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CPE406 Energy from Biomass and Waste > Biofuels via Thermochemical Conversion > Flashcards

Biofuels via Thermochemical Conversion Flashcards

(78 cards)

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1
Q

What is the definition of a biofuel?

A

Any fuel (solid, liquid or gaseous) that is produced from organic matter (living or once living material) in a short period of time is viewed as a biofuel. They burn cleaner than fossil fuels (less particulates, NOx, SOx) and are biodegradable unlike fossil-derived fuels.

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2
Q

Why is it hard to capture CO2 emissions in the transportation sector and why are biofuels critical to this issue?

A

Because there are millions of separate mobile sources the only way to reduce GHG from transport is by substitution of fossil fuels by biofuels.

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3
Q

What category of conventional/advanced biofuels to first gen, second gen, and third gen biofuels fall into?

A

1st - conventional

2nd+3rd - advanced

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4
Q

What are 1st gen biofuels produced from?

A

Food crops (sugar, starch or lipid) inc palm, rapeseed, soy, beets and cereals

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5
Q

Give 3 examples of 1st gen biofuels

A

Sugarcane ethanol, starch-based/corn ethanol, biodiesel

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6
Q

Where are 1st gen biofuels already produced on a large scale?

A

US and Brazil

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7
Q

What are 2nd gen biofuels produced from?

A

Non-food biomass (cellulose, hemicellulose or lignin) inc virgin wood, agricultural waste, forestry waste and energy crops (eg. miscanthus)

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8
Q

Give 2 examples of 2nd gen biofuels

A

Cellulosic ethanol, synthetic diesel

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9
Q

Name 4 oxygenate biofuels and which classification they come under

A

Methanol (2), ethanol (1 or 2), butanol (1 or 2), DME (2)

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10
Q

Name 4 hydrocarbon biofuels and which classification they come under

A

Diesel (1 or 2), gasoline (2), jet fuel (2), SNG (1 or 2)

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11
Q

Name one non-oxygenate, non-hydrocarbon biofuel and which classification it is

A

Hydrogen (1 or 2)

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12
Q

What are 3rd gen biofuels produced from?

A

Autotrphic organism algae

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13
Q

Give two examples of 3rd gen biofuels

A

Biodiesel, butanol

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14
Q

Give 4 disadvantages of 1st gen biofuels

A
  1. Low productivity of biofuels per hectare
  2. High fertiliser requirement
  3. Food vs fuel competition
  4. Land availability issues
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15
Q

Give 3 advantages of 2nd gen biofuels

A
  1. Wider range of biomass feedstocks
  2. Higher quality of biofuels products
  3. Products compatible with conventional fuels
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16
Q

Give 4 advantages of 3rd gen biofuels

A
  1. Very high yields (up to 9000 gallons of biofuel per acre - 10x what the best traditional feedstock has achieved)
  2. Diversity of cultivation (grown in many different ways: open ponds, closed-loop systems and photo-bio-reactors)
  3. Can be grown in places not suitable for agriculture eg. the sea
  4. Fuels produced can be very diverse
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17
Q

Give 1 disadvantage of 3rd gen biofuels

A
  1. Requires large amounts of resources (water, nitrogen and phosphorous to grow)
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18
Q

What does the Renewable Energy Directive say about transport fuels?

A

That 10% of transport fuels sold in all EU countries should be replaced by renewable fuels by 2020 and the use of biofuels must result in an overall GHG saving of 35%. Only 7% of this can come from food crops so the other 3% must come from advanced biofuels (0.5%) and renewable electricity.

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19
Q

What is the Renewable Transport Fuel Obligation (RTFO) and how is it met?

A

It is the UK’s implementation of EU policies on renewable fuels and only biofuels that comply with sustainability criteria are included (35 min. GHG saving). Therefore 450,000 L/y of biofuels for transport must be sold, and this is achieved manufacturers either by supplying biofuels and earning certificates of by buying certificates from companies that supply biofuels.

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20
Q

What is the main focus of biochemical conversion of 2nd gen biofuels?

A

Ethanol

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21
Q

Give some disadvantages of biochemical conversion of biofuels

A
  • A limited fraction of the biomass can be converted with the known enzymatic hydrolysis we have today
  • Lignin is not convertible in any case, but can used for heat or co-product through combustion
  • Limited feedstock variability as the microorganisms must be tailored to the feedstock
  • R&D breakthroughs are needed to improve conversion and reduce costs
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22
Q

Give 5 examples of biofuels from 2nd gen thermochemcial conversion

A

Fischer-Tropsch (FT) fuels, DME, methanol, mixed-alcohols, green diesel

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23
Q

Give 4 advantages of biofuels via thermochemical conversion

A
  1. Can cope with a high degree of feedstock availability
  2. Conversion technologies are available for FT fuels, FME, methanol but R&D is required
  3. Commercial scale-impletation is lacking but there are large overlaps with commerciallt established fossil fuel conversion technologies (eg. syngas to liquid fuels) that could be easily adapted
  4. It makes use of all the cell wall componenets including lignin
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24
Q

What is the main focus of biofuels from thermochemical conversion?

A

Synthetic fuels (fuels from syngas)

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25
Which two main routes are used to produce biofuels thermochemicalle?
Syngas and liquefied biomass
26
What is BTL?
Biomass-to-liquids: the term refers to processes that produce synthetic fuels through a thermochemical route
27
Name the process that converts syngas to gasoline/diesel
Fischer-Tropsch synthesis
28
Describe the 3 processes that can convert syngas to just gasoline
1. methanol used as in intermediate - from syngas to methanol then methanol to gasoline 2. same as above but methanol to gasoline occurs through mobil-olefins-to-gasoline-and-distillate (MOGD) process 3. Syngas conversion directly to gasoline
29
Name two process that convert bio-oil to gasoline
1. Hydrotreating | 2. Hydrocracking
30
What is the aim of the BioTfuel demonstration project in France?
Launched in 2010 to integrate all the stages of the BTL process chain and bring them to market. This has been heavily subsidised by French public funds. The biomass is torrefied, then mixed with some fossil fuel, then gasified in a 1200-1600 deg C, 30-40 bar entrained flow gasifier, then the syngas is conditioned and cleaned before converted into liquid hydrocarn fuels by the Fischer-Tropsch process. Two pilot plants have been built and industrial scale production will begin in 2020.
31
How does the German BTL pilot plant operate?
It started operation in 2013 and processes around 500 kg/h of straw or wood in a decentralised fast pyrolysis process, which turns it into 'biosyncrude' which has a smaller volume and higher energy density. It is then converted to syngas in an 80 bar entrained flow gasifier
32
How did the discontinued Choren process work and why was it discontinued?
Used two gasifiers - oxygen and steam - to produce syngas for Fischer-Tropsch conversion but fell through when building a full scale plant due to financial difficulty.
33
Which three fuels can be produced by thermochemical conversion of synas?
Methanol, gasoline and diesel
34
Give 4 uses of methanol as a commodity chemical
1. as a solvent 2. as anti-freeze in pipelines 3. a chemical feedstock for the production of plastics 4. used for production of gasoline
35
Which catalysts are used to produce methanol?
Cu, Zn or Al
36
Give the 3 reactions that occur over the catalyst in methanol production.
Drawing 48
37
Give an example of a process used to produce methanol
ICI Low Pressure Tech - developined in 1966, 5-10 MPa, 200-300 deg C using a highly selective copper oxide catalyst
38
What is gasoline?
A mixture of hydrocarbons having a carbon number primarily in the range C5-C11 (paraffins/alkanes, aromatics, olefins/alkenes, cycloalkanes)
39
Which 3 ways can gasoline be produced?
1. Fischer-Tropsch 2. via methanol 3. via DME (Ch3OCH3)
40
Who was the MTG process developed by?
ExxonMobil
41
Describe the MTG process.
Fixed beds and fluidised beds of proprietary catalysts are used. Gaseous methanol is used. 1. Dehydration of methanol over Al catalyst to produce DME 2. Dehydration over a zeolite catalyst to produce gasoline Therefore a large amount of water is produces
42
Draw a BFD for the MTG process
Drawing 49
43
What 3 fractions is the gasoline from MTG distilled into
Light gasoline Heavy gasoline HVP gasoline
44
Give a typical example of typical amounts of products obtained from 1000 kg of methanol
387 kg gasoline (C5-C11), 46 kg LPG (C3-C4), 7 kg fuel gas (C1-C2) and 560 kg water
45
What temperature is dehydration of methanol to DME carried out at?
300-320 deg C
46
What temperature is dehydration of DME to gasoline carried out at?
400-420 deg C
47
What was the first MTG plant?
Motuni, New Zealand from 1985-97 to make 1/3 of New Zealand's transport fuels to reduce import requirements and therefore dependence on fossil fuels. It produced unleaded gasoline but was abandoned due to a decrease in crude oil prices. The plant still makes methanol from syngas.
48
What 3 improvements have ExxonMobil mate to MTG technology (2nd gen) and how have they affected the process?
Reduction in heat input requirements, compressor duty and heat EX surface area, reduced capital by 10-15% and the first one of these designs became operational in 2009 (but syngas comes from coal gasification).
49
Why was the Topsue gasoline synthesis created and on what principle does it work??
To reduce investment costs and therefore production costs of synthetic gasoline. Syngas of a H2:CO ratio of close to 1 feeds the process where the synthesis of methanol, DME and gasoline are integrated into one loop by first passing the syngas into an oxygenate synthesis (to produce methanol/DME) and then converting to gasoline in the next reactor.
50
What carbon number range does diesel fall into?
C8-C21
51
What process converts syngas into diesel?
Fischer-Tropsch
52
Why was the Fischer-Tropsch reaction discovered?
To convert coal into liquid fuel in WW2 Germany as access to petroleum was sparse. Interest in the process rose again due to its importance in production of liquid fuels from biomass.
53
What catalyst is usually used in the Fischer-Tropsch process?
Iron or cobalt
54
What H2:CO ratio is needed for Fischer-Tropsch and how is it achieved?
2, through syngas conditioning
55
Is the Fischer-Tropsch reaction endo or exothermic?
Highly exothermic
56
Give 2 motivations for using the Fischer-Tropsch process
1. Liquid fuels are easier to transport than gas fuels | 2. Syngas is converted into value-added chemicals rather than using it as a fuel on its own
57
What is the most well known use of FTS (Fischer-Tropsch synthesis)?
SASOL in South Africa
58
Give the overall reaction for the Fischer-Tropsch process
Drawing 50
59
What are the 4 main products of FTS?
Gasoline, jet fuel, diesel and chemical feedstock
60
What 4 factors does the selectivity of FTS depend on?
1. Process parameters (temperature, pressure, residence time) 2. Catalyst (type and support) 3. Reactor type 4. Syngas composition
61
Name 3 types of reactor used for FTS
1. Fixed-bed 2. Slurry-bed 3. Fluidised bed
62
Draw a fixed bed FTS reactor
Drawing 51
63
Draw a slurry-bed FTS reactor
Drawing 52
64
Give the temperatures and favoured product for LTFTS and HTFTS
LTFTS - 200-240 deg C, diesel | HTFTS - 300-350 deg C, gasoline
65
What is the typical operating pressure of FTS?
20-40 bar
66
Give an example HTFTS
Iron based catalyst, fluidised bed reactor at 340 deg C, gasoline yield 40%
67
Give an example of LTFTS
Cobalt-based catalyst, slurry-bed reactor at 200-240 deg C, diesel yield 20%
68
Why does bio-oil need to be upgraded to be used at a transportation fuel?
Because it has a high oxygen content (40-60%), and this is a huge challenge. It then also needs to be refined.
69
Which is more developed, biofuels from syngas of bio-oil?
Biofuel from syngas
70
What is the typical heating value of bio-oil?
13-18 MJ/kg
71
What is the motivation for hydrotreating bio-oils?
The higher the hydrogen content of a petroleum product, the better the quality due to the high CV. Therefore the addition of hydrogen to the bio-oil is beneficial.
72
Is hydrotreating or hydrocracking more commonly used and why?
Hydrotreating because it is cheaper and commercially available.
73
What conditions and catalyst are used for hydrotreating?
Up to 500 deg C at atmospheric pressure with a NiMo or zeolite catalyst
74
Describe the principle of hydrotreating
Non-destructive hydrogenation that improves product quality without altering the boiling range
75
What operating conditions are expected from hydrocracking?
Over 250 deg C where hydrogenation accompanies cracking, 7-143 bar, dual function catalyst (
76
Describe the catalyst used for hydrocracking
Dual-function catalyst, nickel core provides hydrogenation and silica-alumina or zeolite supports and provides the cracking function (alumina most widely used)
77
Why are aromatic compounds from hydrocracking further refined?
To produce liquid hydrocarbon fuels of high octane number
78
What are the 5 challenges associated with biofuel production from bio-oil?
1. Improving conversion efficiencies 2. Improving catalysts 3. Reduce CAPEX & OPEX 4. Find financial subsidies (required) 5. Cost of biomass (find long-term supply contracts)

CPE406 Energy from Biomass and Waste (8 decks)

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