Purpose

Carbon nanotubes (CNTs) are well known for their mechanical resistance, durability and flexibility, which make them preferable for a wide variety of applications. The global production volume of CNTs is expected to reach 7,000 tons by 2025. This work performs cradle-to-gate life cycle assessments (LCAs) of industrially preferred single- and multi-walled CNTs synthesis processes. The aim is to evaluate global environmental impacts associated with raw materials acquisition and manufacturing and identify hotspots in CNTs production.

Methods

Eight single-walled and seven multi-walled CNTs synthesis processes are evaluated using LCA. A mass based functional unit is selected as 1 kilogram of CNTs produced, and LCAs are conducted using SimaPro 8.5.2 Software with Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI 2.1) and Cumulative Energy Demand (CED) impact categories. It is expected that industrial scale production provides significant material and energy savings as well as reduces environmental impacts per unit mass of the product, due to the use of efficient equipment and recycling of reagents. Therefore, hypothetical scaling up scenarios are applied in order to estimate associated impacts. Lastly, industry-based impact projections are developed for industries where the majority of CNTs are used using the Laplace criterion.

Results and discussion

The results showed that chemical vapor deposition is the most impactful route for manufacturing single- and multi-walled CNTs. Whereas, high pressure carbon monoxide route for producing single-walled CNTs, and arc discharge route for manufacturing multi-walled CNTs are found to be the least environmentally impactful techniques among different processes considered. Results indicate that the preference of synthesis process dominates the overall environmental cost of the CNTs as well as CNTs-enabled products. Additionally, using different scaling up scenarios, it is projected that the environmental emissions associated with producing CNTs may be reduced up to 88% globally. As industries use particular routes to synthesize the CNTs to be embedded in their products, it is found that the sectoral environmental impacts are not proportional with the industrial shares.

Conclusions

CNTs offer technological advances to conventional products (e.g. heated jacket). However, thinking from a global scale, manufacturing CNTs has significant environmental impacts. This study provides segmented impact projections for industries, which then may be used to inform sectoral cradle-to-grave environmental impacts as a function of manufacturing processes. Based on the desired characteristics of produced CNTs (e.g. diameter, surface area), manufacturing CNTs with environmentally responsible production routes may help decreasing global environmental impacts significantly.

中文翻译：

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单壁和多壁碳纳米管合成工艺对全球规模生命周期的环境影响

目的

碳纳米管（CNT）的机械强度，耐用性和柔韧性是众所周知的，这使其在各种应用中均很受欢迎。到2025年，全球CNT的产量预计将达到7,000吨。这项工作是对工业上优选的单壁和多壁CNT合成工艺进行从摇篮到大门的生命周期评估（LCA）。目的是评估与原材料采购和制造相关的全球环境影响，并确定碳纳米管生产中的热点。

方法

使用LCA评估了八种单壁和七种多壁CNT的合成过程。选择基于质量的功能单元作为生产的1千克CNT，并使用SimaPro 8.5.2软件以及用于减少和评估化学及其他环境影响（TRACI 2.1）和累积能量需求（CED）影响类别的工具进行LCA。由于使用了高效的设备和试剂的回收利用，预计工业规模的生产可以显着节省材料和能源，并减少产品单位质量的环境影响。因此，应用假设的放大方案以估计相关的影响。最后，针对使用拉普拉斯准则使用大多数碳纳米管的行业，制定了基于行业的影响预测。

结果与讨论

结果表明，化学气相沉积是制造单壁和多壁CNT最具影响力的途径。然而，在所考虑的不同过程中，发现用于生产单壁CNT的高压一氧化碳路线和用于制造多壁CNT的电弧放电路线是对环境影响最小的技术。结果表明，对合成工艺的偏爱主导了CNT以及具有CNTs功能的产品的总体环境成本。另外，预计使用不同的按比例放大方案，与生产碳纳米管相关的环境排放量有望在全球范围内减少多达88％。随着行业使用特定的路线来合成要嵌入其产品中的CNT，

结论

碳纳米管为传统产品（例如加热外套）提供了技术进步。但是，从全球范围来看，制造碳纳米管会对环境产生重大影响。这项研究提供了针对行业的分段影响预测，然后可用于根据制造过程来告知各个部门从摇篮到坟墓的环境影响。基于所生产的CNT的所需特性（例如直径，表面积），使用对环境负责的生产路线来制造CNT可能有助于显着减少全球环境影响。