Hello seeman, every branch is good and every branch is bad. Coz it totally depends upon your interest in a particular field of engg. If you love dealing with computer stuff you'll good with CS branch whereas CS branch could be a burden for some other person if he/she has no interest in computer related stuff.
So ask yourself do you really want to go for petrochemical branch ? Are you really interested in petrochemicals?
If yes then nothing would be better than this. If no then look something of your interest.

hai seeman khan, actually it was good choice because you are thinking out of the box and also in btech/be in doent depends on which branch are college it was about your intrest if you are desired of chemistry all that then goo with it only your intrest matter if you had passion in it you can make wonders like anything all the best