氢气作为燃料——定义、用途、例子
氢是现代元素周期表上的第一个元素。与所有其他元素相比,它具有最简单的原子结构。在原子形式中,它有一个质子和一个电子。另一方面,在元素形式中,它以称为二氢的双原子 (H 2 ) 分子的形式存在。如果氢失去它的一个电子,它将成为一种基本粒子,质子。
这就是氢气的独特之处。氢是宇宙中最丰富的元素。它在自由状态下的地球大气中并不常见。然而,当我们考虑结合状态的氢时,它是地球表面第三丰富的元素。
什么是二氢?
Dihydrogen, as mentioned above, exists as the diatomic molecule H2 of Hydrogen. It is the primary element in the solar atmosphere and the most abundant in the universe, constituting 70% of the universe’s total mass.
相比之下,由于其轻质,它在地球大气中的含量要少得多(按质量计为 0.15%)。然而,它以多种因素的组合形式出现,如水、植物和动物组织、蛋白质、碳水化合物、碳氢化合物和许多其他化合物。
氢气在工业上是通过石化产品的水煤气变换反应制备的。它是盐水电解的副产品。二氢具有非常高的负解离焓,因此它在室温下相当不活跃。然而,它在适当的条件下与几乎所有元素结合形成氢化物。
氢气的用途
- 二氢的最大用途是合成氨。用于制造硝酸和氮肥。
- 氢气通过多不饱和植物油(如棉籽、大豆等)的氢化用于制造 vanaspati 脂肪。
- 也用于制造LiH、AlH 3 、CaH 2等金属氢化物。
- 氢气用于制造大量有机化学品,特别是甲醇。
CO (g) + 2H 2 (g) ⇢ CH 3 OH (l) (在钴存在下)
- 也用于制备氯化氢(HCL)。它用于在冶金过程中将重金属氧化物还原为金属。
- 氢气在太空研究中用作火箭燃料。
- 它用于在燃料电池中发电。与传统的化石燃料和电力相比,这具有几个优势。与汽油和其他燃料相比,它是无污染的,并且每单位质量的燃料释放更多的能量。
氢气作为燃料
氢气燃烧时会释放大量热量。我们可以比较不同燃料(如甲烷、液化石油气、二氢等)燃烧释放的能量,以摩尔、质量和体积的相同数量表示。
以摩尔、质量和体积表示的各种燃料燃烧释放的能量如下表所述:The energy released on combustion (in kJ) Dihydrogen (in a gaseous state) Dihydrogen (in liquid state) LPG CH4 gas Octane (in liquid state) per mole 286 285 2220 880 5511 per gram 143 142 50 53 47 per litre 12 9968 25590 35 34005
从上表可以推断,以质量为基础,二氢比汽油释放更多的能量(约三倍)。此外,氢气的燃烧将导致比汽油更少的污染。由于二氮作为杂质存在于二氢中,因此唯一的污染物将是二氮的氧化物。
这可以通过降低钢瓶的温度来最小化,这样二氮和二氧之间的反应就不会发生。这可以通过向气缸中注入少量水来完成。虽然在这样做的同时,我们还应该考虑容纳氢气的容器的质量。如果我们考虑相应燃料产生的等量能量,一缸压缩氢气的重量将是一罐汽油的 30 倍。
此外,我们必须通过将氢气冷却到 20K 来将其转化为液态。我们将需要昂贵的绝缘罐进行这种转换。 NaNi 5 、Ti-TiH 2 、Mg-MgH 2等金属合金罐用于储存少量氢气。因此,由于这些缺点和限制,我们开发了替代技术来有效地使用氢气。
氢经济
氢经济是一种有效利用氢气的替代技术。氢经济的基本原理是以液态或气态二氢形式传输和储存能量。主要优点是在这种情况下,能量直接以氢气的形式而不是以电力的形式传输。
目前的进展
- 2005 年 10 月,印度首次启动了使用氢气作为汽车燃料的试点项目。
- 起初,只有 5% 的氢气混合在 CNG 中用于四轮汽车。这个百分比正在逐渐增加,以优化二氢作为燃料的使用。
- 如今,它也用于发电的燃料电池。预计在未来几年将确定经济和更安全的氢气来源,将其用作常见的能源。
示例问题
问题1:什么是二氢?
回答:
In elemental form, Hydrogen exists as a diatomic (H2) molecule called dihydrogen. It occurs in combined form in several factors like water, plants and animal tissues, proteins, carbohydrates, hydrocarbons, and many other compounds. Dihydrogen is industrially prepared by the water-gas shift reaction from petrochemicals. It is acquired as a by-product of the electrolysis of brine. Dihydrogen has a very high negative dissociation enthalpy, thus is it rather inactive at room temperature. Yet, it combines with almost all elements under appropriate conditions to form hydrides.
问题二:什么是氢经济?
回答:
Hydrogen Economy is an alternative technique to use dihydrogen efficiently. The basic principle of the Hydrogen Economy is the transporting and storing of energy in liquid form or gaseous dihydrogen. The primary advantage is that energy in this case is transmitted directly in the form of dihydrogen and not in the form of electric power.
问题3:为什么氢会储存在合金中?
回答:
We need to convert dihydrogen gas to the liquid state by cooling it down to 20K. For this conversion, we require expensive insulated tanks. Tanks of metal alloys like NaNi5, Ti-TiH2, Mg-MgH2, etc are used for storing dihydrogen in small quantities.
Moreover, alloys are used for the following reasons:
- Energy Conversion (as discussed above).
- Hydrogen Separation, recovery and purification.
- Isotope Separation.
- Catalysis.
- Alloy sensors and batteries.
- Storage and transportation of hydrogen.
问题四:氢气是如何大规模生产的?
回答:
Hydrogen is produced on a large scale by electrolysis of water or by thermochemical reaction cycle.
问题 5:比较氢和汽油作为燃料。
回答:
Dihydrogen releases more energy than petrol (about three times) on a mass for mass basis. Additionally, the combustion of dihydrogen will lead to less pollution than petrol. As dinitrogen is present as an impurity with dihydrogen, the only pollutants will be the oxides of dinitrogen. We should also consider the mass of the containers that hold the dihydrogen. If we consider the equal amounts of energy that would be produced by the respective fuels, a cylinder of compressed dihydrogen would weigh 30 times more than a tank of petrol.
问题 6:氢气作为燃料会出现什么问题?
回答:
There are several disadvantages and limitations of dihydrogen as a fuel due to which we have developed alternate techniques to use dihydrogen efficiently. One disadvantage is that the storage of dihydrogen becomes very difficult. We need to convert dihydrogen gas to the liquid state by cooling it down to 20K. For this conversion, we require expensive insulated tanks. Tanks of metal alloys like NaNi5, Ti-TiH2, Mg-MgH2, etc are used for storing dihydrogen in small quantities. This is overall not economical and very expensive.