• Biorefining Technologies
    Used on The Celignis Database


Celignis Analytical has a number of formulae which are used to predict, based on sample compositional data, the potential product yields (on the basis of litres of biofuel and energy (GJ) of biofuel output) that could be obtained when processing biomass samples in seven different biorefining technologies (labelled 1 to 7).

These numbers are estimates and may not be representative of the actual yields that may be achieved in real-world conditions. The data are presented online to customers, on the Celignis Database, in tabulated and graphical formats, providing that the appropriate analysis packages have been selected.

Samples for which data regarding the lignocellulosic sugar composition have been obtained (Celignis Analysis Packages: P7 (Lignocellulosic Sugars), P9 (Lignocellulosic Constituents), P10 (Lignocellulosic Constituents and Extractives), and P11 (NIR Prediction Package) will have data for potential biofuel yields from 5 different representative hydrolysis technologies (Technologies 1-5).

Samples for which data regarding the elemental and ash contents have been obtained (e.g. Celignis Analysis Package: P40 - Combustion Package) will have data for potential biofuel yields from 2 different representative gasification technologies (Technologies 6 and 7).

Summary of Technologies

Five of the technologies (1-5) involve the hydrolysis of biomass polysaccharides and the subsequent fermentation of the liberated monosaccharides to ethanol. Technologies 6 and 7 operate via the thermochemical platform, specifically via the gasification of the biomass and the subsequent catalytic synthesis of fuels.

These technologies are explained in the text below and the following table which compares them on the basis of: commercialisation status; minimum size for a commercial facility; cost of biofuel produced; feedstock flexibility; and potential biofuel yield.

Hydrolysis Technologies

Five different hydrolysis technologies are examined:

1 - Dilute acid hydrolysis of biomass in two plug-flow reactors. This can be considered to representative of a near-commercial dilute-acid hydrolysis facility.

2 - Dilute acid hydrolysis of cellulose in a counter-current reactor with an uncatalysed steam hydrolysis pre-treatment. This more efficient process (for cellulose hydrolysis) may be commercially viable in the future.

3 - Concentrated acid hydrolysis of biomass.

4 - Enzymatic hydrolysis of biomass. Involves a dilute acid pre-treatment and separate fermentation of the monosaccharides from cellulose and hemicellulose (sequential hydrolysis and fermentation - SHF). Cellulase enzymes are produced in a separate reactor to that for hydrolysis. This is the likely setup of the first commercial enzymatic hydrolysis facilities.

5 - Enzymatic hydrolysis and fermentation of biomass via consolidated bioprocessing (CBP) with a liquid hot water pre-treatment step. Here hydrolysis of cellulose, fermentation of the sugars and production of cellulases all take place in one reactor and involve a single micro-organism. This process can be considered to potentially be the most efficient and economical enzymatic hydrolysis technology; however, it is currently not sufficiently developed for commercialisation. There is substantial ongoing research, however, and it is expected that such a process could be viable before 2020.

The following formulae are used to calculate the yield of ethanol according to the hexose and pentose contents of the feedstock and the estimated efficiencies of the technology (based on a literature review). Table 2 then outlines the efficiencies used for the hydrolysis processes based on these equations:

formula1 formula2

formulae terms

Conversion factors and yields for the hydrolysis technologies. Click to enlarge.

technology-specific yields

Thermochemical Technologies

Technologies 6 and 7 are based on the gasification conversion process. Unlike the hydrolysis technologies, which specifically target the structural polysaccharides of feedstocks, the thermochemical processes degrade all volatile components of the feedstock (which includes the lignin, as well as the polysaccharides). Determinations of process yields for these technologies are based on the estimated heating values of the feedstock, as calculated from its elemental composition.

The Higher Heating Value (HHV) is calculated from the ash, carbon, and hydrogen content by:

HHV (MJ/kg)    =    -1.3675 + 0.3137C + 0.7009H + 0.0318 O*

Where O* = the sum of the contents of oxygen and other elements (including S, N, Cl, etc.) in the organic matter, i.e.

O*   =   100%-C-H-Ash.

The Lower Heating Value (LHV), or effective heating value, is more relevant than the HHV in practical operations. It considers the energy required to vaporise the water generated when the hydrogen and oxygen elements of the biomass combine. Hydrogen content then becomes a reducing factor in the heating value. The LHV can be calculated on a dry basis from the equation below:

LHV     =    HHV - 0.22 * H

Where H = Hydrogen content of dry biomass (%)

The two representative gasification technologies used are described below:

6 - Synthesis of mixed alcohols via the catalytic processing of syngas derived from the gasification of biomass. The efficiency of the process is based on the LHV of the feedstock, giving a conversion efficiency of 48.8% to ethanol and 9.6% to higher alcohols, although the calculations will only consider the ethanol produced. The process is considered to be beyond the current state of the art and more likely for commercialisation closer to 2023.

7 - The Fischer-Tropsch (FT) synthesis of a mixed range of linear hydrocarbons from biomass-derived syngas. We use data for an Institute of Gas Technology, direct, oxygen blown, pressurised gasifier with full gas recycle. The overall conversion efficiency, based on the LHV of the feedstock, has been estimated at 47.7%, with 37.92% for FT liquids and 6.65% for net power. Hydrocracking of the waxy FT product is necessary to maximise diesel yields with these cracking conditions producing 60% (by mass) diesel, 25% kerosene and 15% naphtha. Hence, yields (according to the dry LHV) will be 24.68% for diesel, 6.33% for naphtha and 10.04% for kerosene.