How CorroSafe Solved a Tough Material Problem for a Chemical Reactor

The Company

A top chemical maker in India runs a factory that uses special helpers called catalysts to speed up reactions. Their work involves high pressure and very high or very low temperatures.

The Problem

The company needed help to pick the right material for a reactor and its mixing system. The conditions inside the reactor were very harsh.

The reaction used a strong catalyst called Anhydrous Aluminium Chloride in an organic liquid. The temperature was 130 degrees Celsius and the pressure was 30 bar.

Here is what made it so hard:

• A tiny amount of water in the liquid feed created a dry and very corrosive gas called Hydrogen Chloride inside the reactor. This took 5 to 10 hours.
• The system went through a big temperature change every day. It went from 130 degrees Celsius down to minus 15 degrees Celsius using a very cold liquid in a cooling coil.
• To clean the reactor, a water wash was used. This created a very strong acid with a pH near 0.5 and a lot of chloride.
• Other materials had already failed. The company needed a strong and lasting solution.

How CorroSafe Approached the Work

CorroSafe Consultant Pvt Ltd did a careful step-by-step study to find a material that could handle both the dry and wet corrosive conditions.

• They calculated that each batch made about 3 kg of corrosive gas from the water in the feed.
• They checked materials for the high-temperature dry phase and the room-temperature acid wash phase.
• They looked at the effect of small amounts of iron and other metal impurities in the catalyst feed.
• They studied the effect of high pressure and the sudden temperature change from the cooling coil.
• They compared many materials including nickel alloys, reactive metals, glass lined steel, and plastic linings.

What CorroSafe Discovered

• Common materials like carbon steel and standard stainless steel failed quickly because of the wet acid and the pH 0.5 wash.
• Some special metals that work well with pure acid were ruled out. The iron impurity created another chemical during the wash that caused deep pits and cracks.
• Glass-lined steel had a high risk of breaking from the sudden temperature change. Also, standard glass-lined vessels can only handle 6 to 10 bar pressure, not 30 bar. A 30-bar design would be very costly and special.
• Plastic linings like PFA and PTFE had a high risk of gas leaking through at high temperatures and pressures. This would cause hidden rust under the lining. The daily temperature swing also risked the lining coming loose.

CorroSafe Recommendations

CorroSafe gave a tiered set of recommendations. They focused on using a bonded metal cladding to get strength and low cost together.

• First choice: Use a nickel alloy cladding called BCI. This gave the best resistance to both the hot, dry gas and the acid wash with iron impurities.
• Second choice: Use Hastelloy C 22 cladding. This gave very good resistance to local pitting and gaps in the presence of chlorides.
• Third choice: Use Hastelloy C 276 cladding. This was a reliable and flexible choice that works well with both oxidising and non-oxidising acids.

For the agitator or mixer, CorroSafe said it should be made of or covered with the same material as the reactor. This avoids electrical problems between different metals.

Key Lessons from the Case Study

• Gas can be made inside the reactor. Even if you keep air and water out while adding materials, the water already in the feed will create corrosive gas. So the material must be chosen for what happens inside, not just what you put in.
• Small impurities matter a lot. Just 500 parts per million of iron can change a material from good to bad. This shifts the need from one type of alloy to another.
• Mechanical stress is just as important as chemical resistance. A material may resist acid well, but that does not matter if it cannot handle 30 bar pressure or big temperature changes every day.