hi, is this flight route eligible?

Unfortunately, your itinerary is not eligible for any kind of visa free transit scheme. According to the rules of visa free transit policy, your itinerary is:

Thailand - Beijing - Thailand

You have to be aware that visa free transit policy take into account every type of landing, so in the eyes of Chinese immigration authorities, your itinerary is not a transit, but a simple round trip flight.

I advise you to change slightly your flights, if possible, to look like:

Milan - Bangkok - Beijing

Beijing - Hong Kong - Phuket

Or better to say, this will be the portion that will interest the Chinese authorities:

Bangkok - Beijing - Hong Kong

Anything before and after that is not of their interest.

By introducing Hong Kong, your itinerary becomes eligible for 144 hour visa free transit.