Sulphite Pulping

Question 1

How do you measure residual lignin?

Answer 1

Kappa number, this is use of potassium permanganate. You can calculate how much of this is consumed by lignin in the pulp

Question 2

How is the sulphite cooking acid/base produced?

Answer 2

SO2 gas is bubbled into water to form sulphourous acid (H2SO3). This is then neutralised by the addition of a base either calcium/sodium/magnesium. and this will form the corresponding bisphulphite or sulphite

Question 3

Explain lignin reactions in sulfite pulping.

Answer 3

lignin broken down through sulphonation and hydrolysis reactions. Sulphonation makes the lignin more hydrophilic and hydrolysis breaks lignin bonds so new smaller more dissolvable fragments can be formed.
SO2 in water gives sulfurous acid which further dissociates into bislfuate ions (HSO3-) these attack alpha carbon in lignin and make the molecule soluble.
The acidic conditions promote the cleavage of ether bonds.
SULPHONATION AND HYDROLYSIS

Question 4

How does temperature affect delignification in slufite pulping?

Answer 4

Increaes lignin dissolution but also increases carbohydrate decomposition. Need balance

Question 5

Explain how carbohydrates react during sulphite pulping

Answer 5

Glyosidic bonds are cleaved which results in depolymerisation and therefore deterioration in strength. This happens easier with hemicellulose as it has more of an amorphour structure - this why we see more hemicellulose removed compared to cellulose

Question 6

what are the advantages and disadvantages of using calcium as a sulfite pulping base

Answer 6

• complex SO2 absorption
• High scaling tendency
• no base or SO2 recovery possible
  + good availability

Question 7

what are the advantages and disadvantages of using sodium as a sulfite pulping base

Answer 7

+ simple SO2 absorption
+ entire pH range
+ Slowest pulping rate
- complex but base and SO2 recovered

Question 8

what are the advantages and disadvantages of using ammonium as a sulfite pulping base

Answer 8

+ simple SO2 absorption
+entire pH range
+low scaling
- no base recovery

Question 9

what are the advantages and disadvantages of using magnesium as a sulfite pulping base

Answer 9

+relatively simple SO2 absorption
+intermediate pulping rate
+moderate scaling
+ simple recovery of chemicals base and SO2.
-can be expensive

Question 10

What is the advantage of using magnesium as a base during sulphite pulping rather than calcium

Answer 10

Simple SO2 absorption, less scaling, and it is simple to recovery both the base and the SO2, this is not possible with calcium

Question 11

which base is used in a bisulphite pulping process?

Answer 11

Magnesium

Question 12

Which base is used in acid sulphite pulping process?

Answer 12

Calcium

Question 13

what is the effect of wood chip quality of sulphite pulps

Answer 13

Reduction in strength properties. When comparing damaged chips witj undamaged chips there is a clear reduction in both tear and tensile.

Question 14

what by-products do you obtain from sulphite spent liquors?

Answer 14

hexoses and pentoses which can have commercial chemical and fuel uses, or if they are fermented they can be used for animal food and yeast production.
Can also produce ligno sulphonic acids which can be used as dispersion agents

Question 15

Recovery of sulfite cooking chemicals

Answer 15

Oxidation of organic substances (carbohydrate derivatives)
[CH2O]n + O2 → CO2 + H2O
Oxidation of magnesium components
Mg[CH2O]n + O2 → MgO + CO2 + H2O
Slurry preparation of ash (MgO) in water:
MgO + H2O → Mg(OH)2
Oxidation of sulfurous components (Lignosulfonate derivatives)
S[CH2O]n + 5/2 O2 → SO2 + CO2 + H2O
Preparation of cooking chemicals
Mg(OH)2 + 2 SO2 → Mg(HSO3 )2

Question 16

What is the effect of wood chip quality on the strength properties of sulfite pulps?

Answer 16

Reduction in strength properties. When comparing damaged chips with undamaged chips there is a clear reduction in both tear and tensile.

Question 17

State the advantages and disadvantages of the different sulfite processes when using calcium, magnesium, sodium or ammonium as the base.

Answer 17

Calcium – complex SO2 absorption. – High scaling. – difficult liquor incineration with no base or SO2 recovery
Magnesium + simple SO2 absorption. Moderate scaling. + simple chemical recovery and incineration
¬Sodium + simple SO2 absoprtion. + low scaling – complex incineration + base and SO2 recovery. + low scaling. – Slowest pulping rate
Ammonium + simple SO2 absorption. + fastest rate of pulping. + low scaling. +simple incineration. – No base recovery

Question 18

What kind of byproducts do you obtain from black liquor and how do you use them commercially (Sulphite)?

Answer 18

hexoses and pentoses which can have commercial chemical and fuel uses, or if they are fermented they can be used for animal food and yeast production.
Can also produce ligno sulphonic acids which can be used as dispersion agents