BSE 420 | Kraft Fractionation & Lignin Reaction Terms

Nucleophile

an atom or molecule that in chemical reactions seeks a positive center, such as a nucleus of an atom.

• the term comes from “nucleus-loving”

Nucleophiles in Kraft Fractionation

In the kraft pulping process, nucleophiles play a crucial role in breaking down lignin, the complex polymer that binds cellulose fibers in wood. This allows for the separation of cellulose (used for paper production) from lignin. The two main nucleophiles involved are

Hydroxide ion (OH-)

• Provided by strong alkaline conditions (e.g., sodium hydroxide, NaOH)

Hydrosulfide ion (HS-)

• Introduced through sodium sulfide (Na₂S) in the kraft process.

Quinone Methide

A quinone methide is derived from a phenolic compound when the aromatic system of the phenol is disrupted, typically under oxidative or alkaline conditions

Lignin

A complex phenolic polymer that contains various phenolic and non phenolic structure

Kraft Fractionation

The goal of this is to remove the majority of lignin from chips (or other biomass) while minimizing carbohydrate loss and degradation

Esters

organic compounds formed by reaction of a carboxylic acid and an alcohol typically in the presence of an acid catalyst

Carboxylic Acid

is an organic compound containing a carboxyl group (-COOH). This group consists of a carbon atom double-bonded to an oxygen atom (C=OC=OC=O) and single-bonded to a hydroxyl group (-OH)

• General Structure: R−COOH, where R is a hydrogen atom or any alkyl/aryl group.

• Example: Acetic acid (CH₃COOH)

• Key Property: Carboxylic acids are acidic because the hydrogen in the -COOH group can be easily donated as a proton (H+).

Benzoyl Hydroxyl

A benzoyl hydroxyl group is not a standard chemical term but seems to combine two concepts:

• Benzoyl group (C₆H₅CO-): A functional group consisting of a benzene ring attached to a carbonyl group (−CO−).

• Hydroxyl group (-OH): A functional group consisting of an oxygen atom bonded to a hydrogen atom.

Phenolic Hydroxyl

A phenolic hydroxyl refers to a hydroxyl group (-OH) attached directly to an aromatic ring, specifically a benzene ring.

• General Structure: C₆H₅OH (phenol)

• Key Property: Phenolic hydroxyls are slightly acidic because the aromatic ring stabilizes the phenoxide ion formed after losing the proton (H+).

Ether

An ether is an organic compound characterized by an oxygen atom bonded to two alkyl or aryl groups.

• General Structure: R−O−R’, where R and R’ and are alkyl or aryl groups.

• Example: Diethyl ether CH₃CH₂−O-CH₂CH₃

Alkaline Solutions

Aqueous solution with a pH greater than 7, containing soluble hydroxides or alkaline salts. Basic solutions include:

• OH-

• NaOH

• KOH

Alkali Susbtance

An alkali is a substance that produces hydroxide ions (OH−) when dissolved in water, making the solution basic (alkaline). Alkalis are typically soluble bases.

• Sodium hydroxide NaOH: A strong alkali.

• Potassium hydroxide KOH: Another strong alkali.

• Calcium hydroxide Ca(OH)₂: A less soluble alkali.

Vinyl Group

A vinyl ether is a type of organic compound characterized by an ether group (−O−) directly attached to a vinyl group (CH₂=CH—). The general formula for a vinyl ether is:

CH₂=CH−O−R

• CH₂=CH is the vinyl group, containing a double bond between two carbon atoms.

• R is an alkyl, aryl, or other substituent group.

Alkyl

An alkyl is a type of functional group or substituent derived from an alkane (a saturated hydrocarbon) by removing one hydrogen atom

• General Formula: C_nH_2n+1

Saponification

involves fats (triglycerides) reacting with an alkali (basic substance) to produce fatty acids and glycerol

• Triglyceride + Base → Glycerol + Soap

Triglycerides

Triglycerides are esters formed from one molecule of glycerol and three fatty acid molecules. They are the primary form of stored fat in animals and plants.

• Glycerol backbone + 3 Fatty acids

Glycerol

Glycerol, also known as glycerin, is a simple polyol (sugar alcohol) with three hydroxyl groups (-OH).

• Chemical Formula: C₃H₈O₃​

Fatty Acids

Fatty acids are carboxylic acids (R−COOH) with long hydrocarbon chains. They are the building blocks of fats and oils.

• Structure: R-COOH

• R is a long hydrocarbon chain (saturated or unsaturated).

Carbonyl Group

A carbonyl group is a functional group in organic chemistry consisting of a carbon atom double-bonded to an oxygen atom (C=O). It is highly reactive due to the polarity of the carbon-oxygen bond. Examples are:

• Aldehydes R−CHO: The carbonyl group is bonded to one hydrogen atom and one alkyl or aryl group.

  • Example: Formaldehyde (H−CHO)

• Ketones R−CO−R′ The carbonyl group is bonded to two alkyl or aryl groups.

  • Example: Acetone (CH₃−CO−CH₃)

• Carboxylic Acids R−COOH: The carbonyl group is bonded to a hydroxyl group (-OH).

  • Example: Acetic acid (CH₃−COOH)

• Esters R−COOR′: The carbonyl group is bonded to an alkoxy group (-OR').

  • Example: Ethyl acetate (CH₃-COOCH₂CH₃₎

Stillbene

A stilbene is an organic compound that consists of a trans- or cis- configuration of two phenyl (benzene) rings connected by an ethylene group (C=C).

Stilbenes are often associated with various natural and synthetic compounds, including phenolic compounds that can form as part of the lignin degradation process in kraft pulping.

Initial Phase

A fast lignin removal reaction

• The beginning of the pulping process, where lignin begins to soften and dissolve, but most of it remains intact.

Bulk Phase

A slow lignin removal reaction

• The majority of lignin is broken down and removed, with the cooking liquor becoming heavily enriched with lignin fragments.

Residual Phase

A very slow lignin removal reaction

• The final stage where small amounts of remaining lignin are removed, and the pulp is washed to remove the last remnants of chemicals and byproducts.

Aryl Group

An aryl group is a functional group in organic chemistry derived from an aromatic ring, typically a benzene ring (C₆H₆) or a related structure.