Best IES Branch for Chemical Engineers

A person having B.Tech. in chemical engineering can apply for IES? & if 'yes' then what study i will have to do other than my branch & which branch is most suitable for chemical engii. student?. I think envirnmental engii. may be suitable for me, but you suggest me the best. & in which field(post) chemical engii. can get the job. How much, minimum time, a person will take to pass this exam for my branch?