Introduction
Butene -1/Butene-2 mixture is used as a raw material for the production of methylethyl ketone (MEK). MEK is used as a solvent for polymer compounds, paints and adhesives. Besides, it is used as a high-performance solvent in the magnetic tape manufacturing industry in recent years. On the other hand, Buten-1 is used as a raw material in polybutene-1 production, and it is also used as a co-monomer for polyethylene. High purity Butene-1 or Butene /Butene-2 mixture is required in these applications.

GPD Process was developed to produce high-purity Butene-1 and/or Butanes based on years of experience in handling dimethyl formamide (DMF) as extractive distillation solvent in Butadiene extraction operation, which annual commercial capacity is now well over 4.5 million metric tons in terms of product in the world.

Case-1: Butene-1 Purification

Process Feature
GPD Process consists of the following two sections:
(a) Extractive Distillation Section
(b) Butene-1 Purification Section

Butadiene in raffinate from iso-Butene Removal unit (MTBE or iso-Butene Dimerization) must be removed up to the Butene-1 specifications at the Extractive Distillation Section (or Hydrogenation Unit).

Fortunately, the 1st extractive distillation column of GPB (ZEON’s Butadiene Extraction Process, please refer to the "Butadiene Recovery" (GPB Process) Unit can be used for this purpose by changing the operation conditions and slightly modifying the 1st extractive distillation column.

Therefore, in case of adopting GPB Unit, a new extractive distillation column (or Hydrogenation Unit) is not needed in GPD Unit, which enables simplification, low investment cost and low utilities consumption of GPD unit.

Process Description
C4 mixture from naphtha crackers is introduced into the 1st extractive distillation section to remove 1,3-Butadiene and acetylenes. Butene-1 rich stream obtained as the distillate of the extractive distillation column is sent to the 1st Fractionator through iso-Butene Removal Unit (out of scope of ZEON), where iso-Butene is removed.

Then, from the bottom of the 1st Fractionator, Butene-1 rich stream is sent to the 2nd Fractionator, where n-Butane and 2-Butene are removed. Butene-1 of more than 99 wt% purity with the quality required for a linear low density polyethylene (LLDPE) co-monomer is obtained as the distillate of the 2nd Fractionator.

Note : iso-Butene specification
The boiling points of iso-Butene and Butene-1 are so close that it is difficult to separate them by conventional distillation. iso-Butene content in the stream from iso-Butene Removal Unit should meet the specifications required for an LLDPE process.

Case-2: Butane-Butene Separation

Process Description
C4 mixture from FCC Unit and/or Raffinate from GPB Unit with low Butadiene and iso-Butene contents is fed to the extractive distillation column to remove iso-Butane and n-Butane using DMF as solvent. Butenes dissolved in DMF drawn out of the column bottom and sent to the stripping column where Butenes are completely stripped.

Butene gas is sent to the solvent recovery column after being compressed in the compressor.

Commercial Plant
ZEON has several experience in licensing of GPD process as shown in the license records.