Q & A > Question Details
Over past 5 months, we have suffered from increased (by 25%, 30 ton/day) sulfuric acid consumption of our alkylation unit.
Now, we doubt increased non-regenerated alkyl sulfate formed by butadiene and / or increased acid soluble oil formed by olefin polymerization.
1. Actually, the butadiene content of C4 olefin feed has widely been ranged from 0.2 to 1.0% according to our lab analysis (thru PONA analysis), and apparently there is no tend that the butadiene content has been increased. Are there any methods to analyze the butadiene content more precisely. It's known that the butadiene makes non-regenerated alkyl sulfate by strong reaction with sulfuric acid and goes to acid phase, which reduces acid concentration. Are there any methods to analyze the alkyl sulfate content in the spent acid?
2. The C4 olefin feed comes from our RFCC unit which uses ZSM-5 as an additive to boost propylene production as other RFCC's. Can ZSM-5 increase the butadiene content in the C4 olefin feed? Actually, we have used ZSM-5 for a long time in the RFCC unit, and recently we changed the brand of ZSM-5 at the end of last year. Can the butadiene content in the C4 olefin feed be much affected by the type and vendor of ZSM-5?
3. Are there any methods to analyze the acid soluble oil content in the spent acid? Can higher iC4/Olefin ratio reduce the acid soluble oil content in the spent acid?
25/06/2014 A: Amarjit Bakshi, Refining Hydrocarbon Technologies LLC, abakshi@rhtgulfcoast.com
Sulfuric Acid Alkylation :
Economic Summary
Conventional , CDAlky, RHT
Acid Cost MM $/y(1) 10.7 , 5.9 , 5.1
Utilities Cost MM $/y 14.8 , 12.3 , 10.9
Octane Value MM$/y(2) Base , 14.9 , 18.4
Total dollar advantage/y(3) Base , 22.2 , 27.9
(1) Sulfuric Acid at 125 USD/mt, 0.55/.30/20 lbs Acid/gallon alkylate produced.
(2) Octane advantage at 1.0 USD/Octane barrel
(3) Operating cost savings excluding Acid regenration
Acid Regeneration Costs have not be included.
(4) CDAlky uses packing for mixing, loading and unloading of [packing cumbersome in the reactor, needs frequent changes and under mixing pressure drop chance of collapse. Licensor describes that packing used in the mixing.
07/01/2013 A: Amarjit Bakshi, Refining Hydrocarbon Technologies LLC, abakshi@rhtgulfcoast.com
By the way in continuation to my earlier comment, acid consumption is refered to after the base consumption in the process than it is in impurities and depending on the extent of impurities and it is good idea to hydrogenate the diolefins which helps in lower acid consumption, cost of hydrotreating and runs are long and is not that great but helps in reducing the acid consumption and lower ASO and is paid off in short duration depending on the design.
05/01/2013 A: Amarjit Bakshi, Refining Hydrocarbon Technologies LLC, abakshi@rhtgulfcoast.com
Though the main contribution of acid consumption in alkylation process is due to impurities like diolefins , but the question may be also that due to ZSM-5 if you are making more C3= and C5= and more of these are being in feed than the acid consumption will also increase.
There are other options which will save 50 % on Opex as you have already spent the Capex (where saving are also about 40 to 50%) , by changing the operation with revamp and low temperature operation and changing the mixing devices will reduce the acid consumption by just about 50 % in normal case and also the impurities also use less acid producing low ASO. The capex spent in revamp will be paid of in 8 to 12 months with energy savings/acid consumption/ and enhancement of octane number. Please look up the RHT-Alkylation process.
It is listed in the Hydrocarbon Processing refining Handbook 2011 under Refining Hydrocarbon Technologies LLC.
12/10/2012 A: keith bowers, B and B Consulting, kebowers47@gmail.com
You are asking a lot of questions that indicate di-olefin concerns. The olefin feeds should be analyzed by gas chromatography. Butadiene WILL increase sulfuric acid consumption. If fact, concentrated sulfuric acid is used to extract butadiene from mixed C4's. In many units, product alkylate is contacted with fresh acid to remove alkyl sulfates as they dramatically lower the octane number. This is particularly important if making 'aviation' alkylate as even traces of alkyl sulfates will lower the leaded Performance Number by 4-6 'octane'.
DATA on the alky unit feedstocks is essential to resolving your problem