As described above, the flexibility and good generality combined with the ease of recovering the lignin and hemicellulose sugar streams make organosolv pre­treatment one of the most efficient pretreatment techniques. Its fundamentals and effective operation factors for improvement of the enzymatic hydrolysis have been well demonstrated in this literature. However, organosolv pretreatment still possesses several disadvantages [78] as below:

1. A higher cost that is associated with the handling and recovery of the organic solvent.

2. Pretreatment efficiency is still relatively low for softwood and similar feedstocks.

3. Its lignin product tends to be less water-soluble, which may limit its use in some applications.

4. Currently, there are few organosolv pretreatment operations on a commercial scale, and there are fewer commercial sources of organosolv lignin for further exploitation.

To resolve the above problems, further develop organosolv pretreatment technology, and consequently benefit the economics of the entire cellulosic bio-fuel production, we present the following recommendations:

1. Optimizing the effective factors of organosolv pretreatment on certain biomass materials, such as reaction time, temperature, catalyst concentration, biomass — to-solvent ratio, against the delignification and enhancement of sacharifaction by surface response design or orthogonal design.

2. Advancing the pretreatment process by (i) using cheaper and renewable medium; (ii) using highly efficient microwave-irradiation and ultrasonic techniques to re­place the common thermo heating and mechanical stirring methods [82]; (iii) employing two-phase heterogeneous medium; (iv) performing concentration op­eration with preheated aqueous organic fluids [65]; and (v) combining organosolv pretreatment with other methods to achieve higher delignification and hydrolysis efficiencies, especially for softwoods.

3. Improving the fundamental knowledge on the pretreatment technologies espe­cially for some recalcitrant biomasses (such as softwood).

4. Investigating new processes and products from the organosolv lignin and hemicellulose sugars derived from the organosolv process.

5. Conducting economic evaluation of the entire organosolv pretreatment.

6. Demonstrating organosolv-pretreatment technology on a pilot scale to obtain engineering data for industrial scale processing and sufficient refined products for characterization and exploitation.