How Greenhouse Gases Can Be Used to Store Energy
作者：Thomas Ruh，Verena Pramhaas，Patrizia Bartl，Christoph Rameshan 译者：小婧视野
摘要
“地球大气中二氧化碳浓度上升一直是人们关注的问题，因为这会导致全球变暖，其带来的气候变化会对我们的生活环境造成严重的危害。因此，除去一部分二氧化碳对于应对全球变暖所带来的有害影响至关重要。减少大气中二氧化碳的含量的其中一个方法是让二氧化碳转变为其他化学物质，例如甲醇。这种转化不仅可以降低大气中二氧化碳的浓度，而且还可以给风能、太阳能等这类可再生能量提供了一种储存方式。
ABSTRACT
Rising levels of carbon dioxide in Earth’s atmosphere are a problem, because they lead to global warming and changes in climate that are serious threats to the environment we live in. So, getting rid of some of the carbon dioxide would be very important to combat the dangerous effects of global warming. One way to reduce the amount of carbon dioxide in the atmosphere is to turn it into chemicals like methanol. This transformation not only reduces carbon dioxide levels in the atmosphere, but also offers a way to store renewable forms of energy like wind or solar energy.”
CARBON DIOXIDE AND CLIMATE CHANGE
二氧化碳和气候变化
二氧化碳(由一个碳原子和两个氧原子组成的分子，CO2是它的化学式)是一种温室气体,这就意味着二氧化碳会导致所谓的“温室效应”。空气中的二氧化碳和其他温室气体会将地球上一部分原本应该散失回太空中的热量截留到大气中，类似于热量被困在温室内或一个带盖的锅中。这些热量截留的效应对于我们地球上所周知的生命活动至关重要——如果没有了这些热量，大气中的平均温度将会是-18 ℃（0℉）
然而，CO2也是人类造成气候变化和全球变暖的主要因素。燃烧经数百万年沉积形成的化石燃料，如石油和天然气，会使大气中CO2的含量增加，大气中CO2含量增加则会导致更多的热量被截留在大气中，温度也就随之上升。因此，自从人类大规模使用化石燃料进行发电、交通运输（汽车、飞机等）、取暖以来，全球的气温几乎上升了整整一摄氏度！这温度上升幅度听起来并不大，可能我们会觉得没什么，但这温度的轻微上升会给我们敏感的环境平衡带来相当严重的后果。例如：由于极地冰川融化导致海平面上升可能会影响到沿海城市，海水温度升高将会对珊瑚礁的生存带来威胁等。
减少大气中二氧化碳的含量是与全球变暖作斗争的重要一步。有一个可行的办法就是把CO2转化为可以储存起来并今后可供我们作燃料的化学物质。尽管这个方法略有不足之处：虽然生产这些可做燃料的易储存的化学物质可以减少大气中的CO2，但这些化学物质今后作为燃料燃烧时会将二氧化碳重新释放到大气中。然而，由于这个过程毕竟没有新的二氧化碳释放到大气中，因此，随着燃料的循环使用，二氧化碳是保持平衡的，这比使用化石燃料直接向大气中排放新的CO2好多了。
Carbon dioxide (a molecule made up from one carbon and two oxygen atoms—CO2 in chemists’ notation) is a greenhouse gas, which means it contributes to the so-called greenhouse effect. Carbon dioxide and other greenhouse gases in the air trap some of the heat Earth would lose into space, similar to the way heat is trapped inside a greenhouse, or in a pot with a lid. This trapping of heat is necessary for life as we know it on Earth—without it, the average temperature would be about -18°C (0°F) [1].
However, CO2 is also the main contributor to human-made climate change and global warming. By burning fossil fuels like oil or natural gas, which were formed over millions of years, we increase the amount of CO2 in the atmosphere. Increased atmospheric CO2 leads to more heat being trapped and to increasing temperatures. As a result, the average global temperature has risen almost a whole degree since humans started using fossil fuels on a large scale for power plants, transportation (cars, planes, etc.), heating, and so on. That might not sound like a big temperature rise, but this slight increase has drastic consequences on the sensitive balance of our environment. For instance, rising sea levels due to melting polar ice might affect coastal cities, or higher ocean water temperatures may threaten coral reefs [2].
Reducing the amount of carbon dioxide in the atmosphere is a very important step to combat global warming. One possible way to do this would be to remove CO2 by turning it into useful chemicals that we can safely store and later use as fuels. There is a slight shortcoming of this method, though: while production of these easy-to-store chemicals reduces CO2, burning them later as fuel will re-release the carbon dioxide into the atmosphere. However, there is no “new” CO2 released into the atmosphere. The carbon dioxide is therefore kept in balance as the fuel is recycled, which is still much better than using fossil fuels and adding new CO2 to the atmosphere.
WHY ARE WE TALKING ABOUT STORING ENERGY?
为什么我们要谈论到储存能源呢？
你所能想到的每一个活动过程都需要能量——例如，植物的生长，汽车的驾驶，甚至是你正在阅读这篇文章，都需要能量。然而，这些能量并不会在活动结束后消失得无影无踪！物理学中的一个很重要的原理指出，能量既不能凭空产生，也不能被破坏，只能从一种形式转换（或转化）为另一种形式。所以，我们对刚刚提到的活动过程的另一种思考方式就是可以把它们看作是能量转换的过程。比如：植物利用来自太阳光的能量生长，能量便储存在植物新生长的部分中。在汽车中，通过燃烧汽油可以使来自于燃料的能量转变成物体运动的能量（我们把它称为动能）和热量。当你在移动眼睛阅读此文章时，你的身体便会将你摄取的食物所提供的能量转化为你身体的一系列动作。同时你的大脑也利用这些能量来处理和记住你所阅读的内容。所有的活动过程——无论是在自然界还是在使用机器上——基本上都是能量从一种形式转换成另一种形式的过程。
在任何情况下能量都必须来自某个地方。能量的来源包括太阳（称为太阳能）、风或水，但也包括石油或煤这些我们仍在大规模燃烧的化石燃料。大多数情况下，这些来自不同来源的能量会先转化成电能，利用发电厂转化煤和水（的能量），利用太阳能电池转化太阳光能量以及利用风力涡轮机转化风能，然后这些电能为电脑、工厂机器、电动汽车等等设备的运行提供动力。我们还可以把这些能量先储存起来供我们以后使用——这就是所谓的燃料（有时候也被称为能量载体，因为它们确实携带着能量）。
任何形式的燃料之所以都有很大用处，主要有两个原因——运输和储存。图1显示的是不同地区利用风能和太阳能的潜力（意思是使能源转化为可用的能量）差异很大。例如，在非洲，利用太能的平均潜力比欧洲和北美洲地区高。风能则恰恰相反——欧洲的平均风速比非洲大，尤其是在沿海地区。风速越大，利用风力涡轮发电机发电的能力就越强。这种能源分布不均匀的后果是，我们需要设法将能源输送到需要的地方。而有了燃料，我们就可以将能源输送到我们所需要的地方。
Every process you can think of needs energy to take place—for example, plants growing, cars being driven, and even you reading this article. However, this energy is not gone after the process finishes! A very important principle of physics states that energy can be neither created nor destroyed, it is only possible to convert (or transform) energy from one form to another. So, another way of thinking about the processes we mentioned would be to see them as energy conversions.For example, a plant uses energy from the sun to grow, and energy is then stored in the newly grown parts of the plant. In a car, gasoline is burned so that the energy from the fuel can be changed into energy of movement (called kinetic energy) and heat. When you move your eyes to read this article, your body turns the energy provided by the food you eat into movement, and your brain also uses energy to process and remember what you read. All processes that happen—both in nature and using machines—are basically the conversion of one form of energy into another form.
The energy in any process must come from somewhere. Sources of energy include the sun (called solar energy), wind, or water, but also include oil or coal, which are the fossil fuels we still burn on a large scale. Most often, energy from these sources is converted into electricity first, using power plants to convert coal or water, solar cells for sunlight, and wind turbines for wind. The electricity then powers devices like computers and phones, machines in factories, electrically powered cars, and so on. We can also store energy for later use—that is where fuels (sometimes also called energy carriers, because they literally carry energy in them) come in.
Fuels, in any shape or form, are useful for two main reasons—transport and storage. Figure 1 shows that the potential to harness energy from wind and the sun (meaning to make the energy usable) strongly varies for different regions. For instance, in Africa, the potential to harness solar energy is on average greater than in Europe or in North America. The reverse is true for wind energy—the average wind speed is higher in Europe than in Africa, especially near the coasts. And the higher the wind speed, the more electricity can be generated using wind turbines. A consequence of this unequal distribution of energy sources is that we need ways to transport energy to where it is required. With fuels, we can do exactly that: transport energy to where we need it.
Figure 1 - The potential for harnessing solar or wind energy varies for different regions in the world.
图1-世界不同地区利用太阳能或风能的潜力各不相同
On this map, you can see how the average wind speed (blue areas) and the solar potential (red areas) are distributed. You might notice that, surprisingly, the potential for solar energy along the equator is only medium. This is due to clouds that occur in this region of the world (those clouds are also the reason for the large rain forests along the equator). Many areas with very high solar potential are actually deserts1.
在这张地图中，你可以观察到平均风速（蓝色区域）和利用太 阳能潜力（红色区域）是如何分布的。你可能会注意到，令人惊讶的是，赤道沿线的太阳能利用潜力只有中等级别（medium），这是由于这一地带存在云层（这些云层也是赤道沿线有大面积雨林的原因）。许多太阳能潜力非常大的地区实际上是在沙漠地带。
此外，从太阳和风中获取的能量不仅取决于你所处的位置，还取决于时间——例如，在晚上我们无法从太阳中获取能量，风速也会随时间的变化而变化。又比如在一场狂风骤雨中，高风速可产生大量的电能——甚至超过可以使用的量——因此有时候必须停止风力涡轮发电机的运作，防止其受损。如果我们能找到一个方式可以把这些额外的能量储存起来，我们便不需要关闭涡轮发电机，也不用担忧没有阳光时获取不了太阳能。因此，将能源转化为燃料供今后使用是一件很有趣的事情。
Moreover, energy available from the sun and wind does not only depend on where you are, but also on the time—for example, at night we cannot get energy from the sun. Wind speed changes over time as well. During a storm with high wind speeds, for instance, a lot of electricity could be generated—even more than can be used—so sometimes wind turbines must be shut off to prevent damage. If we had a way to store this excess energy, we would not have to shut off wind turbines or worry about solar energy when the sun is not shining. Therefore, methods to convert energy into fuels for later use are very interesting.
METHANOL AND ITS MANY USES
甲醇和它的许多用处
甲醇是一种液体，它属于化学药品大家族的一员，这个大家族被称为“酒精”，简而言之就是由碳原子、氢原子和氧原子以特定方式连接而成。最有名的酒精是乙醇，也就是啤酒或葡萄酒等含有乙醇的酒精饮料。乙醇是如此的闻名遐迩以至于很多人在说酒精时往往指的是乙醇或含有乙醇的饮料。所以，你一定要记住，当一个化学家在谈及酒精时，往往和成年人派对上所说的酒精意思是不完全相同的。（醇和酒精在英语中都为“alcohol” ，译者注）
甲醇是这么多醇类物质中最简单的，因为它仅仅只是由一个碳原子，一个氧原子和四个氢原子组成的。虽是简单，它仍是个非常重要的化工药品。它是生产大量我们日常生活中使用商品的原材料，如塑料、油漆、药物、化肥等。此外，甲醇还可用于储存能源。有些工业加工能将甲醇转变成汽油（类似于化石燃料）或变成生物柴油，然后这些燃料就可以储存起来。如图2所示，1千克甲醇所含的能量与1千克木材所含的能量相似。这张图显示的是不同燃料的热值的比较，也就是单位公斤内该材料所含的能量。这个数值越高，意味着该材料可以储存更多的能量供以后使用。
Methanolis a liquid belonging to a family of chemicals that are called alcohols, which simply means it is made up from carbon, hydrogen, and oxygen atoms that are connected in a specific way. The most famous alcohol is ethanol, which is the alcohol contained in alcoholic drinks like beer or wine. Ethanol is so well known that many people say “alcohol” when in fact they mean ethanol, or any drink that contains ethanol. So, you must keep in mind that a chemist means something quite different from an adult at a party when talking about alcohols.
Methanol is the simplest possible alcohol, because it contains only one carbon, one oxygen, and four hydrogen atoms. However, it is still an important chemical. It is used as a raw material to produce a large number of goods we use in our daily lives, like plastics, paints, drugs, fertilizers, and many more [3]. Additionally, methanol can be used to store energy. There are industrial processes that turn methanol into gasoline (similar to the fossil fuel) or into biodiesel, which can then be stored. Methanol itself can be stored as fuel as well. The amount of energy contained in a kilogram of methanol is similar to the amount in a kilogram of wood, as you can see in Figure 2. The figure shows a comparison of the specific energies for different fuels, which means the amount of energy per kilogram material. The higher this value, the more energy the material can store for later use.
Figure 2 - The specific energy contained in different fuels varies.
图2—不同燃料的热值
Specific energy is the amount of energy set free when we burn a kilogram of any fuel. The unit of specific energy is joule (J) per kilogram (kg)—the capital M is an abbreviation for “mega,” which means that the number shown here are actually millions. The graph shows a comparison of the specific energies in various fuels. A kilogram of methanol contains slightly more energy than a kilogram of wood.
热值是指当我们燃烧一公斤某种燃料时所释放的能量。热值的单位是焦耳（J）每公斤（kg）—大写字母M是 "mega（巨大的） "的缩写，意味着这里显示的数字实际上是数百万。该图显示了各种燃料的热值比较。一公斤甲醇所含的能量比一公斤木材的略高。
TURNING CARBON DIOXIDE INTO METHANOL
将二氧化碳转化为甲醇
如果你把一种化学物质（如二氧化碳）转变成另一种化学物质，这个过程叫化学反应。当化学反应被用来将能源转化为燃料时，我们称这些为化学能转化。有许多不同的化学反应可以将CO2转变成甲醇。有一种直接的方法，这种方法只需用到二氧化碳和氢气，还有另外一些方法，这些方法中间有些步骤（如图3）。所有的这些可能的方法看起来都很简单，因为只涉及到非常简单的化学物质（如氢气和水）。
If you turn a chemical like carbon dioxide into another chemical, this is called a chemical reaction.When chemical reactions are used to convert energy into fuels, we call these processes chemical energy conversion.There are quite a few different chemical reactions to turn CO2 into methanol. There is a direct way, using only carbon dioxide and hydrogen, and there are other ways with steps in between (Figure 3). All these possibilities seem to be quite easy because there are only very simple chemicals (like hydrogen and water) involved.
Figure 3 - A two-step process for turning carbon dioxide (CO2 ) into renewable fuel.
图3—将二氧化碳(CO2 )转化为可再生燃料的两步过程
First we take CO2 and water (H2O), put in energy, such as wind or solar energy, and transform the ingredients into syngas, which is a mixture of carbon monoxide (CO) and hydrogen (H2), using a solid catalyst. Then the syngas is used in a second step to produce renewable fuel like methanol. In this way, we can store the energy we put into the reaction for later use.
首先，我们把二氧化碳和水（H2O），加上风能或太阳能等能源，利用固体催化剂将这些成分转化为合成气，即一氧化碳（CO）和氢气（H2）的混合物。然后将合成气用于第二步骤生产甲醇等可再生燃料。通过这种方式，我们可以将投入反应的能量储存起来，供以后使用。
然而，在此存在一个问题：二氧化碳是一种非常稳定的气体，意味着它不容易与其他化学物质发生反应，那就意味着我们必须使用一种催化剂使CO2发生反应。催化剂是一种可将化学反应变为有可能的物质，如果没有催化剂，这种反应根本就不会发生，或者说反应会十分缓慢。寻找有助于高效、低成本地生产可再生燃料的催化剂，成为当今许多科学家的重要研究领域。
在图3中，我们分两步展示了将二氧化碳转化为甲醇所需的必要物质成分以及过程。首先，二氧化碳与水和催化剂一起混合，然后，需要加入能量启动化学反应，产生合成气。合成气是合成气体的简称，是一氧化碳和氢气组成的混合气体。这些混合气体可在第二步反应中生成像甲醇一样的可再生燃料。
However, there is a problem: carbon dioxide is a very stable gas, which means it does not easily react with other chemicals. That means that we must use a catalystto make CO2 react [4]. A catalyst is a substance that makes a chemical reaction possible that would not happen at all or would only happen very slowly without the catalyst. Finding catalysts that help to produce renewable fuels efficiently and inexpensively is an important field of work for many scientists today.
In Figure 3, we show the ingredients necessary to turn carbon dioxide into methanol in two steps. First, carbon dioxide and water are combined with a catalyst. Then, energy needs to be added to start the chemical reaction that produces syngas, which is short for synthesis gas, a mixture of carbon monoxide and hydrogen. This mixture can then be used to produce renewable fuel like methanol in a second reaction.
TAKE-HOME MESSAGE
打包回家的信息
将二氧化碳等温室气体转化为像甲醇一样的可再生燃料，为我们储存能源提供了可行的方式。要做到这一点，我们可以在时间和地方允许的情况下利用可再生能源（例如：风能和太阳能）。我们可以通过化学反应让可再生能源转化生成甲醇，然后我们可以将甲醇运输到我们需要的地方将其储存起来供我们以后使用。这个过程还可以让我们暂时降低大气中温室气体的含量。更重要的是，这种对大气中已有的二氧化碳的“循环利用”有助于避免因燃烧化石燃料过多而释放出更多的二氧化碳。这可能有助于减轻全球变暖以及由人类活动引起的气候变化，而这两个都是我们这个时代极其重要的问题。
Turning greenhouse gases like carbon dioxide into renewable fuels, such as methanol provides us with a possible way of storing energy. To do this, we can harness renewable energy (for instance, wind or solar energy) where and when it is available. We can use the renewable energy in a chemical reaction to produce methanol, and then we can transport the methanol to where we need it or store it for later. This process also allows us to temporarily lower the amount of greenhouse gases in the atmosphere. More importantly, this “recycling” of the carbon dioxide that is already in the atmosphere helps to avoid the release of additional CO2 through the burning of fossil fuels. This might help to reduce global warming and human-made climate change, which are both extremely serious problems of our time.
Glossary 术语表：
Greenhouse Gas: ↑ A gas in the atmosphere that traps heat, causing higher temperatures. This effect of greenhouse gases is called the greenhouse effect.
温室气体:是指一种在大气中起保温作用的气体，它会使大气的温度升高，这种由温室气体所带来的大气温度的升高被称为温室效应
Human-Made Climate Change: ↑ The change in the Earth’s climate caused by human activities, such as the large-scale usage of fossil fuels.
人类活动造成的气候变化：由人类的各类活动所造成地球的气候变化，例如大规模地使用化石燃料
Energy Conversion: ↑ The process of turning one form of energy (such as wind energy) into another one (such as electrical energy); also called energy transformation.
能量转换：把一种形式的能量能转换成另一种形式的能量（例如将风能转换为电能）
Methanol: ↑ A chemical that consists of one carbon, one oxygen, and four hydrogen atoms. It belongs to a group of chemicals called alcohols, and can be used to store energy or to produce goods of our daily lives.
甲醇：由一个碳原子、一个氧原子和四个氢原子组成的化学物质。它属于醇类化学物质的一种，可以用来储存能量以及生产我们日常生活中的物品。
Specific Energy: ↑ The amount of energy contained in a kilogram of any fuel. This energy is set free if the fuel is burned.
热值：任何含量中单位公斤所含的能量。如果燃料燃烧，这种能量会被释放出来。
Chemical Reaction: ↑ A process in which two (or more) chemicals come together to form new chemicals. For instance, carbon dioxide can react with hydrogen to give methanol and water.
化学反应：两种（或两种以上）化学物质结合在一起形成新的化学物质的过程。例如，二氧化碳与氢气反应可生成甲醇和水。
Chemical Energy Conversion: ↑ The process of turning energy into fuels using chemical reactions. The fuels can then be stored for later used.
化学能转化：利用化学反应将能源转化为燃料的过程。这些燃料储存起来供以后使用）
Catalyst: ↑ A substance that makes chemical reactions possible that otherwise would not take place.
催化剂：使原本不会发生化学反应变为可能的物质
—The End—
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