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ENCH483 > L9 > Flashcards

L9 Flashcards

1
Q

Saccharification

A

The process of breaking a complex carbohydrate (such as starch or cellulose into its monosaccharide components

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2
Q

Fermentation Steps

A
  1. ) Converting feedstock to fermentable sugars
  2. ) Converting glucose to ethanol through fermentation

Challenge is to create yeast that converts other sugars that is not glucose into ethanol

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3
Q

Ethanol fermentation definition

A
  • A biological process which converts sugars such as glucose, fructose, and sucrose to ethanol and CO2 as a side product
  • Yeasts used in the absence of oxygen -> anaerobic fermentation
  • C6H12O6 + Zymase -> 2C2H5OH + 2CO2
  • Zymase is an enzyme complex that catalyses the fermentation. Occurs naturally in yeast
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4
Q

Yeast

A
  • Yeast is reproduced by budding
  • 75% water and 25% dry matter
  • Growth requirements
  • — Water
  • — Carbon source as energy source
  • — Oxygen/lipids
  • — Amino acids and peptides as nitrogen source
  • — Vitamins
  • — Inorganic ions
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5
Q

Frequently used yeast

A

Accharomyces cerevisiae

  • robust and high ethanol yield
  • only ferments C-6 sugars
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6
Q

Feedstock for fermentation to ethanol

A

Lignocellulosic biomass for fuel ethanol

  • Wood
  • Crop residues
  • Purpose grown biomass

Food grains and crops for beverage alcohol and fuel

  • Sugar-based: sugarcane and sugar beet
  • Starched based: corn, sorghum, rice, barley

Food processing residues
- Whey: a by-product from cheese manufacturing

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7
Q

Pre-treatment of starch feedstock

A
  • Separation of fermentable sugars

Step 1
- Break down granular structure of starch with endoenzyme in process

Step 2
- Liquefaction or hydrolysis of starch to dextrins by alpha-amylase enzyme.

Step 3
- Saccharifcation to release glucose molecules from dextrins

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8
Q

Routes of lignocellulosic biomass to ethanol

A

Route 1.) Enzymatic hydrolysis and fermentation

Route 2.) Simultaneous saccharification and fermentation

Route 3.) Direct acid hydrolysis for fermentation

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9
Q

Lignocellulosic biomass pretreatment in route 1

A

Purpose

  • to liberate cellulose and hemicellulose from the lignin seal and its crystalline structure so as to make polysaccharides accessible for a subsequent hydrolysis step
  • Lignin in removed

Methods

  • Physical: milling, grinding
  • Thermal: steam explosion, hot water
  • Chemical: Alkali, acids
  • Biological: selected white-rot fungi
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10
Q

Lignocellulosic biomass hydrolysis of saccharifcation in route 1

A

Purpose
- Cellulose and hemicellulose depolymerized to glucose and xylosa

Method

  • Enzymatic hydrolysis
  • A series of different enzymes degrade molecules into fermentable sugars
  • Techno-economic bottleneck
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11
Q

Lignocellulosic biomass in route 2

A

Simultaneous saccharification and fermentation after pretreatment

  1. ) using a mixture of biomass saccharfication microorganisms and fermentation microorganisms
  2. ) using genetically engineered microorganisms that can do both saccharification and fermentation

Advantages

  • higher ethanol yields due to removal of end product inhibition
  • only one reactor for both steps

Disadvantages

  • difficult to optimize due to microorganism optimal temperature differences
  • genetically engineered organisms in development stage
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12
Q

Lignocellulosic biomass direct acid hydrolysis in route 3

A

Purpose
- Release sugars in lignocellulosic biomass in one step

Method

  • Concentrated acid hydrolysis
  • Dilute acid hydrolysis, higher temperature and longer exposure time
  • Ionic liquid-mediated hydrolysis
  • Solid acid hydrolysis using zeolite catalysts
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13
Q

Challenge: inhibitory substances in lignocellulosic hydrolysis

A

In pretreatment, extractive components and organic or sugar acids also undergo hydrolysis. This produces compounds that inhibit sugar fermentation.

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14
Q

Fermentation configurations considerations

A
  • Type of microorganisms used
  • Their fermentation kinetics
  • Type of lignocellulosic biomass used
  • process economics aspects
  • If there should be immobilization or recirculation of cells
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15
Q

Batch fermentation

A

Rapid batch fermentation

  • Done in a cylindrical-conical fermenter
  • The slope of the bottom should be sufficient for the mash to run out when discharging
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16
Q

Batch process: advantages and disadvantages

A

Advantages

  • Simple and easy to control, especially control of contamination
  • More flexible and capable of handling high ethanol concentrations

Disadvantages

  • Fermenter cleaning is accomplished with clean-in-place equipment
  • Cleaning/sterilization takes 50 mins
  • Lower fermenter usage and higher cleaning costs
17
Q

Continuous fermentation

A

Internal volume of medium remains constant, continuous flow of nutrients into fermenter and constant flow of product out

Continuous stirred rank reactor

  • Fermentation broth is continuously stirred by agitators
  • Composition in reactor is homogenous

Plug flow reactor

  • Uniform velocity profile across radius
  • Reaction proceeds as the reagents travel through the reactor
  • Yeasts have to be constantly fed into the reactor

Cascade continuous fermentation

  • 3-5 fermenters linked in series
  • In balance growth, no need for adding yeast and nutrients
18
Q

Advantages of continuous fermentation

A
  • Fermentation conditions do not change with time
  • higher fermentation efficiency and productivity
  • Reduced vessel downtime for cleaning
  • Flexibility to run in batch mode when necessary
19
Q

Contamination in a fermentation plant

A
  • All equipment can be infected
  • Lactobacillus bacteria and wild yeasts will compete with sacharomyces yeast for nutrients and produce acids as their end products
  • Stressful condition for yeast growth: High ethanol, high temperature and low pH
20
Q

Contamination control and challenges

A

To reduce number of microbes in the feed sugar solution such that the levels of bacterial end products are minima;

  • Low pH
  • Add antimicrobials or antibiotics

Challenges in fermentation of biomass

  • Low conversion of efficiency (loss approx 40% feedstock)
  • Low energy efficiency (pre-treatment, final distillation)

Challenges in fermentation of starch and sugar feed stocks

  • Low energy efficiency (final distillation)
  • competing with food supply

ENCH483 (12 decks)

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