Pulp and Paper

• Cellulose

  • main structural polysaccharide of the plant cell wall
  • comprises at least 50% of wood and 90% of cotton
• Paper

  • made from fibrous material (e.g. wood pulp, rags, straw)
  • usually in thin, flat sheets
  • for writing, printing, drawing, wrapping objects, etc.
  • main and well-known stationery material
• History

  1. 9000 BC - Clay Tablets
  2. 2500 - 2000 BC - Cyperus papyrus, the plant source for the papyrus
  3. 105 - Papermaking in China
  4. Late 14th Century - Rag Paper
  5. 1440 - Printing Press (inventor: Johannes Gutenberg)
  6. 1799 - Fourdrinier Machine
  7. 1851 - Soda Pulping Process
  8. 1857 - Sulfite Pulping Process
  9. 1884 - Kraft (Sulfate) Process
  10. 1909 - Karft comes to United States
• Pulp Processing

  • Chemical
  • Semi-Chemical
  • Mechanical/Thermomechanical
• PULP PROCESSING

  Raw Material

  • wood fibers (main raw mat)
  • *Coniferous (soft) wood is preferred than deciduous (hard)   wood because of longer fiber strands
  • Bark cannot be used: not fibrous enough; unbleachable
  • However, bark can be recovered and converted into a cork-like   material rags (now largely supplanted)
  • cotton and linen (now largely supplanted)
  • other applicable fibrous material
• PULP PROCESSING

  Pulping

  • conversion of wood (or other fibrous material) into mass of liberated fibers
  • aim is to release lignin to obtain the cellulosic fiber from wood
• Chemical Pulping

  Kraft (Sulfate) Process

  • comes from the German word kraft: strong2SO4 and NaOH to pulp wood
  • German chemist Carl F. Dahl in the State of Danzig (now Gdańsk, Poland), ca. 1884
  • uses Na2S, NaOH, Na2CO3 to pulp wood
  • can produce odoriferous chemicals during liquor cooking
  • mostly employs coniferous wood as the raw material
  • black (spent) liquor recovery is an essential factor of the Kraft Process
  • Contains 65-68% of the total chemicals removed during cooking of the liquor
• Chemical Pulping Soda Process

  • uses either Na2CO3 or Na2SO4 in cooking the liquor
  • uses NaOH and Na2CO3 instead of Na2CO3 and Ca(OH)2 in the dissolving liquor
  • did not last too long; largely supplanted by the Kraft Process in the early 20th century
  • used a strong solution  12%  𝑣𝑣⁄𝑣𝑣  of NaOH and Na2CO3, but had very low yields
  • worked well only with deciduous (hard) wood
• Sulfite Process


  Similar to the Kraft Process, but uses different chemicals in cooking the liquor
• Chemicals used


  • Sulfurous acid (H2SO3) instead of caustic (NaOH) solutions
  • Bisulfites (HSO3-) of Na, Mg, Ca, or Al to buffer the cooking liquor
• HPHT (high-pressure, high-temperature) process


  Used in the Sulfite Process
• Raw materials


  • Spruce as the most common
  • Can also use hemlock and balsam
• Waste product


  Waste sulfite liquor
• No industry wide solution has been employed for the recovery of waste sulfite liquor
• Only Mg-based waste liquor is being opted for recovery
• Different manufacturing plants have their own ways to dispose or store waste sulfite liquor
• Kraft Process

  Woodyard section

  • debarking and cutting of logs to specified lengths
  • chipping of wood at pre-selected sizes
  • Wood chippers usually have at least four (4) heavy knives
  • screening of chipped wood
• Kraft Process

  Pulp Processing Section

  • chipped wood enters a Continuous Digester and pre-steamed: 100 kilopascals
  • goes to the high-impregnation zone of the Digester and comes into contact with the cooking (white) liquor: 2-5 hours, 170-176°C, 660-925 kPa
  • Na2SO4 added to the white liquor, which was composed of Ca(OH)2 and NaOH created through causticization
  • solution fed to a blow tank: steam recovery

  RESULTING LIQUOR: BLACK LIQUOR

  • washing is done: remove the majority of the chemical content
  • passed on vibrating screens: removal of knots, unreacted chips, trash, splinters, etc
• Kraft Process

  Bleaching Section

  • chlorine gas (Cl2) for pre-bleaching: initial color removal
  • However, Cl2 is stronger than ClO2, thus only used in pre-bleaching
  • Can also use hypochlorite compounds (e.g. NaClO, HClO)
  • sodium hydroxide (NaOH) treatment: reduces the Kappa Number, κ, of the pulp
  • Kappa Number: dimensionless no. that measures the lignin content of pulp
  • For paper, κ < 5.00
  • chorine dioxide (ClO2): main chemical used in bleaching
• Kraft Process


  1. Blending of pulp with broke pulp and chemical additives to make it relatively thicker and preserve the pulp

  2. White water: a dilute, white stock solution of hot water and fibers, added to the pulp to recover the fibers in the stock solution coming from the previous paper-making process

  3. Pulp refining: using a Jordan engine

  4. Headbox: delivers a uniform pulp slurry on the conveyor wires

  5. Rolling press: large amounts of dewatering

  6. Dryers: effectively remove moisture left after pressing
• White water


  A dilute, white stock solution of hot water and fibers, added to the pulp to recover the fibers in the stock solution coming from the previous paper-making process
• Jordan engine


  • Used for pulp refining
  • Affects cellulose characteristics and the composition of the papermaking furnish
• Joseph Jordan


  American inventor
• Fourdrinier Machine

  • French soldier & mechanical engineer Louis-Nicolas Robert
  • invention funded by British entrepreneurs Sealy and Henry Fourdrinier
  • has four main sections:
  • Wet End Section
  • Wet Press Section
  • Dryer Section
  • Calendar/Ironing Section
• Kraft Process


  1. Liquor Recovery Section

  2. Black liquor is removed from washing of the pulp

  3. Contains 65-68% of the chemicals from the cooking of the pulp in the cooking liquor

  4. Contains around 20% total solids

  5. Black liquor concentrated using multi-effect evaporators (35% total solids)

  6. Sprayed through a recovery furnace/boiler

  7. Na2S becomes a smelt (a molten salt mixture) after recovery, producing a green-colored liquor

  8. Na2S liquor treated with hydrated (slacked) lime, Ca(OH)2

  9. Such process is called causticization

  10. Produces white cooking liquor — to be added with Na2SO4 for 'cooking' chipped wood