(1) It is lawful to supply citric acid provided it contains no impure agent.
(2) You can supply citric acid to one who is not using it in alcohol. Likewise, it is allowable to sell it to one who is using in preparing alcohol made of things other than four prohibited items i.e. raw wine of grape, ripe wine of grape, raisin and dates. But, if you know that he will use it in preparing haram alcohol (made of the four items mentioned above), then selling it to him is makrooh (undesirable), but you can sell if you do not know.
(3) It is makrooh to sell citric acid to one who prepares wine if he will certainly use it for the same purpose.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband