This week sees the start of a test to produce hydrogen stored as sodium borohydride. When dissolved in ultra pure water, that material is just as easily and safely used as conventional fuels. The so-called H2Fuel will certainly simplify the use of hydrogen as a source of energy for transport purposes.
A small reactor was built for the test, into which the H2Fuel was injected. Each sodium borohydride molecule in the solution contains four hydrogen atoms. An activator is required in order to release them, in this case diluted hydrochloric acid which was also injected into the reactor. The sodium borohydride combines with oxygen from the water, thus releasing hydrogen. This hydrogen can then be tapped, as can the leftover sodium boric acid.
The reactor can be found at Plant One, the facility for chemical experiments in the Rotterdam Botlek area.
The use of ultra pure water, the purity of which is comparable with the water used in the chip industry, is essential for the outcome of the process, as pollutants must be avoided where possible.
That was the conclusion about six years ago, when the US Department of Energy conducted research into sodium borohydride. The energy density of the carrier plus the hydrogen turned out to be lower than the standard they had set themselves, namely 14% of that of petrol. The production of hydrogen from sodium borohydride also took too long.
An invention by Gerard Lugtigheid, technical manager and inventor, has produced a solution. He developed a method for the quick and virtually complete release of hydrogen from sodium borohydride by mixing it with ultra pure water and a 5% solution of hydrochloric acid, to work as an activator. The reaction not only releases hydrogen from the sodium borohydride but also from the ultra pure water.
NO PRESSURE TANK
The main objective of H2Fuel is to make hydrogen easier to handle as a source of energy for transport purposes. In gas form, a pressure tank capable of resisting 350 bar would be needed to store 5 kg of hydrogen, in order to cover a distance of 500 km.
The sodium borohydride and pure water slurry on the other hand, can be stored for fuelling in an extremely concentrated form without any reaction taking place. That will only happen once the activator has been added. And so H2Fuel can achieve an energy density equal to 20% of that of petrol. 'A tank of 100 litres of H2Fuel will get you around 1500 km', according to director Rob de Kraa of the H2Fuel Holding.
SEEING IS BELIEVING
One of the objectives of the test at Plant One is to prove that sodium borohydride is a safe method of releasing hydrogen. 'Whoever we talk to, they all find our H2Fuel to be so fantastic that they want to see the process before they'll truly believe in it. The test reactor is also mainly being used to ensure that the volume of hydrogen released can be precisely regulated using software. 'We'll be varying the injection pressure, the pressure in the reactor, the dosage of the substances and so on.' De Kraa expects to complete the first series of tests early next year.
The next step is re-use of the residual sodium boric acid. 'That recycling is essential in our model, and we expect to be able to reclaim 95% of the original sodium borohydride in the end.' The electricity required for that purpose can be supplied through wind turbines or solar panels. 'That will allow us to convert sustainable electricity into fuel.' De Kraa expects Plant One to be able to demonstrate the recycling process by next summer.
THREE TANK CAR
The large-scale use of the H2Fuel will require adjustments to the car. It will have a fuel cell, the reactor and three tanks: one for the sodium borohydride, one for the activator and one for the depleted sodium boric acid. It will also have a special fuelling nozzle and a triple hose. The existing infrastructure therefore requires adjustments, though these are much less drastic than the conversion of infrastructure for high-pressure hydrogen. In terms of safety, the less volatile sodium borohydride even scores better than petrol and diesel, according to De Kraa. 'Upon fuelling, the hydride and activator are added and the acid is extracted, and reprocessed elsewhere. That may sound complicated, but it provides a fuel which has been sustainably produced, which is easy to use and which does not leave behind any harmful emissions at all.'
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