# Biorefineries and platform chemicals: The biorefinery concept and its types Source page: https://www.materialinsights.org/learn/chemicals/biorefineries-platform-chemicals/p2/ [Understanding Chemicals](https://www.materialinsights.org/learn/chemicals/) / [Module 13: Biorefineries and platform chemicals](https://www.materialinsights.org/learn/chemicals/biorefineries-platform-chemicals/) Part 2 of 5 ## The biorefinery concept and its types A biorefinery borrows the logic of an oil refinery: split a complex raw material into a few clean intermediate streams, then upgrade each into many products. The sources group biorefineries by feedstock and by the intermediate they standardise on. Several already exist and make money; others remain concepts. This part walks through the main types and what each one makes. ### 2.1 Fractionate first, then convert: the corn wet mill already does it The US Department of Energy defines a biorefinery as a plant where biomass is converted and extracted into a spectrum of valuable products, modelled on the petroleum refinery. Task 42 adds that it can be a concept, a plant or a cluster, and classifies any biorefinery by four features: platform (the core intermediate such as C6 sugars, syngas, lignin or oil), products, feedstock and processes. Kamm and colleagues describe generations. A generation I plant, such as a dry-mill ethanol plant, takes grain and makes fixed amounts of ethanol, feed and carbon dioxide with almost no flexibility. A generation II plant, such as a corn wet mill, takes the same grain but can swing between products as demand changes. Generation III plants, using mixed feedstocks and many technologies, had not been built by 2006. The corn wet mill is the working model. Corn is steeped in warm, slightly acidic water, then ground in stages to separate germ (oil), fibre, gluten (protein) and starch, the starch washed to 99.5% purity. Johnson gives the yield from a tonne of corn as 684 kg starch, 237 kg corn gluten feed, 45 kg gluten meal and 34 kg oil. Dale and Kim report that over 90% of the corn leaves as products worth more per kilogram than corn itself. The starch stream is where flexibility lives. Converted to a 95 DE glucose syrup, it can be sold as dextrose, fermented to ethanol or other products, or isomerised to high-fructose syrup. Large mills swing output by as much as 50% between fructose syrup and ethanol, accepting some idle capacity as the price of flexibility. Process flowchart Corn wet milling and starch refining Inputs **Corn**1 t (about 39 bushels at 25.4 kg each) **Water**200-250 gal per bushel, mostly recycled (about 30-37 m3 per t) **Sulphur dioxide**to about 0.2% in steep water **Enzymes**alpha-amylase, glucoamylase, glucose isomerase Process steps 1 **Clean and steep** Countercurrent steep tanks, about 50 C for 30-40 h; SO2 controls bacteria; kernels soften 2 **Coarse grind and germ separation** Hydrocyclones remove low-density germ, which holds about 85% of the oil 3 **Fine grind and fibre screening** Attrition mills free starch and gluten; bent screens hold back fibre 4 **Gluten centrifuge and starch washing** Gluten (60% protein) removed; starch washed to 99.5% purity, the only fresh-water entry 5 **Liquefaction** Starch gelatinised up to 108 C for 5 min with thermostable alpha-amylase 6 **Saccharification** Glucoamylase at 55-60 C, pH 4-5, 48-72 h, to about 97 DE (94% glucose) 7 **Finishing** Ferment to ethanol; or isomerise on immobilised enzyme to 42% fructose, enrich by chromatography and blend to 55% fructose syrup; or refine dextrose Outputs **Starch (to syrups, ethanol, starch products)**684 kg **Corn gluten feed (fibre, spent germ, steep liquor)**237 kg **Corn gluten meal, 60% protein**45 kg **Corn oil**34 kg Water figure converted from Johnson's gallons per bushel. Economy-of-scale size is 60,000-80,000 bushels/day (1,525-2,033 t/day). Source: Kamm (2006), Vol 1 Ch 15 Corn wet and dry milling (Johnson); Kent (2012), Ch 31 Industrial enzymes, Kamm pdf pp. 373-379; Kent pdf pp. 1199-1201 In the data #### Wet mill versus dry mill In 1992 US corn wet mills used 11% of the corn harvest and made products worth 7.0 billion dollars; their starch went 31% to fuel alcohol, 36% to high-fructose syrup, 16% to starch and 17% to dextrose. Dean and colleagues explain why new ethanol plants are mostly dry mills: they skip steeping and fractionation, so capital is much lower, but their only co-product, distillers dried grains, is worth less. Johnson notes a wet mill needs 200 to 250 gallons of water per bushel. - Kamm (2006), Vol 1 Ch 1 Biorefinery systems - an overview · pdf pp. 51-52, 60 - Task 42 (2012), Sections 3 and Figure 2 · pdf pp. 6-7 - Kamm (2006), Vol 1 Ch 15 The corn wet and dry milling industry · pdf pp. 373-379 - Kamm (2006), Vol 1 Ch 2 Biomass refining global impact · pdf p. 80 - Kamm (2006), Vol 1 Ch 3 Development of biorefineries · pdf pp. 102-103 ### 2.2 Whole-crop and green biorefineries use every part of the plant A whole-crop biorefinery takes cereals such as rye, wheat, triticale or maize and first separates grain from straw mechanically. The grain goes to starch, meal or glucose-based fermentation; the straw is lignocellulose and can go to a lignocellulosic line or to gasification for syngas. Kamm and colleagues list the starch options: plasticising it into polymers, chemically modifying it (for example carboxymethyl starch), cracking it by hydrogenation to sorbitol, glycols and glycerin, or fermenting it. They note the drawbacks: high raw material cost and costly processing. A green biorefinery processes 'nature-wet' biomass: grass, lucerne (alfalfa), clover or immature cereals. The first step is gentle wet fractionation, typically pressing, which splits the crop into a fibre-rich press cake and a nutrient-rich green juice. Because the lignin-cellulose composite in green crops is less intractable than in straw, and the plant's own water can carry later biological steps, the chemistry is easier. The catch is perishability: crops must be processed fast or preserved as silage or by drying, and each method changes the contents. Scale ranges widely. Kamm reports plants from a few tonnes of green crop per hour on farms to over 100 t per hour commercially. Kromus and colleagues suggest decentralised plants of about 35,000 t of raw material a year and central plants of 300,000 to 600,000 t. Raw material is not free: their cost table puts late-cut grass at 60 euro per tonne of dry matter, against 36 euro for straw, mainly because grass needs more field work per hectare. Process flowchart A green biorefinery Inputs **Fresh green crop (grass, alfalfa, clover) or silage**a few t/h (farm) to over 100 t/h (industrial) Process steps 1 **Harvest and rapid processing or preservation** Wet biomass is perishable; silage or drying preserves it but changes composition 2 **Wet fractionation (primary refinery)** Pressing splits crop into press cake and green juice in their natural form 3 **Green juice line** Proteins, free amino acids, organic acids, enzymes, minerals; used as fermentation medium for lactic acid, amino acids and ethanol 4 **Press cake line** Green feed pellets, fibres for insulation, or raw material for levulinic acid and syngas 5 **Residue line** Juices and residues to biogas with heat and electricity; digestate back to fields Outputs **Protein concentrates and feed pellets**main products **Lactic acid and derivatives, amino acids**from juice **Fibre products**from press cake **Biogas, heat and power**from residues Grass raw material about 60 euro per t dry matter versus 36 euro for straw (Austrian cost data). Source: Kamm (2006), Vol 1 Ch 1 overview and Ch 12 The green biorefinery concept; Task 42 (2012), Section 4.6, Kamm pdf pp. 61-62, 311-312; Task 42 pdf p. 10 Case #### Green crops in history Green fractionation is old. Pirie developed technical methods for extracting protein from grass and alfalfa in 1937. In the United States commercial extraction of chlorophyll and carotene from alfalfa leaf meal began in 1930, and by 1952 Strong, Cobb and Company made 0.5 t of chlorophyll a day; the water-soluble form went into toothpastes, soaps and deodorants. The juices left over were first used as fertiliser and later for biogas. - Kamm (2006), Vol 1 Ch 1 Biorefinery systems - an overview · pdf pp. 41, 58-62 - Kamm (2006), Vol 1 Ch 12 The green biorefinery concept (Kromus et al.) · pdf pp. 311-312 - Task 42 (2012), Section 4.6 Organic solutions platform · pdf p. 10 ### 2.3 Lignocellulosic and two-platform biorefineries: cheap feed, hard chemistry Kamm and colleagues expected the lignocellulosic feedstock (LCF) biorefinery to be the most successful of all, for two reasons: the raw material is abundant and cheap, and its products fit both existing petrochemical markets and new bio-based ones. They quote corn stover or straw at 30 dollars per tonne against 110 dollars for corn grain. The LCF biorefinery splits its feed into three precursor streams. Hemicellulose gives mostly pentose sugars, the classic source of furfural and xylitol. Cellulose gives glucose for fermentation or for chemical routes to hydroxymethylfurfural and levulinic acid. Lignin, the phenolic polymer, is mostly burned. Kamm calls this unsatisfactory, because lignin is full of single-ring aromatics that would be valuable if they could be isolated economically. The two-platform concept, from NREL and the DOE, organises the same idea by intermediate. The sugar platform uses biochemical steps to release and ferment sugars. The syngas platform gasifies biomass, or the residues of the sugar platform, to carbon monoxide and hydrogen and builds products back up from those small molecules. Gasification has the merit of accepting almost any feed, but it uses only the carbon and hydrogen and ignores the protein, oil and other structures nature has already made. The DOE screening was blunt about syngas in 2004: only hydrogen and methanol were near-term prospects, because simple alcohols, mixed alcohols and Fischer-Tropsch liquids from biomass were not economically viable. Kent adds that biomass gasification experience in the US was limited to heat and power, demonstrated at 200 t/day (5 MW) in Vermont. Value chain From lignocellulose: the sugar and syngas platforms - **Lignocellulosic biomass** straw, stover, bagasse, wood - **Hemicellulose (15-25%)** dilute acid, about 120 C - **Xylose and arabinose** - **Furfural** furfuryl alcohol, THF, resins - **Xylitol / arabinitol** sweetener; glycols by hydrogenolysis - **Fermentation products** ethanol with engineered yeast - **Cellulose (35-50%)** pretreatment plus cellulase - **Glucose (sugar platform)** - **Ethanol, lactic acid, other fermentation products** - **HMF and levulinic acid** acid dehydration - **Lignin (15-30%)** - **Boiler fuel for steam and power** usual fate - **Lignosulfonates, phenolic resins, vanillin** small markets - **Whole biomass or residues to gasifier (syngas platform)** CO + H2 - **Hydrogen and methanol** DOE: best near-term prospects - **Fischer-Tropsch liquids, mixed alcohols** not economic in 2004 Source: Kamm (2006), Vol 1 Ch 1 and Ch 9; Werpy & Petersen (2004), Section 6, Kamm pdf pp. 56-58, 63-64, 223; Werpy pdf p. 24 Case #### Furfural to nylon, and back From 1922 Quaker Oats in Cedar Rapids, Iowa, made up to 2.5 t of furfural a day from oat hulls left over from oat flakes, an early example of coupling food and chemicals. Furfural was then the cheapest aldehyde, at 16 to 17 cents per pound, and DuPont used it as a precursor of nylon 6,6 until about 1960. The last furfural-based nylon plant closed in 1961, displaced by petrochemical routes. - Kamm (2006), Vol 1 Ch 1 Biorefinery systems - an overview · pdf pp. 38, 56-58, 63-64 - Werpy & Petersen (2004), Section 6 Syngas results · pdf p. 24 - Kent (2012), Ch 33 Biomass conversion · pdf pp. 1251-1252 ### 2.4 The oleochemical biorefinery: the oldest and closest to petrochemistry Oils and fats are triglycerides: one glycerol backbone carrying three fatty acid chains, which Clements likens to a comb with three long tines. Because the chains are hydrocarbon-like, oleochemistry slots into existing chemical plants more easily than sugar chemistry, and Clements calls it the largest contribution biomass makes to the chemical industry today. The resource is large but mostly eaten. Task 42 puts world vegetable oil production in 2009-10 at close to 140 million tonnes, about 20% of it for non-food uses including biofuel. Wittcoff's figures for 2000 are starker: of 110.8 million tonnes of oils and fats, 88% was eaten, 6% went to animal feed and only 6% to the oleochemical industry. There are three main ways to open a triglyceride. Saponification with caustic soda gives soap and glycerol. 'Splitting', continuous non-catalytic hydrolysis at high temperature and pressure, gives free fatty acids and glycerol and is the main route in the US and Europe. Alcoholysis, or transesterification, swaps glycerol for methanol to give fatty acid methyl esters (FAME), which are biodiesel and also the preferred feed for fatty alcohols. Wittcoff gives the hydrogenolysis of methyl esters to fatty alcohols as 250 to 300 C and 200 to 300 bar. Task 42 counted 7.7 million tonnes of fatty acids and 2.0 million tonnes of fatty alcohols in 2009, mostly for surfactants in soaps, detergents and personal care. Every route also releases glycerol, roughly a tenth of the product mass, which is why glycerol became one of the DOE's twelve platform chemicals. Process flowchart Transesterification of vegetable oil to biodiesel and glycerol Inputs **Crude vegetable oil (rapeseed, soy, palm) or animal fat**reference plant 300 t/day crude rapeseed oil **Methanol**replaces glycerol on each triglyceride (3 per molecule) **Catalyst**alkaline, for example sodium methylate Process steps 1 **Degumming and refining** Hot water or dilute acid removes phospholipids (lecithin); alkali removes free fatty acids as soapstock 2 **Alcoholysis (transesterification)** RCOOR1 + R2OH → RCOOR2 + R1OH; triglyceride + methanol → methyl esters + glycerol 3 **Phase separation** Dense glycerol phase settles from the ester phase 4 **Ester washing and drying** Gives FAME: viscosity about 4.1 mm2/s versus 32.6 for soybean oil; cetane number 46.2 5 **Glycerol recovery** Crude glycerol sold, refined (about 0.20 dollar/lb in 2003) or converted to chemicals Outputs **Biodiesel (FAME)**main product **Crude glycerol**about 0.1 t per t biodiesel (1.4 Mt per 14 Mt in 2009) Sources do not give reactor temperatures for biodiesel; glycerol ratio is from Task 42 world totals. Source: Kent (2012), Ch 34 Fats, oils and waxes; Wittcoff (2004), Ch 13; Task 42 (2012), Sections 4.4 and 6.2; Werpy & Petersen (2004), Section 9.10, Kent pdf pp. 1374-1375, 1393-1395; Wittcoff pdf pp. 441-442; Task 42 pdf pp. 9, 14; Werpy pdf p. 60 In the data #### Glycerol arrives with every tonne Task 42 reports about 14 million tonnes of biodiesel in 2009, co-producing about 1.4 million tonnes of glycerol, against a 2009 glycerol market of 1.8 million tonnes. Kent's table shows global biodiesel output rising from 13.0 million tonnes in 2008 to 17.6 million tonnes in 2010, led by the EU-27 at 10.3 million tonnes. A fuel market that size can flood a chemical market. - Kamm (2006), Vol 1 Ch 5 The lignocellulosic biorefinery · pdf pp. 150-151 - Task 42 (2012), Section 4.4 Plant-based oil platform · pdf p. 9 - Wittcoff (2004), Ch 13 Fats and oils · pdf pp. 438, 442, 451 - Kent (2012), Ch 34 Animal and vegetable fats, oils and waxes · pdf pp. 1374, 1393-1395 ### See it in the table [H₂O Water](https://www.materialinsights.org/commodities/water/)[Mz Maize](https://www.materialinsights.org/commodities/maize/)[Wh Wheat](https://www.materialinsights.org/commodities/wheat/)[Oa Oats](https://www.materialinsights.org/commodities/oats/)[Su Sugar](https://www.materialinsights.org/commodities/sugar/)[NaOH Caustic soda](https://www.materialinsights.org/chemicals/caustic_soda/)[H2 Hydrogen](https://www.materialinsights.org/chemicals/hydrogen/)[CO2 Carbon dioxide](https://www.materialinsights.org/chemicals/carbon_dioxide/)[MeOH Methanol](https://www.materialinsights.org/chemicals/methanol/)[Srf Surfactants](https://www.materialinsights.org/chemicals/surfactants/)[FA Fatty acids](https://www.materialinsights.org/chemicals/fatty_acids/)[FAl Fatty alcohols](https://www.materialinsights.org/chemicals/fatty_alcohols/) ### Check your understanding What makes a corn wet mill a 'generation II' biorefinery rather than generation I? A dry mill makes fixed amounts of ethanol, feed and CO2. A wet mill uses the same grain but has a flexible glucose stream that can swing between products. Why do Kamm and colleagues call the usual use of lignin 'unsatisfactory'? Lignin is a phenolic polymer rich in aromatic units. Burning it gets only fuel value; isolating aromatics economically would add much more. In the oleochemical industry, which product appears as a by-product of splitting, saponification and transesterification alike? Every route that removes the fatty acids from a triglyceride releases the glycerol backbone. [← Part 1: Biomass as a chemical feedstock](https://www.materialinsights.org/learn/chemicals/biorefineries-platform-chemicals/p1/)[Mark read · Part 3: Conversion routes: how the plants work →](https://www.materialinsights.org/learn/chemicals/biorefineries-platform-chemicals/p3/) ## Other sections - [Module overview](https://www.materialinsights.org/learn/chemicals/biorefineries-platform-chemicals/index.md) - [Biomass as a chemical feedstock](https://www.materialinsights.org/learn/chemicals/biorefineries-platform-chemicals/p1/index.md) - [Conversion routes: how the plants work](https://www.materialinsights.org/learn/chemicals/biorefineries-platform-chemicals/p3/index.md) - [Platform chemicals: the DOE top twelve and their families](https://www.materialinsights.org/learn/chemicals/biorefineries-platform-chemicals/p4/index.md) - [Economics and real cases](https://www.materialinsights.org/learn/chemicals/biorefineries-platform-chemicals/p5/index.md) - [Key terms, quiz and sources](https://www.materialinsights.org/learn/chemicals/biorefineries-platform-chemicals/review/index.md)