Free transit entry to Beijing?

Hi,
In December, I have a conference in Hong Kong. I checked flight tickets. I will fly by Air China and will transit in BJ. My trip will be between London - Hong Kong.
I am confused that I am holding 4-year resident permit in the UK, so whether or not I am eligible for free 72/144 hour transit in BJ. My nationality is Vietnamese. I also held a China visa some months ago, but it will be expired soon.

Thank you,