industrially and in this text refers to the higher acids of six or more carbons. These are characterized by lauric, oleic, linoleic, stearic, tall oil and rosin acids as produced for commerical use from products of the meat, agricultural and paper industry. The large volume product of industry is not a pure compound, but a mixture of two or more of the com- pounds meeting certain chemical specifications. At the lower temperatures, the acids may be considered as harmless polar “oils.” However, when the products are heated to the high temperatures necessary for processing and production, significant corrosion of steel can result. Fortunately, there is a wide variety of alloys which have excellent resistance to the conditions of production and subsequent use of the acids. A proper economic analysis

Data reported for the corrosion of metals in the fatty acids are not explicit regarding stream compositons. As a consequence, a comparison of the results obtained in a number of industrial exposures at various temperatures is necessary to gain a proper view of corrosion to be expected in these media. A number of factors can influence the corrosion rates observed: • Light ends (lower acids), if allowed to remain in the mixed fatty acids, can result in a more aggressive environment. • The ratio of fatty to rosin acids affects the corrosion rate. • The presence or absence of water will have an effect, particularly on the corrosion of the stainless steels. • Decomposition products generated by overheating the acids will add to the corrosiveness of the solution. • Pretreatment of the acids may leave traces of ions in the acids that increase corrosivity. • The temperature of the processing operation is a major variable of concern.

of the use of the alternative achieve an optimum selection.

materials is necessary to

TABLE LI

Corrosion of Alloys in Tall Oil Fractions

Corrosion Rate

Conditions a

Temperature ºC (ºF) Time, days Exposure

100(212) 30 Vapor

275(527)

260(500)

300(572) 3 Liquid

25(77) 19 Liquid

265(509) 54 Liquid

265(509) 134 Liquid

265(509) 100 Liquid

220(128) 242 Vapor

250(482) 66 Liq–Vap.

240(464) 50 Liq–Vap.

265(509) 73 Liquid

247(477) 66 Vapor

247(477) 66 Liq–Vap.

220(428) 66 Vapor

260(500) 63 Vapor

195

Liquid

Vapor

Alloy

mm/y mpy

.09 3.4 .06 2.5

Consumed >6.35 >250

– – 11.1 440

– –

Consumed – –

– –

Steel Cast Iron Ni–Resist Type 2 Nickel 200 MONEL alloy 400 INCONEL alloy 600 Type 304 Stainless Steel Type 316 Stainless Steel Type 31 7

.02 0.9 .02 07 .03 1 Nil 0.1

.77 30 .38 15 .20 8 .25 10

.25 .08

–

– 5 8 2

– – 0.9 3.5 0.1 0.5 0.1 0.2

–

31 .09 3.6 .09 3.7

.13 .20 .05

.17 6.6 – –

.23

9 –

–

.15 .28

–

.91 36 1.60 83

–

– – .61* 24*

–

– 6

–

.43

.79

.43*

.15

.79

Nil*

>.76 >30

>7.6 >30

1.57

Nil 0.1

4.70 185

Consumed

–

Nil

0.1

.36 14

<.03 <1

.05

–

Nil 0.1

.86

.84

.20

.08

.05

1.78* 70

08*

.03*

.10

Nil

Stainless Steel CG–8M Casting Type 310 Stainless Steel Type 330 Stainless Steel

– –

Nil

NII

.23

9 –

.08 .10

3 4

–

– 1

Nil Nil Nil 0.1

Nil 0.1 – –

.99* 39 – –

Nil

.02 0.8 – –

Nil

–

.03

–

Nil

0.1

>.76 >30

>7.6 >30

.15

–

Nil

0.1

>.76 >30 – – – – – –

.46

– – – –

–

– 2 – –

–

– – .02 0.7 2.67 105 86 34

– – .61* 24* >2.13 >84 >2.29 >90

–

– – – –

INCOLOY alloy 825 INCOLOY alloy 800 INCOLOY alloy 804 HASTELLOY alloy C HASTELLOY

– – –

.05

Nil

NII

Nil

NII

– –

Nil

0.1

<.03 <1

<.03 < 1

.03

–

Nil

.01 .05

Nil Nil

–

Nil

alloy B Copper CN–7M Casting Titanium

–

– 3 – –

– – >7.6 >30 – – – –

– – >7.6 > 30 – – – –

–

.01 0.3 _ 1.04 41 – –

–

Nil

–

.08

.25

– –

Nil

.71

– –

.03

Nil Nil

.02 .06 – –

Nil Nil

Nil* NII – –

.08

3 –

Nil

– –

–

Nil

–

*Pitted

References 30, 31, 49. 52

a Conditions of the exposures:

1– Field test in vapor of light-odor tall oil fraction during distillation in vacuum column. Water present. 2– Field test in bottom and top of tall oil vacuum distillation column. Oil (presumably crude) from southern kraft pulp mill. 3– Laboratory test in crude tall oil acids from kraft pulp mill distilled under vacuum with agitation of 300 rpm in kettle. 52 4– Laboratory test in crude and semi-refined oil with velocity of 0.3 fps provided in liquid. 5– Field test in base of tall oil distillation column (20% oleic acids, 60% rosin acids and 20% pitch). 30 6– Field test in base of tall oil distillation column (65% fatty acids and 35% rosin acids). 30

7– Field distillation of 65% fatty acid–35 % rosin acids. 31 8– Field distillation of 93% fatty acids–5% rosin acids. 31 9– Field distillation of 90-93% oleic acids with <1% rosin acids with steam injected. Velocity of 62 fps. 31 10– Field test six inches above the outlet of a reboiler on 97% fatty acids,1.5% rosin acids and 1.7% residues with high velocity. 31 11– Field test in heat exchanger head handling 85% fatty acids and 15% rosin acids with steam present. 12– Field test in reboiler nozzle at base of distillation column handling 90-93% oleic acids and 1% rosin acids with steam injected. 13– Field test on distillation column tray near bottom while processing 90% oleic acids, 2% stearic acid, 0.4% rosin acids, 0.5 light ends and 6.4% higher acids with steam present. 14– Field test in top of distillation column handling analysis of No. 13 above. 15– Field test near bottom of distillation column handling 30-32% rosin acids, 8-20% oleic acids and 62-48% higher boiling acids with steam present.

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