Technology Type

Ethanol dehydration is a catalytic process that converts ethanol into ethylene by acid-catalyzed removal of water molecules in fixed-bed reactors operating at elevated temperatures. The process represents an important pathway for producing renewable ethylene from bioethanol derived from sugarcane, corn, or other biomass feedstocks.

Reaction Chemistry and Thermodynamics

The primary reaction is a simple dehydration where ethanol loses one water molecule to form ethylene:

This reaction is endothermic, requiring approximately 45 kJ/mol of heat input to proceed. The positive heat requirement means that reactors must continuously supply thermal energy to maintain conversion, unlike exothermic reactions that generate their own heat.

The reaction pathway is not entirely selective. A competing side reaction occurs where two ethanol molecules combine to form diethyl ether (DEE) plus water:

The reaction pathway selectivity is strongly temperature-dependent and catalyst-dependent as outlined in the next section.

Catalyst Technology

The catalyst is the heart of the dehydration process, providing acid sites that activate ethanol molecules and facilitate water elimination. Gamma-alumina (γ-Al2O3) is the most widely used industrial catalyst due to its balance of activity, selectivity, thermal stability, and cost-effectiveness. Gamma-alumina possesses high surface area (150-300 m²/g) with both Lewis and Brønsted acid sites distributed across its porous structure.

The catalytic mechanism proceeds through ethanol adsorption onto acid sites, forming surface ethoxy intermediates that undergo beta-hydrogen elimination to release ethylene and water while regenerating the active site. The rate-limiting step is typically the carbon-hydrogen bond breaking during elimination, which explains the strong temperature dependence of reaction rates.

On traditional alumina catalysts, diethyl ether formation dominates at temperatures below approximately 250-280°C due to its lower activation energy and exothermic nature. As temperature increases above 350°C on alumina, the unimolecular ethylene-forming pathway becomes thermodynamically and kinetically favored, with ethylene selectivity approaching 95-100% at temperatures exceeding 400°C.

However, advanced zeolite catalysts fundamentally change this selectivity-temperature relationship. Dealuminated ZSM-5 zeolites achieve remarkable ethylene selectivities of 98-100% at temperatures as low as 220-280°C, significantly below the 400-450°C typically required for alumina systems. This superior low-temperature performance results from the zeolite's shape-selective pore structure that constrains transition state geometries, favoring unimolecular ethylene formation over bimolecular ether formation, combined with optimized acid site strength and distribution.

Catalyst deactivation occurs primarily through coke formation, where ethylene and unsaturated intermediates polymerize on acid sites to form carbonaceous deposits that block active sites and pore entrances. Water vapor in the feed partially mitigates coking by gasifying coke precursors. Deactivation progresses from the reactor inlet toward the outlet as a moving front, with catalyst lifetime ranging from months to years depending on operating severity. Regeneration involves controlled combustion of coke deposits in air at 500-600°C to restore activity.

Process Configuration

Reactor Design:
Industrial processes employ fixed-bed tubular reactors packed with catalyst pellets or extrudates. Two main configurations exist: adiabatic reactors arranged in series with inter-stage heating, or multi-tube isothermal reactors with external heat supply through a heated shell.

Operating Conditions:

• Temperature: 350-470°C (alumina catalysts), 220-350°C (zeolite catalysts)
• Pressure: 2-20 bar, typically 3-5 bar
• Weight hourly space velocity (WHSV): 0.5-6.0 h^-¹, optimally 1.5-2.5 h^-¹
• Steam dilution: 0.3:1 to 1.5:1 molar ratio steam:ethanol (optional)

Feed Preparation:
Liquid ethanol (anhydrous 99.5%+ or hydrated 93-96%) is vaporized and heated to reaction temperature. Steam may be added for dilution to suppress ether formation and serve as a heat carrier. Hydrated ethanol feeds are increasingly preferred because water helps suppress catalyst coking and eliminates the cost of molecular sieve dehydration required for anhydrous ethanol.?

Temperature Management:
Since the reaction is endothermic, temperature drops 40-80°C per adiabatic reactor stage as ethanol converts to ethylene. Multiple reactor stages with inter-stage heating maintain temperatures in the optimal range for high conversion and selectivity.

Performance Metrics

Conversion and Selectivity:

• Ethanol conversion: 95-99.9% per pass
• Ethylene selectivity: 94-100% (catalyst and temperature dependent)
• Overall ethylene yield: 94-98%
• Byproducts: Diethyl ether (1-4%), acetaldehyde (<1%), trace higher hydrocarbons

Productivity:
Advanced ZSM-5 catalysts achieve space-time yields exceeding 900-1500 g ethylene per kg catalyst per hour at optimized conditions, enabling compact reactor designs.

Product Recovery

Quench and Separation:
The reactor effluent (350-420°C) containing ethylene, water vapor, unreacted ethanol, and byproducts undergoes rapid cooling to condense water and ethanol while keeping ethylene gaseous. Gas-liquid separation recovers condensed aqueous ethanol for recycle to the reactor.

Purification Steps:

1. Acid washing: Removes trace aldehydes and acidic impurities
2. Drying: Molecular sieve beds reduce water content to <1 ppm
3. Cryogenic distillation: Separates ethylene from ethane, ether, and residual ethanol to achieve polymer-grade purity of 99.9%⁺

The high-purity ethylene meets specifications for polyethylene production, while recovered ethanol and ether streams recycle to the reactor to maximize overall yield.

Energy and Economics

Energy Consumption:

Ethanol dehydration requires thermal energy for the endothermic reaction and heating to 350-470°C, plus electrical power for compression and refrigeration. Heat recovery from high-temperature reactor effluent (350-420°C) can generate steam or preheat feeds. Specific energy consumption figures are process-dependent and should be obtained from technology licensors or recent engineering studies.

Cost Structure:

Economics are dominated by ethanol feedstock costs due to the stoichiometric requirement of 1.68 kg ethanol per kg ethylene. A 2021 European study found profitability highly sensitive to the ethanol-to-ethylene price differential and regional factors including feedstock availability, energy costs, and carbon policies. Capital and operating costs vary substantially by location, capacity, and integration with existing facilities. Project-specific feasibility studies are essential for reliable cost estimation. A 2017 review reveals that existing first-generation bioethylene plants (referencing Braskem) do not function without subsidies as of 2017. 

Process Variants

Feedstock Options:

• Anhydrous ethanol (99.5%+): Requires molecular sieve dehydration; eliminates feed water
• Hydrated ethanol (93-96%): Lower cost; water helps suppress coking; increasingly preferred

Reactor Configurations:

• Adiabatic fixed beds with furnace heating: Most common; simpler design
• Isothermal multi-tubular reactors: Better temperature control; higher capital cost
• Swing reactors: Enable continuous operation during catalyst regeneration cycles

Integration:
Processes may be integrated with upstream bioethanol production (sugarcane mills, corn ethanol plants) or downstream polyethylene production to optimize energy integration and logistics. 

Proprietary Technologies

Chematur E2E Technology (1980s): Chematur Engineering AB developed an ethanol-to-ethylene (E2E) dehydration process based on technology originally created by American Halcon Scientific Design, Inc. in the 1980s, employing proprietary Syndol catalysts composed primarily of Al₂O₃-MgO/SiO₂ (alumina-magnesia on silica support) in a configuration of four adiabatic tubular reactors arranged in series. At least one plant has built in Egypt and was operating as of 2024 since commissioning in 2014.

Petron Scientech K-SEET^SM (1980s): Petron Scientech Inc. (PSI), a subsidiary of KBR, offers the K-SEET? (Kellog-Scientech Ethanol-to-Ethylene Technology) process for catalytic dehydration of ethanol to polymer-grade ethylene, based on technology originally developed by M.W. Kellogg Company in the 1980s and later enhanced by Scientech. The process employs proprietary fixed-bed catalyst systems in adiabatic reactors operating at moderate temperatures and pressures, designed for flexible capacity ranging from small-scale plants to large commercial facilities producing 100,000+ tons per year of ethylene. Petron Scientech has significantly more commercial experience than publicly acknowledged as revealed by the company's experience credentials.

Braskem EtE EverGreen™ (2010): Braskem developed and operates the world's first industrial-scale ethanol dehydration plant at its Triunfo petrochemical complex in Rio Grande do Sul, Brazil, which began production on September 24, 2010, with an initial capacity of 200,000 tons per year of bio-based ethylene from sugarcane bioethanol. The proprietary catalytic dehydration process converts renewable ethanol to polymer-grade ethylene using gamma-alumina-based catalysts in fixed-bed reactors, enabling production of I'm green™ bio-based polyethylene that isclaimed to avoid approximately 3 tons of CO2 per ton of product compared to fossil-based alternatives . Following successful commercial operation and a US$87 million investment, Braskem expanded the plant capacity by 30% to 260,000 tons per year in June 2023, and partnered with Lummus Technology in 2022 to globally license the technology as EtE EverGreen™ for deployment in North America and Asia.

TechnipEnergies Hummingbird^® (2013): a proprietary ethanol-to-ethylene dehydration technology originally developed by BP Chemicals and unveiled in 2013, subsequently acquired by Technip (now TechnipEnergies) in June 2016. The technology employs a proprietary heteropolyacid (HPA) supported catalyst that operates at lower temperatures and higher pressures than conventional alumina-based processes, achieving ultra-high selectivity of over 99% for converting bioethanol to polymer-grade ethylene. Hummingbird^® distinguishes itself through its nearly stoichiometric conversion efficiency that eliminates the need for ethylene fractionation columns, reducing capital costs and process complexity. The technology achieved its first commercial application in 2020 when LanzaTech selected Hummingbird^® for integration with its Alcohol-to-Jet (ATJ) process at the LanzaJet Freedom Pines biorefinery in Soperton, Georgia, producing 10 million gallons per year of sustainable aviation fuel starting in 2022, with the demonstration plant accumulating over 36,000 hours of operation. TechnipEnergies continues to license Hummingbird^® technology and supply its proprietary catalyst for commercial applications targeting sustainable aviation fuel and bio-based chemicals production.

Axens ATOL^® (2014): IFPEN/Axens/Total launched ATOL^® technology in 2014 with ATO 201 catalyst claiming superior economics through simplified purification and high selectivity. Two fixed bed adiabatic reactors, operating at 400–500 °C, are used in this process which produces 50 000–400 000 t a⁻¹ ethylene. As per Sep 2023 ATOL^® commercial bulletin, there are 6 references in the United States, Japan, Brazil and South Korea for both polymer and Sustainable Aviation Fuel (SAF) applications as Atol® technology is also the first step of Jetanol™ process suite (Alcohol To Jet) for the conversion of renewable/low carbon alcohols into SAF.

Tianjin University Ethanol Dehydrogenation (2025): Xinjiang Tianye Huixiang New Materials Co., Ltd. commissioned the largest single-train coal-based ethanol-to-ethylene unit (104,000 t/y) using patented technology domestically developed by Tianjin University + BPE Engineering- representing China's push for non-petroleum olefins self-sufficiency.

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