Control of size and morphology of calcium carbonate crystals made by the reaction of CO2 gas with Calcium Chloride solution.

碳酸钙在工业和消费品中有许多用途。最高价值的材料往往在微米尺寸范围内，这通常是通过研磨较大的材料来生产的，这是非常节能的，并且产生宽的尺寸分布。由于用户想要一个狭窄的尺寸范围，许多材料被回收或丢失。该项目旨在通过自下而上控制其生长来控制尺寸和形态，同时研究可以产生什么样的形状。所使用的方法将是将CO2气体鼓泡通过氯化钙溶液形成碳酸盐。另一个好处是，这是一种捕获CO2的方法，并将其从温室气体的负面环境材料转变为具有多种用途的有价值材料。有很多关于该反应的出版物报道了各种各样的结果，经常出现相互矛盾的情况。该项目认为，更广泛、更深入的研究将有助于理解为什么会获得不同的结果，以及如何更可预测。到目前为止，还没有人从工程角度研究它，并将其转化为工业过程，因此没有关于气泡大小，原材料浓度或温度和添加剂影响的信息。工作是定性的，而不是定量的。因此，需要围绕机制和控制变量进行大量学习，以便将其从学术论文转化为可以生产一致的产品质量的过程。该项目将通过使用良好定义的膜来控制气泡大小和良好控制的流速，并将建立在以前的鼓泡反应器中所做的工作的基础上，最终得到该过程的模型。简单的模型将通过气泡上升时的质量平衡来阐明该过程中发生的事情，并对反应器内许多气泡的相互作用做出反应。从早期的数据来看，作为一个硕士项目，流体力学似乎在控制晶体的形状和尺寸方面发挥着作用，基于胺的添加剂可以对反应速率和晶体形态产生重大影响。希望这种机理的理解将为生产其他特性高度依赖于尺寸和形状的特种晶体的进一步工作提供基础，如碳酸锌。该项目将调查许多表征工具可在整个大学从低温切片和X射线衍射（以建立对更大晶体如何形成的理解）测试新的超声波技术，以跟踪反应速率，并评估结晶的开始是否可以控制，以适应尺寸和形态的好处。作为建模工作的一部分，我们与一位模拟气泡反应器的专家密切合作。Mariano Martin是西班牙萨拉曼卡大学的助理教授，他已经在伊拉斯谟奖学金上访问过一次。目前的过程是分批的，氯化钙随着时间的推移而耗尽。一旦以一种可以控制的方式理解了主要反应，该项目的下一步将是将其发展为一个连续的过程。

Calcium carbonate has many uses in industry and consumer products. The highest value material tends to be in the micron size range which is usually produced through grinding of larger material, which is very energy inefficient as well as producing a wide size distribution. Since users want a narrow size range a lot of material is recycled or lost. This project aims at controlling the size and morphology by controlling its growth from the bottom up and, at the same time investigating what sort of shapes can be produced.The method to be used will be bubbling CO2 gas through a solution of Calcium chloride solution to form the carbonate. An additional benefit is that this is a means of capturing CO2 and turning it from a negative environmental material, due to greenhouse gas, to a valuable material with lots of uses.There is a lot of publications for this reaction reporting a wide variety of results, often appearing to contradict each other. This project takes the view that a broader, more in depth study will help understand why different results are obtained and how it can be more predictable. So far no one has studied it from an engineering perspective with the view point of turning it into an industrial process and so there are no information available on the impact of bubble size, raw material concentrations nor temperatures and additives. Work has been qualitative rather than quantitative. Thus a great deal needs to be learnt around mechanisms and control variables to turn this from academic papers into a process whereby consistent product quality can be produced. The project will be aided by the use of well-defined membranes to control bubble size and well controlled flowrates and will build on work done in previous bubble reactors, ending up with a model of the process.Simple models will elucidate what is happening in the process, through mass balances over a bubble as it rises and reacts to the interactions of many bubbles inside a reactor. From early data, as an MSc project it appears that the hydrodynamics is playing a role in control of the shape and size of the crystal and that amine based additives can have a significant impact on the rate of reaction as well as the crystal morphology.It is hoped that this mechanistic understanding will provide the basis for further work in producing other speciality crystals whose properties are highly dependent on size and shape, such as zinc carbonate.The project will investigate many of the characterisation tools available across the university from cryo slicing and Xray diffraction ( to build up an understanding as to how the larger crystals are formed) to testing novel ultrasonic techniques to track reaction rates and assess if onset of crystallisation can be controlled to the benefit of tailoring size and morphology.As part of the modelling work we are working closely with an expert in modelling bubble reactors. Mariano Martin is an assistant professor at the University of Salamanca, Spain and he has already visited once on an Erasmus scholarship.Currently the process is a batch one, whereby the Calcium chloride is depleted over time. Once the understanding of the main reactions are understood in a way that can be controlled the next step of the project will be to develop this into a continuous process.