Its linked to your steam account and the only way to sell it is to sell the steam account with it.
But
https://support.steampowered.com/kb_...5406-WFZC-5519Buying, Selling, or Trading Accounts
Accounts which have been bought, sold or traded will be disabled. This includes any other accounts in your possession at the time of the sale or trade, regardless of whether those accounts were also sold or not.
