On the other hand, as a good liquid fuel, bio-oil from pyrolysis of biomass, has to be homogenous and its properties should not change significantly during the storage [75]. As pyrolysis liquids contain a high number of compounds with var­ious chemical functionalities, the homogenity of the liquid highly depends on the

A: 0 for less than 10, 1 for less than 10-14, 2 for between 14 and 20, 3 for higher than 20MJ/kg. (Note that typically biomass has 12-14 MJ/kg), B: 1 if furthest from coal, 2 if near toward coal, 3 if very near towards coal, C: 0 for more than 50, 1 for between 35and 50, 2 for between 10 and 35,3 for less than 10 wt% moisture, D: 0 for more than 15,1 for between 6 and 14, 2 for between 3 and 6, 3 for less than 3 wt% ash, E: 0 for less than 10, 1 for between 10 and 25, 2 for between 25 and 50, 3 for more than 50 wt%. (Note that typically almost more than 60 wt% of biomass is volatiles, VM, and fixed carbon, FC)

Table 17.10 Characterization results of pyrolysis liquid from Malaysian empty palm fruit bunch [7]

complex solubility and reactivity of these chemical compounds. Typically, the pyrol­ysis liquids are single-phase liquids contaning varying amounts of solids (char). This char sediment gradually settles at the bottom of the barrel forming a thick sludge over time depending on the density difference between the liquid and particles [76]. Phase separation can occur if the total water content exceeds a certain threshold limit, making the liquid usage as fuel questionable unless it can be emulsified before use [75]. The properties of bio-oil such as moisture content, density, pH, and solid content from Malaysian EFB from palm industry was reported in reference [7] as 50-60 %, 1.2g/cm3, 3, and 0.02-2 %, respectively. The elemental compositions of the bio-oil are given in Table 17.10 [7].

Table 17.12 Yield of liquid fuel from Malaysian empty palm fruit bunch [77]

In this study, the stable single phase mixture of bio-oil contained water ranging from 40 to 60 %. The density of the liquid was 1.2g/cm3, which was higher than that of fuel oil, that is, at around 0.85 g/cm3, and significantly higher than that of the biomass which was at 1.1452 g/cm3 [8]. This indicated that the liquid had approximately 42 % of the energy content of fuel oil on a weight basis, but 61 % on a volumetric basis. This may impose implications on the design and specification of equipment to process and handle the bio-oil such as pumps and atomizers in boilers and engines. More importantly, the CV of the pyrolysis liquid as determined mathematically was 21.62 MJ/kg, compared to 42-44 MJ/kg for conventional fuel oils. Thus, the liquid produced needs to be upgraded to become the alternative substitute for the existing fuel oils.

For the upgrading/purification methods, the common processes are catalytic cracking, hydrogenation, and steam reforming [77-83]. There are two approaches for catalytic cracking of bio-oil: offline catalytic cracking that utilizes bio-oil as raw material and online catalytic cracking which utilizes pyrolysis vapors as raw material [77, 84-90].

Hew et al. reported an upgrading study on bio-oil from Malaysian EFB using an off line heterogeneous catalytic cracking process [77]. They applied Taguchi L9 method to identify optimum operating condition to upgrade empty fruit oil palm bunch-derived pyrolysis oil to liquid fuel, mainly gasoline or organic liquid vapor. The properties of the bio-gasoline obtained are given in Table 17.11.

The yields and optimal conditions for the upgrading process of the bio-oil into liquid fuels are reported in Table 17.12. The equations used to calculate the yield of
organic liquid product (OLP) and the yield of gasoline are as Eqs. 17.10 and 17.11, respectively [77];

YieldOLP = (WeightOLP/Weightbio-oil) x 100% (17.10)

Yieldgasoline = (Weightgasoline/ 12g) X 100% (17.11)

17.2 Summary

Pre-treatment process is essential for subsequent biomass conversion into bio-fuel and chemicals. The challenge lies in overcoming the resistivity of plant cells wall to deconstruct due to entanglement of highly crystalline structure of cellulose which is embedded in a matrix of polymer lignin and hemicelluloses.