Pretty much my thoughts. I can get 99.5% ethyl alcohol with a drop of denaturing agent that boils around 100°C @ atmosphere if I remember correctly.
What are the accepted denaturing agents in the world of regulated processing? Obviously heptane should be ok. Who sets the regulations? Department of Public Health as per FDA standards?
G.O. Joe as usual nailed it.
https://en.wikipedia.org/wiki/Denatured_alcohol
https://ttb.gov/industrial/sda_regs_laws.shtml
https://www.gpo.gov/fdsys/pkg/CFR-2002-title27-vol1/pdf/CFR-2002-title27-vol1-part21.pdf
https://www.gpo.gov/fdsys/pkg/CFR-2003-title27-vol1/xml/CFR-2003-title27-vol1-sec21-151.xml
https://www.ecfr.gov/cgi-bin/text-i...text&node=27:1.0.1.1.17&idno=27#se27.1.21_133
https://www.ecfr.gov/cgi-bin/text-i...ext&node=27:1.0.1.1.17&idno=27#se27.1.21_1112
https://www.grainprocessing.com/alcohol/sda-usage-chart.html