The Thermochemical Conversion of Biomass into High-Value Products: Microwave Pyrolysis - The Economic Utilisation of Food Co-Products - page 53

microwave technology could alleviate this problem, transposing this under-
utilised biomass into a future renewable source of chemicals and fuel.
Buderin et al. demonstrated the effectiveness of microwave-mediated
pyrolysis of Gracilaria macro-algae. It was proved that this biomass source
could be effectively broken down into useful chemicals at temperatures close to
130 1C, which is exceptionally low for such processes, and hence, potentially
more energy ecient than other pyrolysis means. 62 In addition, it was found
that it could be carried out in aqueous media, eliminating costly drying steps
and that there was a critical mass point in which the distribution of products
changed dramatically. At low biomass concentrations it was found that a
slower pyrolysis rate occurred, resulting in a final product distribution of
fermentable anhydro-sugars (i.e. levoglucosan). At high mass concentrations
the rate of reaction dramatically increased, with the final product distribution
being phenol and 4-methyl phenol. This leads to the exciting potential to tailor
the process to product requirements, with the products formed in both cases
being highly sought after.

d n 9 r 3 n g | 8

3.5.2.3 Orange-Peel Valorisation Using Microwaves
Orange processing consists of up to 90% of the largest fruit crop, citrus fruit
that is grown on a scale of over 110million tonnes per year. 63,64 In addition, up
to 60% of the fruit is discarded or pelletised for animal feed after juicing etc. 65
This waste orange peel has been shown to produce valuable products such as
D-limonene, pectin and a form of mesoporous cellulose without the need for
pretreatment using microwave hydrothermal processing (170-200 1C). 66,67
After this success, the experimental procedure was scaled to three litres that
was found to increase the attainable yield of D-limonene from 0.19% (25 mL
scale) to 1.52%. 68 The produced D-limonene was then used to produce a
sustainably derived p-cymenesulfonic acid that had comparable acidic catalytic
properties to that of the much used petroleum derived p-toluenesulfonic acid. 69

3 .

3.5.2.4 General Biomass Microwave Treatment
From the data above and from Table 3.3 it can be seen that the yield of
pyrolysis oil

is dependent on initial conditions (e.g. nature of feedstock,

Table 3.3 Mass balance of what straw microwave pyrolysis.

Yield (mass%)

Feedstock MW Power T/1C additive Char Organics Water Gas

Wheat straw 500 130 - 29.4 15.2 37.2 18.2

Wheat straw 1000 130 - 29 20.6 36.4 14

Wheat straw 1200 140 H 2 SO 4 44.4 7.3 32.9 15.4

Wheat straw 1200 140 HCl 31.8 22.1 27.1 19

Wheat straw 1200 165 NH 3 40.7 17.0 22.3 20

Pine wood 1200 140 - 32.7 26.1 27.7 13.5