美国研究人员开发出从空气中进行碳捕获的新方法

2017-01-10 12:25:09 来源: 中国科技网 作者: 张微编译

美国能源部橡树岭国家实验室的科学家们发现了一种简单、可靠的从大气中直接捕捉二氧化碳的方法,为碳捕获和储存提供了一个新的选择,以应对全球变暖。

最初,橡树岭国家实验室的团队研究从水中去除环境污染物如硫酸盐、铬酸盐或磷酸盐的方法。为了除去这些带负电荷的离子,研究人员合成了一种简单化合物胍,设计用它与污染物进行强结合,形成易于从水中分离出来的不溶性晶体。

在这个过程中,他们发现了一种新方法,能够以最少的能量、投入最少的化学品,来捕获和释放二氧化碳。

“当我们把胍溶液放置在空气中,迷人的棱柱状晶体就开始形成了,” 橡树岭国家实验室的Radu Custelcean说。“通过X光衍射分析它们的结构之后,我们惊奇地发现这些晶体中含有碳酸盐(当空气中的二氧化碳和水发生反应时形成的)。”

数十年的研究引领了碳捕获和长期碳储存策略的发展,以减少或消除电厂二氧化碳的排放(这是一种导致全球气温上升的温室气体)。碳捕获和储存策略包括一个技术系统,从释放点或从空气中直接收集二氧化碳,然后将其运输并储存在指定地点。

一种从大气中吸收二氧化碳的非传统方法(直接空气捕获法),是橡树岭国家实验室在这篇论文中的研究重点,它也可以应用在二氧化碳的排放点。

二氧化碳一旦被捕获,就需要将其从化合物中释放出来,这样气体就可以通过管道输送,并被深埋于地下进行封存。传统的直接空气捕获物质必须要加热到900摄氏度,才能释放出气体——这个过程往往会比最初去除的时候,释放出更多的二氧化碳。橡树岭国家实验室开发的胍类物质是一个低能耗的替代。

“通过我们的方法,我们可以通过将晶体加热到80-120摄氏度来释放与化合物结合的二氧化碳,比起现有的方法,这是一个比较温和的方式,” Custelcean说。加热后,晶体又恢复成了最初的胍类物质。回收化合物经过三个连续的碳捕获和释放周期可以循环利用。

Custelcean介绍,这个直接空气捕获法正在获得关注,这个方法还需要进一步开发和积极实施,让其有效对抗全球变暖。同时,他们需要深入研究胍类物质,它如何才能在现有的和未来的碳捕获、存储应用方面更加有效。

研究团队正在利用橡树岭国家实验室的散裂中子源(SNS)(隶属于美国能源部科学使用者设施办公室)在中子散射方面的专长,研究物质的晶体结构和特性。通过分析结合在晶体中的碳酸盐,他们希望更好地了解二氧化碳捕获和释放的分子机制,有助于设计下一代吸附剂。

科学家们还计划评估能否用太阳能作为持续热源,来释放晶体中的二氧化碳。(张微编译)

以下为英文原文:

Crystallization method offers new option for carbon capture from ambient air

Scientists at the Department of Energy's Oak Ridge National Laboratory have found a simple, reliable process to capture carbon dioxide directly from ambient air, offering a new option for carbon capture and storage strategies to combat global warming.

Initially, the ORNL team was studying methods to remove environmental contaminants such as sulfate, chromate or phosphate from water. To remove those negatively charged ions, the researchers synthesized a simple compound known as guanidine designed to bind strongly to the contaminants and form insoluble crystals that are easily separated from water.

In the process, they discovered a method to capture and release carbon dioxidethat requires minimal energy and chemical input. Their results are published in the journal Angewandte Chemie International Edition.

"When we left an aqueous solution of the guanidine open to air, beautiful prism-like crystals started to form," ORNL's Radu Custelcean said. "After analyzing their structure by X-ray diffraction, we were surprised to find the crystals contained carbonate, which forms when carbon dioxide from air reacts with water."

Decades of research has led to the development of carbon capture and long-term storage strategies to lessen the output or remove power plants' emissions of carbon dioxide, a heat-trapping greenhouse gas contributing to a global rise in temperatures. Carbon capture and storage strategies comprise an integrated system of technologies that collects carbon dioxide from the point of release or directly from the air, then transports and stores it at designated locations.

A less traditional method that absorbs carbon dioxide already present in the atmosphere, called direct air capture, is the focus of ORNL's research described in this paper, although it could also be used at the point where carbon dioxide is emitted.

Once carbon dioxide is captured, it needs to be released from the compound so the gas can be transported, usually through a pipeline, and injected deep underground for storage. Traditional direct air capture materials must be heated up to 900 degrees Celsius to release the gas—a process that often emits more carbon dioxide than initially removed. The ORNL-developed guanidine material offers a less energy-intensive alternative.

"Through our process, we were able to release the bound carbon dioxide by heating the crystals at 80-120 degrees Celsius, which is relatively mild when compared with current methods," Custelcean said. After heating, the crystals reverted to the original guanidine material. The recovered compound was recycled through three consecutive carbon capture and release cycles.

While the direct air capture method is gaining traction, according to Custelcean, the process needs to be further developed and aggressively implemented to be effective in combatting global warming. Also, they need to gain a better understanding of the guanidine material and how it could benefit existing and future carbon capture and storage applications.

The research team is now studying the material's crystalline structure and properties with the unique neutron scattering capabilities at ORNL's Spallation Neutron Source (SNS), a DOE Office of Science User Facility. By analyzing carbonate binding in the crystals, they hope to better understand the molecular mechanism of carbon dioxide capture and release and help design the next generation of sorbents.

The scientists also plan to evaluate the use of solar energy as a sustainable heat source to release the bound carbon dioxide from the crystals.

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