The lexicon of the top500 ( The Encyclopedia for Classification Codes ) explains the codes and definitions in the world of economical classifications.
NAICS Code 3251 Basic Chemical Manufacturing
The NAICS Code 3251 is described as
Basic Chemical Manufacturing Description
This industry group comprises establishments primarily engaged in manufacturing chemicals using basic processes, such as thermal cracking and distillation. Chemicals manufactured in this industry group are usually separate chemical elements or separate chemically-defined compounds.
(2019-08-02)
It belongs to the code group
NAICS Code 325 Chemical Manufacturing