<p>If you want to study math, then pair it with or major in CS or physics to have a bit more applicability.</p>
<p>A chemical engineering curriculum will include all the math that you need for chemical engineering, and the curriculum is (obviously) not primarily math or even mathematical, but (chemical) engineering and physical sciences, so only a supplementary math minor is at most what you’d be looking to add.</p>
<p>If you’re thinking of a PhD in math, then you might as well stop thinking about engineering, you won’t have time for anything else than math, which is far more abstract than engineering. I.e. focus on the math, not engineering.</p>