Abstract

In the conventional leather production process, basic chromium sulphate (BCS) penetrates fully inside the collagen matrix during tanning and forms oligo-nuclear complexes that stabilize the skin structure during basification. Accelerated chromium sulphate complexation by basifying the BCS before full penetration leads to surface tanning and low leather qualities. Therefore, long processing times of 16 h for tanning and basification are common in modern tanneries. We used sodium hydrogen carbonate to basify BCS before penetration. However, instead of conventional tanning we performed CO₂ tanning at 30 bar. The influence of accelerated chromium sulphate complexation on the leather quality was investigated. To estimate the structures of the formed chromium complexes, we considered the pH trend of the tanning solution during basification depending on the amount of basifying agent. The distribution of chromium oxide (Cr₂O₃) and the shrinkage temperature (T_s) in three different layers of the cross section were analysed. The analytics allowed the assessment whether the tanning agent penetrates through the whole cross section or adheres to the surface during CO₂ tanning. We show that CO₂-intensified tanning allows accelerated chromium sulphate complexation and a reduction in the tanning time from 16 to 4 h. The Cr₂O₃ is equally distributed, and T_s above 100 °C meets the standards of high-quality wet blue. However, the pH value of the tanning solution must not rise above 4.5 during basification. Otherwise, the T_s decrease dramatically. The feasibility of the process is demonstrated in a 1700-L drum, with a batch size of about 500 kg. The CO₂-intensified tanning process has high potential to save time and chemicals and reduce emissions in industrial applications and is commercially competitive.

Graphic abstract

中文翻译：

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通过加速硫酸铬络合快速对动物皮肤进行高压鞣制

摘要

在常规皮革生产过程中，碱性硫酸铬（BCS）在鞣制过程中会完全渗透到胶原蛋白基质内部，并形成寡核复合物，从而在碱化过程中稳定皮肤结构。在完全渗透之前，通过碱化BCS可以加速硫酸铬的络合，导致表面鞣制和皮革品质降低。因此，现代制革厂通常需要16小时的鞣制和碱化处理时间。在渗透之前，我们使用碳酸氢钠碱化了BCS。但是，代替常规的鞣制，我们进行了CO ₂30 bar晒黑。研究了硫酸铬的络合促进对皮革品质的影响。为了估计形成的铬络合物的结构，我们根据碱化剂的量考虑了碱化过程中鞣制溶液的pH趋势。分析了三层横截面中氧化铬（Cr ₂ O ₃）的分布和收缩温度（T _s）。该分析允许评估鞣剂在CO ₂鞣制过程中是穿透整个横截面还是粘附在表面上。我们表明CO ₂强化鞣制可以加快硫酸铬的络合速度，并使鞣制时间从16小时减少到4小时。Cr ₂ O ₃是均匀分布的，并且高于100°C的T _s符合高质量湿蓝的标准。但是，在碱化过程中，鞣制溶液的pH值不得超过4.5。否则，T _s急剧下降。该工艺的可行性在1700-L的转鼓中进行了演示，批量大小约为500 kg。在工业应用中，CO ₂强化鞣制工艺具有节省时间和化学品，减少排放的巨大潜力，并且具有商业竞争力。

图形摘要