If I have a business contract with a partner and my partner has a debt that he or she owes (and the debt was long before starting a business with my partner, so I and the business itself have nothing to do the debt), can the debt collector pull money out of our business account when that is also my money?
(Aside from your specific question.)
The combination of your words "business contract" and "partner" raises red flags, friend. Bright, iridescent red flags!
Because in no way should you be in no partnership! And a business enterprise with two or more participating individuals or entities can readily become a partnership by operation of law (imputed) whether or not the members intended it so.
Why is it not recommended? Because it creates unwanted reciprocal agency. Meaning that each partner can independently legally bind not only the partnership but the individual partners as well. Including not just contractually, but civil liability for tortuous conduct. Like running over a pedestrian while on company business.
So heed Q's good advice and get with your attorney, post haste - if not muy pronto.