**9. Relationship with hydrogen society**

Hydrogen economy that is being a focal point in several developed countries can be a chance as well as danger to alcohol fuels. It is a chance because hydrogen can be manufactured with easily distributable alcohols but can be a danger when all liquid fuel-based infrastructure might be changed to the fully gas-based or hydrogen system in the long run.

Due to the concerns on climate change that requires CO2 reduction and the concerns on environmental pollutants like fine particulate and NOx, hydrogen has been hoped eventually to replace all other energy mainstream options. During the last few years, hydrogen economy has reborn as a cure for CO2 and environmental issues like an ultra-fine particles and PM2.5. But due to its high cost in hydrogen production as well as in application tools such as fuel cell and still-unstable infrastructure, hydrogen era might come after few decades of development and trial and errors. In contrast, alcohol fuels have been viewed as a cheap and reliable option in replacing fossil fuels. Especially, the possibility of utilizing abundant biomass prompts to try many ways in technology development and commercialization.

Hydrogen is the most abundantly available element in the universe with immense possibility as essential energy source sometime in the future. At present, however, technologically and economically viable means of its utilization as an affordable energy source are not ready and many countries opt to pursue the hydrogen economy path as a mean for dealing with climate change and pollution problems in their major cities.

Hydrogen economy involves the generation of renewable electricity from photovoltaic cell or wind turbine, and the so-called water-to-gas (PtG or P2G) which involves water electrolysis using the excess electricity to produce hydrogen. Green hydrogen energy generation and utilization is the ultimate goal in hydrogen economy in which society of no CO2 evolution and no fossil fuels will eventually be accomplished. On the other hand, methanol society focuses on the production of CO2-free energy source from renewable biomass or sea algae which grow by photosynthesis in nature. Green hydrogen energy will be further refined to maturity, at least by the 2030s, in such countries that can afford to bear the related high costs.

More specifically, introduction of fuel cell vehicle using hydrogen will initiate and further expand in those countries which suffer from persistent air pollution (China, Korea, Japan, large metropolis areas of the EU and United States). In contrast, alcohol-based energy source such as ethanol and methanol is most suitably applicable in tropical or semitropical countries where biomass resources are abundantly available, while domestic energy sources are not plentiful.

For realization of such alcohol-based energy generation from raw material of (very low) calorific value per unit volume, the current high-cost situation related to the pretreatment and production processes should be solved.
