Fluid Process Engineering (AVT.FVT), RWTH Aachen University, 52074 Aachen, Germany.
Process Systems Engineering (AVT.SVT), RWTH Aachen University, 52074 Aachen, Germany.
J Chromatogr A. 2022 Jul 19;1675:463140. doi: 10.1016/j.chroma.2022.463140. Epub 2022 May 11.
The use of adsorption for the purification of dicarboxylic acids is rather limited and currently predominantly confined to ion-exchange chromatography. A promising, but less regarded alternative is the use of hydrophobic adsorbents. Regarding hydrophobic absorbents, the literature focuses on screenings of adsorbents for purification of (di)carboxylic acids with regard to adsorption equilibria. The investigation of dynamic phenomena in the column received only minor attention. In this contribution, this knowledge gap is addressed. First, the adsorption behavior of itaconic acid species on the hydrophobic, highly-crosslinked polymeric adsorbent Chromalite™ PCG1200C is investigated. For this purpose, adsorption isotherms are determined via frontal analysis at pH values of 2, 3, 4.5, 6.5, and 8 to evaluate the dependency of the adsorption capacity on the dissociation state. Capacities above 150 g L at liquid phase concentrations of 70 g L are observed at a pH of 2. A strong decrease of capacity with increasing pH value, i.e., with increasing fraction of dissociated negatively charged acid species, is observed. Second, pulse experiments at aforementioned pH values are performed. Thereby, in-line Raman spectra are recorded at the column outlet, which allows the direct differentiation of the acid species state of dissociation. The spectral information is evaluated for quantitative concentration profiles of itaconic acid species using Indirect Hard Modeling with mixture hard models that are calibrated subject to ideal as well as non-ideal thermodynamics. In-line measurement errors of ≤ 3.5 g L are achieved for the itaconic acid species. In dependency of the pH of the feed solution, a separation of the individual acid species within the pulse experiments is observed. It is conjectured that the process is dominated by a superposition of species-dependent adsorption characteristics and dissociation reactions.
吸附法在二羧酸的纯化中应用有限，目前主要局限于离子交换色谱法。一种有前途但较少被关注的替代方法是使用疏水吸附剂。关于疏水吸附剂，文献主要侧重于筛选用于（二）羧酸纯化的吸附剂的吸附平衡。在柱中的动态现象的研究只受到了较少的关注。在这篇文章中，填补了这一知识空白。首先，研究了反丁烯二酸在疏水、高度交联的聚合物吸附剂 Chromalite™ PCG1200C 上的吸附行为。为此，通过前沿分析在 pH 值为 2、3、4.5、6.5 和 8 下测定了吸附等温线，以评估吸附容量对离解状态的依赖性。在 pH 值为 2 时，在液相浓度为 70 g/L 的情况下，观察到超过 150 g/L 的容量。随着 pH 值的增加，即随着带负电荷的酸离解物种比例的增加，容量会强烈下降。其次，在上述 pH 值下进行脉冲实验。由此，在柱出口处记录在线拉曼光谱，这允许直接区分酸离解物种的状态。使用间接硬模型对光谱信息进行评估，该模型使用混合硬模型进行校准，这些模型符合理想和非理想热力学。对于反丁烯二酸的物种，可以实现在线测量误差≤3.5 g/L。根据进料溶液的 pH 值，可以观察到在脉冲实验中单个酸物种的分离。据推测，该过程主要由物种依赖的吸附特性和离解反应的叠加决定。
