Chapter Three: Syngas Conversion to Clean Fuels & Chemicals

Polygeneration Concept

-Austria -Combined Heat and Power (CHP) plant with separate gasification and combustion reactors -fast internally circulating fluid bed (1 atm, 900'C), with olivine catalyst continuously recirculated in a burner where char is combusted) -FT synthesis followed by combustion of methane for electrical power and steam generation

Methanol Synthesis Catalysts

-co-precipitated CuO and ZnO on Al2O3 support -catalyst deactivates due to: -poisoning by sulfur and carbonyls -sintering -copper catalyst growth -fouling by carbon deposition Regeneration involves many oxidation-reduction steps

Cleanup Options for Dust & Particulates:

-cyclones, fabric filters, electrostatic precipitators, solvent scrubbing

Cleanup Options for Inorganic Components (sequential):

-first, water quenching for char/ ash -second, hydrolysis of COS (carbonyl sulfide) and HCN (hydrogen cyanide) to convert into H2S and NH3 (sulfur and nitrogen elimination) -halides and ammonia are then washed with water -then, H2S is precipitated, adsorbed, or absorbed -finally, solid or liquid absorbants are used for CO2

FTS Reactors: Slurry Bed

-good SA/ unit volume (can use small particles) -lower operating temp (about 210'C) -SASOL technology, only recently in operation

FTS Reactors: Circulating Fluidized Bed

-good for heat & mass transfer but catalyst gets eroded -can't use particles that are too small, but also must be small enough to be carried by the gas phase -attrition/ erosion of the catalyst -used for gasoline and light olefins -Synthol technology

FTS Reactors: Fluidized bed

-half the cost of circulating fluidized beds -SASOL advanced technology -good heat transfer from bubbling

Liquefaction of Biomass: Pyrolysis or Hydrothermal

-homogenizing of bulky biomass -increased volumetric energy density -minerals at biomass production location (clean liquids) -liquids: more efficient transport and processing -liquids fit better in current fossil refinery/ chemical infrastructure

Advantages of Fischer Tropsch Synthesis

-hydrocarbon production -can be transported in the same way as petroleum products (pipelines, trucks, boats)

Tar Problem

(1) Heavy Tars -condensation leads to fouling (<350'C) -tar dew point is critical parameter (deactivation of catalyst, fouling of equip) (2) Light Tars -heterocyclic compounds (ie phenol) are water soluble, condensate and scrubbing water is poisoned -napthalene can cause crystallization problems

Methanol Use

-40% used to make formaldehyde -also used to make MTBE, ETBE, TAME, DME -DME is a clean diesel fuel but also a precursor for gasoline and a large variety of chemicals and fuels (more desirable)

Syngas Cleaning (Organics, Tars)

-At high temps: more H2, less tar, but ash sintering (slag) present -At low temps: more tar, ash in product gas is dry ash -Different uses determine degree of cleaning and conditioning

Oxosynthesis

-hydroformylation -reaction of CO and H2 with olefins to form isometric mixtures of normal and iso-aldehydes -for solvents, synthetic detergents, flavourings, perfumes, and other products (normal and linear aldehydes) -worldwide production: 7 million tonnes per year -catalyzed by Co or Rh at 110-200'C and 250 atm *reaction occurs in FT process

Gasification

Gasification is the conversion of carbon containing feedstock into valuable syngas which then can be converted into high quality, high value and high energy products

Following Gasification...

Primary gasification is typically followed by a water-gas shift reaction to adjust H2:CO ratio to desired level

Methanol synthesis

-Catalyst used today: CuO and ZnO catalysts on Al2O3 support -2 views on the primary reaction: a) hydrogenation of CO with reverse water gas shift rxn b) hydrogenation of CO2 with water gas shift rxn -role of CO2 and CO are essential -exothermic rxns influenced by T and P -methanol yield increases with Pressure (50-300atm), but rate increases with temp, BUT equillibrium is unfavoured by an increase in T -high P is beneficial but very costly -Therfore we must comprimise with an optimal temp and Pressure

SASOL Technology

-Fisher tropsch technology converts syngas to fuels as well as a wide range of light olefins and chemicals under pressure at a moderate temperature

Production of Syngas

-Gasification of coal or biomass leading to a H2:CO ratio of approximately 1:1 -ratio for gasoline: 0.5:1 -ratio for methanol: 2:1 -steam reforming of natural gas (ENDOTHERMIC RXN): CH4 + H2O + 206 kJ/mole <--> CO + 3 H2 -endothermic, thus run at high temps (700 - 1000'C) and low pressures (since there are 4 moles on the left and 2 on the right). This will drive CO and H2 to react into methane and hydrogen

"Bioliq" Bioslurry Gasification

-Germany research centre -used lignocellulosic waste materials -Three step process: (1) distributed liquefaction by fast pyrolysis in 30-50 regional plants to yield bio oil and char combined in a slurry (different than ICFAR) (2) slurry transport by rail up to 500 km (3) centralized gasification and synthesis plant but, we are still transporting the ash Ash from wood is not a lot, but there is a ton in agricultural residues -Bioliq process keeps opportunity for both chemicals and energy generation -Bioliq uses an entrained flow gasifier operating at high temps, O2 is agent, down flow, ash melted and removed

Early Syngas Products

-Hydrocarbons synthesis from hydrogenation of CO discovered in 1902 by Sabatier and Sanderens -Hydrogen from syngas produced by steam methane reforming (1903), since H2 was important for the war -Haber and Bosch discovered the synthesis of ammonia from H2 and N2 in 1910 -Fischer and Tropsch discovered the production of liquid hydrocarbons and oxygenates from syngas over iron catalyst in 1923 -major development during the world wars since there was a need for H2, ammonia, & fuels

Syngas Cleaning (Inorganics)

-Most problematic: Sulfur based compounds, nitrogen based, chlorinated compounds *sulfur based compounds attack the catalysts *nitrogen based compounds create ammonia and amines *chlorinated compounds form HCl which leads to corrosion of reactors at high temps

Direct Gasification to methane

-Over an Ni catalyst -one reactior that gasifiers and undergoes methanation -the special catalyst lowers the amount of heat required to gasify coal and silmultaneously transforms the gasified coal into methane -self-sufficient, no need to be fired up with purified O2

SASOL Syngas Success

-South African Synthetic Oil Limited (SASOL) -has been producing large quantities o fliquid transportation fuels from Fischer-Tropsh synthesis of syngas for over 60 years. -Syngas produced from the gasification of coal and reforming of natural gas -today, they produce over 6.5 million tonnes per year of FT synfuel

SASOL Process:

-a fluidized iron-based catalyst is added: Fisher tropsch process yields a broad spectrum of hydrocarbons, mainly in the C1 - C20 range -The C2 rich stream is split into ethylene and ethane. Ethane is cracked in a high temperature furnace, yielding ethylene which is then purified. -Propylene from the light hydrocarbon gas is purified and used in the production of polypropylene. -Large quantities of olefins in the C5-C11 range also exist. Alpha olefins (pentene, hexene, and octene are recovered, while the longer chain olefins (C7-C11) are introduced into the fuel pool. -oxygenates are separated and purified to produce alcohols, acetic acid, and ketones including acetone, methyl ethyl ketone (MEK), and methyl iso butyl ketone (MIBK). -Additionally, many chemical products are produced by reforming natural gas via partial oxidation: CH4 + 1/2 O2 --> CO + 2H2 -Fischer tropsch in the slurry reactor process yields waxes and paraffins (second fischer tropsch reactor), bettwe conversion to waxes and paraffins in this reactor

Water Gas Shift Reaction

-adjusts CO: H2 ratio by converting excess CO to H2 and CO2: CO + H20 <--> CO2 + H2 (-41.1 kJ/mol) EXOTHERMIC REACTION (heat produced) A) at high temps (350-475 'C) using iron and chromium oxide catalysts (equillibrium limited) B) at lower temps (200-250'C) using copper, zinc oxide, and alumina (kinetically limited).. copper catalysts don't like high temps because they sinter Therefore, we must separate (A) and (B) into two separate reactors so that they can operate at idea temps and with idea catalysts. Cool between reactors to push equilibria to the right to convert remaining CO (intercooling)

Methanol to Olefin Process (MTO)

-alternative process developed by exxon mobil based on intermediated of <TG: --production of light olefins at hight T lower P and with lower acidity catalysts, not commercial

Fischer Tropsch Economics

-biomass feedstock about double that of coal -rule of thumb cost is $100/tonne

Syngas to Hydrogen

-hydrogen primarily produced from steam reforming of methane, followed by water gas shift reaction -50% of hydrogen comes from the steam -60% of hydrogen is used for ammonia production, followed by refining (23%) and methanol production (9%) -reforming is endothermic, favoured by low T and low P -water gas shift reaction is exothermic, favoured by low T -pressure swing adsorption after the shift purifies the hydrogen to more than 99.9%

Methanol to Gasoline (MTG)

-methanol can be made to gasoline, also produced small amounts of liquefied petroleum gas, fuel gas, and water. Done in fixed or fluid beds

Syngas

-mixture of hydrogen and carbon monoxide (with some CO2, methane, and moisture) -don't confuse with SNG (synthetic natural gas) -important basic platform feedstock for chemical and fuel industries -H2 and CO are the fundamental building blocks for a variety of products traditionally produced from petroleum oil -can be produced from natural gas, coal, petroleum coke, MSW, and biomass

Products of Fischer Tropsch:

-no aromatics, high cetane number, olefins, paraffins and oxygenated products, can make sulfur-free diesel if sulfur is properly removed at beginning -syngas can be converted into a wide range of linear alkanes and alkenes by catalytic hydrogenation of CO -high temp Fischer Trop synthesis yields olefins/ alcohols that can be eventually made into gasoline -low temp FTS yields waxes, paraffin, and eventually hydrocracked into diesel. Done in a slurry tubular reactor

Bioliq Gasification

-pressurized high capacity entrained flow agasifier -30-100 bar and T>1200'C -H2:CO ratio adjusted to 2 (instead of 1) by water-gas shift reaction and CO2 removal -product is rather clean, low in CH4, and tar-free -high C conversion -after cleaning, syngas converted to FT diesel, methanol, DME, methane, and hydrogen

FTS Reactors : Multi Tubular Reactor

-requires large catalysts (not a good SA to volume ratio) -not the best reactor -used by ARGE

Cleanup Options for Tar:

-scrubbing with organic liquid (methyl ester) -catalytic steam reforming with Ni or Ru catalyst on silica or alimina or olivine -high temp cracking

Ethanol From Syngas

-syngas fermentation (produce EtOH from syngas using microbes that are obligate anaerobes (acetogens) such as clostridium family -clostridium family is the same family that is used for butanol formation

Syngas cleaning and conditioning

-syngas produced at high temperatures -necessary to purify it in order to remove particles and sulfur compounds -it must be cooled before purification -it is essential to recover heat, hence the usefulness of well designed heat-exhange systems

Temperature Effects on Gasification

-temperature is often based on the properties of ash -under the melting point for a fixed-bed gasifier -over the melting point for a slag gasifier -As the temperature increases, the O2 consumption increases, in doing so, the methane production will be reduced

Methanol Synthesis

-typical operating conditions: 50-100 bar and 220-270'C -take place in fixed or fluidized beds with conversions of approx 20% (not very high) and recycle of unreacted syngas -liquid phase (slurry) synthesis with solvent at 220-230'C allows for a conversion up to 90% -to be economical: must produce 600-2000 tonnes/day

Ammonia Synthesis

-used for fertilizers (urea), disinfectants, nitric acids, and refrigerants -good market, constantly increasing -exothermic reaction at high pressures and moderate temps. catalyst with oxides of aluminum calcium etc. Haber-Bosch Process: N2 + 3H2 --> NH3 Syngas stripped of CO prior to use through water gas shift reaction (decrease CO, increase H2), produces CO2 which is stripped in a scrubber with liquid (cheap) and methanation (expensive)!

Methanol

-used for fuels, chemicals, pharmaceuticals, petrochemicals, and polymers -very toxic if inhaled, and fatal if ingested -has high octane number (105) and burns clean and readily -used as a racing fuel -used for biodiesel production via transesterification -high volatility -excellent solvent -recently popular for direct methanol fuel cells -methanol economy has greater potential than hydrogen

Lanzatech

-waste gas to useable chemicals using native and synthetic organisms

Biomass Potential

Biomass can be used to produce both high quality transportation fuels and high value chemicals

What produces the greatest revenue? (transportation fuels, chemicals/plastics/rubber, other)

Chemicals/plastics/rubber generates the most revenue, yet the petroleum industry produces mostly transportation fuels (70%) and only 4% chemicals!

Methanation (generally exothermic)

Methanation of CO: (1) CO + 3H2 <--> CH4 + H2O *favoured by high pressure, low temp (strongly exothermic) Methanation of CO2: (2) CO2 + 4H2 <--> CH4 + 2H2O *favoured by high pressure, low temp (strongly exothermic) Both reactions are linked to water gas shift: CO + H2O <--> CO2 + H2

Fischer Tropsch Synthesis

Overall Process: -gasification -catalytic fischer tropsch synthesis -upgrading (ie hydrocracking) can be gas-to-liquids (GTL), coal-to-liquids (CTL), or biomass to liquids (BTL)

Exploring SYNGAS pathways/products

Products include: -methane, -hydrogen, -methanol --> formaldehyde, acetic acid, DME, MTBE, olefins, gasoline, diesel, ethanol... -ammonia -normal & iso-aldehydes (via oxosynthesis) -Ethanol

Torrefaction

makes feedstock more easily storable over time (water removal, pretreatment step)