Fouling during emulsion polymerization

乳液聚合过程中的结垢

• 批准号: 504119618
• 负责人: Professor Dr. Diethelm Johannsmann
• 金额: --
• 依托单位: Institut für Chemische und Thermische Verfahrenstechnik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/504119618?language=en
• 关键词: Fouling; during; emulsion; polymerization

The research project aims at a deeper understanding of the mechanisms that lead to the formation of deposits on the reactor walls as well as heat transfer surfaces during emulsion polymerization. Therefore, the initial phase of the deposit formation shall be tracked in-situ by two complementary measures: firstly, a quartz crystal microbalance (QCM) integrated into the reactor wall and, secondly, a heating finger that can be withdrawn vertically from the reactor in a stepwise manner. In this way, the state of deposition at the respective time is preserved for later inspection. A comprehensive time-resolved characterization of all processes in the bulk and at the surface combined with the correlation of these processes with each other provides a comprehensive view on all mechanisms contributing to the deposit formation. The characterization shall include both chemical parameters, such as the composition of the fouling material, and physical parameters, such as the particle size, the roughness and the softness of the deposited layer. The characterization shall allow to distinguish between particle fouling and reaction fouling, the former also occurring in non-reactive dispersions. Preliminary investigations have shown that under certain conditions a thin polymer layer (thickness < 1 µm) forms on the wall, which stabilizes this surface against the formation of further, thicker fouling layers. Which system parameters bring about such a passivation is poorly understood and shall be investigated thoroughly. With regard to the materials, a focus shall be on polyacrylates and polyvinyl acetate (pVAc). pVAc tends to crosslink and has a glass transition temperature below the reaction temperature. It is usually stabilized with grafted chains of polyvinyl alcohol (PVOH). Insufficient solubility of PVOH in water at high temperatures may promote fouling. Acrylates are available with different glass transition temperatures. Hard and soft particles differ in the extent to which the spheres deform into polyhedra while the coating is still forming ("wet sintering"). The use of the QCM opens special opportunities in the analysis. In particular, the growth of a planar layer can be distinguished from cluster growth. According to one of the working hypotheses, planar layers tend to passivate the surface against the deposition of thick layers more efficiently than clusters. Furthermore, the QCM can estimate an effective shear modulus. A shear modulus increasing with time indicates compactification of the layer, possibly by wet sintering. The project aims to break new ground in terms of both a description of the mechanisms involved and of quantitative modelling.

该研究项目的目的是更深入地了解导致反应器壁上形成沉积物以及在乳液聚合过程中传热表面的机制。因此，应通过两种完成措施在原位跟踪沉积物形成的初始阶段：首先，集成到反应堆壁中的石英晶体微量平均水平（QCM），其次，可以以逐步的方式从反应器垂直撤回的加热手指。这样，保留了相关时间的沉积状态以供以后检查。批量和表面上的所有过程的全面时间分辨表征与这些过程相关的相关性相结合提供了对有助于沉积形成的所有机制的全面视图。表征应包括化学参数，例如结垢材料的组成和物理参数，例如粒度，粗糙度和沉积层的柔软度。表征应允许区分粒子结垢和反应结垢，前者也发生在非反应性分散体中。初步研究表明，在某些条件下，壁上形成了薄的聚合物层（厚度<1 µm），这使该表面稳定在进一步，更厚的结垢层的形成下。哪些系统参数引起了这种钝化的理解很少，应彻底研究。关于材料，焦点应放在聚丙烯酸酯和乙酸聚氯乙烯（PVAC）上。 PVAC倾向于交联，并且玻璃过渡温度低于反应温度。通常用聚乙烯醇（PVOH）的移植链稳定它。在高温下，PVOH在水中的溶解度不足可能会促进结垢。丙烯酸酯具有不同的玻璃过渡温度。硬质和软颗粒在涂料仍在形成时变形为多面体的程度不同（“湿烧结”）。 QCM的使用在分析中为特殊机会打开了机会。特别是，可以将平面层的生长与簇增长区分开。根据一个工作假设，平面层倾向于比群集更有效地钝化厚层的沉积。此外，QCM可以估计有效的剪切模量。随着时间的推移，剪切模量增加表明层的压实，可以通过湿烧结。该项目的目的是在描述所涉及的机制和定量建模的描述方面打破新的基础。