H2Tech - Q1 2021 - 24

SPECIAL FOCUS

ADVANCES IN HYDROGEN TECHNOLOGY

FIG. 2. Process flow showing how H2 is liquefied for transport as a cryogenic liquid, is transported as a compressed gas or is transported
within an organic carrier (LOHC).
CH3

CH3
- 3H2
∆H = 205 kJ/mol

MCH

+ 3H2

TOL

FIG. 3. Chemical reaction formula used
for the SPERA Hydrogena process.

position and obvious improvements to
health, the environment and quality of
life. Benefits on a more global basis would
be commensurately similar.
Options for hydrogen deployment.
While the future for H2 looks bright, production, transportation, distribution and
a host of associated infrastructural issues
need to be considered. Assuming H2 availability, how to get it from where it is made
to where it is most needed (and at a reasonable cost) is of paramount interest.
Historically, H2 has been transported
either as a compressed gas in tube trailers or as a cryogenic liquid. Both methods
have pros and cons, but transportation selection and cost are ultimately determined
by how much H2 must be transported and
over what distance.
Prior studies undertaken for localized
distribution have considered and compared these conventional methodologies
with newer, more promising options of
transporting H2 bound by a chemical carrier, known generically as a liquid organic
H2 carrier (LOHC).
FIG. 2 shows how H2 is liquefied to 20K
(-253°C/-423°F) for transport as a cryogenic liquid. This is an energy-intensive
operation that uses around 30% of the contained H2 energy to complete the liquefaction process. The cryogenic H2 is then
24 Q1 2021 | H2-Tech.com

transported from the liquefaction point to
the point of use by truck. As per U.S. Department of Transportation (DOT) limitations on truck transport of liquefied H2,
approximately 4,000 kg of H2 can be transported per truckload. At the delivery site,
the liquid can be cryo-pumped to the dispensing point for subsequent vaporization.
At present, transportation of liquid H2 is
available only by truck; therefore, the scale
of transportation is limited, and further
technology development is required for
large-scale liquid transportation by ship.
Alternatively, H2 at approximately 540
bar (7,830 psi) can be transported by tube
trailer from a terminal to a dispensing
point where final compression (to around
700 bar/10,000 psi) is accomplished prior
to ultimate utilization. U.S. DOT regulations also limit the amount of H2 that can
be transported per tube-trailer truckload
to approximately 1,050 kg of H2 per truck.
Lastly, the LOHC option may be considered as a viable alternative. LOHC is a
suitable technology for large-scale, longdistance H2 transportation, or for largescale or daily to seasonal H2 storage, as will
be discussed in more detail in this article.
In all of these cases, the distance of transport, the volume of material being transported and the distribution particulars
will drive the best choice for the particular
H2 application at hand.
Advances in hydrogen storage/
transport technology. The SPERA

Hydrogena process is an H2 storage and
transportation technology for large-scale
and long-distance transportation. H2 is
chemically fixed to toluene and converted
to methylcyclohexane, according to the

reaction shown in FIG. 3. Methylcyclohexane is a convenient carrier for H2, as it is
easy to store and transport under ambient
temperature and atmospheric pressure.
In the SPERA process, H2 is stored and
transported in large-scale quantities at a
competitive cost, since cryogenic liquefaction or compression to very high pressures is not required.
The SPERA process is based on a
simple process configuration. Methylcyclohexane and toluene react in fixed-bed,
tubular-type reactors in the vapor phase.
FIG. 4 shows simplified process flow diagrams of the hydrogenation and dehydrogenation processes for the overall SPERA
process. In the hydrogenation process,
toluene feed is vaporized in the vaporizer
(1) and mixed with H2 including recycle
gas. The mixed feed is superheated to the
reaction temperature (2) and then enters
the top of the reactor (3), which is a fixedbed, tubular reactor charged with a semiconventional hydrogenation catalyst. In
the reactor tubes, toluene reacts with H2
to produce methylcyclohexane.
Hydrogenation of toluene is an exothermic reaction. The generated heat is
removed by cooling water to control the
reaction temperature, and the heat is subsequently recovered as medium-pressure
steam, which can be further utilized as
needed. The generated steam is clean energy without carbon emission. The effluent
gas from the tubular reactor is cooled, the
condensed methylcyclohexane is separated (6) from the recycle gas, and the liquid
product (methylcyclohexane) is sent to
storage tanks. Recycle gas is then returned
to the reactor after being mixed with
fresh H2 feed. Very high product yield is

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