11.08.2015   Advances in Biofuels

Second-Generation Biofuels: Palm Lignocellulosic Biomass

There is an untapped potential of palm lignocellulosic biomass (EFB, palm shell, mesocarp fibre) for power generation—either as biomass to solid (BTS), biomass to liquid (BTL) or biomass to gas (BTG).

Palm lignocellulosic biomass consists of lignin, cellulose, hemicellulose and ash in different chemical compositions (Table 1.3) (Loh et al. 2012) which determine the types of second-generation biofuels to be produced. For example, cellulose and hemi — cellulose can be converted into liquid biofuels (bioethanol, bio-oil, synthetic diesel) whereas lignin as biochar fuel. Lignin is a complex polymer of phenylpropane units, which are cross-linked to each other with a variety of different chemical bonds to provide cell wall mechanical strength. Cellulose is a long chain glucose molecule

Table 1.3 Chemical compositions (%) of oil palm biomass

Chemical composition

(%)

Empty fruit bunches (EFB)

Oil palm trunks (OPT)

Oil palm fronds (OPF)

Palm shella

Lignin

19.67 ± 6.80

20.51 ± 4.01

20.50 ± 2.20

50.7

Holocellulose

78.00 ± 8.70

75.00 ± 5.02

80.33 ± 3.18

43.5

1. a-cellulose

46.17 ± 11.17

42.32 ± 5.18

40.10 ± 9.70

20.8

2. Hemicellulose

32.30 ± 7.82

32.35 ± 1.65

37.05 ± 3.35

22.7

Ash

3.2 ± 2.31

1.6 ± 0.35

3.28 ± 0.87

4.44

aAbdullah et al. (2010)

Table 1.4 Potential use of oil palm biomass as fuels

Calorific value (CV)a,

CVa, range

Barrel of oil

Type of oil palm biomass

average (MJ/kg)

(MJ/kg)

equivalent (mil)

EFB

18.88

18.00-19.92

19.4

Mesocarp fibre

19.06

18.80-19.58

20.8

Shell

20.09

19.50-20.75

13.0

Palm oil mill effluent (POME)

16.99

16.10-17.65

3.1

aLoh et al. (2012)

linking primarily with p (1-4) glycosidic bond. The presence of hemicelluloses in bundles in the cellulose molecule can enhance the stability of the cell wall. Hemicellulose consists of branched polymers such as xylose, arabinose, galactose and mannose. It also cross-links with lignin creating a complex web of bonds. Cellulose and hemicellulose are made up of a majority of monomer glucose and xylose, respec­tively; thus, these sugars can be extracted for further use (Saka et al. 2008).

As a rule of thumb, an oil palm contains 10% oil and the remaining 90% palm biomass. Based on this, the oil palm industry generates up to 80 million tonnes dry biomass a year. As oil palm biomass has caloric value (Table 1.4) comparable to commercial fossil fuels, their potential use as fuels is tremendous in terms of barrel of oil equivalent derived.

However, most of the oil palm biomass is currently mulched or returned back to the field as biofertiliser to improve soil fertility (MPOB 2010). There are also many other competitive uses (especially for EFB and POME) including fibre processing into mat­tress, furniture-based manufacturing, pulp and paper making, cement manufacturing etc., besides being used for power generation (as boiler fuel) in palm oil mills.