How Greenhouse Gases Can Be Used to Store Energy
作者：Thomas Ruh，Verena Pramhaas，Patrizia Bartl，Christoph Rameshan? 譯者：小婧視野
摘要
“地球大氣中二氧化碳濃度上升一直是人們關(guān)注的問題，因為這會導致全球變暖，其帶來的氣候變化會對我們的生活環(huán)境造成嚴重的危害。因此，除去一部分二氧化碳對于應對全球變暖所帶來的有害影響至關(guān)重要。減少大氣中二氧化碳的含量的其中一個方法是讓二氧化碳轉(zhuǎn)變?yōu)槠渌瘜W物質(zhì)，例如甲醇。這種轉(zhuǎn)化不僅可以降低大氣中二氧化碳的濃度，而且還可以給風能、太陽能等這類可再生能量提供了一種儲存方式。
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
二氧化碳和氣候變化
二氧化碳(由一個碳原子和兩個氧原子組成的分子，CO2是它的化學式)是一種溫室氣體,這就意味著二氧化碳會導致所謂的“溫室效應”。空氣中的二氧化碳和其他溫室氣體會將地球上一部分原本應該散失回太空中的熱量截留到大氣中，類似于熱量被困在溫室內(nèi)或一個帶蓋的鍋中。這些熱量截留的效應對于我們地球上所周知的生命活動至關(guān)重要——如果沒有了這些熱量，大氣中的平均溫度將會是-18 ℃（0℉）
? 然而，CO2也是人類造成氣候變化和全球變暖的主要因素。燃燒經(jīng)數(shù)百萬年沉積形成的化石燃料，如石油和天然氣，會使大氣中CO2的含量增加，大氣中CO2含量增加則會導致更多的熱量被截留在大氣中，溫度也就隨之上升。因此，自從人類大規(guī)模使用化石燃料進行發(fā)電、交通運輸（汽車、飛機等）、取暖以來，全球的氣溫幾乎上升了整整一攝氏度！這溫度上升幅度聽起來并不大，可能我們會覺得沒什么，但這溫度的輕微上升會給我們敏感的環(huán)境平衡帶來相當嚴重的后果。例如：由于極地冰川融化導致海平面上升可能會影響到沿海城市，海水溫度升高將會對珊瑚礁的生存帶來威脅等。
? 減少大氣中二氧化碳的含量是與全球變暖作斗爭的重要一步。有一個可行的辦法就是把CO2轉(zhuǎn)化為可以儲存起來并今后可供我們作燃料的化學物質(zhì)。盡管這個方法略有不足之處：雖然生產(chǎn)這些可做燃料的易儲存的化學物質(zhì)可以減少大氣中的CO2，但這些化學物質(zhì)今后作為燃料燃燒時會將二氧化碳重新釋放到大氣中。然而，由于這個過程畢竟沒有新的二氧化碳釋放到大氣中，因此，隨著燃料的循環(huán)使用，二氧化碳是保持平衡的，這比使用化石燃料直接向大氣中排放新的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?
為什么我們要談論到儲存能源呢？
你所能想到的每一個活動過程都需要能量——例如，植物的生長，汽車的駕駛，甚至是你正在閱讀這篇文章，都需要能量。然而，這些能量并不會在活動結(jié)束后消失得無影無蹤！物理學中的一個很重要的原理指出，能量既不能憑空產(chǎn)生，也不能被破壞，只能從一種形式轉(zhuǎn)換（或轉(zhuǎn)化）為另一種形式。所以，我們對剛剛提到的活動過程的另一種思考方式就是可以把它們看作是能量轉(zhuǎn)換的過程。比如：植物利用來自太陽光的能量生長，能量便儲存在植物新生長的部分中。在汽車中，通過燃燒汽油可以使來自于燃料的能量轉(zhuǎn)變成物體運動的能量（我們把它稱為動能）和熱量。當你在移動眼睛閱讀此文章時，你的身體便會將你攝取的食物所提供的能量轉(zhuǎn)化為你身體的一系列動作。同時你的大腦也利用這些能量來處理和記住你所閱讀的內(nèi)容。所有的活動過程——無論是在自然界還是在使用機器上——基本上都是能量從一種形式轉(zhuǎn)換成另一種形式的過程。
在任何情況下能量都必須來自某個地方。能量的來源包括太陽（稱為太陽能）、風或水，但也包括石油或煤這些我們?nèi)栽诖笠?guī)模燃燒的化石燃料。大多數(shù)情況下，這些來自不同來源的能量會先轉(zhuǎn)化成電能，利用發(fā)電廠轉(zhuǎn)化煤和水（的能量），利用太陽能電池轉(zhuǎn)化太陽光能量以及利用風力渦輪機轉(zhuǎn)化風能，然后這些電能為電腦、工廠機器、電動汽車等等設(shè)備的運行提供動力。我們還可以把這些能量先儲存起來供我們以后使用——這就是所謂的燃料（有時候也被稱為能量載體，因為它們確實攜帶著能量）。
任何形式的燃料之所以都有很大用處，主要有兩個原因——運輸和儲存。圖1顯示的是不同地區(qū)利用風能和太陽能的潛力（意思是使能源轉(zhuǎn)化為可用的能量）差異很大。例如，在非洲，利用太能的平均潛力比歐洲和北美洲地區(qū)高。風能則恰恰相反——歐洲的平均風速比非洲大，尤其是在沿海地區(qū)。風速越大，利用風力渦輪發(fā)電機發(fā)電的能力就越強。這種能源分布不均勻的后果是，我們需要設(shè)法將能源輸送到需要的地方。而有了燃料，我們就可以將能源輸送到我們所需要的地方。
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.
? ?圖1-世界不同地區(qū)利用太陽能或風能的潛力各不相同
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.
在這張地圖中，你可以觀察到平均風速（藍色區(qū)域）和利用太 陽能潛力（紅色區(qū)域）是如何分布的。你可能會注意到，令人驚訝的是，赤道沿線的太陽能利用潛力只有中等級別（medium），這是由于這一地帶存在云層（這些云層也是赤道沿線有大面積雨林的原因）。許多太陽能潛力非常大的地區(qū)實際上是在沙漠地帶。
此外，從太陽和風中獲取的能量不僅取決于你所處的位置，還取決于時間——例如，在晚上我們無法從太陽中獲取能量，風速也會隨時間的變化而變化。又比如在一場狂風驟雨中，高風速可產(chǎn)生大量的電能——甚至超過可以使用的量——因此有時候必須停止風力渦輪發(fā)電機的運作，防止其受損。如果我們能找到一個方式可以把這些額外的能量儲存起來，我們便不需要關(guān)閉渦輪發(fā)電機，也不用擔憂沒有陽光時獲取不了太陽能。因此，將能源轉(zhuǎn)化為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
甲醇和它的許多用處?
甲醇是一種液體，它屬于化學藥品大家族的一員，這個大家族被稱為“酒精”，簡而言之就是由碳原子、氫原子和氧原子以特定方式連接而成。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飲料。乙醇是如此的聞名遐邇以至于很多人在說酒精時往往指的是乙醇或含有乙醇的飲料。所以，你一定要記住，當一個化學家在談及酒精時，往往和成年人派對上所說的酒精意思是不完全相同的。（醇和酒精在英語中都為“alcohol” ，譯者注）
甲醇是這么多醇類物質(zhì)中最簡單的，因為它僅僅只是由一個碳原子，一個氧原子和四個氫原子組成的。雖是簡單，它仍是個非常重要的化工藥品。它是生產(chǎn)大量我們?nèi)粘Ｉ钪惺褂蒙唐返脑牧希缢芰?、油漆、藥物、化肥等。此外，甲醇還可用于儲存能源。有些工業(yè)加工能將甲醇轉(zhuǎn)變成汽油（類似于化石燃料）或變成生物柴油，然后這些燃料就可以儲存起來。如圖2所示，1千克甲醇所含的能量與1千克木材所含的能量相似。這張圖顯示的是不同燃料的熱值的比較，也就是單位公斤內(nèi)該材料所含的能量。這個數(shù)值越高，意味著該材料可以儲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.
圖2—不同燃料的熱值
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.
熱值是指當我們?nèi)紵还锬撤N燃料時所釋放的能量。熱值的單位是焦耳（J）每公斤（kg）—大寫字母M是 "mega（巨大的） "的縮寫，意味著這里顯示的數(shù)字實際上是數(shù)百萬。該圖顯示了各種燃料的熱值比較。一公斤甲醇所含的能量比一公斤木材的略高。
TURNING CARBON DIOXIDE INTO METHANOL
將二氧化碳轉(zhuǎn)化為甲醇
如果你把一種化學物質(zhì)（如二氧化碳）轉(zhuǎn)變成另一種化學物質(zhì)，這個過程叫化學反應。當化學反應被用來將能源轉(zhuǎn)化為燃料時，我們稱這些為化學能轉(zhuǎn)化。有許多不同的化學反應可以將CO2轉(zhuǎn)變成甲醇。有一種直接的方法，這種方法只需用到二氧化碳和氫氣，還有另外一些方法，這些方法中間有些步驟（如圖3）。所有的這些可能的方法看起來都很簡單，因為只涉及到非常簡單的化學物質(zhì)（如氫氣和水）。
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.
圖3—將二氧化碳(CO2?)轉(zhuǎn)化為可再生燃料的兩步過程
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，我們把二氧化碳和水（H2O），加上風能或太陽能等能源，利用固體催化劑將這些成分轉(zhuǎn)化為合成氣，即一氧化碳（CO）和氫氣（H2）的混合物。然后將合成氣用于第二步驟生產(chǎn)甲醇等可再生燃料。通過這種方式，我們可以將投入反應的能量儲存起來，供以后使用。
然而，在此存在一個問題：二氧化碳是一種非常穩(wěn)定的氣體，意味著它不容易與其他化學物質(zhì)發(fā)生反應，那就意味著我們必須使用一種催化劑使CO2發(fā)生反應。催化劑是一種可將化學反應變?yōu)橛锌赡艿奈镔|(zhì)，如果沒有催化劑，這種反應根本就不會發(fā)生，或者說反應會十分緩慢。尋找有助于高效、低成本地生產(chǎn)可再生燃料的催化劑，成為當今許多科學家的重要研究領(lǐng)域。
? ? ? 在圖3中，我們分兩步展示了將二氧化碳轉(zhuǎn)化為甲醇所需的必要物質(zhì)成分以及過程。首先，二氧化碳與水和催化劑一起混合，然后，需要加入能量啟動化學反應，產(chǎn)生合成氣。合成氣是合成氣體的簡稱，是一氧化碳和氫氣組成的混合氣體。這些混合氣體可在第二步反應中生成像甲醇一樣的可再生燃料。
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
將二氧化碳等溫室氣體轉(zhuǎn)化為像甲醇一樣的可再生燃料，為我們儲存能源提供了可行的方式。要做到這一點，我們可以在時間和地方允許的情況下利用可再生能源（例如：風能和太陽能）。我們可以通過化學反應讓可再生能源轉(zhuǎn)化生成甲醇，然后我們可以將甲醇運輸?shù)轿覀冃枰牡胤綄⑵鋬Υ嫫饋砉┪覀円院笫褂谩＿@個過程還可以讓我們暫時降低大氣中溫室氣體的含量。更重要的是，這種對大氣中已有的二氧化碳的“循環(huán)利用”有助于避免因燃燒化石燃料過多而釋放出更多的二氧化碳。這可能有助于減輕全球變暖以及由人類活動引起的氣候變化，而這兩個都是我們這個時代極其重要的問題。
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?術(shù)語表：
Greenhouse Gas:?↑?A gas in the atmosphere that traps heat, causing higher temperatures. This effect of greenhouse gases is called the greenhouse effect.
溫室氣體:是指一種在大氣中起保溫作用的氣體，它會使大氣的溫度升高，這種由溫室氣體所帶來的大氣溫度的升高被稱為溫室效應
Human-Made Climate Change:?↑?The change in the Earth’s climate caused by human activities, such as the large-scale usage of fossil fuels.
人類活動造成的氣候變化：由人類的各類活動所造成地球的氣候變化，例如大規(guī)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.
能量轉(zhuǎn)換：把一種形式的能量能轉(zhuǎn)換成另一種形式的能量（例如將風能轉(zhuǎn)換為電能）
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：由一個碳原子、一個氧原子和四個氫原子組成的化學物質(zhì)。它屬于醇類化學物質(zhì)的一種，可以用來儲存能量以及生產(chǎn)我們?nèi)粘Ｉ钪械奈锲贰?/p>
Specific Energy:?↑?The amount of energy contained in a kilogram of any fuel. This energy is set free if the fuel is burned.
熱值：任何含量中單位公斤所含的能量。如果燃料燃燒，這種能量會被釋放出來。
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.
化學反應：兩種（或兩種以上）化學物質(zhì)結(jié)合在一起形成新的化學物質(zhì)的過程。例如，二氧化碳與氫氣反應可生成甲醇和水。
Chemical Energy Conversion:?↑?The process of turning energy into fuels using chemical reactions. The fuels can then be stored for later used.
化學能轉(zhuǎn)化：利用化學反應將能源轉(zhuǎn)化為燃料的過程。這些燃料儲存起來供以后使用）
Catalyst:?↑?A substance that makes chemical reactions possible that otherwise would not take place.
催化劑：使原本不會發(fā)生化學反應變?yōu)榭赡艿奈镔|(zhì)
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