英语语法分析

The preservative used is usually ethylene glycol or propylene glycol, as alcohol will evaporate quickly and the traps will dry out.

常用防腐剂是乙二醇或丙二醇，因为随着酒精快速挥发，捕集器也随之恢复干燥。

That too means less propylene, since it is also a by-product of petrol production.

既然丙烯也是石油工业产品的副产物，这也意味着其产量缩水。

The trouble is that the ethane route to making ethylene produces virtually no propylene.

问题在于这种用乙烷制作乙烯的生产流程几乎不会伴有丙烯产生。