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Abstract
It has been discovered that the addition of sodium borohydide to ethanolamine process streams is effective at preventing corrosion as well as color formation of metals.
Corrosion Inhibitor for Ethanolamines Plants
Corrosion in amines plants
has been a problem for decades. Even materials such as 304 and 316 stainless
steels can corrode at unacceptably high rates in some amines processes.
Therefore, a method for preventing this corrosion is needed.
It was found that
ethanolamines process streams (i.e., unrefined mixtures of monoethanolamine,
diethanolamine, and triethanolamine) became much less corrosive when sodium
borohydride was added. In most cases, the corrosion was reduced by a factor of
ten. For example, when ammonia column tails (crude ethanolamines) was heated at
180 °C for 48 hours with 304 and
316 SS corrosion coupons in a closed titanium Parr vessel, corrosion rates as
high as 4-5 mils per year were observed. But when 2000 ppm by weight of sodium borohydride was added, the
corrosion rates were always < 0.5 mpy.
Sodium borohydride treatment
is effective in the presence of common impurities in the ethanolamines process,
such as carbon dioxide, and even in partially aqueous streams. Metals that
exhibit less corrosion with sodium borohydride include 304, 316, and 2205 stainless steels.
It is not known why the sodium borohydride is effective at
preventing corrosion. Sodium borohydride also prevents color formation and this
mechanism is understood to involve reduction of intermediate aldehydes.
