Oxygen Delignification Liquor Storage & Tank Compatibility

Storing Oxygen Delignification Liquor? Start Here

Oxygen delignification liquor is the alkaline process stream used in the kraft bleach plant's oxygen ("O") stage, where unbleached brownstock pulp is treated with a sodium-hydroxide charge in the presence of pressurized oxygen to strip residual lignin before chlorine-dioxide bleaching. It is not a single compound but a working formulation: a caustic-soda alkali charge (typically dosed at a fraction of a percent up to several percent on oven-dry pulp), dissolved or pressurized oxygen, a small magnesium-sulfate addition to protect cellulose viscosity, and a growing load of dissolved lignin fragments and organic carboxylates. The liquor is strongly alkaline (pH ~11–13) and runs hot (about 80–130°C) under oxygen pressure inside the reactor. Material of construction matters because the same fluid behaves very differently when stored cold as makeup caustic versus when it is hot, pressurized, and oxygen-charged in the process loop.

Is Polyethylene (HDPE / XLPE) Safe for Oxygen Delignification Liquor?

Honest verdict: S (compatible) for the storable form — with an important boundary. Polyethylene is one of the best plastics for caustic soda: HDPE and crosslinked polyethylene (XLPE) resist sodium hydroxide and other strong alkalis across the full concentration range and do not suffer the caustic stress-corrosion cracking that plagues metals. For storing makeup caustic, dilute oxygen-stage liquor, or filtrate at ambient to moderate temperature, a poly tank is an excellent, corrosion-free choice (use a higher specific-gravity poly rating for denser charges).

Where poly stops: the active delignification reaction is run hot (~80–130°C) and under 80–100 psig of oxygen. That combination of elevated temperature and internal pressure is outside the service window of any atmospheric polyethylene tank — poly's practical caustic temperature ceiling is around 60°C, and poly tanks are not pressure vessels. The reactor, hot piping, and oxygen-contact equipment are stainless-steel pressure duty. Match the vessel to the actual state of the liquor: poly for cold/ambient storage, stainless for the heated pressurized stage.

Material compatibility at a glance

The storable, tank-relevant forms (makeup caustic soda and dilute alkaline liquor at ambient to moderate temperature) are well served by HDPE/XLPE and PP. The active delignification reaction itself runs at roughly 80–130°C under 80–100 psig oxygen — that duty belongs to 316 stainless pressure equipment, not a poly tank.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

• Severe caustic burns: the sodium-hydroxide charge causes severe skin and eye damage — full chemical splash PPE, face shield, and gloves are mandatory.
• Oxidizing / fire-intensifying environment: the oxygen-enriched process stream can intensify combustion; keep oil, grease, and organics out of oxygen-contact equipment.
• Hot, pressurized service: reactor liquor is at ~80–130°C under pressure — burn and pressure-release hazards; never confine in atmospheric vessels.
• Metal corrosion: strongly alkaline; corrosive to aluminum and a stress-corrosion-cracking risk for hot carbon steel.
• Incompatible reactions: violent neutralization with strong acids; isolate from acid storage and dosing.
• Always follow the site SDS: exact composition, concentration, and hazard rating are formulation- and mill-specific.

Common questions

What is oxygen delignification liquor made of?

It is an alkaline process liquor: a sodium-hydroxide (caustic soda) charge plus dissolved or pressurized oxygen, usually a small magnesium-sulfate addition to protect pulp viscosity, process water, and a growing load of dissolved lignin and organic carboxylates removed from the pulp. Exact ratios are mill- and SDS-specific.

Can I store it in an HDPE or XLPE poly tank?

Yes for the storable form. Polyethylene resists caustic soda at all concentrations and is corrosion-free, so HDPE/XLPE is a good choice for makeup caustic and dilute alkaline liquor at ambient to moderate temperature. It is NOT suitable for the hot (~80–130°C), pressurized, oxygen-charged reactor duty — that requires stainless pressure equipment.

What pH and temperature does it run at?

The liquor is strongly alkaline, typically pH ~11–13, and the oxygen stage is operated hot — roughly 80–130°C — under about 80–100 psig of oxygen pressure. These are representative process values; the stored/cooled liquor is far less aggressive than the in-reactor stream.

Why does material of construction matter so much here?

Because the same fluid is benign when stored cold but aggressive when hot and pressurized. Cold caustic liquor suits poly and PP; hot oxygen-stage liquor demands 316 stainless. Aluminum is attacked by the alkali, and hot carbon steel risks caustic stress-corrosion cracking. Matching the vessel to the actual state of the liquor prevents both corrosion failures and pressure hazards.