8 replies to this topic

[shpereira]

Hi. I only began working in a food and beverage based industry a few months back. Recently, I faced this problem where one of our processes required addition of 10% HCL conc. The method was carried out in plastic blue drums and manual stirring. Upon inquiry, I found out that all steel mixers, agitators, corroded due to the heavy action duty of HCL. Obviously, one's go to response would be to replace steel with another corrosion resistant metal which we are working on. However, I thought, why not added small proportion of anti corrosion or corrosion inhibitors to my HCL. I read that amines are good inhibitors but since I am only a beginner in the food industry, I don't know how far this is acceptable. Also, how does amine prevent corrosion? Is there any other alternative? The purpose of adding HCl is to boost the acidic value of the extract that we are processing. Thank You.

[breizh]

You might consider coated impeller & shaft  !

HCL and Steel are not very much compatible ....

Breizh 

[shpereira]

Yes. I have decided a hastelloy c-276 to be coated over the steel material. Also use the same as agitator. Any thoughts?

[breizh]

Hastelloy is very expensive ! 

 

No possibility to use glass lined agitator or plastic material . Consider to consult vendors (lightnin , chemineer or local)

 

Breizh 

Edited by breizh, 25 March 2013 - 02:12 AM.

[shpereira]

It is expensive. But glass lining would mean breakable parts in my product. And it is food industry. 

Will speak to local vendors and see how far that helps.

Thanks 

[isbarqi]

Amine based corrosion inhibitors are usually used for acid cleaning and boiler water treatment. I don't think it can effectively work for continuous exposure of concentrated acid nonetheless.

Coating your metal or change to glass would be the way,,,,

[Art Montemayor]

Shpereira:

 

I am going to assume you have a Chemical Engineering training background. I make this assumption in order to qualify the degree of understanding on the subject of corrosion and use of inhibitors.

 

Your first sentence in your post is the most important information in this query. I say this from practical, first-hand experience. You are using a very reactive ACID (HCL) in your process equipment, and as Breizh has correctly alerted you, you should be aware that you are subjecting any exposed carbon steel surface to immediate attack by the HCL. I also have to assume what you failed to tell us: the inhibitor operation is a batch operation and you are rinsing (washing) the acid and its reacted products out of your equipment with either water or another fluid prior to putting the equipment back into operation for a food-grade production product.

 

I would be very, very cautious and careful of adding ANY inhibitor, additive, or external fluid to a food grade production operation without the expressed, written approval of local government inspection agencies and authorities. I don’t know where you are located, but if it is India then I would expect that the local government authorities would be very involved in ensuring that all food-grade products produced are not contaminated with un-authorized compounds or ingredients. Serious and grave consequences could be the result for anyone allowing un-approved ingredients in food-grade products supplied to the populace.

 

My advice is FORGET about adding any amine to your process. Amines are used in recirculating systems – like cooling water – as corrosion inhibitors. But they are never applied to the surface of a material that is supposed to process food-grade products. Here, you are contemplating a serious and hazardous situation that could endanger a lot of innocent people and close your operation immediately. Always check with local health and food authorities when even thinking of such an operation. Additonally, adding amines to the equation goes directly against chemical engineering expertise: amines are basic in nature (the ammonia radical) and yet you state, “The purpose of adding HCl is to boost the acidic value of the extract that we are processing”. That means that you would be NEUTRALIZING the effect that you need. This doesn’t make engineering sense.

 

In your industry I would expect you to be using 100% glass-lined equipment or stainless steel. I couldn't justify the use of carbon steel.

[shpereira]

Hi Art,

 

Thank you for your detailed reply.

 

As you stated correctly, use of an inhibitor would alter the reaction. I was reading various ways to arrest corrosion without having to change material and I read a paper on surfactants. But I know now, that this cannot be applied to a food based industry.

 

However, just for your understanding, after the gymnemic acid is boosted ( We are processing this herb called Gymnema Sylvestre) some KOH is added to this. This is to neutralize the HCL (any remaining quantity if it should be present. Most of the water + acid is washed off after giving sedimentation).  Neutralization is part of the end process. So I am not even going close to think about mixing chemical substances with my food product, ok? And it is a batch process.

 

We were earlier using SS for agitation and mixing, but that too didn't work out as it begun corroding and entering our product.

 

Glass lined equipment is the go-to choice, but we have failed to locate a vendor so far. 

 

 

However, you did mention something very interesting about using amines to inhibit corrosion in Cooling towers, which is again a problem we face in my company. In India, most of the water comes from well and under ground, which is fresh water. This fresh water is added to the cooling towers and never treated unless there is an impeding issue of scaling and things like that. 

[arthurzhuo]

Use the PFA lined valve or pipe for the corrosive liquid.