It 应该是人称代词,指代前面提及到的一件事。不定式是主语补足语。类似于 He is expected to win. We are expected to work on Saturdays.
所以原句没有问题,不需要修改和改动。
这句话我觉得有点别扭:It is expected to increase China’s production capacity of 1-butene from 1 Mtpa to more than 2 Mtpa within the next 3-5 years.
我给改成了:It is expected that China’s production capacity of 1-butene will increase from 1 Mtpa to more than 2 Mtpa within the next 3-5 years.
第一句话是哪里有问题吗?还是语法没问题,就是别扭?
第二句话应该比较好吧?