|Chiyoda’s hydrogen supply chain concept. Click to enlarge.|
Japan-based Chiyoda Corporation announced that a demonstration plant located in its Koyasu Office and Research Park has successfully achieved expected performance using a liquid organic hydrogen carrier (LOHC) technology.
The demonstration was a test run to prove Chiyoda’s “Large-Scale Hydrogen Storage and Transportation System” including (1) hydrogenation to fix hydrogen to toluene (C7H8) producing methylcyclohexane (MCH: C7H14), with a liquid phase at ambient temperature and pressure; (2) storage and transportation of MCH; and (3) dehydrogenation to extract hydrogen from MCH by using a Chiyoda-developed catalyst. MCH has 6.1 wt% of gravimetric hydrogen content and 47% of volumetric content theoretically.
MCH can be transported with a chemical tanker the as same as toluene. On the demand site, hydrogen is generated from MCH by a dehydrogenation reaction, and toluene is recovered for the recycle use. Chiyoda says that its LOHC system is suitable for large-scale storage and long distance transportation due to the ambient condition with the low potential risk.
This system can utilize existing infrastructures—including oil tanks and tankers for storage and transportation—without the need for cryogenic technologies such as is used for LNG and liquefied hydrogen. Chiyoda suggests that proves that it is possible to supply and deliver hydrogen on a commercial basis.
Chiyoda calls the MCH in this system “SPERA (a Latin word for hope) Hydrogen”, reflecting its ambition to establish a hydrogen supply chain.
Organic Chemical Hydrides (OCH) can store and transport hydrogen under ambient temperature and pressure. In this approach, hydrogen is fixed to an aromatic compound such as toluene via hydrogenation reaction. Toluene is converted to methylcyclohexane (MCH). Chiyoda employed a toluene and MCH system because that system has a wide temperature range under which system can be kept in its liquid state. Other systems require a solvent to maintain the liquid state. Because toluene and MCH system are in the liquid state under from -95 to 101 °C, solvent is not needed in any reasonable circumstance, Chiyoda suggests.
|Gravimetric and volumetric content of hydrogen storage systems. Click to enlarge.|
In the OCH method, hydrogen gas volume is reduced to <1/500 under ambient condition. (Natural gas volume is reduced to <1/600 by liquefaction using -163 °C as LNG.) Although liquefied hydrogen (LH2) reduces hydrogen gas volume <1/800, the method needs -253 °C and boil-off gas treatment.
By contrast, the OCH method is suitable for large-scale storage and transportation, since the method has relatively high storage density in spite of ambient condition and no loss of hydrogen during long-term massive storage.
In Japan, both OCH and LH2 are under development as large-scale hydrogen storage and transportation methods. The practical use target of LH2 with large LH2 tankers is 2025, Chiyoda says.
Both toluene and MCH can be transported commercially by a middle-range class chemical tanker with more than 50,000 tons of toluene or MCH. The amount of hydrogen transported by such a chemical tanker is more than 3,000 tons of hydrogen—equivalent to the fuel for 600,000 FCVs with 5kg hydrogen, according to Chiyoda.
Although the OCH method was investigated in the 1980s as a method to transport hydrogen from hydraulic power in Canada to Europe, a viable dehydrogenation process did not exist in those days, and hence the process was not commercialized.
Chiyoda claims to have developed a high performance and long life dehydrogenation catalyst. Platinum clusters (<1nm) are impregnated on alumina supports of which pore size is controlled uniformly to increase the catalytic activity; the platinum cluster is partially modified with sulfur atoms to prevent coking. Although a usual platinum-impregnated alumina carrier is of an egg shell type in which the platinum cluster is dispersed only in the rim of the catalyst pellet, the Chiyoda catalyst is of a uniform type in which the platinum cluster is uniformly well dispersed around the inside of the catalyst pellet.
|Estimated surface model of developed dehydrogenation catalyst. Click to enlarge.|
The Chiyoda dehydrogenation catalyst shows MCH conversion > 95%, toluene selectivity >99.9% and hydrogen yield of more than 95% under the condition of around 350 °C, 0.3 MPa and LHSV =2.0 h-1. Hydrogen can be generated at more than 1,000 Nm3-H2/h/m3-cat. Catalytic performance has been shown to be stable for more than 1 year continuously.
The catalyst will be exchanged after deactivation of the catalyst; platinum can be recovered from the spent catalyst. Since the recovered platinum will be used for the catalyst production for next charge, catalyst cost is estimated to be the same as petrochemical catalysts.
Chiyoda also developed a dehydrogenation process using its catalyst in a simple fixed bed tubular reactor.