Is it permissible to continue working for a company that sells alcoholic beverages, knowing that the nature of one's work is in the IT department, and how can the money earned from this work be purified?

If the company engages in permissible activities other than selling alcohol, and the employee's work is not related to selling alcohol nor does it assist in it, then there is no impediment to him remaining in the job. However, if the company's activity is restricted to selling alcohol, or if the employee's work is directly related to its sale, then he is not permitted to remain in this job because it is assisting in sin, and he must leave it immediately. He will not be held accountable for his past work before he became aware [of its impermissibility].