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.

该PFI：AIR技术转化项目的重点是转化技术，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（CO2）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，以评估这种基于固体氧化物膜的绿色电解工艺用于半导体和太阳能级硅生产的可扩展性和成本效益。一旦成功实施，这一进程将显示出优于目前进程的若干优点。它们包括：- 相对于二氧化硅（SiO2）还原所需的自由能，非常低的能量使用;使用需要很少或不需要预处理的廉价原材料;没有碳热还原，其每千克硅（Si）产物排放10千克CO2，并且其污染物通常将硅的纯度从天然石英岩中的99.6%降低到冶金级（MG）Si中的97-98%;通过三氟化硼（BF 3）挥发去除硼的固有可能性;工艺中不含任何碳或氯;不存在导致全氟和/或全氯碳排放的阳极效应。目前用于Si生产的方法包括流化床还原法、高纯度二氧化硅的碳热还原、炉渣/晶体精炼、液体Si电解精炼以及氯化物和氟化物的电解。这些方法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，一端封闭的氧离子传导稳定氧化锆（SOM）管将用于从放置在SOM管内的惰性阳极分离溶解在熔融焊剂中的纯二氧化硅（SiO2）。为了确保产品纯度，将采用在较低施加电位下使用二次阴极的预还原步骤来去除比Si电负性更强的杂质。杂质负载的二次阴极将被移除，然后采用液体锡阴极，所施加的电势将被增加以还原二氧化硅。被还原的Si将进入液态锡阴极中的溶液中。与Si相比，较少的电负性杂质离子将保留在焊剂中。因此，更多和更少的电负性杂质的杂质氧化物不与二氧化硅一起沿着被还原。Si在高温下可溶于液体锡中，但在较低温度下，纯Si和Sn不混溶。这将允许在电解后采用定向凝固来生产高纯硅锭，并证明这是一种具有成本效益的无碳方法，用于从市售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与我们的工业合作伙伴合作的研究机会，并使该技术更接近商业化。该研究计划亦会提供一套丰富的个案研究资料，供本科生及研究生课堂教学之用。清洁金属公司Infinium及半导体级硅的消费者SunEdison Semiconductors将参与该研究计划，以评估从市售硅源开始大规模生产硅的绿色技术的质量、可扩展性及成本效益。