Week 10 Flashcards

Question

What is the mechanism of the produciton of ethanol from starch crops (dry milling)?

Answer 1

Grain --(Mill dry grain directly)--> Seed granules + protein-rich, fibrous dried distillers grains (DDG) --(Amylase + other enzymes (used on former)--> Glucose --> Yeast --(fermentation)--> Ethanol (5-12%) --(Distillation)-->Ethanol (95-99.8%)

Answer 2

C2H5OH + 3O2 --> 2CO2 + 3H2O

Answer 3

Gasoline is a range of hydrocarbons (C5H12 to C12H26) Per litre, ethanol contains about two-thirds as much energy as gasoline Ethanol though has a higher octane rating than gasoline and adding it to gasoline increases the octane rating – reducing the likelihood of ‘knocking’ (premature fuel combustion) and thus increasing efficiency.

Answer 4

Ethanol contains oxygen (unlike gasoline) and this can aid the combustion process, reducing the emission of carbon monoxide, unburned hydrocarbons and carcinogenic particulates. This also leads however to more reaction with atmospheric nitrogen and (marginally) increased nitrogen oxide (NOx) emissions.

Answer 5

Ethanol is low in sulphur (almost none), thus SOx emissions are reduced. Carbon in ethanol was only recently fixed from the atmosphere thus net CO2 emissions may be greatly reduced

Answer 6

European Biodiesel production accounts for 41% of the world total Main European crops are rapeseed and sunflower Main US crop is soybean

Answer 7

Most storage lipids are triacyl glycerols that accumulate in sub-cellular organelles called oil bodies

Answer 8

Biodiesel is methyl or ethyl esters of fatty acids Ester: carboxylic acid in which -OH (hydroxyl) group is replaced by an -O-alkyl (alkoxy) group Transesterification reactions with methanol or ethanol

Answer 9

Triglyceride + Alcohol --> Fatty acid methyl esters (FAME) (Biodiesel) + Glycerin or Glycerol

Answer 10

The levels of free fatty acids are assayed and quantity of base required to neutralize the acid is determined.

Answer 11

An amount of base (usually NaOH or KOH) slightly in excess of that required for neutralisation is dissolved in the alcohol (methanol or ethanol). Alcohol/base is reacted with the oil at elevated temperature (typically 50oC) for several hours (4 to 8 typically).

Answer 12

The lower layer of the process is composed primarily of glycerol and other waste products. The upper layer composed of biodiesel and alcohol is separated away and the alcohol removed (by distillation or extraction with water - the latter requires that the product is dried). Often there are several washes with water to remove alcohol, hydroxide and soap.

Answer 13

Methanol is usually used as the catalyst in the commercial production of biodiesel as it is cheaper than ethanol and glycerol extraction is less problematic

Answer 14

Glycerol is the primary co-product – used as a lubricant and in cosmetics and ink and as a preservative. Off-sets only about 5% of the cost of biodiesel production though.

Answer 15

Biodiesel contains 88 – 95% of the energy of petroleum diesel Mixed with petroleum diesel it improves lubricity and raises cetane value (cetane number is a measure of ignition quality)

Answer 16

Biodiesel is sensitive to cold. At lower temperatures it may gel. Biodiesel has detergent-like properties, loosening and dissolving residues in engines and storage tanks. It can corrode rubber and rubber parts of conventional diesel engine need to be replaced. Microbial degradation can be a problem but 1% petroleum diesel is sufficiently toxic to prevent this

Answer 17

Food vs fuel: insufficient arable land to sustain both ‘Field-to-wheel’ analysis: CO2 emissions are still high

Answer 18

Wheat - 32% Sugar Beat - 3% Rape seed - 9% Total used - 44%

Answer 19

UK petrol market ~ 14 million T/year 10% target requires 2.1 million T of bioethanol 3.5 T bioethanol /ha Thus require approximately 0.6 million ha. This is ~10% of total arable land – just for 10% requirement and just for petrol.

Answer 20

UK diesel market ~21.3 million T/year 10% target requires 2.33 million T of biodiesel 1.3 T biodiesel/ha Require approximately 1.8 million ha. This is ~31 % of total UK arable land – just for 10% requirement and just for diesel!

Answer 21

Maize: 3,900 L/ha - GHG emissions 35-52% lower than gasoline Sugarcane: 7,200 L/ha - GHG emissions 80% lower than gasoline

Answer 22

Rapeseed, Soybean and Oil Palm - 5,700 L/ha - GHG emissions 29 - 65% lower than diesel

Answer 23

Oil Palm, Waste cooking oil, waste animal fats, rapeseed, soy and camelina - GHG emissions 45 - 70% lower than diesel

Answer 24

Corn - 1:1 (LKg^-1)(staw to crop), 0.29LKg^-1 ethanol, 0.29 alchohol: crop ratio

Answer 25

Rice - 1.4:1 (LKg^-1)(staw to crop), 0.28 LKg^-1 ethanol 0.39 alchohol: crop ratio

Answer 26

Wheat - 1.3:1 (LKg^-1)(staw to crop), 0.29 LKg^-1 ethanol, 0.38 alchohol: crop ratio

Answer 27

Total potential alcohol production from crop residue: 491 GL year-1 491 GL of alcohol could replace 353 GL of gasoline (32% of the global gasoline consumption)

Answer 28

Primary cell walls of adjacent cells are separated by the middle lamella Some plants synthesise a multi-layered secondary cell wall (S1, S2, S3 opposite)

Answer 29

Pectic polysaccharides (pectins) are a group of highly hydrated polysaccharides rich in galacturonic acid (GalA). They are major components of the middle lamella.

Answer 30

They include homogalacturan (HGA) – highly methylated chains of α(1-->4)-GalA, xylogalacturanan, a class of substituted HGAs and rhamnogalacurans.

Answer 31

Cellulose is the main polysaccharide: 15-30% of primary cell walls and more of secondary cell walls.

Answer 32

Several dozen β(1-->4) glucan chains are tightly linked by hydrogen bonds and form a paracrystalline array called a microfibril. The β(1-->4) glucan chains in a microfibril are parallel.

Answer 33

Cross-linking glycans (sometimes called hemicelluloses) hydrogen bond to the cellulose microfibrils.

Answer 34

The major cross-linking glycans are xyloglucans (XyGs) and glucuranoarabinoxylans (GAXs). XyGs cross-link the cell walls of all dicots and about half of monocots but the “commelinoid” monocots (includes the grasses) have GAXs.

Answer 35

Found in dicots and noncomelinoid moncots The have about equal quantities XyGs and cellulose. The XyGs span gaps between microfibrils and lock them inton position. The XyG-cellulose matrix is embedded in pectin.

Answer 36

Type II walls have GAXs instead of XyG and are pectin poor

Answer 37

The secondary cell walls of many plants are modified by the incorporation of lignins, irregular, insoluble polymers of phenylpropanoid derivatives For example, Norway spruce lignin is almost entirely coniferyl alcohol while paracoumaryl alcohol is found almost exclusively in grasses

Answer 38

Synthesised from monolignols, either coniferyl alcohol, sinapyl alcohol or paracoumaryl alcohol. Different plants use different monolignols.

Answer 39

Species - Cellulose % : Hemicelulose % : Lignin % Hardwood stems - 40 -55 : 24 - 40 : 18 - 25 Softwood stems - 45 - 50 : 25 - 35 : 25 - 35 Wheat straw - 30 : 50 : 15 Rice straw - 36 - 47 : 19 - 25 : 10 - 24

Answer 40

Commercially, fungal enzymes are used to degrade lignocellulose. Trichoderma reesei cellulases are the current industry standard.

Answer 41

Endoglucanase - randomly cleaves intermolecular (chain) bonds Exoglucanase (exocellobiohydrolase) - removes 2 - 4 glc moieties from the chain ends Cellobiase (β-glucosidase) - hydrolyses glucose dimers

Answer 42

Pectin degradation involves pectinases (endopolygalacturonases), pectate lyases, pectate methylesterases and other enzymes specific for the non GalA sugars

Answer 43

These are extremely diverse molecules with a very wide array of different sugars and linkages. Although in nature there are enzymes that are able to break all of the linkages, commercially these linkages pose a significant problem.

Answer 44

Anaerobic fungi (Piromyces spp., Neocallimastix spp. and Orpinomyces spp.), which form part of the rumen microﬂora are source xylanases Thermophilic fungi (such as Theromascus aurantiacus, Acremonium thermophilium) are being actively investigated as sources of these enzymes.

Answer 45

Glucuranoaribnoxylans (GAXs) can be depolymerised by endo-β(1-->4) xylanases following removal of side chains with α-arabinofuransidases, α-glucuronidases, ferulic acid esterase and acetyl esterases. Depolymerisation results in xylooligosaccharides (incl. xylotriose and xylobiose) that can be degraded to xylose by β-xylosidases.

Answer 46

Lignocellulosic material --(Pretreatment: Milling and/or treatment with acid or alkali and/or treatment with steam)--> either Enzymic hydrolysis or Acid hydrolysis --->Complex mixture of monosaccharides and non-degraded polymers (especially lignin) --Fermentation--> Ethanol (5-12%) --Distillation--> Ethanol (95-99.8%)

Answer 47

Difficult to release the sugars Many of the sugars are not fermented by yeast

Answer 48

Pre-treatments are designed to increase accessibility of the substrate to enzymes. Steam pre-treatment disrupts the lignin barrier – impregnation with SO2 reduces time and temperature required. Acids and alkalis hydrolyse a variety of chemical bonds.

Answer 49

Enzyme cellulase concentrations of 4000 U g-1 got 80% glucose release Steam explosion pretreatment solubilised starch and 230°C temperature steam explsuion gets 90+% of sugars When sugars feed to 4x yeat get 90% conversion to ethanol

Answer 50

Cane bagasses - 424 L/tones biomass Corn strover - 428 L/tones biomass Rice straw - 416 L/tones biomass Saw dust - 383 L/tones biomass

Answer 51

Commercial ligocellulose bioethanol facility. The plant, owned and operated by the Mossi & Ghisolfi Group, will produce bioethanol from agricultural residues and Arundo donax (‘Giant cane’, a grass). The capacity is 50 million L per annum

Answer 52

Yield - Photosynthetic efficiency and stomatal patterning Feedstock quality - Cellulose quantity and structure and Lignin quantity and quality Resource Use Efficiency - Water use efficiency and Nitrogen use efficiency (NUE)

Answer 53

Glucose to Pyruvate through glycolysis consuming 2NAD+ (Done twice) Pyruvate --(pyruvate decarboxylase)--> Acetaldehyde --(alchohol dehydrogenase)--> Ethanol (releasing NAD+) NAD+ main product Ethanol is waste product

Answer 54

Eukaryotic microorganisms Classified in the kingdom Fungi (both Ascomycota and Basidiomycota) ~1,500 species Unicellular (=‘yeast’ form; may also exhibit filamentous forms) Reproduce by budding or binary fission’

Answer 55

Saccharomyces cerevisiae Reproduces through budding

Answer 56

Botryococcus braunii - 25-75% of dry weight Schizochytrium - 50-77% of dry weight Nannochloropsis sp - 31-38%

Answer 57

Doubling times during exponential growth can be as short as 3.5 h Annual oil production from high-oil microalgae can be in the range of 58,700 to 136,900 L per hectare

Answer 58

“If this microalgal oil is used for biodiesel production, it would take approximately 1.0-2.5% of the current cropland in the US to meet 50% of the US transportation fuel needs” - Cheng & Timilsina (2011)

Answer 59

High oil content - 136,900 L oil/ha year 121,104 kg biodiesel/ha year Medium oil content - 97,900 L oil/ha year 86,515 kg biodiesel/ha year Low oil content - 58,700 L oil/ha year 51,927 kg biodiesel/ha year Only upper estimate fullfuls the quote

Answer 60

Used since 1950s. Natural waters (lakes, lagoons, and ponds) and artificial ponds or containers. Raceway ponds are the most commonly used artificial system Direct flow of water with areas of CO2 infusion until harvested at the end

Answer 61

Closed systems usually of glass or plastic tubes (generally <10 cm diameter) Input of culture medium and CO2 Pumped around in across layers of 3d tubes but extremely expensive in part due to stacking layers

Answer 62

Algae photobioreactors or algal ponds --> Biomass harvested --> filtrated --> centrifuged --> Products Oil extraction --> Anaerobic digester to make biogas or animal feed Biodiesal process to make biodiesel

Answer 63

Heterotrophic production in which microalgae are grown on organic carbon substrates such as glucose in tank bioreactors can be employed. In one study using Chlorella protothecoides lipid concentration increased from 14.5% to 55.2% - autotrophic vs phototrophic growth

Answer 64

Some species can grow mixotrophically: photosynthesis utilises light for growth while aerobic respiration uses an organic carbon source.

Answer 65

Lipid% of dry mass can be increased by nitrogen limitation. Lipid levels increase and composition changes – triacyl glycerols increase and free fatty acids decrease. Cell proliferation is prevented but carbon is still assimilated by the cell and converted to TAG lipids that are stored within existing cells thereby increasing the concentration

Answer 66

BUT it can be argued that lipid yield is a more important consideration than % lipid. E.g. in Dunaliella salina: N-sufficient conditions lipid yield: 0.46 g l-1 day-1 N-limiting conditions light 0.12 g l-1 day-1

Answer 67

Development or selection of fast-growing, high-lipid strains Development or selection of thermo-tolerant strains Development or selection of oxygen-tolerant strains Improved competitiveness of oil-rich strains against wild strains;

Answer 68

‘Biorefining’ algae and developing co-products such as animal feed from the protein-stream or human food including ‘functional’ foods or using waste streams as ‘bio-fertiliser’.Reduced capital costs including the use of cheaper equipment; Reduced operating costs including improved, lower-cost harvesting;

Answer 69

‘Genome shuffling’ - random mutagenesis, multiple rounds of sexual reproduction – combined with growth in increasingly saline conditions After 4th genome shuffling the best lived in 700 nM NaCl concentrations The progenitor strain – ‘initial’ – doesn’t grow at >300 mM NaCl