The impurities are washed out with methanol,I think,before this gas is sent on to reactors where it’s changed into oil.

The impurities are washed out with methanol,I think,before this gas is sent on to reactors where it’s changed into oil.
It be many years before this problem be solved.在这个问题被解决之前过去了许多年
It won’t be long till this new type of oil be avaible.
在这种油的新形式可以利用之前将不会过太久
1.I think是插入语?
2.till,until,before等引导的时间状语从句到底有什么区别?
3.以上我翻译有什么错误没?
4.reactors where it’s changed into oil.→it’s changed into oil in the reactors?