Iowa-based Renewable Energy Group Inc. will use $100 million from a new debt offering to back or redeem the Gulf Opportunity Zone bonds issued in connection with a biorefinery in Geismar.

REG’s plans to buy the Dynamic Fuels LLC facility, which makes fuel from animal and waste fats. The biorefinery was a joint venture of Tyson Foods Inc. and Syntroleum Corp.

The biorefinery has been shuttered for more than a year and will cost an estimated $20 million to restart.

Renewable Energy Group’s convertible senior notes pay an interest rate of 2.75 percent but contain an option allowing the notes to be converted to stock under certain conditions. The initial conversion rate is 75.4 shares of REG stock per $1,000 in notes, or $13.26 per share. REG shares closed Thursday at $10.01.