Looking for advice of potential CRA's for multi-acid fluid 1

[XL83NL]

Hi all, for a new to build project we are designing, we are looking for advice on potential corrosion resistant metallic alloys that can withstand the corrosive media. The project has an R&D charachter with new technology, however there's a limited budget available. Unlike commercial plants the material selection has great impact on overall plant cost and return value, as the units are typically used for short periods of time. Hence material selection is of great importance.

Right now it all seems to become quite (if not too?) expensive since we cant find a suitable metallic alloy that has a balance of reasonable price and availability vs corrosion resistance and process conditions. Potential candidates have been glass lining, tantalum and zirkonium, however they are either too expensive, or put limits on equipment design which stops the process from working. Hastelloy alloys would be a good alternative however, but not sure if theyd work.

The fluid present are;
[ul]
[li]Polyols[/li]
[li]Ethylene oxide (max ~10wt%)[/li]
[li]Propylene oxide (max ~10wt%)[/li]
[li]Potassium hydroxide (max ~2.0 wt%)[/li]
[li]Disodium pyrophosphate (dissolved in water)[/li]
[li]Sucrose (dissolved in water)[/li]
[li]Glycerine[/li]
[li]Water[/li]
[li]Natural oil epoxides[/li]
[/ul]The following fluids are present only briefly at start of a new batch[ul]
[li]Acetic acid w/ H202 (or peracetic acid /w H20)[/li]
[li]Hydrogen peroxide (H2O2)[/li]
[li]Sulphuric acid. In reaction H2SO2 giving Caro's acid (Pyranha) [/li]
[li]Filter aid (e.g. perlite) powder also occasionally present[/li]
[/ul]
Temperaturerange: 120 ÷ 160 °C (occasionally 200°C).

Any ideas would be greatly appreciated!

 

[EdStainless]

The only two things on the list that worry me are the Acetic acid and the Sulfuric acid.
What concentrations and temps would those 'brief' exposures be?
What alloys have you ruled out?
I would start looking at Alloy 20 and AL-6XN, good corrosion curves are available for both alloys.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[XL83NL]

Thanks Ed.

Pyranha is also considered to be problematic. The products make up a very strong oxidising environment. Currently tests are done with several inconels and titanium. Ruled out are 316 and duplex. Glass lining seems to be a potential issue due to temperature and ph. I'll post concentrations tomorrow when I have data at hand.

 

[XL83NL]

Here's some info about the orst case scenario

The main problem is the combination of H2O2(35%), Sulfuric acid(1-5%) and peracetic acid (5-10%). In 2nd stage initial concentration of KOH can be up to 1.5 - 2.0% by weight. During the dosing process, the concentration of KOH is gradually decreased as the total products volume increases. The final concentration is again 0.2 - 0.3% by weight of KOH. Then acidic neutralization agent is added to form slightly acidic conditions. In initial stage of this operation mode there can be up to 50% of water in the initial reactor charge. This water is evaporated at later stage.

Temperatures around 100-120 °C.

 

[metengr]

Based on the additional information and estimated temperature range, I would evaluate the following alloys;
Alloy C22 or 59.

 

[XL83NL]

Thanks. Just out of curiousity, why C22 and 59 and not Alloy 20 or AL-6XN?

 

[moltenmetal]

Modest temperatures, dilute acid and an oxidant? Fluoropolymer lining is my first answer! If it has to be metallic, a C alloy is relatively risk free for a pilot unit- then a corrosion coupon campaign inside the pilot unit will let you know if anything cheaper will stand up to those conditions longer term. Accelerated corrosion testing will tell you nothing useful in my opinion, because you have a time-variant composition and redox potential in each batch.

 

[metengr]

Absolutely agree with moltenmetal.

 

[XL83NL]

Thanks guys. Ill check this info with the team and see if fluoropolymer lining is an option. In a similar plant (with like chemicals, other p,T) our customer can do some testing, so they should have experience to know if FP lining is an option (unless there's some info I wasnt told about why FP lining is not suitable).