Sulfuric Acid Characteristic

Hello Milo, We use Sulfuric Acid as a catylist to produce Alkylate (gasoline). We react Olefin with Isobutane. Just trying to recall by products, such as water (dilution) causing corrosion. Fellow CR4 directed me to info below. Not sure why is spent more corrosive.

When sulfuric acid first contacts carbon steel, iron sulfate (FeSO4) is produced. The iron sulfate coats the steel and forms a "passivation" film which then protects the carbon steel from further corrosion. Flammable hydrogen gas (H2) is also produced by the corrosion reaction: Fe(S) + H2SO4(l) --> FeSO4(s) + H2(g)

In that case my thinkiing is that the additional h2 o in the spent acid then dissolves/removes the iron salt FeSO4 "passivation film" exposing more steel.

milo

i agree, you can see corrosion in carbon steel even at 98% sulfuric at the liquid line due to possible dilution by humidity. The corrosion is a function also of the velocity of the fluid, high velocity will remove the oxide layer and cause further corrosion.

FAQ on Handling of Sulfuric Acid - Dupont

http://www2.dupont.com/Clean_Technologies/en_US/assets/downloads/Equipment_FAQs.pdf

S

I agree with milo's post. If you want to reduce the potential for reaction with the steel surface though, I would recommend you consider use of an appropriate corrosion inhibitor at an adequate concentration in the acid solution; one specific to the steel type and other components in the acid solution. I studied the action of these inhibitors (typically organic types) and found they are quite specific to the chemistry of the steel and the concentration levels.

My old chemistry teacher said that near pure sulfuric acid is mostly molecular, where the more it gets diluted, the more it's ionic. (H+ and SO4-). It's more reactive in that form, since the molecule is fairly stable.