Light Alkanes to Aromatics: Bruce Gates, University of California, Davis
Conversion of C2 & C3 alkanes to aromatics
Starting points for discussion
•existing technology (UOP CyclarTM process)
•catalysts reported to be metal-containing zeolites
•substantial research reported for such conversions
•related issue topic covered yesterday:
methane conversion to aromatics
Thermodynamically, conversion of
propane to aromatics
less uphill than
methane to aromatics
ΔG◦400 (kJ/mol)
reaction
6 CH4
→
C6H6 + 9 H2
399
2 C3H8
→
C6H6 + 5 H2
136
REPORTED CATALYSTS
acidic zeolite (e.g., HZSM-5) or, better,
zeolite-supported metals such as Zn, Ga, Mo
(also used for methane conversion)
less than fully characterized
metals possibly present as carbides (or oxycarbides);
not in metallic state
both inside & outside zeolite pores
CATALYSTS UNDERGO RAPID DEACTIVATION
• catalysts rapidly coked
• require frequent regeneration
• regeneration might contribute to
catalyst deactivation
Feed propane
&/ or but ane
Light gas
product s
endot hermic
UOP Cyclar TM Process, developed by BP & UOP
Source: www.uop.com/ cyclar- process- produces- high- quality - aromatic- products
Sabic process operat ing in Saudi Arabia
SUGGESTED REACTION NETWORK
Numerous authors suggest dehydrogenation catalyzed by
metal-containing function (e.g., molybdenum carbide)—slow reaction—
& subsequent oligomerization & cyclization catalyzed by zeolite acidic sites
Source of figure: www.uop.com/cyclar-process-produces-high-quality -aromatic-products
CyclarTM Process
Feed: propane and/or butane
Aromatic (benzene, toluene, xylenes) yields said to be 5860%
H2 product (may be ~5% yield)
Rapid catalyst deactivation requires
“continuous” regeneration,
moving bed reactors
(catalyst residence time presumably of days)
Catalyst lifetime said to be not short
Source: www.uop.com/ cyclar- process- produces- high- quality - aromatic- products
Possible opportunities for discovery of improved catalysts
Metal-containing molecular sieves
Active for reactions including (de)hydrogenation
large & growing class of catalytic materials
many structurally nonuniform & less than well characterized
Catalytic performance depends strongly on structure of
metal-containing species
Synthetic routes allow some tuning of structure & catalytic properties
less common routes include
organometallic synthesis
atomic layer deposition
Example: Catalysts made by ALD with
dimethyl zinc (among others)
Characterized by IR, NMR, XAS, TPR, …..
Reaction at atmospheric pressure, 823 K
Zinc species not simple (not molecular)
Are there good opportunities to make well-defined
species containing metals such as Zn, Ga, &/or Mo in
zeolites?
Single-site catalysts?
E. J. M. Hensen et al. ACS Catal. 2012, 2, 71.
Candidate research directions
Vary
metal or combination of metals in molecular sieve
molecular sieve (& pore structure)
Attempt to tailor metal-containing catalytic sites
single sites on/in molecular sieve framework
multi-atom sites (clusters)
Understand chemistry of synthesis & catalysis
Relate catalytic activity, selectivity, stability to structure
(use theory, spectroscopy of functioning catalysts)
Deeper characterization of catalysts
Investigate co-feeds with methane
Comparison process: Chevron AromaxTM
Feed: alkanes such as n-hexane, n-heptane
Products: aromatics such as benzene & toluene
Catalyst: Pt clusters in LTL zeolite with exchange ions
such as Ba2+ & promoters such as halides
This is naphtha reforming without the acidic function in the catalyst.
Starting points for discussion
•existing technology (UOP CyclarTM process)
•catalysts reported to be metal-containing zeolites
•substantial research reported for such conversions
•related issue topic covered yesterday:
methane conversion to aromatics
Thermodynamically, conversion of
propane to aromatics
less uphill than
methane to aromatics
ΔG◦400 (kJ/mol)
reaction
6 CH4
→
C6H6 + 9 H2
399
2 C3H8
→
C6H6 + 5 H2
136
REPORTED CATALYSTS
acidic zeolite (e.g., HZSM-5) or, better,
zeolite-supported metals such as Zn, Ga, Mo
(also used for methane conversion)
less than fully characterized
metals possibly present as carbides (or oxycarbides);
not in metallic state
both inside & outside zeolite pores
CATALYSTS UNDERGO RAPID DEACTIVATION
• catalysts rapidly coked
• require frequent regeneration
• regeneration might contribute to
catalyst deactivation
Feed propane
&/ or but ane
Light gas
product s
endot hermic
UOP Cyclar TM Process, developed by BP & UOP
Source: www.uop.com/ cyclar- process- produces- high- quality - aromatic- products
Sabic process operat ing in Saudi Arabia
SUGGESTED REACTION NETWORK
Numerous authors suggest dehydrogenation catalyzed by
metal-containing function (e.g., molybdenum carbide)—slow reaction—
& subsequent oligomerization & cyclization catalyzed by zeolite acidic sites
Source of figure: www.uop.com/cyclar-process-produces-high-quality -aromatic-products
CyclarTM Process
Feed: propane and/or butane
Aromatic (benzene, toluene, xylenes) yields said to be 5860%
H2 product (may be ~5% yield)
Rapid catalyst deactivation requires
“continuous” regeneration,
moving bed reactors
(catalyst residence time presumably of days)
Catalyst lifetime said to be not short
Source: www.uop.com/ cyclar- process- produces- high- quality - aromatic- products
Possible opportunities for discovery of improved catalysts
Metal-containing molecular sieves
Active for reactions including (de)hydrogenation
large & growing class of catalytic materials
many structurally nonuniform & less than well characterized
Catalytic performance depends strongly on structure of
metal-containing species
Synthetic routes allow some tuning of structure & catalytic properties
less common routes include
organometallic synthesis
atomic layer deposition
Example: Catalysts made by ALD with
dimethyl zinc (among others)
Characterized by IR, NMR, XAS, TPR, …..
Reaction at atmospheric pressure, 823 K
Zinc species not simple (not molecular)
Are there good opportunities to make well-defined
species containing metals such as Zn, Ga, &/or Mo in
zeolites?
Single-site catalysts?
E. J. M. Hensen et al. ACS Catal. 2012, 2, 71.
Candidate research directions
Vary
metal or combination of metals in molecular sieve
molecular sieve (& pore structure)
Attempt to tailor metal-containing catalytic sites
single sites on/in molecular sieve framework
multi-atom sites (clusters)
Understand chemistry of synthesis & catalysis
Relate catalytic activity, selectivity, stability to structure
(use theory, spectroscopy of functioning catalysts)
Deeper characterization of catalysts
Investigate co-feeds with methane
Comparison process: Chevron AromaxTM
Feed: alkanes such as n-hexane, n-heptane
Products: aromatics such as benzene & toluene
Catalyst: Pt clusters in LTL zeolite with exchange ions
such as Ba2+ & promoters such as halides
This is naphtha reforming without the acidic function in the catalyst.