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Biorefineries > Bio-based Processes > Flashcards

Bio-based Processes Flashcards

1
Q

In the pulping process, what is the condition of wood fibers (and cellulose chains) when they are separated from the wood matrix?

A

They are kept as long, unbroken and strong as possible.

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2
Q

what is the common source of manufacturing pulp and paper?

A

Pulp and paper are manufactured from raw materials containing cellulose fibers, e.g. generally wood, recycled paper, and agricultural residues, etc.

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3
Q

what is an integrated mill?

A

is one where pulp and paper both are manufactured on-site

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4
Q

what is the advantage of an integrated mill?

A

it has the advantage of using common utilities for both pulping and papermaking e.g. energy, steam, water, etc.

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5
Q

what is a non-integrated mill?

A

It is the one where the pulp is brought or bought to it from the outside.

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6
Q

what is the advantage of a non-integrated mill?

A

1- smaller
2- more easily controlled entities.
3- In addition, it is not always possible to produce both products at the same place, e.g. lack of raw material.

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7
Q

what are the names of the steps of the Kraft Process?

A 
1-Debarking
2-Chipping
3-Impregnation
4-Cooking
5-Washing
6-Screening
7-Bleaching
8-Drying or pumping to the mill
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8
Q

What are the types of pulping processes?

A

Mechanical pulping - Chemical pulping

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9
Q

describe mechanical pulping?

A

it involves the separation of fibers from each other by mechanical energy applied to the wood matrix causing the gradual break of the bonds between the fibers.

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10
Q

What does mechanical pulp consist of?

A

fiber bundles, single fibers, and fiber fragments

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11
Q

what is the objective of mechanical pulping?

A

to maintain the main part of the lignin in order to achieve high yield with acceptable strength properties and reasonable brightness

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12
Q

what ate the types of mechanical pulping processes?

A 
they are 4 types:
1- Stone Ground wood Pulping (SGW) 
2- Pressure Ground wood Pulping (PGW) 
3- Thermo-Mechanical Pulping (TMP)
4- Chemi-Thermo-Mechanical Pulping (CTMP)
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13
Q

describe chemical pulping?

A

it uses chemicals, most commonly alkaline and sodium sulfide, to dissolve lignin.

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14
Q

what is the condition of fibers in chemical pulping?

A

They remain their length and strength very well.

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15
Q

Which one has more yield on wood, mechanical pulping or chemical pulping?

A

Mechanical pulping.

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16
Q

why is the yield on wood is lower in chemical pulping than in mechanical?

A

due to the fairly non-selective dissolution of wood components; In addition to lignin also the hemicelluloses are dissolved.

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17
Q

what are the types of Chemical pulping processes?

A

they are two?
1- Kraft (sulfate) Pulping, the main process of pulp mills today
2- Sulfite Pulping, e.g. Borregaard

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18
Q

in a wood cell, where can most of the lignin be found?

A

in the middle lamella (ML).

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19
Q

in a wood cell, where can most of the cellulose be found

A

in S2.

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20
Q

when was kraft pulping (sulfate pulping) first invented?

A

in 1897

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21
Q

what are the advantages of the kraft process in comparison to the sulfite pulping process?

A 
1- Shorter cooking time
2- Stronger reinforcement pulp
3- Good chemical recovery
4- Energy efficiency
5- Valuable side products, e.g. tall-oil
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22
Q

describe the pretreatment in the kraft process?

A

1- debarking the logs to the desired cleanliness (by removing the loose bark flow and also removing the sand and small stones from it)
2- chipping
3- screening
4- chip transport and storage

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23
Q

what is the purpose of cooking in the kraft process?

A

to extract fiber binding lignin with the help of chemicals and heat. Fibers containing mostly cellulose are kept as long, unbroken and strong as possible in order to maintain their strength properties.

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24
Q

what are the chemicals used in kraft cooking?

A

white liquor, i.e. sodium hydroxide (NaOH) and sodium sulfide (Na2S)

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25
Q

what is the function of sodium hydroxide and sodium sulfide in kraft cooking?

A

Sodium hydroxide degrades lignin and sodium sulfide fastens cooking reactions and decreases cellulose degradation caused by sodium.

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26
Q

why do we pre-steam the chips in overpressure before cooking?

A

to remove the air in chips and improve the impregnation of the coming chemicals.

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27
Q

how is the impregnation done in the kraft process?

A

by increasing temperature and pressure to drive the cooking chemicals into the chips.

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28
Q

what happens to lignin and hemicelluloses in cooking?

A

lignin dissolves and hemicelluloses dissolve partially

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29
Q

what are the typical kraft pulping process conditions?

A

Liquid-wood ratios: 4,5 – 5

Cooking temperature: 170 – 175 C⁰ Cooking time: 4-5 h

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30
Q

what is black liquor?

A

it is a white liquor that has reacted in cooking and to which wood compounds have dissolved. The black color comes from lignin compounds colored by alkali.

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31
Q

How is black liquor separated?

A

it is separated in the washing step.

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32
Q

what is the main purpose of pulp screening?

A

to separate harmful impurities from pulp with minimal fiber loss and acceptable cost level

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33
Q

what is the classification of the impurities in pulp?

A

they can be classified by their origin:
1- Impurities originating from wood material, i.e. knots, fiber bundles, extractives, and bark.
2- Non-wood impurities coming with wood material or coming later into the process like stones, sand, metal, plastic, etc.

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34
Q

what is oxygen delignification?

A

a direct extension of the lignin removal process which takes place during cooking. It fragments and oxidizes lignin into a form which is dissolvable in alkali, destroys the color compounds, the colored chromophores of lignin and removes impurities from the pulp.

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35
Q

what is the objective of bleaching?

A

to increase the brightness of pulp by removing the residual lignin. Without any significant losses in pulp strength.

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36
Q

how do Lignin, carbohydrates, and extractives in wood look like before pulping?

A

they are slightly colored

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37
Q

how do Lignin, carbohydrates, and extractives in wood look like after pulping?

A

after pulping and as a result of the pulping reactions, the residual lignin fragments are highly colored, colored chromophores.

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38
Q

what does Enocell, Uimaharju produce?

A 
1- Viscose cellulose for the production of textile fibers and other end-uses needing strong fibers
2- Micro cellulose
3- Lignin based products for adhesives
4- Gaseous and liquid biofuels
5- Biochemicals from side streams
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39
Q

Define the thermochemical conversion of biomass?

A

Biomass is converted into different energy products such as heat, electricity and
transport fuels by thermochemical processes.

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40
Q

what are the types of Thermochemical conversion?

A 
Can be divided into 4 subgroups based on the product qualities and ratios by controlling
process conditions.
1- Pyrolysis
2- Gasification
3- Liquefaction
4- Combustion
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41
Q

what are the major groups of substances resulting from the thermochemical conversion of cellulose-containing biomaterials?

A

three major groups of substances;
1- Gases
2- Condensable liquids
3- Solid products

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42
Q

what are the advantages of Thermochemical conversion methods?

A

1- rapid.
2- eliminate large volumes of water (compared with saccharification-based
processes) and other external chemicals

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43
Q

what are the disadvantages of Thermochemical conversion methods?

A

1- unselective reactions which give a large number of products at low
individual yields.
2- suffer from high economical cost and technical challenges

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44
Q

what does the choice of the conversion process depend on?

A

1- Economics,
2- The Type of biomass feedstock,
3- The Desired form of bioenergy and
4- The environmental aspects.

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45
Q

why does a pretreatment stage is required prior to a thermochemical conversion?

A

because of the non-homogeneity and high water content of biomass feedstocks

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46
Q

what is pyrolysis?

A

a thermochemical treatment which can be applied to any organic (carbon-based)
product.
In this treatment, the material is exposed to a high temperature of 350 - 800 ̊C with relatively low pressure
and in the absence of oxygen goes through chemical and physical separation into different molecules

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47
Q

what are the types of pyrolysis used in thermochemical conversion of the biomass?

A

1- Conventional pyrolysis mainly for making charcoal
2- Fast pyrolysis or Flash pyrolysis, high temperature (mainly production of liquids)
3- Vacuum pyrolysis (mainly production of liquids)

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48
Q

what is the liquid end product in pyrolysis often called?

and in which applications was it tested?

A

bio-oil, biocrude or pyrolysis liquid

and is used in industrial kiln, boilers, diesel engines and gas turbines.

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49
Q

in pyrolysis, where are Alkali and other mineral components of the biomass are predominately entrapped?

A

in the char residue

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50
Q

describe fast pyrolysis?

A

it involves very high heating and heat transfer rates that require a finely ground biomass feed of typically less than 3 mm as biomass generally has a low thermal conductivity

51
Q

what is the temperature of fast pyrolysis?

A

carefully controlled temperature of around 600 – 800 °C

52
Q

what should be done in fast pyrolysis to obtain bio-oil products?

A

rapid cooling of the pyrolysis vapors

53
Q

how long is the residence time in fast pyrolysis?

A

Short vapor residence time of 2 seconds or less.

54
Q

what are the advantages of fast pyrolysis compared to traditional pyrolysis?

A

More advanced to traditional pyrolysis and can be
controlled with a high yield of liquid of about 80% wt. on
dry feed. By-products char and gas also formed which is
used within the process so there are no waste streams.

55
Q

what are the process conditions of vacuum pyrolysis?

A

1- Process performed under vacuum (10-20 kPa)
2- The temperature typically lies somewhere between
350 and 520°C
Compared to fast pyrolysis, longer residence times,
(e.g.40 s) are employed.

56
Q

what are the advantages of vacuum pyrolysis?

A

1- it gives a more even spread of products
2- Increase of Bio-oil production reaching 23.6 ± 4.3 wt.% compared to 18.7 ± 5.0 wt.% for
conventional or slow pyrolysis
3- Decreased pressure/temperature reduces adverse
chemical reactions
4- Because of the lower pressure biomass fragments
tend to evaporate more easily

57
Q

what happens in the Gasification of biomass?

A

Thermal conversion of solid fuel into a valuable gaseous product called syngas and a solid product called char

58
Q

what is the use of syngas?

A

It can be used for power generation or biofuel production

59
Q

what are the main constituents of syngas?

A

1- carbon monoxide (CO),
2- hydrogen (H2),
3- methane (CH4) and
4- carbon dioxide (CO2).

60
Q

what are the minor constituents that can be found in syngas?

A

1- Hydrogen sulfide (H2S)
2- Hydrogen chloride (HCl)
3- Inert gases, such as nitrogen (N2)

61
Q

what is the temperature of the gasification of biomass?

A

800-1000°C

62
Q

Syngas reactions are reversible or irreversible?

A

Reversible

63
Q

what does the outcome of syngas reactions depend on?

A

It depends on the chemical equilibrium in the process conditions

64
Q

what are the steps of the gasification process of biomass?

A 
1- Particle heat up
2- Drying
3- Pyrolysis/Volatilisation
4- Volatile combustion
5- Charcoal combustion
6- Charcaol gasification
7- Char fragmentation
65
Q

what are the steps of syngas conditioning?

A 
1- Reforming
2- Cooling
3- Filtering
4- Water-gas shift
5- Ultra-cleaning
66
Q

what happens in the reforming of syngas?

A

Reforming
This is the transformation of tar and heavy hydrocarbons present in the syngas into more
valuable gaseous compounds (H2 and CO).
condensation of tar on cold surfaces is prevented by removing it and therefore aids in eliminating plugging problems downstream in the syngas treatment line.
CnH2n+2 + nH2O→ nCO + (2n+1)H2
The reformer reactor operates at temperatures 800-950 ̊C

67
Q

what happens in the filtering of syngas?

A
  • The mechanical filtering of fine particulates and contaminants done in further
    downstream processes. Filter materials are ceramic, metal or teflon.
  • Temperature range from 180 and 800°C and is dependent on the temperature durability of filter material
68
Q

what happens in the water-gas shift of syngas?

A
  • This is a common catalytic process used to produce H2. It is a convenient way to
    increase the H2 yield in the syngas.
  • The processing of liquid biofuels often requires a special mixture reagent (H2 and CO)
    and the ratio is adjusted with water-gas shift.
  • Syngas at temperatures 200-500°C is fed to the water-gas shift reactor
69
Q

what happens in the ultra-cleaning of syngas

A

This is the removal of trace chemical contaminants from syngas that can be harmful in the
catalytic conversion processes, for example, in the production of liquid hydrocarbon.
Wet scrubbing enables the removal of various impurities from syngas flow. Impurities such as;
1- Alkaline and heavy metals
2- Sulphur compounds and NH3
3- Traces of tar left in syngas

70
Q

what are the applications of bio-based syngas?

A

it can be used as a raw material in the chemical
industry.
 alcohols (methanol, ethanol and mixed alcohols)
 synthetic natural gas (SNG = CH4)
 H2 (in the production of other chemicals)
 fertilizers
 liquid biofuels

71
Q

describe liquifaction process of biomass?

A

liquefaction is the thermochemical conversion of biomass into liquid fuels by processing in a hot, pressurized water environment for sufficient time to break down the solid biopolymeric structure to mainly liquid components

72
Q

how similar liquefaction is to pyrolysis?

A

it is similar of hydrous pyrolysis, but compared to pyrolysis liquefaction is
carried at lower temperatures and heating rates

73
Q

what are the operating conditions of liquefaction?

A

Operating at 300-350°C of temperature and pressures from 4 to 22 MPa with or without
additives.

74
Q

do we need to dry the biomass prior liquefaction?

A

NO

75
Q

what are the types of liquifaction processes?

A

1- Direct liquefaction (non-catalytic aqueous process)

2- Catalytic liquefaction (in the presence of reducing CO or H2)

76
Q

describe the combustion process of biomass?

A

Biomass combustion is the most common energy conversion technology offering the advantages of low cost, low risk, and high efficiency.
Organic matter → CO2 + H2O + char + heat

77
Q

mention some characteristics of the biomass combustion process?

A

1- Chemical reactions are exothermic, with every 10 Kelvin increase in temperature reaction speed is doubled.
2- Most of the combustion reactions are vapor phase reactions due to high temperatures.
3- Combustion can be maintained only when there is enough heat present to raise the temperatures of unburned gases to sufficient levels.
4- A flame is burning most efficiently when there us just enough oxygen to burn the existing fuel

78
Q

Define High (or Upper) heating value?

A
  • The amount of heat produced by the complete combustion of a unit quantity of fuel (mass or volume).
  • The amount of heat released when fuel is combusted and the products have returned to a temperature of 25°C. The water vapor formed during combustion is condensed and is liquid
79
Q

Define Lower Heating Value?

A

Determined by subtracting the heat of vaporization of the water vapor from the higher heating value. This treats any H2O formed as a vapor. The energy required to vaporize the water, therefore, is not released as heat.

80
Q

what is Lignocellulosic biomass mainly composed of?

A

plant cell walls, with the structural carbohydrates (cellulose and hemicellulose) and heterogeneous phenolic polymer lignin as its primary components

81
Q

what is the approximate content of lignocellulosic biomass?

A

in agricultural residue, 40% cellulose, 30% hemicellulose and 15% lignin on a dry weight basis.

82
Q

what are the key stages of the conventional biochemical conversion process?

A

1- pre-treatment,
2- Enzymatic Hydrolysis & fermentation,
3- Separation

83
Q

what is the preliminary size of biomass after reduction by mechanical means? (for pretreatment)

A

Preliminary size reduction to 10-30 mm

84
Q

in pretreatment (biochemical conversion) what is the advantage of the reduction of biomass size?

A

The smaller the size, the more efficient mass and heat transfer for subsequent pretreatment and enzymatic hydrolysis.

85
Q

what is the role of pretreatment in biochemical conversion?

A

It helps in the deconstruction of Lignin carbohydrate complexes (LCCs) for efficient enzymatic hydrolysis of cellulose

86
Q

what are the types of pretreatment technologies?

A

1- physical pretreatment,
2- chemical pretreatment,
3- solvent fractionation and,
4- biological decomposition

87
Q

what would an ideal pretreatment process be like?

A

it should maximize sugar yield from cellulose and hemicelluloses, and in the meantime minimize energy consumption and environmental impact

88
Q

what are the characteristics of physical pretreatment?

A
  • Mechanical size reduction of biomass by either chipping, grinding or refining.
  • Increase of surface area of biomass.
  • Decrease in the degree of polymerization (DP) and crystallinity of cellulose.
  • No use of chemicals
  • High power consumption in reducing the size of biomass from millimeters to micrometers
89
Q

what are the types of physical pretreatment?

A

1- Using Steam Explosion (SE)

2- Using liquid hot water (LHWE)

90
Q

Describe Steam Explosion (SE) process?

A
  • It involves heating the feedstock at elevated temperature (160 to 260°C) and pressure (0.69–4.83
    Mpa) for a short duration (a few minutes), followed by depressurizing the system to disrupt the structure of LCCs.
  • It is tested at pilot scales worldwide due to its simple process design, low capital investment and less impact on the environment. Batch and continuous processes exist.
91
Q

Describe Liquid hot water (LHWE) process?

A

It involves the pre-heating of slurry with a heat exchanger. It is further heated by steam via another heat exchanger and passes through the reactor for pretreatment. It is pH-dependent (pH 5-7 preferable)

92
Q

what is the disadvantage of Liquid hot water (LHWE) process?

A

When pH drops below 4, the formation of inhibitor- furfural and hydroxymethylfurfural from xylose and glucose respectively takes place.

93
Q

what is the commonly used chemical in chemical pretreatment?

A

Sulfuric acid with concentration < 2%.

94
Q

what are the operating conditions of chemical pretreatment?

A

Deconstruction of LCCs under less severe conditions, either lower temperature or shorter reaction time

95
Q

what are the disadvantages of chemical pretreatment?

A

1- The treatment process not economical when a high concentration of acid is used as acid recovery is difficult
2- the need for acid-resistance stainless steel equipment or coating to avoid corrosion

96
Q

Describe Solvent fractionation of biomass?

A
  • This is the use of either organic or aqueous organic solvent with or without catalysts to deconstruct LCCs
  • Examples of solvents that can be used are Methanol, ethanol, ethylene glycol, triethylene glycol, tetrahydrofurfuryl alcohol, glycerol, n-butanol, acetone, phenol etc
97
Q

what is the advantage of Solvent fractionation?

A

Pure and low-molecular-weight lignin can be recovered as a by-product

98
Q

what are the disadvantages of Solvent fractionation?

A

1- high cost of organic solvents.
2- intensive energy consumption associated with solvent recovery.
3- difficulty in the treatment of concentrated black liquors left after solvents are evaporated and loss of sugar in the liquor.

99
Q

is the use of ionic liquid for dissolving cellulose from biomass and deconstruct the crystalline
structure of cellulose molecules for enzymatic hydrolysis applicable?

A

No, it is still under study.

100
Q

describe biological decomposition of biomass?

A

It is the use of microorganisms to breakdown lignocellulosic biomass under mild conditions without
special requirements for equipment. Both bacteria and fungi can be used

101
Q

what is the Predominant species used for the breakdown of the biomass in biological decomposition?
(in case of producing biofuel)

A

rot fungi (white-rot fungi) that is assiociated with wood decay.

102
Q

what are the advantages of biological decomposition?

A

1- Energy-saving.
2- Environmentally friendly.
3- No chemicals or expensive equipment.

103
Q

what are the disadvantages of biological decomposition?

A

1- Extremely low degradation rate, requires as long as weeks for significant change in the structure of biomass.
2- Significant biomass loss during the process.
3- Control of microbial growth and metabolism is unreliable.
(and that’s why biological pretreatment is not attractive from a commercial standpoint)

104
Q

what happens in enzymatic hydrolysis & fermentation?

A

further depolymerization of cellulose to yield glucose

105
Q

which enzyme is used to breakdown cellulose into glucose?

A

Cellulase enzyme

106
Q

what are the two constraints making been a bottleneck in the commercial production of bioethanol?

A

1- the heterogeneous characteristics of the enzymatic hydrolysis which significantly compromise the reaction rate and increases the enzyme dosage.
2- expensive due to the difficulty of their fermentation production

107
Q

what are the strategies that have been developed for cellulose hydrolysis and ethanol fermentation?

A

1- Separate hydrolysis and Co-fermentation (SHF).
2- Simultaneous saccharification and Co-fermentation (SSF).
3- Simultaneous saccharification, filtration and fermentation (SSFF).

108
Q

what are the operating conditions of separate hydrolysis and co-fermentation (SHF)

A

1- The process is under varying bioconversion conditions.
2- Optimum temperature for hydrolysis is 50°C and
35°C for ethanol fermentation

109
Q

what are the drawbacks of separate hydrolysis and co-fermentation (SHF)?

A

Accumulation of glucose produced during
saccharification inhibit cellulase enzyme (ᵦ-
glucosidase component that catalyse hydrolysis of
cellobiose to glucose)

110
Q

Describe Simultaneous saccharification and Co-fermentation (SSF)?

A
  • Glucose produced is rapidly converted to ethanol by yeast.
  • Continuous removal of inhibitors from the reaction.
  • Higher production rates.
  • One bioreactor used for the process
111
Q

what is the drawback of simultaneous saccharification and co-fermentation (SSF)?

A

Unable to recover the fermenting organism as it is usually mixed with biomass

112
Q

Describe Simultaneous sacharification, filtration and

fermentation (SSFF)?

A
  • An integrated design for both SHF and SSF
  • Able to mitigate drawbacks experienced from SHF and SSF
  • Enzyme and fermenting organisms can be used at different optimal conditions.
  • Possible to reuse the fermenting organism several times.
  • Use membranes to separate hydrolysis and fermentation
113
Q

Describe separation?

A
  • This is the purification stage and has to do with a distillation process. In this stage, bioethanol is separated from water and lignin.
  • Different distillation technologies have been developed in order to improve both energy and separation efficiencies.
114
Q

What are the distillation technologies available?

A 
1- Cyclic distillation
2- Dividing- wall column distillation
3- High-gravity distillation
4- Internal heat-integrated distillation
5- Membrane distillation
6- Reactive distillation
115
Q

Describe Cyclic distillation?

A

Technology different from the conventional distillation concept of continuous counter-current contact of vapor and liquid phases flowing simultaneously

  • Operation mode is based on different phases (liquid and gas) movement in column.
  • Operation is achieved by controlled cycling or by stage switching.
  • Can allow for higher feed rates to be processed
  • It has lower energy input
116
Q

what does controlled cycling consist of?

A

It consists of a repeating sequence of a vapor-flow period (VFP), followed by a liquid-flow period (LFP).
In VFP, the thrust of the rising vapor prevents liquid downflow while for LFP, period when the liquid flows down the column (dropping by gravity).

117
Q

Describe dividing-wall column distillation

A
  • A thermally coupled column integrated into a single shell.
  • Capable of separating mixtures of three or more
    components into high purity products.
118
Q

what are the advantages of dividing-wall column distillation?

A

1- High thermodynamic efficiency due to
reduced remixing effects.
2- 25 – 40% lower energy requirements.
3- High purities for all product streams.
4- lower maintenance costs,
5- 40% smaller footprint and 20% less piping.
6- Up to 30% lower investment costs due to the reduced number of equipment units

119
Q

Describe High-gravity distillation (Higee)?

A
  • In this process, a device is a rotating packed bed instead of the conventional vertical column arrangement and separation is based on varying/different boiling points of components.
  • Higee uses centrifugal force to create artificial gravity.
  • By increasing the rotational velocity of the device, it is possible to generate a mean acceleration as high as 200 times the earth’s acceleration of 9.8 m/s2.
  • Small size or footprint and low weight.
120
Q

in High-gravity distillation, what does the increased acceleration result in?

A

1- Higher flooding velocities → accommodating greater liquid and gas rates.
2- Thinner liquid films and smaller bubble sizes → lower resistance to mass transfer and increasing the mass transfer flux

121
Q

Describe Internal heat-integrated distillation?

A
  • This is a heat-pump-assisted distillation column.
  • It has two sections in the column; rectifying section (operates at a higher pressure and serves as a heat source, stripping section (serve as a heat sink).
    • Can achieve energy savings up to 70% compared to conventional distillation columns
122
Q

Describe Membrane distillation?

A
  • This is a thermally-driven separation process and allows for only vapor molecules to pass
    through the hydrophobic membrane.
  • The vapor pressure gradient that allows for separation is caused by a difference in temperature
    across the membrane.
  • It occurs at low operating temperatures.
  • It is a cost-effective process, which requires less demand for membrane characteristics.
  • It is also applicable for desalination of brackish water and sea water
123
Q

Describe Reactive distillation?

A
  • Both reaction and distillation take place in the same piece of equipment.
  • Reactants are converted to products and simultaneously separated.
  • The setup may consist of multiple catalyst systems, gas, and liquid traffic over the catalyst, separation, mass flow and enthalpy exchange. All in one system.
  • Better conversion and selectivity.
  • Less waste and byproducts.
  • Typically more than 40–50% savings in capital and operating costs

Biorefineries (2 decks)

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