Technology

Historical Context

Developed by Catalytic Distillation Technologies Inc. (CDTech) in the late 1980s, this technology emerged as a response to the U.S. Clean Air Act amendments, which mandated oxygenated gasoline additives like MTBE. CDTech pioneered catalytic distillation, integrating chemical reaction and separation in a single unit. The technology was later acquired by Lummus Technology, which now markets it as CDMtbe® (for MTBE) and CDEtbe® (for ETBE).

Process Summary

The CDMtbe®/CDEtbe® process converts isobutylene and methanol (or ethanol) into methyl/ethyl tertiary-butyl ether through catalytic distillation.

Figure 1 - Etherification Reaction

Key innovations include:

• Two-stage reaction system: Fixed-bed reactor + catalytic distillation column
• High conversion: >99% isobutylene conversion, exceeding equilibrium limits
• Space efficiency: Integrated reaction-separation reduces footprint by 30–50%
• MTBE Purity: ≥95 wt%
• Methanol Recovery: >99% via extraction/distillation
• Energy Consumption: claimed to be 30% lower vs. conventional processes
• Footprint: claimed to be 40% lower vs. conventional processes 

Process Flow

1. Feed Pre-treatment:
   • Mixed C₄ hydrocarbons (from FCC/RFCC or steam crackers) and methanol/ethanol are pressurized and preheated.
   • Isobutylene concentration typically ranges from 15–50% in the C₄ stream.
2. Primary Fixed-Bed Reactor: 
   • Feed enters an adiabatic fixed-bed reactor with acidic ion-exchange resin catalyst (e.g., sulfonic acid resin).
   • Operating conditions: 50–90°C, 10–20 bar (liquid phase maintained).
   • Achieves 80–90% isobutylene conversion before catalytic distillation.
3. Catalytic Distillation Column (CD Column):
   • Reactor effluent flows to a distillation column with catalyst-structured packing.
   • Simultaneous reactions and separation occur:
     • Isobutylene + Methanol → MTBE (exothermic).
     • Unreacted isobutylene further converts in the reactive zone.
   • MTBE collects at the bottom (95+ wt% purity), while unreacted C₄s and methanol vaporize overhead.
4. Methanol Recovery System:
   • Overhead vapor passes through a water wash scrubber, extracting methanol into aqueous phase.
   • Methanol-water mixture is distilled to recover >99% methanol for recycling.
   • Purified C₄s (butene-1/butene-2) exit as byproducts.

Material Balance

 A typical overall material balance is shown in Table 1. Isobutylene conversion is above 98%.

Table 1 - CDMtbe typical overall material balance

The MTBE product composition is shown in Table 2. 

Table 2 - CDMtbe MTBE product composition

Commercial Experience

• First commercial unit: 1989 (refinery application)
• Global deployments:
  • 2014: More than 85 CDMtbe® units licensed with a total capacity exceeding 13,000,000 MTA of MTBE
  • 2023: Nearly 150 CDMtbe^® (and related etherification) units licensed globally
• Feedstock flexibility: Processes FCC, RFCC, steam cracker, and dehydrogenation unit C₄ streams
• Integration: Often paired with CDIB® technology for high-purity isobutylene production
• Environmental compliance: Zero waste gas emission; closed-loop water reuse

References

1. U.S. Department of Energy, Office of Scientific and Technical Information, 5^th Jan 1993, CDTECH MTBE process technology. CDTECH MTBE process, ETDEWEB.
2. U.S. Department of Energy, Office of Scientific and Technical Information, 1^st Jan 1989, Catalytic distillation technology and MTBE production, Conference: National Petroleum Refiners Association annual meeting, San Francisco, CA (USA), 19-21 Mar 1989.
3. CB&I, 28^th Feb 2014, MTBE from Refinery C₄ Feeds Using CDMtbe^® Technology Profile. 
4. Lummus Technology > Process Technologies > Refining > Clean Fuels > Ethers > CDMtbe^®/CDEtbe^®. (Retrieved via the Web Archive, captured 14^th Jun 2021)
5. Lummus Technology, 15th Mar 2023, Butadiene LLP selects Lummus and BASF technologies for petrochemicals plant in Kazakhstan, Digital Refining.
6. Steven I. Kantorowicz, ABB Lummus, 7^th-8^th May 2002, Focus on Profit: C₄ Processing Options to Upgrade Steam Cracker and FCC Streams, Presented at: 2^nd Asian Petrochemicals Technology Conference, Seoul, Korea.
7. Joseph A. Shaeiwitz, 27^th Apr 2005, Energy Balances and Numerical Methods Design Project - Production of Methyl Tertiary-Butyl Ether, West Virginia University, Chemical and Biomedical Engineering (CBE).
8. Edwin L. Kugler, 13^th Dec 2004, MTBE Production - Material Balance Project, West Virginia University, Chemical and Biomedical Engineering (CBE).