*2.2.2. Chemical-based conversion*

In a chemical approach, cellulose in a raw biomass can be converted to biofuel. Another new process has been introduced to convert cellulose to chemical 5-hydroxymethylfurfural (HMF). Cellulose, through catalytic conversion, can be converted to HMF [24], and recently formation of HMF through catalytic conversion in ionic liquid produced more than 50% of HMF [25–28]. HMF is oxygen rich and hydrogen deficient that can be used for biofuel production through a reduction process that led to the production of 2,5-hexanedione (HD) [29]. Meanwhile, recently one report indicates that direct electrochemical method to convert HMF to HD without any means of catalysis or hydrogen. Instead HD is produced using water and metal electrode to open up furan ring in HMF and selectively in one-step mode [30].

There is another process called 'thermochemical' that involves thorough deconstruction of feedstock and develops the resulting intermediates into different types of fuels and fine chemicals. Thermochemical process consists of three processing parts which include gasification or devolatilisation to produce raw syngas, syngas conditioning and removal of other residual gases such as H2 S and CO<sup>2</sup> and finally conversion of syngas to fine chemicals such as olefins, aromatic mixed alcohols and fuel for transportation [31].
