The train to Antwerp Central takes 32 minutes each way. Train station is in the basement of the airport. Your call if 2 hours in Antwerpen is enough. The station is enough reason to make this trip imo. You can then take the "pre-metro" (underground tram) to the Groenplaats, marvel at the cathedral, have a drink and return.
If you want to have a shower on arrival then they might let you in at the Diamond lounge, but it will be crowded. The "Loft" at the A-Pier is a better option but quite a long walk so I wouldn't combine it with a trip to Antwerp because it will cost too much time.
Flying out of A is now very fast and efficient since the new building "connector" is ready: seldom a queue at security. Still quite a distance to walk.