US EPA

8158802 

Meetings & Symposia 

Production of ammonium perchlorate using titanium substrate lead dioxide anodes 

Unnikrishnan, K; Mukundan, K; Pillai, KR 

2007 

9 

5664-5670 

English 

Ammonium Perchlorate (AP) is the work horse oxidizer universally used in all composite solid propellant formulations. AP is made by the double decomposition of Sodium Perchlorate with a suitable ammonium salt. Sodium Perchlorate in turn is manufactured by the electrolytic oxidation of Sodium Chlorate using special anodes. Only two materials can be used as anodes in the industrial production of Perchlorates: Platinum and Leaddioxide. Platinum is very costly and its availability is also limited. Lead-dioxide, on the other hand, is very cheap, but due to its brittle nature, requires a suitable substrate over which it has to be coated to form an anode. ISRO set up an experimental plant (APEP) in 1979 at Aluva in Kerala State. The new plant adopted the less expensive lead dioxide as the anode material. A process developed by Central Electrochemical Research Institute (CECRI) Karaikudy was scaled up to set up a 110 T/annum plant. The Graphite Substrate Lead-dioxide Anodes (GSLA) had several disadvantages like short service life, low current efficiency etc. A new anode system namely, Titanium Substrate Lead-dioxide Anodes(TSLA) was developed by ISRO to overcome these problems. Due to its superior corrosion resistance, the Titanium substrate can be re-used after the useful service life of the lead-dioxide coating. However, this very same property of formation of a protective layer of TiO2 over the surface prevents the coating of an adherent layer of Lead dioxide directly over the Ti metal surface. An appropriate intermediate layer of conductive oxides is required for electrodeposition of a layer of Lead dioxide. TSLA system was found to be superior to GSLA with respect to current efficiency, cell voltage, and reusability of substrate. The TSLA system is only one-tenth as costly as Platinum (the most preferred anode among Perchlorate manufacturers), but gives almost the same current efficiency, and runs at a lower cell voltage. The net operating cost of TSLA based system is less than that of GSLA and Platinum based systems. APEP is now being augmented to a production level of 800 T/annum. The electrolytic cells were modified to improve the production capacity, and as a result, the very same cells could meet the additional requirement of Sodium Perchlorate for the augmented production, and a power saving of around 20% could be achieved. Improvements in the process of conversion of Sodium Perchlorate to AP have resulted in improved yield and better control of particle size distribution (a very crucial parameter for propellant oxidizer). The new processing facilities set up in the plant are running on a semi-automated mode with a PLC system to control the various process steps. The new plant also incorporates a recovery plant to extract AP from the plant effluents which not only makes the effluent more environment-friendly, but results in higher %yield of the product too. The state of the art plant, APEP, has been able to meet all the requirements of propellant grade AP for the various launch vehicle projects of ISRO. Copyright IAF/IAA. All rights reserved.