3 sentences

1. 他在一家化工厂工作。

   tā zài yī jiā huà​gōng chǎng gōng​zuò.

   He works in a chemical plant.

   Source: Dong Chinese Dictionary

2. 石油化工是该城市近年来重点发展的支柱产业。

   shí​yóu huà​gōng shì gāi chéng​shì jìn​nián lái zhòng​diǎn fā​zhǎn de zhī​zhù chǎn​yè.

   The petrochemical industry has been a key pillar industry for the city in recent years.

   Source: Dong Chinese Dictionary

3. 他在大学里主修化工专业。

   tā zài dà​xué lǐ zhǔ​xiū huà​gōng zhuān​yè.

   He majored in chemical engineering in university.

   Source: Dong Chinese Dictionary