UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015

CPT-II

UNIT 2 : Pulp and Paper Products

SYLLABUS

Unit no and name Major Learning Outcomes Topics and Sub-topics

(in cognitive domain)

2a. Explain pulp and paper 2.1. Fundamentals of Pulp and

paper

2b. Distinguish methods of 2.2. Methods of pulp production

pulp production

2
Pulp and Paper 2c. Describe various steps of
Products pulp production 2.3. Sulphate (Kraft) pulp
process

2d. Draw flow diagram explain 2.4. Manufacturing of paper

manufacturing of paper using using Fourdrinier machine
Fourdrinier machine

2e. Identify major engineering 2.5. Paper manufacturing

problems of paper
manufacturing

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 1
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

2.1. Fundamentals of Pulp and Paper

 PULP
 Pulp is commercial cellulose derived from bamboo, wood, baggase, fibre
crops or waste paper by mechanical or chemical methods.
 Pulp is one of the most abundant raw materials worldwide.
 A pulp mill is a manufacturing facility that converts wood chips or other
plant fibre source into thick fibreboard which can be shipped to a paper mill
for further processing.
 Pulp can be manufactured using mechanical, semi-chemical or fully
chemical methods (Kraft and sulphite processes).
 The finished product may be either bleached or non-bleached, depending
on the customer requirements.
 Wood and other plant materials used to make pulp contain three main
components (apart from water):

No Components Properties
1 Cellulose fibers Desired for papermaking

2 Lignin Three-dimensional polymer that binds the

cellulose fibres together

3 Hemicelluloses Shorter branched carbohydrate polymers

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 2
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

 The aim of pulping is to break down the bulk structure of the fibre source,
be it chips, stems or other plant parts, into the constituent fibres.
 Chemical pulping achieves this by degrading the lignin and hemicelluloses
into small, water-soluble molecules which can be washed away from the
cellulose fibres without depolymerising the cellulose fibres.
 The various mechanical pulping methods, such as ground wood (GW) and
refiner mechanical (RMP) pulping, physically tear the cellulose fibres one
from another. Much of the lignin remains adhering to the fibres.
 Strength is impaired because the fibres may be cut.
 There are a number of related hybrid pulping methods that use a
combination of chemical and thermal treatment to begin an abbreviated
chemical pulping process, followed immediately by a mechanical treatment
to separate the fibres.
 These hybrid methods include thermo-mechanical pulping, also known as
TMP, and chemi thermo-mechanical pulping, also known as CTMP.
 The chemical and thermal treatments reduce the amount of energy
subsequently required by the mechanical treatment, and also reduce the
amount of strength loss suffered by the fibres.

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 3
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

 PAPER
 Paper is defined as matted or felted sheets of fibres, usually cellulosic
and generally formed on a fine wire screen from a water suspension.
 Paper are classified by use requirements or by characteristics of the
paper.
 Examples are
1. Wrapping paper:-bag paper, grease-proof paper
2. Tissue paper:-cigarette, carbon, toilet, towel, napkin papers
3. Book papers:-coated or uncoated, lithograph offset, textbook
papers
4. Writing papers;-bond weight, linen papers
5. Ground wood printing papers:- catalogue, newsprint, tablet,
poster, wall papers
6. Paper board:- heavier, less flexible, laminated paper stock.

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 4
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

2.2. Methods of Pulp Production

 Commercial processes are generally classified as mechanical, chemical, or semi

chemical pulping methods.

1.Mechanical Pulping

 The earliest and one of the most common mechanical pulping methods is
the ground wood process, in which a ground wood bolt is pressed
lengthwise against a rough, revolving grinding stone.
 The wood fibers are torn out of the wood, abraded, and removed from the
stone surface with water.
 A different process, called refiner mechanical pulp (RMP) utilizes chips,
which are shredded into fibers between large rotating disks of a device
called a refiner.
 The basic RMP process has evolved to employ thermal and/or chemical pre-
softening of the chips, which reduces energy use and modifies resultant
pulp properties; this is typically termed thermo-mechanical pulp (TMP).
 Mechanical pulping has the advantage of converting up to 95% of the dry
weight of the wood input into pulp, but the mechanical action requires a
large energy input.
 The pulp forms a highly opaque paper with good printing properties, but
the paper is relatively weak and discolours easily with exposure to light.
 Newsprint is a major product of mechanical pulp.

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 5
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

 Mechanical pulps are generally produced from long-fibered softwood

(conifer) species.
 The smaller, thinner fibers from hardwoods are more severely damaged by
the mechanical action, hence yield a weaker paper.
 However, some hardwoods, such as poplar, which produces very bright
pulp, are mechanically pulped and blended with softwood mechanical pulps
to improve optical properties.

2. Chemical Pulping

 In chemical pulping, the fibers in wood are separated by dissolving away

the lignin component, leaving behind a fiber that retains most of its
cellulose and some hemi-cellulose.
 Yields of chemical processes are on the order of 40 to 50% of the dry
weight of the original wood input. Kraft (Sulfate) Process.
 Because of advantages in chemical recovery and pulp strength, the kraft
process dominates the industry.
 It represents 91% of chemical pulping and 75% of all pulp (Appendix 2,
Section G).
 It evolved from an earlier soda process (using only sodium hydroxide as the
active chemical) and adds sodium sulfide to the cooking chemical
formulation.
 This is the process associated with the foul odour problem in the
environment.

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 6
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

 A number of pulp grades are commonly produced, and the yield depends
on the grade of product.
 Unbleached pulp grades, characterized by a dark brown colour, are
generally used for packaging products and are cooked to a higher yield and
retain more of the original lignin. Bleached pulp grades are made into white
papers.
 Nearly half of the kraft production is in bleached grades, which have the
lowest yields.
 Effective alkali and sulfidity refer to conditions of certain key chemical
aspects of the process.

3. Semi Chemical Pulping

 A number of processes are hybrids of chemical and mechanical methods

and have intermediate yields.
 Generally, chips are partly softened or digested with chemicals and then
are mechanically converted to fiber, usually in disk refiners.
 Chemi-mechanical pulping, typically used on hardwoods, softens chips prior
to usual mechanical action and has yields in the 80 to 90% range.
 Semi-chemical pulping involves greater cooking and delignification prior to
mechanical refining.
 Yields are somewhat lower, depending on the degree of cooking.

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 7
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

2.3. Sulphate (Kraft) Pulp Process

 Most popularly used process.

 This is an alkaline process.
 Na2SO4 is added to the cooking liquor. So its common name is sulfate
process.
 The presence of sodium sulfide makes bleaching of pulp easier and the
paper produced has better strength.

 Raw Materials
 Bamboo or Wood.
 Lime make-up (NaOH)
 Salt cake (Na2SO4) make -up
 Sulfur Na2S
 Steam

 Chemical Reactions Involved

(i) Digestion (hydrolysis and solubilization of lignin)

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 8
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

R-R’ + NaOH→ R”COONa + ROH

R-R’ + Na2S → Mercaptans

(ii) Chemical recovery from black liquor

(a) Smelting

2NaR + air →Na2CO3 + CO2

(lignin)

Na2SO4 + 2C →Na2S + 2CO2

(from R) (white liquor)

(b) Causticizing

Na2CO3 (aq) + Ca(OH)2 (s) → 2NaOH (aq) + CaCO3 (s)

(green liquor) (white liquor)

CaCO3→CaO + CO2

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 9
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

CaO + H2O→Ca(OH)2

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LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 10
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

 Process Description

(a)Chipper bin:-

 Chips are fed in this device.

 Cut logs are conveyed to the chipper where rotary disks with heavy knives
reduce the wood to size 2-5cm flat chips.

 Size reduction is done to maximize penetration of process chemicals.

(b) Digester tower:-

 Continuous digester tower is 25 – 30m tall.

 Chips are preheated with volatilizing turpentine and non-condensable

gases.

 For controlling digestion temperature, cooking liquor is withdrawn as side

streams and circulated through heat exchanger.

 Digestion is done to free lignin and other non-cellulosic content.

 Cooking time is about one and a half hours at 170°C.

 To avoid mechanical weakening of fibres, digested chips are cooled with

recycled black liquor.

 Temperature is maintained at 140-180°C and pressure at about 10 atm.

 Bottom temperature is maintained at 65°C .

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 11
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

(c) Blow down valve:-

 This valve reduces the pressure of the stream from 80atm to 1atm before
entering blow tank.

(d) Blow tank:-

 When hot pulp slurry is passed to the blow tank, heat is recovered in the
form of steam.

 The chips are preheated with this recovered steam.

 The blow tank has high concentration of pulp and low concentration of
water.

(e) Screens:-

 Pulp is screened so as to remove wood knots and undigested residues.

(f) Series of filters

 Pulp is filtered to separate black liquor for chemical recovery plant.

 Black liquor is also recycled back to digester for cooling the digested chips.

 Hot water is added to second filter for better filtration.

 Bleaching of pulp
 To produce white paper, the pulp is bleached.
 The chemicals used to bleach pulp must be environment friendly.
 Bleaching with chlorine produces dioxins and other undesirable products.
 So, nowadays pulp is bleached with hydrogen peroxide, ozone, chlorine
dioxide, oxygen etc.

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 12
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

 The objective of bleaching is to remove small fractions of lignin that

remains after digestion.
2.4. Manufacturing of Paper Using Fourdrinier Machine

 Paper is a sheet material made of fibers which are held together by

hydrogen bonds.
 In wet process, fiber suspension in water is made and it is then made into
sheet and dried.
 Paper making process is generally done on Fourdrinier machine.

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 13
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

2.4.1 Raw Materials

 Paper pulp; ground wood, bleached and unbleached sulphite and sulphate,
semi chemical pulp.
 Reuse pulp
 Miscellaneous cellulose pulp;- straw, linen, cotton and rags
 Speciality pulp :- inorganic fibres like asbestoses and glass.
 Water
 Non fibrous raw materials for filling, sizing and coating purpose like:-clay,
talk, titanium dioxide, zinc sulphide, calcium carbonate, alum, rosin, glue,
waxes, casein, glycerol, dyestuff etc.
2.4.2 Functional Role of Various Units

(a) Beater

 Beater mechanically disintegrates the pulp fibers to make paper stronger,

uniform, dense, opaque etc.

 It consists of metal blades attached with rotating drum.

 Finely ground fillers (to increase brightness, flexibility, softness and

weight) and coloringagents are also added.

(b) Jordan

 It is a conical refiner or Jordan engine.

 Metal bars and stones are set inside.

 Here, pulp is deformed, defibered and dispersed.

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 14
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

(c) Web forming

 99.5% water fiber slurry are made to run on an endless belt at a speed of
50m/min to 500m/min.

 Pulp fibers are arranged into web.

 Water is drained out by gravity.

 Shaking motion is provided for better interlocking of fibers on mat.

 White water is collected and it is reused to conserve water and additives

and to avoid pollution.

(d) Pressing

 Free water is removed by pressing with pressure roll, water mark roll and
suction roll.

 Water content is reduced to 60-65% water.

(e) Drying

 Additional water is removed by smoothing rolls and series of steam-

heated metal drying rolls.

 Water is reduced from 60-65% to 5-6%.

(f) Finishing

 Here paper is passed through a series of calendaring rolls for producing

smooth paper.

 It is wounded on a large winding roll.

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 15
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

2.5 Major Engineering Problems of Paper Manufacturing

 The major engineering problems faced by paper manufacturing
industries in India are given below.
1. Shortage of fibrous raw materials
 There is lack of forest resources in India.
 So it require long-range planning for development of improved bamboo
harvesting, utilisation of bagasse, eucalyptus and reed grass.
 It also requires more effective collection and reuse of waste paper.
2. High price and shortage of chemicals
 Shortage of sulphur, salt cake (Na2SO4) and chlorine with high prices
place the Indian paper industries at a great disadvantage in attempting
to export paper products.
3. Procurement of plant and equipment
 Pulping equipment is relatively simple and is being built in India but
paper making machinery is quite elaborate and expensive.
4. Sizing of paper requires modification.
5. Modification in paper machines
 Some modifications are required in paper machines to improve
properties of paper like tensile strength.

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 16
 UNIT 2 PULP AND PAPER PRODUCTS 07 MARKS 2015
CPT-II

ASSIGNMENTS
1. Define Pulp and List out methods of Pulp production and explain any one
in brief. 04 Marks
2. Define Paper and Write down raw materials for Paper manufacturing.
03 Marks

3. Write Short Note On Bleaching Of Pulp .

07 Marks
4. Discuss three methods of pulp production. 07 Marks
5. Explain Kraft process for Pulp manufacturing with its chemical reaction and
neat flow diagram. 07 Marks
6. Differentiate sulfite and sulfate pulp process. 07 Marks
7. Describe Fourdrinier Machine method for paper making with neat flow
diagram. 07 Marks
8. List Out Major Engineering Problems Face By Paper Industries And
Explain Its. 07 Marks

VIKASSINGH B CHAUHAN
LECTURER IN CHEMICAL ENGINERING
KJ POLYTECHNIC BHARUCH Page 17