Assalaamu alaykum. Is hexane halal? It is used in the production of many cooking oils as a solvent. Could you please verify this? This is really important since oil is an essential food used in everything. May Allah reward you.

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger. 

We do not know the nature of this substance which you are asking about. To find out whether it is harmful or not, you should refer to the specialists in this regard.

What we can say from an Islamic point of view is that in principle all things are pure and permissible, not impure and forbidden.

Shaykh Ibn Taymiyyah said, "In principle, things are pure, and it is not permissible to consider something as impure or forbidden except with evidence; as Allah says (what means): {…while He has explained in detail to you what He has forbidden you, excepting that to which you are compelled.} [Quran 6:119]"

Allah also says (what means):{And Allah would not let a people stray after He has guided them until He makes clear to them what they should avoid.} [Quran 9:115] Also, the Prophet said, "One of the worst sins a Muslim could commit is asking about something that was not prohibited to the Muslims but it became prohibited to them because of his asking."

Besides, Salmaan Al-Faarisi, may Allah be pleased with him, narrated that the Prophet said, "What is lawful is what Allah has made lawful in His Book, and what is unlawful is what Allah has made unlawful in His Book; and whatever He kept silent about is pardoned." [At-Tirmithi and Ibn Maajah]

Allah knows best.