A commuter jet flight crew; suffering from the loss of de-icing capability; asked for and received special handling to return to ORD when they encountered moderate icing. In the process the flight may have entered C90 airspace wihtout authorization.

Narrative

We had PIREPs indicating light to moderate rime icing and light chop from 14000 to FL190. A regional jet departure off ORD checked on climbing to 15000; I gave him the PIREP info and climbed him to FL230. He acknowledged. As aircraft was climbing thru FL180 he said (with urgency); we need lower immediately and return to ORD. I descended him to 16000 (the aircraft was still over C-90 airspace which goes up to 15000). I then called C90 and told them that I needed lower on said aircraft and that he needed to return to ORD. The Controller acknowledged and said descending to 16000 approved. This is still my airspace at 16000 and I wasn't given any lower. As the aircraft reached 16000 he again stated (with urgency) that he needed lower. Believing that he was in an emergency status; I issued a descent to 11000; at this point the aircraft was at the edge of C90 airspace; and I'm not sure if he may have clipped it as he descended. There was NO other aircraft or limited beacon codes in the immediate area. After the aircraft descended; I inquired if he were declaring an emergency; He responded 'no; we're OK now'. I asked him if he could accept routing over the inbound fixes back to ORD and he said yes. I coordinated with the receiving controller and shipped him to that sector. I later found out from the PLANO Controller that the aircraft did not have any operating de-icing equipment; and they were in moderate rime icing; thus his urgency.