About 2.5 hours from Tianjin Airport to Beijing. The bus will stop at Bawangfen Bus Station, in Beijing CBD. It is about 10km from the bus station to your hotel. If you want to take subway, you can walk to Dawang Lu station of SUbway Line 1 from Bawangfen. Then get off at the next stop (Guomao) to change to Line 10 to Sanyuanqiao. Get out from Exit D, you will see the building of Ibis.

You can also catch the CRH (high speed bullet train) from Tianjin to Beijing. It only takes 30 minutes, and arrives at Beijing South Railway Station.

Sorry, I left out some info. Catch the shuttle bus from Tianjin Airport to Tianjin Station, then catch the bullet train to Beijing South Station.
The bus stand is in front of the airport departure hall. The fare is RMB10. The bus will stop about 200m before the train station south entrance. Just walk along the footpath and you will see the train station.
As you enter the train station, the ticket counter is on your left. Tickets to Beijing South cost RMB58 (or RMB69 first class). The waiting hall is on Level 1.
(Bullet trains start with 'C' and run every 15 minutes in peak times, and every 30 minutes during off peak.)