(119c) Acetylene Converters Troubleshooting

Braskem, a Brazilian player among petrochemical manufacturers, produces monomers, resins and chemicals specialties. The overall Ethylene capacity is 3,600 KTA, distributed in six Olefins plants.

One of the main sections at Olefins process is the Acetylene Converter. This paper reports a troubleshooting held in Olefins Plant II, a Tail-End process in Bahia, that begun with the premature lost of the catalyst activity and resulted in the lost of this catalyst bed. 

The acetylene is a by-product of the cracking of ethane up to vacuum gas oil in the furnace area. As the cracking temperature of the furnaces is increased the acetylene content increases and the reverse is also true.  

The Tail-End acetylene conversion in the Olefins plants promote a hydrogenation of acetylene, as a purification procedure, where the acetylene is selectively converted in the concentrated mono-olefin stream after the major fractionation steps have been completed and just prior to the final separation to guarantee the ethylene specification. 

Braskem Olefin plants in Bahia, referenced as UO1 and UO2, employ a Süd-Chemie last generation catalyst for their acetylene converter reactors. In UO2 plant, there are three beds designed for having two beds operating in series and the third bed for regeneration procedures and stand-by position.  

After an operating cycle, the reactor in stand-by position was then placed in a position to be swapped into an on-line condition. The regenerated reactor exhibited exceptionally low catalyst activity when placed into the tail position.  A second regeneration and successive attempts at swapping the bed into both the lead and tail positions produced no improvement at all in catalyst activity. This behavior pointed to the possibility that some type of permanent catalyst poison was deactivating the catalyst. The deactivated catalyst was then unloaded and a new fresh charge of catalyst was provided at emergency schedule to prevent an unexpected shutdown of UO2 plant. 

A sample of deactivated catalyst was sent to Süd-Chemie -USA and also to an independent laboratory for analysis.  When the catalyst sample was submitted to a test run, the performance behavior observed at Braskem, of very low activity, was confirmed. When this sample was regenerated ex-situ according to specific laboratory regenerating procedures and the test run was repeated, the activity was completely restored, by comparing its performance with a fresh reference of the same catalyst. 

A thorough survey was held and no contaminants were found on the exhaust catalyst. The TGA analysis confirmed no coke present in the catalyst, concluding that the carbon had been removed successfully during plant regeneration. The XPS analysis did not identify any poison in the surface, neither palladium. In spite of this, the X rays analysis confirmed the presence of the expected quantity of palladium in the bulk of catalyst. The conclusion was that, due to the lower temperature used during the oxidation step, silver had occluded the palladium sites at the catalyst surface during regeneration.The regeneration procedure was successfully reviewed, reducing the purges of methane and steam steps and increasing the air concentration during oxidation step, in order to guarantee an optimum temperature peak in the bed.