Emissions and Controls

7/28/2019 Emissions and Controls

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Introduction

Cellulose acetate is a man-made substance that is derived from the naturally occurring

organic compound - cellulose. Cellulose is the main structural ingredient of plants, and is usually

considered to be the most common organic compound on Earth. Cellulose acetate is manufactured

out of wood pulp by a purification process. It is a renewable and biodegradable substance, providing

a cheap source of quality fibre that can be used in many manufacturing processes. Commercial

production of this compound is usually performed by treating cellulose in the form of wood pulp

with various chemicals. Cellulose is most abundant material and is the key building block for most

plants. The chemical structure is composed of repeating segments of anhydro glucose units.

Global Industry Analysts, Inc (GIA) announces the release of a comprehensive global

report on Cellulose Acetate markets. Increasing demand from filter tow sector represents the

major factor driving cellulose acetate market growth. Additionally, increase in the smoking

population in regions such as Eastern and Central Europe, India, China and Latin America is

being attributed as a major factor steering growth of tow consumption in these regions, which

is directly propelling the cellulose acetate market.Cellulose acetate is a mature product and

has experienced a decline in volumes in practically all major world areas except China,

Central Europe and Russia during the last several years. New polymers and textiles with

enhanced properties have eroded textile fiber applications formerly held by cellulose acetate.

It is estimated that the global market will grow at 1 to 2% per year to reach 840,000 to

850,000 tonnes by 2015.

Applications

In general cellulose acetate has excellent properties. They are moulded and extruded

into various consumer products such as brush handles, tool handles, toys, steering wheels,

and a range of miscellaneous products. Cellulose acetates are used in lacquers and protective

coatings for various substances such as paper, glass, metal, leather and wood. Cellulose


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acetate films are commonly used in photographic and cinematographic films as well as X-ray

films, microfilms and graphical films. Special castings of cellulose acetate films widely used

for water purification, blood purification dialysis, air separation and for a wide Varity of

biotechnology applications like separation of proteins, enzymes and various bio molecules.

In addition to its importance as a synthetic fiber, particularly for use in the clothing

industry, cellulose acetate has a number of other applications. These include magnetic

computer tape, absorbent surgical dressings, and some types of adhesives.

Cellulose acetate manufacturing process

Commercial production of cellulose acetate mainly involves in three stages. They are

activation, acetalyation and hydrolysis.

Activation

Cellulose pulp containing 4 to 7 (wt %) of moisture was mixed with equal parts of

water or preferably glacial acetic acid to swell the pores of the fibers and thereby enhance

mass transfer for the subsequent reaction steps. Investigation by previous researchers cotton

pulp showed that activated pulp is acetylated far more quickly compared with non-activated

pulp.

Acetylation


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Activated pulp reacts with acetic anhydride with glacial acetic acid as solvent and a

concentrated sulfuric acid (7-10 % based on cellulose) acting as a catalyst.

Acetate groups easily substitute the sulfoester groups. The reaction is carried in exothermic

reaction, the temperature controlled at 40 - 45 C and to form a product as cellulose tri-

acetate. The acid catalyzed hydrolysis of the tri-acetate to an average degree of substation of

2.4 acetyl group per glucose unit. The cellulose tri-acetate contains approximately 2.9-3

acetyl groups per glucose unit. The rate of the reaction as well as the extent of cellulose

degradation is dependent on the amount of acid and the reaction temperature.

Hydrolysis

Cellulose tri-acetate, the product from the previous reaction, was partially hydrolyzed, which

consumes the excess anhydride to obtain cellulose acetate.


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Raw material requirements

Raw material used for manufacturing cellulose acetate are cellulose (pulp

(C6H10O5)n), Sulfuric Acid (H2SO4), acetic anhydride ((CH3CO)2O) and acetic acid

(C2H4O2)

Table 1.1 Physical properties of the raw materials

Property Cellulose Sulphuric acid Acetic

anhydride

Acetic acid

Density (gr/cm3) 1.5 1.77 1.082 1.06

Viscousity (centi poise) - 26.7 - 1.2

Molecular wt(kg ) 162 98.08 102 60

Melting point (c) decomposes 10.5 -73.1 17

Boiling point(c) - 280 139.8 119


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Raw materials for manufacture of cellulose acetate, capacity 60,5000 metric tons/year. An

considering 300 days of production per day requirement of raw materials are defied

according to the defined problem.

Cellulose: The production of high quality cellulose acetate requires that special attention be

paid to the selection of key raw material. The cellulose bases generally consist of highly

purified cotton linters with an alpha-cellulose content of above 99% and celluloses from

wood pulp which contain between 90

97% alpha-cellulose.

Acetic acid is generally used as a pretreatment reagent, which for some processes can

contain small amounts of sulfuric acid to further improve the diffusion of the acetylating

reagents. It is believed that the pretreatment process causes a partial swelling of the cellulose

by splitting the hydrogen bonds so that the acetylating reagents can enter the fibers more

rapidly.

The recovery of the incurred large amounts of acetic acid is a decisive factor for the

profitability of a process.

Recovery of Acetic Acid. Depending on the process, 2 6 parts of 15 25 % dilute acetic

acid per part of cellulose accumulate. They must be reprocessed to glacial acetic acid and

acetic acid anhydride.

Emissions and Controls

Air pollutant emissions from cellulose acetate production include solvents, additives, and other

organic compounds used in fiber processing. In the production of all cellulose acetate, i. e., tow,staple, or filament yarn, solvent emissions occur during dissolving of the acetate flakes, blending and


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filtering of the dope, spinning of the fiber, processing of the fiber after spinning, and the solvent

recovery process. The largest emissions of solvent occur during spinning and processing of the fiber.

Filament yarns are typically not dried as thoroughly in the spinning cell as are tow or staple yarns.

Consequently, they contain larger amounts of residual solvent, which evaporates into the spinning

room air where the filaments are wound and into the room air where the wound yarn is

ubsequently transferred to beams. This residual solvent continues to evaporate for several days until

an equilibrium is attained. The largest

emissions occur during the spinning of the fiber and the evaporation of the residual solvent from the

wound and beamed filaments.

VOC control techniques are primarily carbon adsorbers and scrubbers. They are used to

control and recover solvent emissions from process gas streams from the spin cells in both the

production of cigarette filter tow and filament yarn. Carbon adsorbers also are used to control and

recover solvent emissions from the dryers used in the production of cigarette filter tow. The solvent

recovery efficiencies of these recovery systems range from 92 to 95 percent. Fugitive emissions from

other post-spinning operations, even though they are a major source, are generally not controlled.

In

at least one instance however, an air management system is being used in which the air from thedope

preparation and beaming areas is combined at carefully controlled rates with the spinning room air

that

is used to provide the quench air for the spin cell. A fixed amount of spinning room air is then

combined with the process gas stream from the spin cell and this mix is vented to the recovery

system.

It is at present not possible to obtain the doubly substituted form of cellulose

directly via the acetylation phase due to the nature of the solid-liquid reaction. A higher

water content helps to minimize the degradation of cellulose.

0.55 0.55 H = -3.3kJ/g water

2 3

CTA + H OCDA + CH COOH D


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The reaction is terminated by the addition of magnesium, calcium or sodium acetate.

Emissions and Controls

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