PFI:AIR - TT: Cost-Effective Membrane-Based Green Electrolytic Process for Solar and Semiconductor Grade Silicon Production

PFI:AIR - TT：用于太阳能和半导体级硅生产的经济高效的基于膜的绿色电解工艺

• 批准号: 1601583
• 负责人: Uday Pal
• 金额: $ 20万
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-04-15 至 2020-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1601583&HistoricalAwards=false
• 关键词: PFI; AIR; TT; Cost; Effective

This PFI: AIR Technology Translation project focuses on translating technology that will change the state-of-the-art silicon production process from an energy-intensive and environmentally detrimental one into a cost-effective green process. The new process is an order of magnitude better in energy cost than current practices, and also emits well below half the carbon dioxide (CO2) of the most efficient existing metallurgical processes. The goal of the project is to generate the necessary process data to evaluate scalability and cost-effectiveness of this solid-oxide-membrane-based green electrolytic process for semiconductor and solar grade silicon production. Upon successful implementation, this process will demonstrate several advantages over current processes. They include: very low energy usage relative to free energy required for silicon dioxide (SiO2) reduction; use of inexpensive raw materials that require little to no pre-treatment; no carbothermic reduction, which emits 10 kg of CO2 per kg silicon (Si) product and whose contaminants typically reduce purity of silicon from 99.6% in natural quartzite to 97-98% in metallurgical grade (MG) Si; possibility of inherent boron removal by borium triflouride (BF3) volatilization; absence of any carbon or chlorine in the process; and there are no anode effects resulting in perfluro and/or perchloro carbon emissions. Current methods for Si production include, fluidized bed reduction processes, carbothermic reduction of high-purity silica, slag/crystal refining, liquid Si electrorefining, and electrolysis of chlorides and fluorides. Some of the major limitations of these processes include extensive raw materials pre-processing, low yields, detrimental environmental impact and substantial energy requirements. In the proposed process, a one-end-closed oxygen-ion-conducting stabilized zirconia (SOM) tube will be used to separate pure silica (SiO2) dissolved in molten flux from an inert anode placed inside the SOM tube. To ensure product purity, a pre-reduction step using a secondary cathode at lower applied potentials will be employed to remove impurities that are more electronegative than Si. The impurity-laden secondary cathode will be removed, and then employing a liquid tin cathode the applied potential will be increased to reduce silica. The Si reduced will go into solution in the liquid tin cathode. Less electronegative impurity ions compared to Si will remain in the flux. Thus impurity oxides of both more and less electronegative impurities are not reduced along with silica. Si is over 95 atom% soluble in liquid tin at high temperatures but at lower temperatures pure Si and Sn are immiscible. This will allow directional solidification to be employed after electrolysis to produce high-purity Si ingots and demonstrate this as a cost-effective carbon-free method for mass production of Si from commercially available sources of silica. This project will provide research opportunities for graduate and undergraduate students to work with our industrial partners and move the technology closer towards commercialization. It will also provide a rich set of case-study materials for introduction into both undergraduate and graduate classroom teaching.Infinium, a clean metals company, and SunEdison Semiconductors, consumer of semiconductor grade silicon will be engaged in the research program to assess quality, scalability and cost-effectiveness of the green technology for mass production of silicon starting from commercially available sources of silica.

这个PFI: AIR技术翻译项目的重点是翻译技术，将最先进的硅生产工艺从能源密集型和环境有害的工艺转变为具有成本效益的绿色工艺。新工艺在能源成本上比目前的做法好一个数量级，而且排放的二氧化碳也远低于现有最有效的冶金工艺的一半。该项目的目标是生成必要的工艺数据，以评估用于半导体和太阳能级硅生产的基于固体氧化膜的绿色电解工艺的可扩展性和成本效益。在成功实现之后，此流程将显示出优于当前流程的几个优点。它们包括：相对于二氧化硅（SiO2）还原所需的自由能，能耗非常低；使用廉价的原材料，几乎不需要预处理；没有碳热还原，每千克硅（Si）产品排放10千克二氧化碳，其污染物通常会将天然石英岩中的硅纯度从99.6%降低到冶金级（MG） Si的97-98%；三氟化硼（BF3）挥发去除固有硼的可能性；加工过程中不含任何碳或氯；而且不存在导致全氟和/或高氯碳排放的阳极效应。目前生产硅的方法包括：流化床还原法、高纯度二氧化硅碳热还原法、渣/晶精炼法、液态硅电精炼法、氯化物和氟化物电解法。这些工艺的一些主要限制包括大量的原材料预处理、低产量、有害的环境影响和大量的能源需求。在所提出的工艺中，将使用一端封闭的氧离子导电稳定氧化锆（SOM）管从放置在SOM管内的惰性阳极中分离溶解在熔融助焊剂中的纯二氧化硅（SiO2）。为了确保产品纯度，在较低的应用电位下使用二次阴极进行预还原步骤，以去除比Si电负性更强的杂质。除去含杂质的二次阴极，然后采用液态锡阴极，增加施加电位以减少二氧化硅。还原后的Si将进入液态锡阴极的溶液中。与硅相比，更少的电负性杂质离子将留在通量中。因此，电负性较强和电负性较弱的杂质氧化物不随二氧化硅一起还原。Si在高温下可溶于液态锡95%以上，但在较低温度下，纯Si和Sn不能混溶。这将允许定向凝固在电解后用于生产高纯度的硅锭，并证明这是一种具有成本效益的无碳方法，用于从商业上可用的二氧化硅来源大规模生产硅。该项目将为研究生和本科生提供研究机会，与我们的工业合作伙伴合作，使技术更接近商业化。它还将为本科生和研究生的课堂教学提供丰富的案例研究材料。清洁金属公司Infinium和半导体级硅的消费者SunEdison半导体将参与这项研究计划，以评估从商业上可用的硅源开始大规模生产硅的绿色技术的质量、可扩展性和成本效益。