Abstract

Because of a lack of reliable models to predict the water activity (a_w) of H₂SO₄ solutions, the standard sulfuric acid solution (SSL) method requires a periodic check and adjustment of the acid concentration to ensure that equilibrium will be reached at a predetermined a_w point. To establish a reliable equation describing the a_w of H₂SO₄ solutions, five molecular activity models, i.e. nonrandom two-liquid (NRTL), Wilson, universal quasi-chemical (UNIQUAC), modified NRTL-1 (M-NRTL 1) and modified NRTL-2 (M-NRTL 2), were introduced and compared in this study. Each of the models was applied to the 542 literature vapor-liquid equilibrium data points of H₂SO₄ solutions. The results showed that the NRTL model was the best with respect to its accuracy and simplicity. This NRTL model significantly simplified the implementation of the sulfuric acid solution method for MSI measurements. Excellent agreement was found between this simplified SSL method and the conventional saturated salt solution (SSS) method for MSI measurements of both microcrystalline cellulose (MCC) and apples at 25 °C. Therefore, this newly improved SSL method, based on the NRTL model, could be an inexpensive, convenient and reliable alternative to the conventional SSS method in food MSI measurements in the future.

• Highlights

• The NRTL model can accurately predict the a_w of H₂SO₄ solutions.

• The NRTL model can significantly simplify the known sulfuric acid solution (SSL) method.

• This improved SSL method is valid and reliable for use in MCC and apples.

• A working table of the a_w of H₂SO₄ solutions was developed for ease of use.

摘要

由于缺乏可靠的模型来预测H ₂ SO _4溶液的水分活度 ( _aw ) ，标准硫酸溶液 (SSL) 方法需要定期检查和调整酸浓度，以确保在一个预定的_w点。建立一个可靠的方程来描述H ₂ SO ₄的_w解决方案，介绍了非随机二液（NRTL）、Wilson、通用准化学（UNIQUAC）、改良NRTL-1（M-NRTL 1）和改良NRTL-2（M-NRTL 2）五种分子活性模型并在本研究中进行了比较。_{各模型均应用于542个文献H 2} SO ₄气液平衡数据点解决方案。结果表明，NRTL 模型在准确性和简单性方面是最好的。该 NRTL 模型显着简化了用于 MSI 测量的硫酸溶液方法的实施。在 25 °C 下对微晶纤维素 (MCC) 和苹果进行 MSI 测量时，这种简化的 SSL 方法与传统的饱和盐溶液 (SSS) 方法之间的一致性非常好。因此，这种基于 NRTL 模型的新改进的 SSL 方法在未来可以成为食品 MSI 测量中传统 SSS 方法的廉价、方便和可靠的替代方案。

• 强调

• NRTL模型可以准确预测H ₂ SO ₄溶液的a _{w 。}

• NRTL 模型可以显着简化已知的硫酸溶液 (SSL) 方法。

• 这种改进的 SSL 方法在 MCC 和苹果中使用是有效且可靠的。

• 为了便于使用，我们开发了H ₂ SO _4溶液的_{w w}工作表。