Viscous rayon production from 1000 kg of poplar wood

1. Md Hafizur Rahman
Student ID#0890587
Department of Chemical Engineering,
Lakehead University, Thunder Bay.
Email: mrahma19@lakeheadu.ca
Course Supervisor:
Prof. Dr. Sudip Rakshit, P Eng
Bioenergy and Biorefining Process, [ENGI-5651-FA]
7 April, 2020
Design Assignment: Viscous rayon production from
1000 Kg of poplar wood

2. Md Hafizur Rahman | Term paper on Bioenergy and Biorefining Process
Dissolving pulp manufacturing process from poplar wood
Introduction:
Dissolving pulp is a high-grade cellulose pulp, with low contents of hemicellulose, lignin, and
resin. There are two mainly dissolving pulping processes named Acid Sulfite (AC) and
prehydrolysis kraft pulping (PHK) and here prehydrolysis kraft pulping has been chosen because
of getting high purity cellulose content dissolving pulp that is required for viscous rayon
processing
Dissolving pulp manufacturing process description:
Mechanical Cursing Unit, U-100: Combination of chipping, grinding, and/or milling to reduce
cellulose crystallinity Size usually 10-30 mm after chipping and 0.2-2 mm after milling or
grinding. Vibratory ball milling more effective than ordinary ball milling in reducing cellulose
crystallinity of spruce and aspen chips and in improving their digestibility.
Prehydrolysis Unit, V-101:
Prehydrolysis was carried out in heated stainless-steel digester of rotating at 1 rpm. Prehydrolysis
was carried out with addition of 0.25 % mineral acid (HCl)2
at 140 C hot water. The wood and
hot water ratio was maintained 1:5 mass ratio. The time required for this this process is about 60
minutes. Effluent from prehydrolysis process remain high amount of reducing sugar.
Kraft Cooking Unit, V-102:
Kraft pulping is a full chemical pulping method using sodium hydroxide (NaOH) and sodium
sulfide (Na2S) at pH above 12, at 160-180°C (320-356°F), corresponding to about 800 kPa (120
psi) steam pressure, for 0.5-3 hours to dissolve much of the lignin of wood fibers. The rate of
delignification approximately doubles for an increase in reaction temperature of 8°C if other
process parameter remains constant. Biomass: liquid ratio is maintained 1:4 (w/v).
Bleaching Process Unit, V-103:
Hydrogen peroxide is the most widely used oxidative bleaching agent in (chemi) mechanical
pulp bleaching. The per-hydroxyl anion, HOO-, is generally accepted as the active bleaching
species in alkaline hydrogen peroxide systems. The anion is in equilibrium with undissociated
hydrogen peroxide and the addition of alkali (usually sodium hydroxide) forces the equilibrium
towards the anionic form. The normal ranges of operating conditions are peroxide application: 1
– 5% (w/w); pH range: 10.5 – 11.2; temperature: 45 -85 C; retention time: 30-120 minutes;
consistency: 4 – 35% 3
.

3. Md Hafizur Rahman | Term paper on Bioenergy and Biorefining Process
Drying Unit, V-104: By using heat energy/natural air drying and dissolving pulp was dried
before storing it for sale or further processing.
Mass Balance over dissolving pulping process: Reference attached process flow diagram
(PFD-1) and all calculation dry basis.
Poplar wood biomass compositing: Cellulose 50% Hemicelluloses 30 % Lignin 20% or less1
Overall mass balance over stream (1) and (14),
Yield1
30.0.05% , So B14 = 1000 X 0.3005= 300.5 Kg
Cellulose mass balance:
1000 X 0.50=Cout + 300 X 0.9627, Cout = 211.19 Kg.
211.19 Kg of cellulose goes through different unit’s outlet and washing. Assuming that, from
stream (2) 5 Kg, stream (5) 112 Kg, stream (8) 75 Kg and steam (11) 19.19 Kg.
Hemicellulose mass balance:
1000 X 0.30 = Hout + 300.5 X 0.0355 , Hout= 289.33 Kg.
289.33 Kg of Hemicellulose is going out through the different outlet but more from
prehydrolysis unit (V-101), So assuming that, from stream (2) 3 Kg, stream (5) 270 Kg, stream
(8) 10 Kg and steam (11) 6 Kg.
Lignin and other mass balance:
1000 X 0.20 = Lout + 300 X 0.0018 , So Lout = 199.46 Kg ~ 200 Kg.
200 Kg of Lignin will be out from different unit’s outlet stream but more from Kraft cooking (V-
102), So assuming that, from stream (2) 2 Kg, stream (5) 20 Kg, stream (8) 166 Kg and steam
(11) 12 Kg.
Individual Unit mass balance & required chemical calculation:
U-101, Mechanical cursing unit: say .1% biomass loss during processing from this unit.
So, B3 = 1000 X 0.99 = 990 kg.

4. Md Hafizur Rahman | Term paper on Bioenergy and Biorefining Process
V-101, Prehydrolysis unit: From steam (3) and (4), HCl is required = .0025 X 990 X 5= 12.37
Kg of 100% HCl , (Assuming the all the chemical washed out after unit operation)
Biomass balance, B3 = B6 + (112 + 270 + 20) , So, B6 = 588 Kg.
V-102, Kraft cooking unit, NaOH is required = 0.16 X 588 = 94 Kg
Na2S is required = 0.2 X 588= 117.6 Kg
Biomass balance, B6 = B9 + (75 + 10 + 166), So B9 = 337 Kg
V-103, Bleaching unit, Say 2.5 % H2O2 of Biomass used ,
So, Hydrogen peroxide is required =.025 X 337, H2O2 = 8.42 Kg.
Biomass balance: B9 = B12 + (19.19+ 6+12), B12 = 300 Kg.
V-104, drying Unit, here only water removing and as our calculation is dry basis so,
B12 = B14, => B14 = 300 Kg of Dissolving Pulp from 1000 Kg of poplar wood
------------------------------------------------------------------------------------------------------

5. Md Hafizur Rahman | Term paper on Bioenergy and Biorefining Process
Viscous rayon manufacturing process
Introduction:
There are various processes developed for regenerated cellulose fiber production, but my design
topic viscose rayon is manufactured process. Viscose Rayon are more like natural cellulosic
fibers, such as lint or cotton, than those of thermoplastic, petroleum- based synthetic fibers such
as Nylon, Polyester etc.
Viscous rayon manufacturing process description: In viscous rayon production facility
involves with dissolving pulp as feed stock. Dissolving pulp content higher brightness and more
uniform molecular weight distributions with >90 % α-cellulose polymer. Cellulose pulp is solid,
and reaction required more time to take place. So here every step is considered as batch process.
Viscous rayon manufacturing process overviews are described here. (Reference PFD)
1) Steeping process, V-201:
The wood pulp sheets are treated with 17-20% aqueous caustic soda at a temperature 18-
25°C. The high DP cellulose (1000) is converted into soda cellulose. These celluloses are
allowed to soak until they become dark brown in color. This takes about 1-4 hours. The
excess caustic soda solution is drained off and sheets are pressed out by a hydraulic press to
squeeze out excess caustic soda solution called pressing fluid
2) Shredding, V-202:
The pressed soda cellulose is shredded mechanically to yield finely divided, fluffy particles
called "crumbs". This step provides increased surface area of the soda cellulose. Within 2-3
hours this soda cellulose become fine crumbs
3) Aging, V-203:
The soda cellulose is aged under controlled conditions of time and temperature (between 18
and 30°C) for 48 hours in order to depolymerize the cellulose to the desired degree of
polymerization to obtain almost ideal solution of cellulose. In this step, the average

6. Md Hafizur Rahman | Term paper on Bioenergy and Biorefining Process
molecular weight of the original pulp is reduced by a factor of 2-3 and DP is decreased from
800 to about 350.
4) Xanthation, V-204:
After ageing, the crumbs of soda cellulose are transferred to rotating, airtight, hexagonal
drum called “Churner”. Carbon disulphide about 10% of the weight of the crumbs is added
to the churner for 3 hours by rotating the mixers at a slow speed of 2 [rpm] to get sodium
cellulose xanthate.
5) Dissolving, V-205:
Sodium cellulose xanthate is in the form of small balls. This falls into a mixer called
dissolver which is provided with a stirrer for 4-5 hours. In this step dilute caustic soda added
to get viscous concentration 6.5% caustic soda and 7.5% cellulose. Cellulose xanthate
dissolves to give clear brown thick liquor, like honey
6) Ripening, V-206:
Viscose solution requires blending, ripening and filtration to give a solution having best
spinning qualities. This step is carried by storing the viscose solution for 4-5 days at 10-
18°C.
7) Spinning process, U-207:
The viscose solution is forced through a spinnerette, having many fine holes (0.05-0.1mm)
diameter. The spinnerette is submerged into a solution containing the chemicals (sulphuric
acid (8- 10%), Sodium sulphate (16-24%), Zinc Sulphate (1-2%), Glucose 2% and balanced
water) called coagulation bath and bath temperature is maintained 40-45 C
Washing step, U-208 involves washing out all chemical adhering with viscous filament and
this filament is run through the Drying unit, U-209 to get moisture off. Finally, the filament
is winding up for sale.

7. Md Hafizur Rahman | Term paper on Bioenergy and Biorefining Process
Chemical Reactions: [Reference: PFD-2]
Unit Reactants Products
V-201: [C6H10O5]n + nNaOH → [C6H9O4-ONa]n + nH2O
Cellulose Caustic Soda Soda Cellulose
V-204: [C6H9O4-ONa]n + nCS2 → [C6H9O4-OCS2Na]n
Soda Cellulose Sod. Cellulose Xanthate
U-207: [C6H9O4-OCS2Na]n + ½ H2SO4 → [C6H10O5]n + CS2 + ½ Na2SO4
Sod. Cellulose Xanthate Viscose Rayon
Materials Balance: Reference of PFD-2.
Basis: 100 kg of dissolving pulp from PHK of poplar wood
Dissolving pulp cellulose’s reactivity2
is 70%. Cellulose is polymer of long chain glucose
unit. Cellulose average molecular weight is called anhydroglucose unit (AGU) and it is 162
g/mol.
100 Kg of dissolving pulp say, 70% reactivity, Need NaOH = = 51.85 Kg
Say 20 % of NaOH solution, 207. Kg of H2O and 51.85 Kg of NaOH. So, 260 Kg of 20%
NaOH solution.
V-201, Steeping unit,
Total mass balance, 100 Kg Cellulose + 260 Kg 20% NaOH solution = 360 Kg,
Reference-6 : 100 Kg of pulp gives 310 Kg Na-Cellulose moist.
So, pressing fluid= 360-310= 50 Kg, assuming pressing fluid have same 20% NaOH
solution.
So stream (2) 50 Kg pressing fluid have 10 Kg NaOH and 40 Kg H2O.
Stream (4) fluid 310 Kg Na-Cellulose having 100 Kg pulp, 210 of 20% NaOH solution (42
Kg NaOH and 168 Kg H2O).
V-202, V-203 Shredding and Aging unit, no chemical adding only mechanical mixing,

8. Md Hafizur Rahman | Term paper on Bioenergy and Biorefining Process
Stream (5) and steam (6) 310 Kg Na-Cellulose moist (crump) (100 pulp, 42 Kg NaOH and
168 Kg H2O).
V-204, Xanthation unit, CS2 adding through the steam (7), 10 % of Na-Cellulose (crumbs) ,
So mass of carbon disulfide = 310 X 0.1= 31 Kg.
So, Stream (8) sodium cellulose xanthate solution of 310 Kg.
V-205, Dissolution unit (Viscous gel preparation unit): Mass balance
Stream (8): 100 Kg pulp, 42 Kg
NaOH, 168 Kg H2O, 31 Kg Na2S
Cellulose mass balance: Stream
(10) will be 6.5 % NaOH and
cellulose 7.5% 6
100/(341+X+Y) = 0.075 ….. (i)
NaOH mass balance:
(Y + 42)/(341+Y+X) = 0.065……(ii)
By solving equation (i) and (ii) get X= 947 Kg H2O and Y= 44.5 Kg of NaOH
So stream (9) total solution weight, M = 991 Kg and solution is 4.5 % of NaOH solution.
So total viscous solution mass, Z = (991+341) = 1332 Kg.
V-206, Ripping unit: no chemical adding only mechanical separation like filtration.
U-207, Spinning unit where sodium cellulose xanthate reacted with H2SO4 and form
regenerated cellulose and NaSO4 .

9. Md Hafizur Rahman | Term paper on Bioenergy and Biorefining Process
From stream (14) to washing unit, U-208 and from U-208 to Drying unit (U-209) regenerated
cellulose, nothing changes. After Drying unit viscous filament remain 10-13 % moisture. As
per reaction if no loss produced viscous rayon will be same amount of dissolving pulp used
on dry basis.
But here if we consider 10 % moisture and 5% loss during different unit washing.
Then final produced viscous rayon = 100 Kg X 1.05 = 105 Kg of 10% moisture.
1000 Kg of poplar wood produced = 300 kg of dissolving pulp.
So from 1000 Kg of poplar wood viscous rayon = 105 X (300/100) = 315 Kg of viscous
rayon of 10 % moisture.
Constrain, energy input, cost analysis/ comparison of cost of relative cost of fossil fuel
or natural fiber (cotton) :
i) Poplar biomass cost USD 25 to 60 per dry ton but transportation cost USD 75 to 90
per dry ton. So, biomass collection cost affects a lot
ii) Other than chemical consumption there is huge amount of water used in pulping
process and this water contaminate with chemical and biomass extractive- need extra
efforts/ cost for wastewater treatment.
iii) Starting from mechanical comminution to final drying unit of pulping process
consumed more energy (2908 KW hour/ton pulp production)
iv) Viscous rayon processing using carbon disulfide toxic chemical in unit V-204 and
finally produced from unit U-207 is prohibited by environmental and this chemical
severely impact on nature.
v) There is no enough data like equipment’s sizing with capital cost and from there
depreciation value, working capital, labor cost etc. and for that real costing is not
possible within this time frame but it is a future opportunity.
vi) Price10
of cotton fiber yarn USD 4/ Kg and viscous rayon yarn USD 2.04/Kg but
viscous rayon has similar comfort properties like cotton fiber. On the other hand,
fossil feedstock of polyester price around USD 2 /Kg but textile comfortless very less
than viscous.

10. Md Hafizur Rahman | Term paper on Bioenergy and Biorefining Process
Reference
[1] František Kačík et al, (2012),” Chemical Profiles of Wood Components of Poplar Clones
for Their Energy Utilization”, energies
[2] Hüeyin KIRCI et al, (2002), “Production of Dissolving Grade Pulp from Poplar Wood by
Ethanol-Water Process”, TÜBİTAK
[3] https://www.pulpandpapercanada.com/pulping-bleaching-1000143592/
[4] Dongfeng Li et al, (2012), “Production of Dissolving Grade Pulps from Wood and Non-
Wood Paper-Grade Pulps by Enzymatic and Chemical Pretreatments”, ACS
[5] https://textilelearner.blogspot.com/2013/06/viscose-rayon-manufacturing-process.html
[6] http://textilelibrary.weebly.com/viscose-rayon-mfg-process.html
[7] František Kačík et al, (2012),” Chemical Profiles of Wood Components of Poplar Clones
for Their Energy Utilization”, energies
[8] Hüeyin KIRCI et al, (2002), “Production of Dissolving Grade Pulp from Poplar Wood by
Ethanol-Water Process”, TÜBİTAK
[9] https://www.pulpandpapercanada.com/pulping-bleaching-1000143592/
[10] https://www.yarnsandfibers.com/?s=rayon%2Bprices

11. V-101
PROCESS FLOW DIAGRAM OF DISSOLVING
PULP PRODUCTION FROM POPLAR WOOD
Lakehead University
Department of Chemical Engineering
STREAM NO->
Cellulose Kg
Lignin Kg
Hemicellulose Kg
HCl Kg
NaOH Kg
Na2S Kg
H2O2 Kg
-1-
500.00
200.00
300.00
-
-
-
-
-2-
5.00
2.00
3.00
-
-
-
-
-3-
495.00
198.00
297.00
-
-
-
-
-4-
-
-
-
12.37
-
-
-
-5-
112.00
20.00
270.00
12.37
-
-
-
-6-
383.00
178.00
27.00
-
-
-
-
-7-
-
-
-
-
94.00
117.6
-
-8-
75.00
166.00
10.00
-
94.00
117.6
-
-9-
308.00
12.00
17.00
-
-
-
-
-10-
-
-
-
-
-
-
8.42
-11-
19.19
12.00
6.00
-
-
-
8.42
-12-
288.81
0.19
11.00
-
-
-
-
-13-
-
-
-
-
-
-
-
-14-
288.81
0.19
11.00
-
-
-
-
BASIS (DRY): 1 TON (1000 KG) OF POPLAR WOOD FEED (STREAM-1)
Drawn by Md Hafizur Rahman,Student Number# 0890589, mrahma19@lakeheadu.ca
V-102 V-103 V-104
pretreatment
Kraft
cooking Bleaching
Poplar
woodhandling
(Chipping, grinding, milling)
Drying
U-100
Biomass supply
U-100
Mechanical
crushing unit
3
4
5 8
6 9
7
12
13
14
Mineral Acid Kraft Chemical Bleaching Chem.
V-101
Prehydrolysis
unit
V-101
Kraft cooking
unit
2
1
10
11
[170° C, pH>12]
0.25% HCl Active alkali:16% NaOH,
Sulphidity: 20% Na2S,
[140° C, pH=2]
Dissolving
pulp
[45-85° C, pH 10-11]
Peroxide (H2O2)3
: 1 – 5% (w/w)
1000 Kg (dry basis) of
poplar wood biomass
Cellulose 50%
Hemicelluloses 30 %
Lignin 20% or less1
V-103
Pulp bleaching
unit
V-104
Pulp drying
unit
1
14
1
František Kačík et al, (2012),” Chemical Profiles of Wood Components of Poplar Clones for Their Energy Utilization”, energies
2
Hüeyin KIRCI et al, (2002), “Production of Dissolving Grade Pulp from Poplar Wood by Ethanol-Water Process”, TÜBİTAK
3
https://www.pulpandpapercanada.com/pulping-bleaching-1000143592/
300 Kg (dry basis) dissv.
pulp (Yield 30.05%)
Cellulose 96.27%
Hemicelluloses 3.55 %
Lignin and other 0.18%2
10 Kg
-5 Kg Cellulose
-3 Kg Hemicellulose
-2 kg Lignin
404.47 Kg
-112 Kg Cellulose
-270 Kg Hemicelluloses
-20 kg Lignin
-12.37 Kg HCl
462.6 Kg
-75 Kg Cellulose
-10 Kg Hemicelluloses
-166 Kg Lignin
-94.0 Kg NaOH
-117.6 Kg Na2S
45.61 Kg
-19.19 Kg Cellulose
-6 Kg Hemicelluloses
-12 Kg Lignin
-8.42 Kg H2O2
PFD-1

12. PROCESS FLOW DIAGRAM OF VISCOUS
PRODUCTON FROM DISSOLVING PULP
Lakehead University
Department of Chemical Engineering
Drawn by Md Hafizur Rahman, Student Number# 0890587, mrahma19@lakeheadu.ca
Date : 7-April-2020
Shredding Aging
(Depolymerisation)
Xanthation
Steeping
(Alkali cellulose) Dissolution
Dissolving pulp
V-201
Steeping Vessel
4
3
5 6
7
8 10
NaOH solution
CS2 Feeding
U-210
Winding unit
V-205
Dissolution
Vessel
1
Drying
Neutralization,
purificatoin,
finishig
Winding
Blending,
ripening, filteration,
deareation
Viscous Rayon 18 16 13
14 Washing fluid
Coagulation Bath12
V-201
11
2
NaOH Solution 9
H2SO4-8-10%
Na2SO4-16-24%
ZnSO4-1-2%
Glucose 2%
Balanced H2O
1517
V-202 V-203 V-204 V-205
V-206U-207U-208U-209U-210
17-20% aq solution
[18- 25°C, 1-4 hours] [18- 30° C, 48 hours] [20 - 30°C, 3 hours]
V-202
Shredding Vessel
U-209
Drying unit
V-202
Aging Vessel
U-208
Washing unit
V-202
Xanthation Vessel
U-208
Wet spinning
unit
V-206
Gel preparation
unit
Spinning
(wet)
[40 - 50°C]
10% of the weight of
Soda cellulose (crumbs)
991 Kg soln
4.5 % aq solution
947 Kg H2O
44.5 Kg NaOH
Note# 1 :100 kg of pulp [1] gives about 310 kg of [4] moist soda cellulose
Source-2: https://textilelearner.blogspot.com/2013/06/viscose-rayon-manufacturing-process.html
Source 1: http://textilelibrary.weebly.com/viscose-rayon-mfg-process.html
4-5 days at 10-18°C
100 Kg (dry basis)
dissolving pulp
Cellulose 96.27%
Hemicelluloses 3.55 %
Lignin and other 0.18%
260 Kg of 20% NaOH Sol
51.85 Kg NaOH
207.4 Kg of H2O
50 Kg of 20% NaOH Sol
-10 Kg NaOH
-20 Kg of H2O
1332Kg Viscous gel
1115 Kg H2O
86.5 Kg NaOH
7.5 % Cellulose
6.5 % NaOH
105 Kg Viscous rayon
of 10% moisture
[ 2-3 hours] [4-5 hours]
PFD-2