Cracked Ammonia

I'm on a similar pursuit but I am doing it on behalf of a customer who hasn't confirmed they want the job done yet.

My preliminary investigations indicated that a firm called Nova-Gas might well be able to supply an instrument for this task. This job has been stalled for six months but I'd be very interested to know how you get on. I'm also going to be interested to see what other replies you get. It's hard work getting information on special atmospheres.

U said right, its hard getting info especially when its uncommon task. Thanks to all of them thosea are taking out time and sharing their knowledge to help out others here on CR4.

There is famous quote " Knowledge increases by sharing "

Can you tell me what other conditions exist in the gas stream. Mainly temp. and pressure, as well as any species which are present in PPM levels. Do you know what level of ammonia to expect? We have monitored some streams for NH3, however it is tricky as it is very reactive.

Brian.

Hi Brian,

Conditions are : This is high pressure cracking at 6-6.5 bar & 850°C in vertical retort furnace.

The input Ammonia is : Unhydrus, 99.75% purity with OIL PPM 3.7 & Moisture 0.25%.

The plant is being operated at 70 to 90% capacity, Full load capacity is 30NM3/Hr

Hope this will provide you required details and looking forward for your reply. Thanks.

Limbkar

Until you find an instrument capable of providing you with a direct readout of uncraked ammonia, there remains an older but viable means of determining uncracked ammonia concentration. Collect some from a sidestream in a sample bomb at atmospheric pressure and known temperature, add a measured amount of distilled water, and shake to make the ammonia dissolve in the water as ammonium hydoxide. Hydrogen and Nitrogen will hardly dissolve. Titrate a measured amount of resulting ammonium hydoxide with an acid such as known concentration dilute sulfuric (perhaps 1 normal) to neutral PH. The PH transition will be very sharp since you will be titrating a strong acid against a moderatly strong base, so watch for the transition with an indicator such as phenolthaline.

Since you know the volume of gas collected, the amount of water used to absorb uncracked ammonia as the hydoxide and amount and concentration of acid used in the titration, you will be able to back calculate the volume percentage of uncracked ammonia. When doing so, bear in mind that both hydrogen and nitrogen are diatomic, whereas ammonia as NH2 is not. You should easily be able to determine NH2 concentration to one part in 50 or one part in 100, or better if you are very careful

Hope this helps.

Bernie Katz

Bernie Katz

Hi Bernie Katz,

Thanks for the procedures. I would try out soon.

LIMBKAR

Ion Mobility Spectrometry does a great job in monitoring ammonia down to sub ppb levels. It may be a bit expensive for your purposes. See:

http://www.pmeasuring.com/molecular/industrial/applications/petrochemical/ammonia

I cannot agree with Bernie's method of ammonia analysis. Ammonia does not quantitatively form ammonium hydroxide when absorbed in water at neutral pH. Part of it will be present as dissolved ammonia, and part as ammonium hydroxide. Also, ammonium hydroxide is a weak base, so that phenolphthalein is not an appropriate indicator. The proper method would be to absorb the NH3 in a standardized acid, then back-titrate to methyl red indicator endpoint. With some care and proper conditions (<< 1N), you may be able to get accurate results in the ppm range.

Tad

The Phenolphthalien indicator pH is about 8.3. This is a bit high to make a direct determination for the presence of ammonia in the vapor stream. You can titrate and back calculate the quantity of ammonium ion in the water. However, the water needs to be very pure, having no buffering capacity. You will need to know the temperature and pressure, The volume of gas and water, and the coefficients at those temp and press for ammonia absorption and equilibrium with ammonium. An electric pH probe can be used also, more effectively.