Anthraquinone (CAS 84-65-1) is a pulping additive used in selected soda and kraft cooking systems to accelerate delignification and help preserve carbohydrates [1][2]. Its value depends on the fiber, cooking conditions, target pulp properties and distribution of the additive in the liquor. For mills using or evaluating AQ, the practical objective is to reach the required Kappa number with an acceptable balance of screened yield, cooking time, chemical use and pulp quality. Powder handling and dosing requirements also influence material selection. View industrial anthraquinone powder specifications.
The Role of Anthraquinone in Alkaline Pulping
Anthraquinone (AQ) participates in a redox cycle with its reduced form, anthrahydroquinone (AHQ). Oxidation of reducing carbohydrate end groups helps limit alkaline peeling, while reactions involving the reduced AQ species promote lignin removal [1][3]. This combination explains its use as a cooking additive where delignification and carbohydrate preservation need to be balanced.
Faster delignification can create opportunities to adjust cooking time, temperature or chemical charge, or to preserve more yield at the required pulp quality [2]. These are process-dependent options rather than improvements guaranteed to occur together. The useful operating change depends on the mill's reference cook, production target and main capacity constraint.
In soda-AQ and kraft-AQ systems, AQ works within the alkaline cooking process. Its role in the digester is distinct from subsequent bleaching operations. Changes made during cooking therefore need to be assessed alongside the pulp properties required by the downstream process.
Applications in Soda and Kraft Pulping
The main distinction between soda-AQ and kraft-AQ is the cooking liquor. Feedstock examples help describe the applications, but they are not exclusive classifications of either process.
| Comparison point | Soda-AQ | Kraft-AQ |
|---|---|---|
| Principal cooking chemicals | Sodium hydroxide-based liquor | Sodium hydroxide and sodium sulfide |
| Feedstock examples | Wood and non-wood fibers, including cereal straw [1] | Wood-chip applications [3] |
| Reference for evaluating AQ | A comparable soda cook using the same feedstock and pulp target | A comparable kraft cook using the same feedstock and pulp target |
| Performance measures | Yield, Kappa number, viscosity and relevant pulp properties | Screened yield, Kappa number and relevant pulp properties |
Anthraquinone in Soda Pulping
Soda pulping uses sodium hydroxide as the principal cooking chemical. AQ-assisted soda cooking has been studied with both woody and non-woody materials, including cereal straw [1]. The appropriate operating conditions depend on the feedstock and intended pulp properties.
A laboratory study on barley straw examined AQ concentration, cooking time and refining while assessing Kappa number, viscosity and other pulp properties [1]. It illustrates the need to consider interacting operating variables when assessing a non-wood system. Its experimental settings remain specific to that feedstock and study.
Anthraquinone in Kraft Pulping
In kraft cooks, AQ is used with sulfide-containing liquor. Because AQ is largely insoluble in water, how it reaches the interior of a chip matters. Mechanism work on kraft-AQ pulping found that AQ dispersed in a caustic lignin solution adsorbed selectively on wood, and proposed a transport route into the chips [3].
For commercial operation, the question is which production constraint AQ addition could address: cooking time, fiber consumption, chemical charge or yield at the required pulp quality. AQ cost and handling requirements also form part of that assessment [2]. The application should fit the mill's process and end-use requirements.
Assessing Pulp Yield and Cooking Performance
Performance assessment brings together screened pulp yield, Kappa number, cooking time, temperature, effective alkali and the resulting pulp properties. The purpose is to establish the operating balance that meets the mill's production and quality targets.
Comparisons need a clear baseline. Yield figures taken at different Kappa numbers, different cooking conditions or different fiber are not directly comparable. A higher yield at a higher Kappa number may simply mean less lignin was removed. Reading a gain as a pure "yield increase" can be misleading.
Yield is also not the only outcome. Strength, bleachability and downstream handling can all change. A mill whose recovery boiler or digester capacity is the real limit may value shorter cooks differently from one that is limited by wood cost. The economic assessment needs to include AQ cost, any changes in handling and the value of the operating improvement to the particular mill [2].
End-use requirements also affect material selection. In its published English version of Recommendation XXXVI dated 01.02.2023, BfR no longer recommends anthraquinone as an additive to raw material for food-contact paper and board [5]. This is a recommendation with a defined scope and version. Current applicable requirements and customer chemical policies must therefore be considered alongside process performance, particularly for sensitive end uses.
Anthraquinone Powder: Dispersion and Dosing Considerations
Parent anthraquinone has very low water solubility. Under alkaline cooking conditions, reduction produces more soluble AHQ species, while distribution and transport remain important to the process [1][3]. Powder wetting and dispersion therefore matter before and during cooking. A uniform dispersion is not the same as dissolution of the parent AQ in water.
Particle size, wetting, mixing and the point of addition are therefore application variables. They affect how evenly AQ is distributed through the liquor and how it contacts the fiber [3]. A mill should look at how the powder is metered, how it is fed into the liquor or with the chips, how dust is handled, and how consistently each cook receives the same addition.
Powder is not the only form. Water-soluble derivatives such as anthraquinone-2-sulfonic acid have been studied in the mechanism work [3]. Some suppliers sell liquid products as well. AWPC's SAQ™, for example, is an aqueous alkaline liquid containing an anthraquinone-derived substance for kraft cooking [4]. That is a different product from Soda-AQ as a process, and from CAS 84-65-1 powder.
Selection between powder and a liquid product depends on active content, formulation identity, handling equipment, storage and the particular supply arrangement. These variables need to be compared on an equivalent basis.
For the powder Unilong supplies, see industrial anthraquinone powder, CAS 84-65-1.
References
- Ferrer, A., Vargas, F., Jameel, H., Rojas, O. J. (2015). Influence of operating variables and model to minimize the use of anthraquinone in the soda-anthraquinone pulping of barley straw. BioResources 10(4), 6442–6456. Read source. Back to text
- Hart, P. W., Rudie, A. W. (2014). Anthraquinone—A review of the rise and fall of a pulping catalyst. TAPPI Journal 13(10), 23–31. Read source. Back to text
- Chai, X.-S., Samp, J., Hou, Q. X., Yoon, S.-H., Zhu, J. Y. (2007). Possible mechanism for anthraquinone species diffusion in alkaline pulping. Industrial & Engineering Chemistry Research 46(15), 5245–5249. Read source. Back to text
- Air Water Performance Chemical Inc. SAQ™ product page. Read source. Back to text
- BfR (2023). Recommendation XXXVI, Paper and Board for Food Contact, version 01.02.2023 (English unofficial translation; German version binding). Read source. Back to text
Post time: Oct-27-2026