ISO 23772:2023 PDF

Name: ISO 23772:2023 — Pulps — Kraft liquor — Determination of residual alkali using potentiometric titration
SKU: ISO 23772:2023
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Pulps — Kraft liquor — Determination of residual alkali using potentiometric titration

Название (английский):

ISO 23772:2023

Pulps — Kraft liquor — Determination of residual alkali using potentiometric titration

Статус документа:: Действующий
Формат:: Электронный (PDF)
Количество страниц:: 7
Дата публикации:: 10 марта 2023 г.
Издание:: ISO IS 23772 edition 1 version 1
ICS:: 85.040

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Описание (английский):

This document describes a procedure for determining the content of residual alkali in Kraft black liquors having a dry matter content up to 40 %. The method is based on a potentiometric titration with hydrochloric acid and is intended for black liquor samples with an initial pH ≥ 11,0. The lower limit of determination is 0,1 g/l of eq. NaOH.

Abstract

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Overview

ISO 23772:2023 - Pulps: Kraft liquor - Determination of residual alkali using potentiometric titration defines a laboratory procedure to measure residual effective alkali in Kraft black liquor. The method is intended for black liquors with up to 40% dry matter and initial pH ≥ 11.0, using a potentiometric titration with hydrochloric acid (HCl). The method’s lower reporting limit is 0.1 g/L equivalent NaOH.

Key topics and technical requirements

Principle: Alkaline species in the sample are titrated potentiometrically to the first inflection point (pH ≈ 11.0–11.5). Sodium carbonate is added to sharpen the inflection; NaOH is optionally added for samples with pH 11.0–12.5.

Reagents: Analytical-grade HCl (1 M, known to 0.001 M), Na2CO3 (1 M), NaOH (1 M, known to 0.005 M), ethanol for electrode cleaning, and pH 7.0 & 11.0 buffers.

Apparatus: Automatic titrator or pH meter with a motorized burette and recorder; combined or separate glass/reference electrodes (high-sodium pH electrode recommended); fume hood.

Sampling & pretreatment: Keep sample bottles full and sealed to prevent oxidation; swirl (do not shake) when homogenizing; dilute if dry matter > 40% (target ≈ 20%).

Procedure highlights: Sample volumes typically 10–20 mL (measured to ±1%); titrate under stirring; record HCl volume at the first inflection point (or at pH 11.5 if no clear inflection).

Calculations: Residual alkali is calculated from acid consumption, corrected by a factor (0.95) and a correction term (−0.012) to remove contributions from other alkaline species. Results are reported as g/L NaOH or g/L Na2O (conversion factors given).

Safety: Hydrogen sulfide may form-perform titration under a hood.

Applications and users

ISO 23772:2023 is applicable to:

Quality control and process laboratories in pulp & paper mills monitoring black liquor causticity.

Analytical and environmental labs performing routine alkali balance or recovery system checks.

R&D teams studying kraft pulping chemistry and process optimization. Benefits include standardized, reproducible measurements for process control, material balance, and regulatory reporting.

Related information

Precision and reproducibility data are provided in Annex A of the standard (inter-laboratory results).

The document references background work such as SCAN N33-94 for correction-factor justification.

Prepared by ISO/TC 6 (Paper, board and pulps); see ISO for related pulp and analytical standards.

Keywords: ISO 23772:2023, Kraft liquor, residual alkali, potentiometric titration, black liquor, NaOH, HCl, pH 11, laboratory method.

ISO 23772:2023 PDF

Abstract

Похожие стандарты

Overview

Key topics and technical requirements

Applications and users

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