Question

A company producing cola wants to increase the production of "green bottles" made of PET (polyethylene terephthalate). Therefore, they plan to build a plant to produce ethylene glycol (one of the two monomers of PET) from sugarcane residues (bagasse). The capacity will be \(500 \mathrm{kt}\).year \({ }^{-1}\). a. Make a block process diagram of how this biorefinery could look like. b. Give the main reactions taking place in the process leading to ethylene glycol. c. How much bagasse (kt.year \(^{-1}\) ) would be needed in this process when bagasse is assumed to consist of \(38 \mathrm{wt} \%\) cellulose \((\mathrm{db}), 27 \mathrm{wt} \%\) hemicellulose, \(20 \mathrm{wt} \%\) lignin, \(3 \mathrm{wt} \%\) proteins, \(9 \mathrm{wt} \%\) extractives (water soluble), and \(3 \mathrm{wt} \%\) ash. Consider ethanol to be an intermediate product, which is only made from the cellulose part via enzymatic hydrolysis and subsequent sugar fermentation. d. Which products can be made from the noncellulosic part of bagasse?

Short answer

Answer: The main components and steps involved in designing a biorefinery process for producing ethylene glycol from sugarcane bagasse include pretreatment, hydrolysis, fermentation, and product separation, as well as intermediate steps for ethanol and ethylene production.

Step-by-step solution

A. Block Process Diagram

To make a block process diagram of the biorefinery, first, identify the main components and steps of the process. Start with feedstock/bagasse input, followed by the individual steps like pretreatment, hydrolysis, fermentation, and product separation. Each step must be represented by blocks, and arrows will indicate the flow of material between blocks. Include important intermediate products, such as ethanol and ethylene glycol, in the diagram.

B. Main Reactions for Ethylene Glycol Production

The main reactions leading to ethylene glycol production include: 1. Pretreatment: Bagasse is pretreated to break down its complex structure and make the cellulose accessible. This often involves using heat, pressure, and chemicals. 2. Hydrolysis: Enzymatic hydrolysis converts cellulose into glucose. 3. Fermentation: Microorganisms ferment glucose to ethanol. 4. Ethylene Production: Ethanol is dehydrated to produce ethylene. 5. Ethylene glycol production: Ethylene is oxidized and hydrated to form ethylene glycol.

C. Calculate Bagasse Demand

To calculate the amount of bagasse needed for the process, first determine the amount of cellulose required to produce 500 kt of ethylene glycol per year. 1. Assume 100% conversion of cellulose to ethanol and 100% conversion of ethanol to ethylene glycol. In this case, the total mass of cellulose required equals the mass of ethylene glycol produced: 500 kt.year \(^{-1}\). 2. Next, calculate the amount of bagasse required based on cellulose content. Bagasse consists of 38 wt% cellulose. Divide the cellulose demand by the cellulose content in bagasse: \(\frac{500}{38\%} = 1315.8 \mathrm{kt.year}^{-1}\). Hence, 1315.8 kt.year \(^{-1}\) of bagasse would be needed for this process.

D. Products from Noncellulosic Parts of Bagasse

Noncellulosic parts of bagasse can be used to produce various products. Here are some examples: 1. Hemicellulose: It can be converted into xylose and lignin-derived compounds, which have multiple applications, such as in the production of biofuels, acids, or solvents. 2. Lignin: Can be used as a binder, adhesive, or as a source of heat or energy through combustion. It can also be converted into high-value materials, such as carbon fiber or aromatic chemicals. 3. Proteins: Can be extracted and used as animal feed or as a source of bioactive peptides. 4. Extractives (water-soluble): Can be used for producing bio-oils or functional chemicals. 5. Ash: Can be used as a fertilizer or as a construction material.

Key concepts

Ethylene Glycol Production

In the quest to manufacture environmentally friendly packaging, one critical component is ethylene glycol, a building block for producing polyethylene terephthalate (PET), commonly used for making beverage bottles. Its production from biomass, such as sugarcane residues (bagasse), represents a sustainable alternative to petroleum-based counterparts.
The journey from bagasse to ethylene glycol includes several steps. Initially, the bagasse undergoes pretreatment to break down the complex structure, making cellulose accessible for enzymes. The pretreated material then enters enzymatic hydrolysis, where cellulose is converted into glucose. This sugar is then fermented by microorganisms to produce ethanol. In the subsequent stage, dehydration of ethanol yields ethylene, which after oxidation and hydration, transforms into ethylene glycol.

Key Advantages

• Reduction in the reliance on fossil fuels
• Decreased carbon footprint of packaging materials
• Potential to recycle agricultural waste

Overall, ethylene glycol production from biomass is not just a chemical process; it's a stride towards sustainable industrial practices.

Bagasse Conversion

Bagasse, the fibrous residue left after sugarcane is processed for sugar, presents an opportunity to extract value from what might otherwise be considered waste. This biomass is composed mainly of cellulose, hemicellulose, and lignin. Each of these components can be converted into various valuable substances through bio-refinery processes.
Conversion of bagasse to valuable products typically starts with mechanical and chemical pretreatment methods to separate and breakdown complex biomass. The cellulose portion is hydrolyzed and fermented to produce ethanol, which can further lead to the production of ethylene glycol, as discussed previously. Other non-cellulosic components can be utilized in myriad ways, transforming them into biofuels, bio-oils, fertilizers, and even materials for construction and manufacturing industries.

Benefits of Bagasse Conversion

• Minimizes waste and pollution by recycling biomass
• Creates a wide array of bio-based products
• Enhances the sustainability of sugarcane industries

The bagasse conversion process highlights the circular economy in action, where every part of the biomass is used to its fullest potential.

Biomass Sustainable Energy

Biomass energy, derived from organic materials like bagasse, plays a significant role in the realm of sustainable energy solutions. It's a renewable source that can be constantly replenished and converted into electricity, heat, or liquid fuels, providing a greener alternative to non-renewable resources.
Sustainable biomass energy is obtained through biological processes, such as anaerobic digestion or combustion. These processes can convert the energy stored in biomass to a usable form. The conversion of bagasse not only generates energy but also fits into a larger strategy of reducing greenhouse gas emissions, managing waste, and creating economic opportunities in rural areas.

Energy Security and Sustainability

• Promotes energy diversification and security
• Supports rural development and agricultural sectors
• Aligns with global goals to mitigate climate change

Investment in biomass for sustainable energy production is an essential step towards a more resilient and environmentally conscious energy future.