You are looking at several issues here. First, you will be creating friction between the lift buckets and the plastic tube. Even if you have some clearance, the pellets will still rub on the side walls.
If the top of the silo is 10', then you will have to lift about 14-15' so the output will gravity feed into the silo. At 2' spacing in the tube, you will have about 6 to 7 buckets lifting at any one time. weight on each bucket will be between 25 to 30 lbs each, resulting in a vetical lifting weight of about 175 to 210 lbs, not including the weight of chain and buckets.
An option is to get an electric lifting hoist mounted on a swing post and use the 500 to 1000 lb bags with the dump valve on the bottom.
My pellet supplier supplies me with 1000 lb bags of pellets which I move with my tractor. I dump it into my feed bin when ever I need.
Silo's wouldn't work for me because I feed three different types of pellets to my horses.
Just my 2 cents worth