According to my knowledge, IIT Kanpur Chemical Engineering will give you a better perspective even in your noncore fields. So if you get a chance in IIT K then just go for it, it's one of the finest IITs in India, and the experience you will get there is incomparable.
Both Chemical Engineering and CS have a great scope with CS salaries a bit on the higher side. But non-CS profiles make it easily into B schools and the IIT tag will help you get into MS programs easily. It will also become easier to pursue Ph.D./ MBA from foreign universities.
Take Chemical Engineering if
Take CS BITS Pilani if
Trust me when I say that both choices will shape your career effectively and you will be able to earn well either way.