Travel from Lisbon to Tbilisi, through Amsterdam and Kiev

According to this page, you still need a valid passport in order to transit Ukraine.

Bumping old post for future reference:

The IATA database used to contain slightly wrong info. You can Transit Kiev at least if you have a through ticket on Ukraine International Airlines, using an EU ID Card.

It's been updated since, however

You can look more for more specific information then the Visa page from Timatic which is in use by the airlines:

Admission and Transit Restrictions:

• Transit refused to holders of National ID Cards issued to nationals of Portugal.

So passport is required for transit through Kiev.

EDIT

Link above is broken.

Information from KLM Timatic page:

Admission and Transit Restrictions:

• Transit refused to holders of National ID Cards issued to nationals of Portugal.

• Except when transiting through Kiev Boryspil (KBP) on Ukraine International Airlines (PS).

VISA NOT REQUIRED.

Having been to Boryspil last week I haven't seen any other airline flying to Kiev... Or may be I wasn't there late enough to see any EU based airlines...