Technology Type

Overview

Methyl tert-butyl ether (MTBE) and other oxygenated fuel additives are produced industrially by reacting isoolefins with alcohols in the presence of an acidic catalyst. The process encompasses the etherification of both isobutylene and isoamylenes with either methanol or ethanol, creating a diverse range of ether products including MTBE, ETBE, TAME, and TAEE. This technology is widely used in refineries and petrochemical plants to enhance gasoline octane and reduce emissions.

Figure 1 - Molecular structure of MTBE, ETBE, TAME and TAEE

Feedstock Sources

• Isobutylene:
  Sourced from C₄ hydrocarbon streams such as those from fluid catalytic cracking (FCC), steam crackers, or via isomerization and dehydrogenation of butanes
   
• Isoamylenes:
  Derived from C₅ raffinate streams, typically obtained from FCC or steam cracking processes, including 2-methyl-1-butene and 2-methyl-2-butene
   
• Methanol:
  Typically produced from natural gas or coal via steam reforming followed by CO hydrogenation.
   
• Ethanol:
  Can be derived from various sources, typically by hydration of ethylene, but also including biomass fermented into bioethanol.

Production Methods

There are two main ways to produce ethers from isoolefins:

• Conventional Process:
  Which is mainly a reactor and separate distillation column with conversion range 87-92% for isobutylene (MTBE/ETBE) and 85-91% for isoamylenes (TAME/TAEE).
   
• Reactive Distillation Process:A more recent method for the production of ethers dating back to the 1980s when scientist Smith recorded the first patent for the production of MTBE through this method. The reactive distillation method exhibits a lot of features that make this process attractive and practical with a conversion reaching 99%⁺ for isobutylene and up to 92% for isoamylenes.

The present description covers both conventional and reactive distillation processes for all ether products.

Core Reactions

Primary Etherification Reactions:

• Isobutylene + Methanol → MTBE
• Isobutylene + Ethanol → ETBE
• Isoamylenes + Methanol → TAME
• Isoamylenes + Ethanol → TAEE

Figure 2 - Etherification Reaction between isobutylene and methanol into MTBE

• Catalyst: Acidic ion-exchange resin (e.g., sulfonated polystyrene-divinylbenzene, , Amberlyst 16)
• Typical Conditions: 40–100°C for isobutylene, 40–80°C for isoamylenes, 1–10 bar

Main Process Configurations

1. Conventional Fixed-Bed Reactor Process

• Step 1: Isoolefins (isobutylene and/or isoamylenes) and alcohol (methanol or ethanol) are mixed and fed into a fixed-bed reactor containing acidic resin catalyst.
• Step 2: The reaction mixture exits the reactor and is sent to a distillation column.
• Step 3: Ethers (MTBE, ETBE, TAME, TAEE) are separated as bottom products; unreacted alcohol and hydrocarbons are taken overhead for recycling or further processing.

2. Reactive Distillation Process

• Step 1: Reaction and separation are combined in a single distillation column packed with catalyst.
  Step 2: As the reactants flow through the column, isoolefins and alcohol react to form ethers, which are simultaneously separated from unreacted components by distillation.

  Advantages: Higher conversion efficiency (up to 99% for isobutylene, up to 92% for isoamylenes), lower energy consumption, and reduced capital costs due to fewer equipment requirements. Enhanced operational flexibility for mixed-feed processing (C₄ and C₅ streams).

Process Flow Summary

1. Feed Preparation:

• C₄ and C₅ streams are treated to remove impurities (e.g., butadiene, water)
• Alcohol (methanol or ethanol) is mixed in stoichiometric or slight excess proportion to isoolefins

2. Etherification Reaction:

• Feed enters the reactor (fixed-bed or reactive distillation column).
• Isobutylene reacts with methanol to form coresponding ethers.

3. Separation:

• Reactor effluent is sent to a distillation column.
• Ethers are recovered as the bottom product (≥95% purity).
• Overhead contains unreacted alcohol and hydrocarbons, which are recycled.

4. Alcohol Recovery:

• Unreacted alcohol is recovered from the overhead stream, purified, and recycled.

5. Product Purification:

• Final ether products are further purified if necessary and sent to storage or blending.

Process Efficiency and Yields

• Isobutylene Conversion: Up to 99% (especially with reactive distillation)
• Isoamylene Conversion: Up to 92% (reactive distillation), 85-91% (conventional process)
• Product Purity: Typically ≥95% for all ethers
• Energy Consumption: Lower in reactive distillation processes compared to conventional setups
• Operational Flexibility: Modern units are designed to handle feedstock fluctuations, alcohol selection, and maintain high yields across different ether products

Product Diversity and Applications

Alternative Routes

• Via Butane:
  n-Butane is isomerized to isobutane, then dehydrogenated to isobutylene, which is finally etherified with methanol to produce MTBE.
   
• From Raffinate Streams:
  MTBE can also be produced from raffinate-1 or C₄ raffinate streams via etherification with methanol.

Technology Features

• Feedstock Flexibility:
  The etherification process is capable of handling mixed C₄/C₅ hydrocarbon streams with either methanol or ethanol as the alcohol feedstock.
   
• Product Adaptability:
  Existing plants can often be retrofitted to switch between alcohol feedstocks (methanol vs. ethanol) based on market conditions, regulatory requirements, or feedstock availability.
   
• Environmental Benefits:
  Ethanol-based ethers (ETBE and TAEE) provide renewable content advantages and improved environmental profiles compared to their methanol-based counterparts, particularly in regions with abundant bioethanol supply.

References

1. ANIL PARS Industrial Process Company > Portfolio Item > mtbe-production-honeywell-technology - Technical Evaluation of MTBE Production with 60KTY Capacity. (Accessd 21^st Jun 2025)
2. Procurement Resource > Production Cost Report Store > Methyl Ter-butyl Ether Production Cost Report. (Accessd 21^st Jun 2025)
3. Bernhard Schleppinghoff, Martin Becker, US Patent US4503265A, Priority Date 18^th Nov 1982, Process for the production of methyl tert.-butyl ether (MTBE) and of hydrocarbon raffinates substantially freed from i-butene and from methanol, Current Assignee: Erdoelchemie GmbH, Status: Expired.
4. INTRATEC > Reports > Previews > Report MTBE E411 Cost Analysis - MTBE Production from Butane - 2021. 
5. Alan Mawlud Amin, Aree Salah Tahir, 2015 - 2016, Production of Methyl Tertiary Butyl Ether (MTBE), Slideshare
6. Features of the dehydrogenation process of butane - MEL Science
7. 2021 - MTBE Production from Butane - Report MTBE E41A Cost Analysis - United States - INTRATEC
8. Sep 7, 1992 - U.S. REFINERS CHOOSE VARIETY OF ROUTES TO MTBE - Oil&Gas Journal