Document
Superfund Tax on Chemical Substances; Request To Modify List of Taxable Substances; Notice of Filing for Bromobutyl Isobutylene Isoprene Rubber (x = 7071, y = 59, z = 50)
This notice of filing announces that a petition has been filed requesting that bromobutyl isobutylene isoprene rubber ((C<INF>4</INF>H<INF>8</INF>)<INF>x</INF>(C<INF>5</INF>H<IN...
SUPPLEMENTARY INFORMATION:
Request To Add Substance to the List
(a)
Overview.
A petition was filed pursuant to Rev. Proc. 2022-26 (2022-29 I.R.B. 90),
as modified by
Rev. Proc. 2023-20 (2023-15 I.R.B. 636), requesting that BIIR be added to the list of taxable substances under section 4672(a) of the Internal Revenue Code (List). The petition requesting the addition of BIIR to the List is based on weight and contains the information detailed in paragraph (b) of this document. The information is provided for public notice and comment pursuant to section 9 of Rev. Proc. 2022-26. The publication of petition information in this notice of filing is not a determination and does not constitute Treasury Department or IRS confirmation of the accuracy of the information published.
(b)
Petition Content.
(1)
Substance name:
Bromobutyl isobutylene isoprene rubber ((C4
H8)x
(C5
H8)y
(Br2)z); x = 7071, y = 59, z = 50).
The substance is also known as BIIR.
(2)
Petitioner:
Exxon Mobil Corporation, an exporter of BIIR.
(3)
Proposed classification numbers:
(i)
HTSUS number:
4002.39.00.
(ii)
Schedule B number:
4002.39.00.
(iii)
CAS number:
68441-14-5.
(4)
Petition filing dates:
(i)
Petition filing date for purposes of making a determination:
April 8, 2023.
(ii)
Petition filing date for purposes of section 11.02 of Rev. Proc. 2022-26, as modified by section 3 of Rev. Proc. 2023-20:
July 1, 2022.
(5)
Description from petition:
BIIR is a synthetic rubber commonly used for the inner liner of tubeless tires.
BIIR is made from butylene and bromine. Taxable chemicals constitute 99.01 percent by weight of the materials used to produce this substance.
(6)
Process identified in petition as predominant method of production of substance:
The predominant method of regular butyl rubber production is using a carbocationic polymerization reaction of isobutylene and a comonomer of isoprene. The catalyst system used is typically composed of aluminum chloride, boron trifluoride or similar dissolved in a methyl chloride solvent. Monomer feed of isobutylene and isoprene dissolved in a methyl chloride solvent are fed to a reactor operated at approximately −100 °C to control the rapid exothermic polymerization reaction generating a high molecular weight butyl rubber polymer. To obtain this high molecular weight polymer it is necessary for the feed monomers to be as pure as possible ensuring that the feed system stays as dry as possible. The methyl chloride and unreacted monomers are flashed overhead and recycled back to the feed system while the polymer is precipitated out as a solid which is finished and packaged.
The polymerization process for BIIR starts with the exact same process for regular butyl rubber outlined above. A subsequent halogenation step is then carried out in a well agitated vessel to ionically substitute a bromine molecule to the polymer backbone while the polymer is dissolved in an appropriate solvent. The solvent is then flashed precipitating out a solid which is then baled and packaged.
(7)
Stoichiometric material consumption equation, based on process identified as predominant method of production:
7071 C4
H8
(Isobutylene) + 59 C5
H8
(Isoprene) + 50 Br2
(Bromine) → [7071 C4
H8
+ 59 C5
H8
+ 50 Br2] (BIIR)
(8)
Tax rate calculated by Petitioner, based on Petitioner's conversion factors for taxable chemicals used in production of substance:
(i)
Tax rate:
$9.63 per ton.
(ii)
Conversion factors:
0.97 for butylene, 0.02 for bromine.
(9)
Public docket number:
IRS-2025-0042.
Michael Beker,
Senior Counsel (Energy, Credits, and Excise Tax), IRS Office of Chief Counsel.