A Technical Study Paper on NaOH–Ethanol as a Practical Alternative to ASTM D664

Author: Vivek Patel

Abstract

Total Acid Number (TAN) is a key indicator of corrosivity in crude oil and bitumen. Industry standards (e.g., ASTM D664) specify alcoholic KOH titration in a mixed non-aqueous solvent with potentiometric endpoint detection. This technical study paper investigates a practical, internally validated alternative that substitutes NaOH in ethanol for KOH in isopropanol (IPA) while keeping the solvent system, instrumentation, and endpoint detection principles intact.

This study outline:

• Analytical rationale
• Reagent preparation
• Titrator configuration on a Mettler Toledo T9
• Matrix-matched standardization
• QC strategy
• Expected performance
• Troubleshooting guidance

This alternative method is not ASTM-reportable, but it is fit-for-purpose for internal trending, method exploration, training, or research.

1. Background & Rationale

TAN quantifies acidic constituents in petroleum products and is traditionally reported as mg KOH per gram of sample. The ASTM D664 method uses KOH in IPA and detects the equivalence point potentiometrically. In some labs, NaOH is more available and economical. Although the neutralization chemistry is identical, solvent–base interactions differ: NaOH behaves far better in ethanol than IPA (higher ion mobility, cleaner endpoints). This study evaluates whether a NaOH–ethanol variant can provide reliable internal measurements for bitumen while maintaining disciplined QC.

2. Instrumentation (Mettler Toledo T9)

Titrations were performed on a potentiometric titrator capable of non-aqueous dynamic equivalence-point detection (example used: Mettler Toledo T9).