Materials from Biomass

Discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry

This dotpoint can be argued many ways, all of which are valid if supported by logical reasoning. However most arguments can be categorised under the headings of ‘scarcity’ and ‘environmental impact’, so it may do well simply to remember these headings and to argue them whatever way you choose.
The need for alternative sources of petrochemical product derivatives comes down to two main points: scarcity and environmental impact.

  • Petrochemical products are derived from non-renewable sources of crude oil. With some experts placing the lifespan of current petroleum sources well under 50 years, and natural gas sources within 100 years, alternative sources are required simply because current production trends are
  • As roughly 95% of crude oil is used up as fuel, the consumption of fuel products has an enormous impact upon the In comparison to other potential fuels such as ethanol, the current petrol products consumed by most of the world burns relatively uncleanly, leading to environmental problems such as the greenhouse effect and acid rain. The biodegradability of many products also places considerable strain on our landfills. Alternative sources of compounds obtained from the petrochemical industry may at the least alleviate such problems.

Remember- Alternative sources of the petrochemical products must be discovered for both practical reasons of scarcity and for fear of doing irreparable harm to our environment.

Use available evidence to gather and present data from secondary sources and analyse progress in the recent development and use of a named biopolymer. This analysis should name the specific enzyme(s) used or organism used to synthesise the material and an evaluation of the use or potential use of the polymer produced related to its properties

There are many possible biopolymers that you may choose to satisfy this dotpoint. For the purposes of this guide, a biopolymer commonly used by students will be examined.
The headings below have been used as a general template. When answering any questions, be sure that you have answered exactly what the question is asking for, as they may sometimes attempt to focus on a specific point. Be prepared to also focus on something as simple as the advantages and limitations of using the chosen biopolymer.
First developed in 1925 by Maurice Limoigne, Polyhydroxybutanoate, or PHB, is a naturally occurring biopolymer which has been produced in laboratories for its many special uses.

Production

PHB is produced by feeding bacteria on a nutrient-rich diet until large colonies of the bacteria begin to form. At this point, glucose is withdrawn from the diet, and the bacteria will automatically secrete PHB as an energy store, similar to the body fat of humans.

One bacterium which produces PHB is Alcaligenes eutrophus. In recent times, genetic engineering techniques have enabled scientists to locate the specific gene responsible for the secretion of PHB, and then to transfer this to bacterium such as Escherichia coli, more commonly known as E. Coli. Advantages to using E. Coli generally centre around the fact that scientists are more familiar with the bacterium, and as such, find it much easier to work with, providing a faster production rate.

Properties and Uses

  • Naturally occurring- As a biopolymer, PHB is both non-toxic and renewable, offering an eco- friendly alternative to most
  • Biodegradable- Decomposing into carbon dioxide and water, PHB has a large environmental advantage over other polymers which take up large amounts of space in
  • Physically similar to polypropylene- Although PHB has a chemical structure markedly different from the polymer polypropylene, its physical properties are quite similar. As such, it can be readily used as a substitute in many of its
  • Biocompatible- Compatible with biological systems, PHB has a highly practical application in the medical industry with items such as medical

Development & Impact

Although the development of genetic engineering techniques has been remarkable, the costs of production of biopolymers such as PHB are still too high to make the process economically viable. This was most noticeable by the initiation and subsequent termination of the production of PHB shampoo bottles and razor handles.

Despite this, applications within the medical industry have been comparatively successful, as the non- toxic and biodegradable nature of PHB removes the need for follow-up surgeries to remove medical sutures, which will now decompose over time.

However, in general, such success is constrained by its low usage. With increasing petroleum prices and decreasing PHB production costs, it may be possible for PHB to one day to emerge on the market after further research and innovation. Certainly, its impact upon the environment will be significant.

Explain what is meant by a condensation polymer

Not all molecules condensed out during condensation polymerisation are water molecules, as in the polymerisation of cellulose.

A condensation polymer is a polymer chain formed by the joining of monomer units which condense out small molecules as the polymer forms (Parts of the actual monomer detach in order to ‘unlock’ the monomer and enable polymerisation). One example of a condensation polymer is cellulose, which is formed from glucose monomers condensing out water molecules as they join.

Remember- A condensation polymer forms by joining together monomer units which have been ‘un- locked’ by simultaneously releasing small molecules.

 

Describe the reaction involved when a condensation polymer is formed

The easiest way to gain an understanding of a condensation polymer is by going through an example of how a common condensation polymer is formed. I will lead on from dotpoint 1.2.3 and use cellulose as an example.

In the formation of cellulose, glucose molecules join together in a chain, where in between every consecutive glucose molecule a hydroxyl group (-OH) from each glucose molecule condenses out as a water molecule, leaving a single oxygen linking the two monomers. This process occurs between every monomer unit which is added to the chain, forming the condensation polymer cellulose. Alternating monomers are inverted in the chain.

figure 1

Don’t forget to include the water molecule which is condensed out!

Remember- In the formation of cellulose, glucose molecules join by condensing out a water molecule between ever two glucose molecules, and inverting every alternate glucose molecule.

 

Describe the structure of cellulose and identify it as an example of a condensation polymer found as a major component of biomass

This dotpoint requires you to be able to differentiate between intermolecular bonding (Between molecules) and intramolecular bonding (Within a molecule). The structure of cellulose, in particular its insolubility, relates to the strength of the intermolecular bonds.

Due to the hydrogen bonding present within the molecule, cellulose is insoluble because the inter- molecular forces cannot be easily broken. It is also important to note that when glucose monomers combine to form cellulose, every second glucose unit is effectively flipped upside down. This produces a reasonably linear molecule, increasing the density and strength of the molecule.

For the purposes of this dotpoint, it would also be useful to note that cellulose is a major component of biomass, where biomass can be defined as any material produced by living organisms. This most frequently refers to plant material and animal excreta.

Remember- Cellulose is a dense, insoluble condensation polymer commonly found in various forms of biomass such as grass, trees and trees. It is a condensation polymer and a major component of biomass.

 

Identify that cellulose contains the basic carbon-chain structures needed to build petrochemicals and discuss its potential as a raw material

This dotpoint is really leading up to the potential of cellulose as an alternative source of petrochemical products. The main point is to note the verb ‘discuss’, and argue the Fors and Againsts of using cellulose.

Cellulose contains a basic carbon-chain structure common to many of the compounds used within the petrochemical industry. Readily abundant and renewable, cellulose presents a tempting alternative to the non-renewable resources currently used such as petroleum.

However, although there are two primary methods of converting cellulose to its glucose components, acid digestion and enzyme digestion, both processes require an immense amount of energy in order to overcome the strong hydrogen bonds present within the cellulose structure. As a result of the energy input required, these processes simply aren’t economically viable, and as such there are currently no means of converting cellulose into the traditional monomers used in the polymerisation of materials such as PVC and Teflon.

Producing cellulose is no longer a significant barrier, as modern bacterial production methods in- volving strains such as E. Coli present many opportunities in the mass production of cellulose-based substances. However, it is only when cellulose can be effectively broken down that it can be used effectively as an alternative to crude oil.

Although the inability to convert cellulose into its glucose components in any economically viable manner does prevent its use as an alternative source of petrochemical products, should this barrier be overcome cellulose has virtually unlimited potential given its abundance and chemical make-up.