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 技术翻译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且对环境有害的工艺转变为具有成本效益的绿色工艺。新工艺的能源成本比目前的做法低一个数量级，而且排放的二氧化碳 (CO2) 也远低于最高效的现有冶金工艺的一半。该项目的目标是生成必要的工艺数据，以评估这种用于半导体和太阳能级硅生产的基于固体氧化物膜的绿色电解工艺的可扩展性和成本效益。成功实施后，该流程将展现出优于当前流程的多项优势。它们包括： 相对于二氧化硅 (SiO2) 还原所需的自由能而言，能耗非常低；使用廉价的原材料，几乎不需要预处理；无碳热还原，每公斤硅 (Si) 产品排放 10 公斤二氧化碳，其污染物通常会将硅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（BF3）挥发固有除硼的可能性；过程中不含任何碳或氯；并且不存在导致全氟和/或全氯碳排放的阳极效应。目前的硅生产方法包括流化床还原工艺、高纯二氧化硅的碳热还原、炉渣/晶体精炼、液体硅电解精炼以及氯化物和氟化物的电解。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传导稳定氧化锆（SOM）管将溶解在熔融焊剂中的纯二氧化硅（SiO2）与放置在SOM管内的惰性阳极分离。为了确保产品纯度，将采用在较低施加电势下使用二次阴极的预还原步骤来去除比硅更具电负性的杂质。将去除充满杂质的辅助阴极，然后采用液体锡阴极，增加施加的电势以减少二氧化硅。还原的硅将进入液态锡阴极的溶液中。与 Si 相比，助焊剂中残留的电负性杂质离子更少。因此，更多和更少电负性杂质的杂质氧化物不会与二氧化硅一起被还原。在高温下，Si 的原子百分比超过 95% 可溶于液态锡，但在较低温度下，纯 Si 和 Sn 是不混溶的。这将允许在电解后采用定向凝固来生产高纯度硅锭，并证明这是一种经济有效的无碳方法，可以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与我们的工业合作伙伴合作的研究机会，使该技术更接近商业化。它还将为本科生和研究生课堂教学提供丰富的案例研究材料。Infinium（一家清洁金属公司）和SunEdison Semiconductors（半导体级硅的消费者）将参与该研究项目，以评估从商业可用的二氧化硅来源大规模生产硅的绿色技术的质量、可扩展性和成本效益。