Petrolium Alkylation C5s

There are issues with the C5s you are using - there are impurities, that are causing amphiphiles which form emulsions - so have your C5s analyzed for constituents and then study the alkylation chemistry of each one, and the culprit can be determined through the method of elimination. For the analysis a GC should suffice.

Hello Editor, Thank you for response. Just to give you a background, we are generally a C3 and C4 alkylation unit with a very minute amount of C5s. We've gotten hit with a big amount of C5s and not sure which C5 that have caused us to get into a very high phase of emulsion, which cause it to get carry over to down stream equipments. Have any idea which C5s (i.e. dienes, pentylenes, etc.) that may have caused this. We have not been monitoring our C5s GC closely, just total count of C5s. Thank you Any thoughts? Radalin538

Perhaps the degree of mixing of hydrocarbon and acid is too high? This could make breaking the emulsion after the reactor much more difficult.

Acid and hydrocarbon naturally form an emulsion upon mixing. This is why we use acid as a catalyst, to surround droplets of hydrocarbon with acid. However the degree of mixing can be crucial from a reaction standpoint and from a downstream separation standpoint.

Any thoughts?

-David

Your response is rather interesting. However, consider that the alkylation also involves the use of an alkyl-substance and naturally the Sulphuric acid catalytic component exists as a hydroxonium ion and of smaller quantity relative to the hydrocarbon, hence the acids will exists as droplets in the oil instead of the acids surrounding droplets of the hydrocarbon - as you have stated.

The only way the hydrocarbon forms the emulsion - as per your suggestion - is only if the reaction did not proceed to completion, and more of the alkyl-substance is needed to drive the reaction to completion.

"However, consider that the alkylation also involves the use of an alkyl-substance and naturally the Sulphuric acid catalytic component exists as a hydroxonium ion and of smaller quantity relative to the hydrocarbon"

What is meant by alkylation involves the use of an alkyl-substance?

Where does the hydroxonium ion (H₃O+) come from?

The Acid/HC ratio is important and is typically >1 to reduce unwanted polymerization reactions. Optimum ratios are 1:1 to 1.7:1.

-David

Hello ChemE, We normally operate at 60% ACID to 40% HC, and this does reduce polymers

What is 60% to 40% are these in moles or grams?

Now how does the ploymerization come about?

by sulphuric acid catalyzed alkylation you should have something of a molar-reaction like this:
H_nC₅T + CH₃-X -->(H₃O+) --> H_nC₅-CH_{3 ^{+ X-T}}

with the recovery of the H₃O+ to power the next molar-reaction and again and again until the reaction is complete. So why do you need nearly one-to-one loading of the catalysts to the C5s? One-to-one loading of the catalysts, does not make sense? Perhaps one-to-one loading of the alkyl-substance by which I mean CH₃-X to the C5s, think about it.

By the way acid catalysis uses H₃O+ for the catalyzing reaction. H+ the shorthand most people write never exists in life - only existing as H₃O+ - except in dry reactive ions and in plasmas.

Catalyst used for our reaction is H2SO4.

I gathered that you are using H₂SO₄ which naturally dissociates as follows

H₂SO₄ + H₂O -> H₃O⁺ + HSO₄^-

and or

H₂SO₄ + 2H₂O -> 2H₃O⁺ + SO₄^2-

That is how we get the hydroxonium ion, H₃O⁺, in the reaction.

Now may I ask what exactly you mean by C₃s and C₄s? what are the exact chemicals because I answer by concept analysis from the reaction mechanism, which may or may not change depending on what C₅s you have.

Also may I ask again what you mean by 60% to 40%? Are these in moles or gram-weights

Alkylation units are pretty close to moisture free. 98.5% H2SO4 or anhydrous HF is used because lower concentrated acids are corrosive.

The reaction consists of 2 carbocations and an iso-alkane. The carbocations are generated through protonation of the alkene by the protic acid, not H₃O+. The results are the alkylate and regenerated acid. C3's and C4's are short for propanes and butanes which are other feedstocks used in alkylation processes.

What your feedstock is depends on the market and what your products are. Usually you either run C3's with C4's or just C5's. C5's have the added bonus of producing an alkylate that can be used in gasoline blending and also in MTBE production if the market is there.

The 60% and 40% are in liquid volume %.

We use C3= (propylene) and C4= (Butylene) to react with Isobutane using H2SO4 as catalyst. In the Reaction zone (reactor) we maintain 40% hydrocarbon and 60% Acid, inside the reactor and acid settler. This ratio help reduce polymerization.

Thank you, I now recognize that the potential source of the polymerization is the breakage of the alkene double bond. Now your needs are better defined.

The use of protic acid as Chem119 has stated is very similar to dry reactive ions chemistry I had studied extensively in the past, though the mechanism of the protic acid is slightly by "simultaneous hybridization" - hence the progression without water and non-actual existence of the H⁺ as I had observed.

Off the cuff, I will say that your reaction is not complete for the residence time of the reactor. You possibly have the incomplete reactants becoming emulsion. I believe that the higher concentration of C5s is depriving the C3s and C4s of the Isobutane; also you may be having C5 dienes which are aggresively competing with the C3 and C4 alkenes. Try increasing very slightly the isobutane concentration, and check for changes. If you notice any then increase it some and check again; maintain your mixing intensity of previous setting.

Get back and let us know the results for the initial very slight increase of isobutane. Good luck

Hello ChemE119, Tried lowering mixer and this help slightly and currently can not check Acid/ HC ratio due to leaky valve. Currently looking more toward a type of C5s that may have triggered this, causing tight emulsion. Thank you. Any other thought would be greatly appreciated. radalin538

This is interesting because H2SO4 is favored over HF when alkylating C5s. Did any process conditions change as the feed changed?

Reactor Temp?

Space Veolocity?

iC4 fraction in Reactor Effluent?

Do you know who licenses the alky technology? Maybe they could be of some assistance.

No change except for the feed composition. Sorry not chem major here, that's why seeking help. Already called Dupont/ Stratco, no suggestion from them yet, aside from what we already know, that there were a big increase of C5s with the feed.