[Shadow1 (OP)]

Why it is so hard to be made, and can it be made by distillation at high temperature or with the reaction between the acid chloride and a salt of acetic acid (sodium acetate). And how do they make it in industrial scale.

[Bored chemist]

"can it be made by distillation at high temperature or with the reaction between the acid chloride and a salt of acetic acid (sodium acetate)"
Yes.
" how do they make it in industrial scale."
http://en.wikipedia.org/wiki/Acetic_anhydride#Production