Bioconversion of Carbon Dioxide into Methanol

This approach, even if quite appealing, is not economically and energetically affordable unless NAD formed upon oxidation of NADH is efficiently recycled, increasing thereby the ratio CH3OH/NADH to limits that can be acceptable for a biotechnological production of methanol. 

More robust enz5mies have been obtained [95] by encapsulation. TEOS is better used with Ca-alginate as agent for producing a Ca-silicate cage, as it avoids any interference with the production of methanol in the case of non-complete hydrolysis of TMOS [97, 98]. Co-encapsulated enzymes work better than singly encapsulated ones [99]. 

Among the chemicals, hydrazine and sodium dithionite-SDT [100, 101] have been used. The latter has been slowly added up to a stoichiometric amount - see (9.3) - to NAD after all NADH is oxidized to NAD , producing 5 mol of methanol per mol of NADH. Addition of excess of SDT causes a rapid deactivation of the enzymes. 

In order to avoid such detrimental contact, the oxidation of NADH and the reduction of NAD have been carried out in separate boxes to obtain a ratio of CH3OH/NADH up to 35 [102]. 

For the chloroplast photosystem, only 0.25 mM NADH was obtained in 30 min, which is below the NADH regenerating activity of PTDH. 

---