C3 Petrochemicals LLC plans to build a propane dehydrogenation (PDH) plant near Alvin, Texas, to produce polymer-grade propylene and chemical-grade propylene, according to an air quality permit application the company filed with the U.S. Environmental Protection Agency.3 Petrochemicals LLC plans to build a propane dehydrogenation (PDH) plant near Alvin, Texas, to produce polymer-grade propylene and chemical-grade propylene, according to an air quality permit application the company filed with the U.S. Environmental Protection Agency.