biology

Lignocellulosic biomass

Lignocellulosic biomass is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Lignocellulosic biomass rather than just read about it. In short: Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of biofuels.

Key takeaways

Lignocellulosic biomass belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lignocellulosic biomass to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lignocellulosic biomass from memory before moving on to harder problems.

Reference excerpt

Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of biofuels. It is composed of two kinds of carbohydrate polymers, cellulose and hemicellulose, and an aromatic-rich polymer called lignin. Any biomass rich in cellulose, hemicelluloses, and lignin is commonly referred to as lignocellulosic biomass. Each component has a distinct chemical behavior. Being a composite of three very different components makes the processing of lignocellulose challenging. The evolved resistance to degradation or even separation is referred to as recalcitrance. Overcoming this recalcitrance to produce useful, high value products requires a combination of heat, chemicals, enzymes, and microorganisms. These carbohydrate-containing polymers contain different sugar monomers (six and five carbon sugars) and they are covalently bound to lignin. Lignocellulosic biomass can be broadly classified as virgin biomass, waste biomass, and energy crops. Virgin biomass includes plants. Waste biomass is produced as a low value byproduct of various industrial sectors such as agriculture (corn stover, sugarcane bagasse, straw etc.) and forestry (saw mill and paper mill discards). Energy crops are crops with a high yield of lignocellulosic biomass produced as a raw material for the production of second-generation biofuel; examples include switchgrass (Panicum virgatum) and elephant grass. The biofuels generated from these energy crops are sources of sustainable energy.

Chemical composition

Lignocellulose consists of three components, each with properties that pose challenges to commercial applications.

lignin is a heterogeneous, highly crosslinked polymer akin to phenol-formaldehyde resins. It is derived from 3-4 monomers, the ratio of which varies from species to species. The crosslinking is extensive. Being rich in aromatics, lignin is hydrophobic and relatively rigid. Lignin confers structural integrity to plants. Lignin is so heterogeneous and so recalcitrant that its value is almost exclusively measured as a fuel. hemicellulose is composed of branched polysaccharides. A particular problem is that hemicellulose is covalently linked to lignin, usually through ferulic acid component of the lignin. This makes it difficult to extract the sugars necessary for conversion to biofuels. Next to cellulose hemicellulose is the second most abundant source of carbohydrates in a plant. cellulose is a homopolymer of glucose. It is very poorly soluble in most solvents, so glucose is extracted through chemical and biological breakdown achieved by cellulolytic enzymes. This extraction is made easier by the fact that the strands of cellulose are integrated into, but not covalently attached to the lignin-hemicellulose component.

Dedicated energy crops

Many crops are of interest for their ability to provide high yields of biomass. Some can be harvested multiple times each year. These include poplar trees and Miscanthus giganteus. The premier energy crop is sugarcane, which is a source of the readily fermentable sucrose and the lignocellulosic by-product bagasse.

Application

Pulp and paper industry Lignocellulosic biomass is the feedstock for the pulp and paper industry. In this process lignin and hemicellulose are typically separated from the plant material leaving the fibrous cellulose component to be processed for paper production, or 'chemical cellulose'. Through the pulp process most of the lignin is removed and discharged as waste material in the form of effluent/wastewater before then being used as low-value fuel to generate electricity and heat. Some lignin from paper waste is alternatively used as lignosulfonates and sulfonated lignins.

Sugar In principle, the world's current sugar demand could be fulfilled by repurposing pulp and paper mills for lignocellulosic sugar production, making it a promising resilient food.

Biofuels

Direct combustion Lignocellulosic biomass, in the form of wood fuel, has a long history as a source of energy. Straw and other forms of lignocellulostic biomass has more recently been used for electricity generation in the form of uncompressed (bale) and compressed (pellet) fuels. Pelleting allows the fuel to be economically transported over further distances. First generation pellets are limited to a co-firing rate of 15% in modern IGCC plants. Pretreatment before pelletization changes the physical and chemical properties of biomass fuel. Torrefaction (a mild pyrolysis) increases the energy density of straw and makes it hydrophobic. The resulting pellets have fuel properties similar to coal.

Conversion Since the middle of the 20th century, the interest of biomass as a precursor to liquid fuels has increased. To be specific, the fermentation of lignocellulosic biomass to ethanol is an attractive route to fuels that supplements the fossil fuels. Biomass can be a carbon neutral source of energy in the long run. However depending on the source of biomass, it will not be carbon neutral in the short term. For instance if the biomass is derived from trees, the time period to regrow the tree (on the order of decades) will see a net increase in carbon dioxide in the Earth's atmosphere upon the combustion of lignocellulosic ethanol. However, if woody material from annual crop residue is used, the fuel could be considered carbon-neutral. Aside from ethanol, many other lignocellulose-derived fuels are of potential interest, including butanol, dimethylfuran, and gamma-valerolactone.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Lignocellulosic biomass

Start with the simplest possible case. Write down what Lignocellulosic biomass claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lignocellulosic biomass before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lignocellulosic biomass ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lignocellulosic biomass

In research: Lignocellulosic biomass appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lignocellulosic biomass in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lignocellulosic biomass is common in secondary-school and first-year university syllabi. It links to neighbouring topics Biological matter, Biomass, Cellulose, so understanding it makes those chapters shorter.
In everyday life: Look for Lignocellulosic biomass outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Lignocellulosic biomass in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lignocellulosic biomass means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Lignocellulosic biomass out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lignocellulosic biomass in simple terms?

Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of biofuels.

Why does Lignocellulosic biomass matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lignocellulosic biomass?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lignocellulosic biomass.