1. 1
CHAPTER II
Introduction
Sodium carboxymethyl cellulose (Na‐CMC or only CMC) is water soluble cellulose ether which permits
the preparation of water solutions with a viscosity which may vary between a few mPa‐sec and several
thousand mPa‐sec.
CMC has the following formula:
Fig. 1: Structure of carboxymethyl cellulose (Biswal
and Singh, 2004)
CMC is produced by reaction of monochloroacetic‐acid (MCA) (abt. 70% solution in ethanol) with alkali‐
cellulose which is obtained by processing cellulose with a solution of caustic soda in water (min. 45%).
Alkalization of the cellulose and etherification of alkali‐cellulose with MCA take place in the presence of
an indifferent organic solvent (ethanol) which is soluble in water.
Since operation started in 2001 until mid of 2006, HKS plant found some operational problems, whether
caused by operational processes as well as changes in market conditions that led to the limited
production capacity and low ability to reduce production costs which ultimately lead to loss of market
competitiveness.
Humpus carboxymethyl Cellulose plant operated in semi batch has an installed capacity of 15 T/D for
Technical grade and 4 T/D for other line is Purified grade.
2. 2
2.1 PROCESS DESCRIPTION
The entire CMC‐plant consists of the following process groups:
Tank farm
Here, all the liquid raw materials introduced into the process are stored and prepared. Likewise the
dosing is effected from here according to the respective formula.
Cellulose preparation
Here, the cellulose raw‐material, delivered in sheets, is ground, stored and dosed.
Production line for technical CMC
a) Reaction and stripping unit
b) Drying unit
c) Milling and screening unit
d) Blending unit
e) Weighing and packing unit
Production line for purified CMC
a) Reaction unit
b) Washing and extraction unit
c) Alcohol stripping and recovery unit
d) Drying unit
e) Milling and screening unit
f) Blending unit
g) Weighing and packing unit
Utilities
Here, the supply of steam, cooling water (32 °C), chilled water (5 °C), compressed air and process water
are prepared and kept ready for operation of the production of CMC.
3. 3
Rectification and purification of the entire diluted and polluted ethanol from the above‐mentioned
process lines
2.1.1 Tank Farm
The concentrated ethyl‐alcohol, needed for the reaction is delivered by a tank‐truck and filled by
pump P‐1.08 into storage tank B‐1.04. If required, the alcohol temperature may be reduced by spray
cooling. The used water of this spray cooling is collected in tank B‐7.01 and delivered by pump P‐7.01
back to cooling tower W‐7.01.
The required amount of alcohol for every reactor‐batch is delivered by pump P‐1.05 via heat‐
exchanger W‐1.01 to the respective reactor R‐3.01 for technical CMC or R‐4.01 for purified CMC.
Prerequisite for this dosing of alcohol to one of the reactors is the correct adjustment of the
temperature. As long as the temperature is too high, the piping route for the alcohol remains in reflux
operation back to tank B‐1.04. As soon as the adjusted temperature value is reached, the piping route
for dosage of alcohol into the reactors is automatically released.
The amount of alcohol needed for the reaction is controlled fully automatically by a computerized
system according to the recipe needed for the required type of CMC.
The concentrated alcohol needed for the preparation of the MCA‐solution in tank R‐1.01 is affected by
means of pump P‐1.04.
Diluted Ethyl‐Alcohol
The diluted and purified ethyl‐alcohol with a concentration of approx. 75 %, received from the
rectification unit after heat‐exchanger W‐5.05, is collected in tank B‐1.05.
For the first production of this diluted washing alcohol, concentrated alcohol from tank B‐1.04 via pump
P‐1.05 and process‐water are delivered to tank B‐1.05.
The batch‐wise required amount of diluted alcohol to the slurry‐tanks R‐4.02 and R‐4.03 is delivered to
these slurry‐tanks by pump P‐1.06 after passing heat‐exchanger W‐1.02 for temperature adjustment.
5. 5
This operational group is designed for purified linters and for wood‐pulp produced in form of sheets.
For CMC production it is necessary to grind the cellulose mainly to make it powdery. Only in that
form, the cellulose can be used to produce CMC of very high quality.
The wood pulp sheets are fed manually to belt‐conveyor H‐2.01 with integrated metal detector H‐
2.01.1. As metal parts are hazardous and may cause dust‐explosions in the cellulose mills, the motor of
the belt is stopped automatically if any metal is detected.
From the belt‐conveyor H‐2.01 the cellulose sheets are fed to the pre‐cutter Z‐2.01 where the sheets
are cut in order to get a free flowing product which can be transported pneumatically and which can
easily be dosed to the fine‐grinding mills Z‐2.02 and Z‐2.03.
The precut cellulose is transported pneumatically by ventilator V‐2.01 via pressure‐release vessel A‐
2.01 (safety installation) to filter‐cyclone F‐2.01 where all the cellulose (including the dust) is separated
and falling via cell‐feeder X‐2.01 into the intermediate storage bunker B‐2.01 which is used as head
container for the subsequent fine grinding mills Z‐2.02 and Z‐2.03.
The filter‐tubes of the filter‐cyclone F‐2.01 are cleaned automatically by pulsed air jet.
The filtered transport air passes ventex‐valve A‐2.04 (safety installation) and is discharged by ventilator
V‐2.01 through the roof of the building.
The intermediate bunker B‐2.01 is equipped with a distribution device B‐2.01.1 for precut cellulose so
that the filling level of the integrated discharge screw‐conveyors H‐2.02 and H‐2.03 is always kept in
optimum position.
By these screw‐conveyors H‐2.02 and H‐2.03 the cellulose is dosed via magnet cascades A.2.02 and A‐
2.03 to the subsequent fine‐grinding mills Z‐2.02 and Z‐2.03. Here the cellulose is powderized to an
optimal particle size for the reactivity in the reactors R‐3.01 and R‐4.01.
In order to minimize the hazard risk of thermal depolymerization of the cellulose by the released
grinding energy, the mills Z‐2.02 and Z‐2.03 are cooled by cold water.
The fine‐ground cellulose is transported pneumatically by ventilator V‐2.02 via pressure‐release vessel
A‐2.05 (safety installation) to cyclone F‐2.02 where most of the cellulose is separated from the
transport‐air and falls via cell‐feeder X‐2.02 into the dosing bunker B‐2.02.
8. 8
For viscosity adjustment an exact quantity of hydrogen peroxide solution from tank B‐9.02 may be
added to reactor R‐3.01. By application of H2O2 of course only a decrease of the degree of
polymerization or viscosity, respectively is possible.
f) Dosing of MCA‐solution
According to the recipe the required quantity is dosed by pump P‐1.02 to the reactor R‐3.01.
Precondition is that the jacket cooling of the reactor is running with cooling water. Depending on the
required grade ∙of technical CMC more alcohol has to be added to change from a paste process to a
slurry process in order to ensure a homogeneous etherification during the next process step.
g) Etherification
For an optimum and homogeneous etherification the temperature of the reaction mixture should be
within the range of 65‐75 °C. So, when all the required MCA‐solution is dosed, the reactor R‐3.01 is
heated with steam via injector P‐6.03 and hot water circulation pump P‐6.02.
The chopper mills have to be switched on during this etherification process. They are accelerating the
mixing process and also producing energy which is needed for the etherification.
When the etherification temperature is reached, the etherification time is running. Depending on the
required grade of technical CMC between 60 and 90 minutes are needed.
At the end of the etherification time a sample has to be taken in order to test whether the reaction has
been completed and the pH of the final reaction mixture is within the correct range.
For pH adjustment it is possible to dose an exact quantity of acetic‐acid from tank B‐9.03 to the reactor
R‐3.01.
h) Recovery of alcohol
When all chemical reactions have been completed, the alcohol needed for the control of the process
conditions for the alkalization and the etherification has to be recovered.
This is done in two steps.
9. 9
Valve 3126 HVK is switched over from reflux to reactor R‐3.01 to alcohol condensate collecting
vessel B‐9.01,
Heating of the jacket of reactor R‐3.01 with hot water and steam,
Application of a controlled vacuum on reactor R‐3.01 by vacuum pump V‐3.01,
Cooling of condensers W‐3.01 and W‐3.02 with chilled water (5 °C), collecting diluted alcohol in
vessel B‐9.01.
The chopper mills have to be switched on during this recovery process. They are accelerating the mixing
process and also producing energy which is needed for the recovery.
After a certain time, a sample has to be taken in order to check the final alcohol moisture and to decide
whether to switch over to the next process step.
The above mentioned second step is described in the next process step.
i) Stripping
As an evaporation of all the alcohol absorbed and adsorbed by the technical CMC fibers is not possible
by the combination of vacuum and heat, a stripping of the technical CMC with life steam is necessary in
order to reduce the alcohol content, adhered to the technical CMC to a value below 0.1 %.
Valve 3126 HVK should remain in direction to alcohol condensate collecting vessel B‐9.01,
Heating of the jacket of reactor R‐3.01 with hot water and steam,
Application of a controlled vacuum of 700 to 800 mbar to the reactor R‐3.01 by vacuum pump
V‐3.01,
Cooling of condensers W‐3.01 and W‐3.02 with cooling water (32°C), collecting diluted alcohol in
vessel B‐9.01.
The chopper mills have to be switched on during this stripping process. They are accelerating the mixing
process and also producing energy which is needed for the stripping.
After a certain time, a sample has to be taken in order to check the final alcohol moisture and to decide
whether to switch over to the next process step.
The final water moisture content should be within the range of 40 to 50 %.
j) Cooling of reactor
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d) Dosing of soda‐lye
When the required vacuum in reactor R‐4.01 is reached and the temperature of the alcohol/cellulose
mixture is below l5 °C, the required quantity of soda‐lye from tank B‐1.02 via pump P‐1.03 is dosed to
the reactor. For an optimum and homogeneous activation of the cellulose the temperature of the
alkalization mixture should not be too high. So, if the temperature reaches l8 °C, the dosing of soda‐lye
is stopped automatically and only started again when the temperature is below l5 °C.
e) Alkalization
When all the required soda‐lye is dosed, the alkalization time is running. Depending on the required
grade of purified CMC, between 60 and 90 minutes are needed.
For viscosity adjustment an exact quantity of hydrogen peroxide solution from tank B‐9.02 may be
added to reactor R‐4.01. By application of H2O2 of course only a decrease of the degree of
polymerization or viscosity, respectively is possible.
f) Dosing of MCA‐solution
According to the recipe the required quantity is dosed by pump P‐1.02 to the reactor R‐4.01.
Precondition is that the jacket cooling of the reactor is running with cooling water. Depending on the
required grade of purified CMC more alcohol has to be added to change from a paste process to a slurry
process in order to ensure a homogeneous etherification during the next process step.
g) Etherification
For an optimum and homogeneous etherification the temperature of the reaction mixture should be
within the range of 65 – 75 °C. So, when all the required MCA‐solution is dosed, the reactor R‐4.01 is
heated with steam via injector P‐6.05 and hot water circulation pump P‐6.04.
The chopper mills have to be switched on during this etherification process. They are accelerating the
mixing process and also producing energy which is needed for the etherification.
When the etherification temperature is reached the etherification time is running. Depending on the
required grade of purified CMC between 60 and 90 minutes are needed.
15. 15
At the end of the etherification time, a sample has to be taken in order to test whether the reaction has
been completed and the pH of the final reaction mixture is within the correct range.
For pH adjustment it is possible to dose an exact quantity of acetic‐acid from tank B‐9.03 to the reactor
R‐4.01.
h) Cooling of reactor R‐4.01
When all chemical reactions have been completed, the reactor R‐4.01, including the crude CMC batch, is
cooled down with cooling water of approximately 32 °C, and afterwards with chilled water of
approximately 5 °C in order to prepare the next batch.
i) Discharge of the crude CMC batch for purification
When the cooling process is finished and in order to prepare the reactor for a next batch the complete
contents of crude CMC is discharged via discharge flaps 4148/4149 HVK into one of the slurry
tanks R‐4.02 or R‐4.03 of the washing process group.
2.1.8 Washing Unit for Purified CMC
As soon as all reaction steps are completed, the crude mixture of CMC and alcohol, received directly
from the reactor R‐4.01, is discharged via slurry distributor A‐4.06 into one of the slurry‐tanks R‐4.02 or
R‐4.03.
Here the CMC is suspended in diluted alcohol from tank B‐1.05 or, in order to minimize the alcohol
consumption, in the spent alcohol from belt filter F‐4.02 (see P & I diagram 42041147/2). By means of
intensive stirring with agitator R‐4.02.1 or R‐4.03.1 the by‐products as sodium‐chloride and sodium‐
glycolate are dissolved.
After a short residence time this suspension is conveyed by means of a special slurry‐pump P‐4.02 to the
continuously, pressure enclosed and under inert‐gas (nitrogen) working belt filter F‐4.02. Here the CMC
is washed in counter‐current flow with diluted alcohol in several washing sections.
The belt filter F‐4.02 is working principally as following:
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The sealing liquid for all pumps P‐4.05 to P‐4.13 is water which is stored in tank B‐4.12 and transported
by pump P‐4.03 via heat exchanger W‐4.10 to the above‐mentioned pumps P‐4.05 to P‐4.13.
The final area of belt‐filter F‐4.02 is foreseen for mechanical drying of the CMC cake by means of
vacuum‐pump V.4.03.
As soon as the purified CMC cake has been mechanically dried it is disintegrated by double paddle mixer
X‐4.01 in order to get a free flowing powdery material and afterwards this purified CMC is dosed via cell
feeder X‐4.02 into the next processing step, the alcohol recovery.
2.1.9 Alcohol Recovery Unit – Stripping Process
For removing and recovering of the alcoholic residual moisture, adhering to the CMC after the washing
unit, the CMC is treated with live‐steam under vacuum in an alcohol stripper R‐4.04. Hereby the alcohol
adhered to the CMC is removed and exchanged against water.
The alcohol‐wet purified CMC from belt‐filter F‐4.02 is dosed via cell‐feeder X‐4.02 into the stripper R‐
4.04. Here the purified CMC mass is treated with life steam under constant mixing. The mixing tools are
designed in such a way that they are additionally provided with a transport function to the discharge
area of the stripper R‐4.04.
The alcohol and water vapors are sucked ‐off the stripper by vacuum pump V‐4.02, passing the filter F‐
4.03 where CMC fines are separated and are condensed in heat exchanger W‐4.06.
A controlled vacuum of 700 to 800 mbar is adjusted in the stripper R‐4.04.
The double jacket of the stripper R‐4.04 is heated with steam via injector P‐6.07 and hot water
circulation pump P‐6.06.
The condenser W‐4.06 is cooled with cooling water (30 °C).
The diluted alcohol of approximately 60 %, discharged from the condenser W‐4.06, is flowing to the
collecting vessel B‐9.01.
The alcohol content, adhered to the purified CMC after the stripping process, must have a value below
0.1 %.
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At the end of the stripping process the now only water‐wet purified CMC is discharged via a cell
feeder X‐4.07 into the next process step, the drying unit.
2.1.10 Drying of Purified CMC
After the stripping process the purified CMC contains a considerable amount of moisture. With this
water content the possible fields of application for the purified CMC are rather limited.
Drying of purified CMC is done continuously in three steps, with hot air, with warm air and with cold air.
From cell feeder X‐4.07 the water wet purified CMC of approx. 40 % moisture is falling by gravity into
the dryer T‐4.01.
The water‐moisture content of the purified CMC has to be reduced to a value of about 8 %.
The dryer is a so‐called vibrational transport, fluidized bed dryer. This means the complete dryer is
vibrating and the powdery material is transported by this vibrational action through the dryer.
In the first section of the dryer T‐4.01 the material is equalized in order to get a plane surface.
Hot air with approx. 150 °C temperature is introduced via filter F‐4.04, ventilator V‐4.04 and air‐heater
W‐4.08 into the first drying section of the dryer.
Warm air with approximately 100 °C temperature is introduced via filter F‐4.05, ventilator V‐4.05, and
air‐heater W‐4.09 into the second and third drying section of the dryer.
Ambient air is introduced via filter F‐4.06 and ventilator V‐4.06 into the last section of the dryer.
The feed of cold (ambient) air has the following reason:
As the subsequent process after the drying is the milling, and as this milling process of purified CMC
generates energy which increases the temperature of the product, the purified CMC has to be cooled
down before entering the mill in order not to exceed a temperature of approximately 80 °C. Otherwise,
with temperatures higher than 80 °C, the product is depolymerized and you will lose of viscosity of the
final bagged product. Also the color may change to a more yellowish product.
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The distillation column K‐5.01 is heated with live steam from steam generator D‐6.01.
The salt‐containing diluted alcohol from tank B‐5.01 is delivered by means of pump P‐5.04 to the
condenser (dephlegmator) W‐5.01 on the top of the distillation column K‐5.01. Here the diluted
alcohol becomes preheated by the alcohol vapors from the column K‐5.01.
The preheated, diluted alcohol is passing either plate heat exchanger W‐5.02 or W‐5.07 where this
alcohol is heated up to nearly the boiling point temperature using waste water (approx. 103 °C) from the
sump of the column K‐5.01. The flow of this sump water is effected by pump P‐5.01 and the level of the
sump Is controlled. The waste water is going to the waste water treatment unit.
The reason for the installation of two plate heat exchangers W‐5.02 and W‐5.07 is based on the fact that
if one is blocked and has to be cleaned, a second one is available so that the production must not be
stopped.
The heated diluted alcohol is fed to the distillation column K‐5.01. Depending on the concentration of
this alcohol you can choose three different trays of the column K‐5.01 for feeding this alcohol, tray
No. 23, 25 or 27.
The alcohol vapors from distillation column K‐5.01 are preheating the diluted alcohol (from tank B‐
5.01) in condenser W‐5.01 (as mentioned above) and afterwards becoming condensed in condenser W‐
5.03 and in the additional condenser W‐5.04.
The concentrated alcohol condensate is collected in tank B‐5.02. The level of this tank is controlled.
By means of pump P‐5.02 the concentrated alcohol is conveyed via a three way valve either back to the
top of the distillation column K‐5.01, depending the temperature of the alcohol vapors at the top of the
column (reflux of the alcohol), or via heat exchanger W‐5.05 to tank B‐1.01 for concentrated alcohol in
the tank farm.
The purified, diluted alcohol of approximately 75 % by weight is discharged through three possible side
outlets (trays) of the distillation column K‐5.01, tray No. 21, 23, or 25, depending on the concentration
needed.
This diluted alcohol is conveyed by pump P‐5.03 via heat exchanger W‐5.06 to tank B‐1.05 for diluted
alcohol in the tank farm.
23. 23
Process water must be prepared ready for consumption and all valves to all consumers of
compressed air in the plant must be opened.
Steam
The steam generator including the water preparation system D‐6.01 has to be started.
The condensate collector B‐6.01 and the condenser W‐6.01 have to be put ready for operation.
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Production capacity per batch depends on capacity of reactor R‐3.01 and R‐4.01, beside also the
performance of the unit and other equipment such as utilities are very important, ie; cooling water, chill
water, boiler or steam regeneration, compress air, and so on.
Highest production capacity during operation achieved in November 2003 was 2.6 T/D for purified and
4.5 T/D for Technical grades, while average production during 2001 to 2006 reach 1.4 T/D and 2.1 T/D
for each grades such as Purified and Technical.
Figure 1. Block Diagram Humpuss Carboxymethyl Cellulose Plant
