How many plastic containers(20L) palm kernel oil will be in 20ft container?

I think a 20ft container is 20ft x 8ft x 8ft. If you convert it into metric that's 6.1m x 2.44m x 2.44m which is 36.29m³. A cubic metre is the same measure as 1000 litres. If your container was filled with perfectly square containers which fitted snugly and no space was left unfilled, you'd have 36,290 litres of palm kernel oil (meaning 1,814 plastic containers).

However, there will always be space required for the packaging itself and space wasted if the packaging is, say, drum-shaped. Factoring that in, I'd expect a full container to carry between 1000 and 1500 plastic containers.