Production of Hydrogen

Hydrogen energy is belonging to the secondary energy. On the Earth where the human beings depend upon for life, although hydrogen is the richest element, the natural hydrogen exists extremely few. Therefore, the hydrogen gas can be obtained after possessing the hydrogen-contained matters. The richest hydrogen-contained matter is water (H2O), next is various fossil fuels (i.e. coal, petroleum, natural gas) and biomass. So in order to develop and utilize this ideal clean energy, it is necessary to exploit the hydrogen resources, that is to research and develop the diverse hydrogen production methods From the long perspective, producing the hydrogen by use of water as raw materials is the most promising methods due to the fact that the raw materials will not be run out, and the energy released by the hydrogen combustion can also generate products---water, which will not create the environmental pollution. The current main methods to produce hydrogen are via various fossil fuels that are limited in reserves and will pose the environment pollution in the course of production. Other methods to convert diverse hydrogen-contained matters to produce hydrogen are now on the stage of secondary position or under the development. However along with the expanding of hydrogen applications, the requirement will be increasing, and it will be another approach to supply hydrogen resources.

Various Hydrogen Production Methods

1.        Hydrogen Production by Electrolysis

Hydrogen production by electrolysis has been one of the current methods that is applied broadly and has become more mature. The hydrogen production by water as the raw material is the reverse process to combust hydrogen and oxygen to generate water. Therefore, it is only required a certain energy with a certain type to split out the water. The production efficient to split out the water by supply of electricity can be fixed from 75% to 85% generally, with the simple process and no pollution but heavy consumption of power. So its application was restrained. So far the process and equipment for water electrolysis are increasingly improved. The pole material for the electrolysis reactor has been meliorated. The electrolyte was used to employ strongly alkaline liquid. In recent years, solid-state high polymer ion exchanging membrane was researched and employed as electrolyte. And this membrane can also play the function to separate the pole in electrolysis tank. The parameters such as high temperature and high pressure are employed in the electrolysis process so as to be useful for the proceeding of reaction. But the energy consumption for water electrolysis is still comparatively higher, with the power consumption of 4.5 to 5.5kWh for producing per cumber meter hydrogen gas. The electricity can be supplied by various primary energies, including fossil fuels, nuclear power, solar energy, water energy, wind energy and ocean energy. The nuclear power, water energy and ocean energy are abundant which can be utilized in a long term. The hydropower abounds in China. Therefore, it has promising penetration by use of hydropower to produce hydrogen. The solar energy is unexhausted. The method to produce hydrogen by use of photo electricity is called solar-hydrogen energy system of which research has been conducted in foreign countries. Accompanying with the improvement of solar cell conversion efficiency, decline of cost and prolonging of service life, its promising is invaluable.

Moreover, the solar energy, wind energy and ocean energy can also produce hydrogen by electrolysis, and utilize the hydrogen as carrier to adjust and store the converted energy making the energy supply for the consumer more convenient and flexible. The rich electricity of the power supply system in the valley can also be used to produce hydrogen so as to store the energy. There are hundreds and thousands of hydrogen production plants in diverse scale in China, primarily with small-scale hydrogen production plants, aiming to produce the hydrogen to be raw material other than energy.

Regarding the tasks of pole process and material in the electrolysis reaction, Nankai University and Capital Teacher’s Training University have once organized the research. Along with the expanding of its applications, the hydrogen production methods by electrolysis will be increasingly developed.

The hydrogen production method to split out the water in the thermo-chemical circle by use of water as raw material avoids the high temperature (higher than 4000K) requested by the thermal destruction directly using the water, and can reduce the energy consumption, which has attached great importance. This method is to add an intermedium in the water reaction system. After seeing diverse reaction stages, the water is finally decomposed to hydrogen and oxygen without consuming the intermedium. The reacting temperatures in each stage are quite lower. In recent years, more than 20 kinds of thermo-chemical circulation methods have been researched and developed, of which some have been test run.

The photochemical hydrogen production is to catalyze and decompose the photo to produce hydrogen by use of water as raw material. The process to catalyze the photo refers to the reaction system contained with catalyzer under the sunlight to prompt the water destruction to generate the hydrogen due to the existing of catalyzer. There were research reports in overseas from the 1970s. Units such as the sensitization institute under Chinese Academics of Science have also imitated the research. This method is promising, but still on the stages of basic research so far.

2.        Hydrogen Production by Fossil Fuels

To produce hydrogen via coals, petroleum and natural gas as the raw material has been the primary method so far. The produced hydrogen gas can be used mainly to be the chemical raw material, for example to generate compound ammonia, and compound methanol. Sometimes, some of the hydrogen-contained gases can be used as gas fuels to supply for the municipal coal gas. The hydrogen production by fossil fuels include the procedures of hydrogen-contained gases manufacturing, transformation reaction of the content of CO in gases and purification of hydrogen gases. China has achieved mature technologies of this method and established industrialized production plants.

1)        Hydrogen Gas Production by Coals as Raw Materials

The hydrogen-contained gas production by coals as raw materials has mainly two catalogues: one is to carbonize the coal (or called high-temperature carbonization); another is the gasification of the coal. The carbonization refers to produce the carbon and coke oven gas as by-products in the temperature of 900°C to 1000°C under the circumstance that the coal is separated from the air. Among the composition of coke oven gas, hydrogen covers 55-60% (in volume), methanol 23-27%, carbon monoxide 5-8%. 300 –350m³ coal gas can be obtained from each ton of coal as the municipal coal gas or the raw material to produce the hydrogen.

The gasification of coal means that the coal is to react with gas agent and transformed to gas products under the condition of high temperature and normal pressure or pressurization. The gas agent can be water steam or oxygen (air). The gas products contain with the composition of hydrogen gas, with its content various along with diverse gasification methods. The gasification aims to produce the chemical raw material or municipal coal gas. Large-scale industrial gasification oven is generally a kind of fixed bed-type gasification oven. The produced coal gas is composed with hydrogen representing 37 to 39%, carbon monoxide 17 018%, carbon oxide 32%, and methanol 8-10%. China has large-scale oven, with each production reaching 100,000m3/h. Another innovative oven is the gas current bed gasification oven, taking coal-water slurry as raw material. China has lunched the research and development from the 1960s and so far has established industrial production plants to produce compound ammonia, compound methanol raw material gas of which coal gas is composed with hydrogen of 35-36%, carbon monoxide of 44-51%, carbon oxide of 13-18%, methanol of 0.1%. Its characteristic is the low content of methanol. China has a lot batch of medium and small-scale compound ammonia factory, taking coal as raw material. After gasified, the produced hydrogen-contained coal gas can be the raw material of compound ammonia. This is one kind of method to obtain the hydrogen resources with the Chinese characteristic. To employ OGI fixed bed-type gasification oven can produce the coal-water gas in an intermittent way. This plant can be invested with few input and is easy to operate, of which gas products are composed with hydrogen and carbon monoxide, among which hydrogen gas can reach more than 60% and can produce pure hydrogen after being transformed. For the hydrogen production method by gasification, its equipment expense covers the main part of the investment. The coal gasification under the earth has also attached the attention in recent several decades. This technology has the advantages of high utilization rate in coal resources, and decline or avoiding the destruction of surface environment. Mr. Yuli of China Mining University developed and perfected the new technology of coal-water gas production. Among the coal gas, the hydrogen content reaches more than 50%. It has been industrially test run in Tangshan, with the daily production of coal-water gas of 50,000m3. If it can be further transformed or purified by pressure swing adsorption method, cheap hydrogen gas can be produced. This method has a promising market penetration in China.

2)        Hydrogen Production by Taking Natural Gas or Lightweight Oil as Raw Material

The method to produce the hydrogen is under the circumstance that the catalyzer exists and is to react with the water steam. The reaction can be conducted under the temperature of 800 to 820°C. Among the gas produced in accordance with this method, the hydrogen gas composes 74%. Its production cost primarily depends upon the price of raw material. Due to the high price of lightweight oil in China, resulting in the expensive production cost, its applications are therefore limited. The majority of large-scale compound ammonia and compound methanol factory are employed the natural gas as the raw material to catalyze the water steam to be converted into hydrogen. China has made lots of cutting edge research in this field and established a batch of industrial production plants. China has been developed and employed the intermittent type natural gas and steam conversion process to produce hydrogen, and prepare the raw material for the small-scale compound ammonia factory. In this method, it is not required to adapt the high temperature alloy conversion oven, with the low investment input on plant.

3)        Hydrogen Production by Taking Heavy Oil as Raw Material and Partly Oxidation

The raw materials of heavy oil include the residual oil in normal pressure or pressure declining or the combustion oil after the petroleum has been deeply processed. The hydrogen gas can be obtained after heavy oil is to be reacted with water steam and oxygen. While part of heavy oil is combusting, it can provide the heat required by the conversion and heat absorption reaction and a certain reaction temperature. The gas product composes by hydrogen covering 46%, carbon monoxide 46%, carbon oxide 6%. Among the hydrogen production cost in this method, the raw material expense covers 1/3. Due to the cheap price of heavy oil, as a consequence, this method has drawn much attention. China has set up large-scale hydrogen production plant to partly oxidize heavy oil, utilizing for preparing the raw material of compound ammonia.

3.        Hydrogen Production by Biomass

The biomass resources are abundant and it is also an important renewable energy. Hydrogen can be obtained by way of gasifying the biomass or by use of microorganism.

1)        Hydrogen Production by Gasifying Biomass

The hydrogen-contained combustion gas can be produced by compressing the raw material of biomass such as core wood, sawdust, straw or haulm to make the gasification or cracking reaction in the gasified oven or cracked oven. A certain of results have been achieved in the field of biomass gasification technology. Guangzhou institute of energy conversion has conducted the research of biomass gasification for many years. Among the gasification products, hydrogen represents about 10%, with the thermal value of11MJ/m³, which can be used as fuels in the countryside. However, the content of hydrogen is still lower. In overseas, due to the improvement of conversion technology, the gasification of biomass can be large-scale produced coal-water gas, with increasing content of hydrogen.

2)        Hydrogen Production by Microorganism

The hydrogen production technology by microorganism also draws the right consequences. The hydrogen gas can be produced by use of microorganism to make the enzyme catalysis reaction under the normal temperature and normal pressure. It mainly has two catalogues, including nourish microorganism by energy conversion and photosynthesis of microorganism. The former includes various fermented microorganisms, such as anaerobic and facultative aerobic bacteria. The original ground substance is various carbohydrate and protein. So far there is hydrogen production patent by use of carbohydrate ferment, and its produced hydrogen can be used as energy to generate electricity. The hydrogen production process between the photosynthesis microorganism such as micro-algae and photosynthesis bacteria has related to the photosynthesis, thus called hydrogen production by photosynthesis. In the early of 1990s, the microorganism institutes under Chinese Academic of Sciences and Zhejiang Agricultural University have once conducted the separation and selection research on hydrogen-produced purple non-sulfur photosynthesis bacteria, and research on hydrogen production in the process of sewage treatment by fixed type photosynthesis bacteria. Results have been achieved. In foreign countries, a kind of optimized biology reactor applied to produce hydrogen by photosynthesis bacteria has been designed, with the scale of daily production of 2800m³. In this method, various industrial and domestic organic wastewater and waste materials of agricultural products are applied as the ground substance, and the photosynthesis bacteria are continuously cultivated. Whilst producing the hydrogen, wastewater can be purified and unicellular protein can be obtained. Therefore, it has great prospect.

4.        Hydrogen Production by other Hydrogen-contained Matters

In foreign countries, research has been made to produce hydrogen from the sulfureted hydrogen. H₂S resources abound in China, for example among the natural gases exploited in the Zhaolanzhuang oil and gas field in Hebai province, the content of H₂S is higher more than 90% and the reserves reach several ten million tons. It is a precious resource. There are different methods to produce hydrogen from the sulfureted hydrogen. From the 1990s, China started extensive research. For example, the Petroleum University conducted the research on hydrogen production under dual reaction system by indirect electrolysis and sulfur. Progress has achieved and the expanding experiment is undergoing. The sensitization institute under Chinese Academic of Sciences has also organized the research on sulfureted hydrogen decomposed by multi-phase enzyme catalysis, and research on hydrogen production by decomposing the sulfureted hydrogen by microwave plasma panel. All of these research results will create conditions to take full benefits of the precious resources, to provide clean energies and chemical raw materials.

5.        Recovery of Hydrogen as Byproducts in Various Chemical Process

Large amount of byproducts---hydrogen gas will be released in various chemical processes, such as salt-electrolysis alkaline manufacturing, ferment wine process, compound ammonia in chemical fertilizer industry and petroleum-refined industry. If appropriate measures can be applied to separate and recover the hydrogen gas, billions of cumber meters of hydrogen gas can be obtained in each year. This is an indispensable resource, which should be recovered and reused.