• Feedstock Evaluation
    for Biochar Production
    At Celignis Biomass Lab


Biochar is a carbon-rich solid material produced by the pyrolysis of biomass. This involves heating the feedstock in the absence of oxygen, which results in the formation of a high-carbon material that can potentially be used in a wide variety of applications, including: as a soil amendment, a component of biobased materials, and in pollution remediation. Biochar can be made from a variety of feedstocks, including wood, agricultural residues, and municipal solid waste.

There are two key considerations when producing biochar from biomass:
1. Biochar Yield - Defined as the percentage by mass of the original biomass that ends up as biochar.
2. Biochar Quality - A wide-encompassing term that considers how suitable the physical and chemical properties of the biochar are for the desired end-use.

Both of these parameters are affected by the conditions under which the feedstock is pyrolysed. These conditions include temperature, heating rate, and residence time. For example, high temperatures will lead to lower yields of biochar, as more of the biomass becomes volatile at higher temperatures, but can also result in the formation of a biochar of higher quality for certain applications (for example those that require a material of a higher carbon content).

How Feedstocks can Influence Biochar Yield and Quality

The yield and quality of biochar will also be greatly influenced by the physico-chemical properties of the starting biomass feedstock. In simple terms, biomass can be considered to be the sum of the various chemical constituents that make up the material. Each constituent will behave differently under the pyrolysis conditions employed and will therefore lead to different yields and compositions of biochar.

Under this assumption, it is useful to consider how each of the main constituents of biomass behave when exposed to prolysis conditions.


Lignocellulosic biomass feedstocks are the most abundant type of biomass. They are primarily composed of lignin and the polysaccharides cellulose and hemicellulose, along with smaller amounts of extractives and ash.

Cellulose undergoes a series of stages of degradation in the pyrolysis process, starting with dehydration at lower temperatures (100 to 200 oC), followed by depolymerisation at temperatures of 314 to 400 oC, with carbonisation leading to biochar production at temperatures over 400 oC. Cellulose is mostly volatile in slow-pyrolysis conditions meaning that much of the polymer will end up in the (non-condensible) gas rather than the biochar.


While cellulose is a homopolymer composed of only one sugar (glucose), hemicellulose is a complex polysaccharide that can contain other sugars. There are a number of different types of hemicellulose, these differ according to the sugar units that constitute the main backbone of the polymer as well as according to the amount and composition of the side-groups attached to this backbone.

Due to their heterogeneity, different hemicelluloses behave in different ways in slow-pyrolysis. However, in general, hemicellulose degrades at a lower temperature (220 to 315 oC) than cellulose. Given the more volatile nature of this polysaccharide, biochar yields from hemicellulose are even lower than from cellulose, with the majority of the material ending up in the (non-condensable) gas.


lignin is a highly heterogeneous cross-linked polymer composed of aromatic subunits. It has a higher carbon content than cellulose and hemicellulose and also experiences a more gradual profile for decomposition than these polymers, with the temperature range being 250 to 500 oC. There are characteristic differences in lignin composition between hardwoods, softwoods, and herbaceous feedstocks.

Lignin typically produces higher biochar yields than cellulose and hemicellulose, with lesser amounts of the polymer ending up in the gas or liquid fractions.


Extractives are defined as extraneous components that may be separated from the insoluble cell wall material by their solubility in water or neutral organic solvents. Solvents of different polarities are required to remove different types of extractives. Hence the extractives are often classified according to which solvent can extract them (e.g. ethanol-soluble-extractives).

Generally, extractives are more volatile than the structural components of biomass (cellulose, hemicellulose, and lignin) and therefore undergo thermal degradation at lower temperatures. This means that the majority of the extractives are likely to go to gas, rather than biochar, production in slow pyrolysis.


Different proteins have varying thermal stabilities and undergo different thermal degradation pathways during pyrolysis. Furthermore, the presence of nitrogen-containing compounds resulting from protein pyrolysis can have implications for the use of biochar as a soil amendment. Nitrogen is an essential nutrient for plant growth, and biochar produced from nitrogen-rich biomass can be a source of plant-available nitrogen in soil. However, the availability of nitrogen from biochar can vary depending on the pyrolysis conditions and the specific nitrogen-containing compounds formed during pyrolysis.


Ash wil be retaining in the biochar as it will not become volatile under the conditions employed for slow-pyrolysis. However, during pyrolysis, ash does undergo thermal transformation, which leads to the formation of a range of compounds, including oxides, carbonates, and silicates. At higher temperatures, ash undergoes more rapid thermal transformation, leading to a higher yield of oxides and silicates. Conversely, at lower temperatures, ash undergoes slower thermal transformation, leading to a higher yield of carbonates.

The presence of ash in biochar can have implications for its use as a soil amendment. Ash can be a source of plant nutrients, such as potassium, calcium, and magnesium, which can enhance plant growth. However, ash can also contain potentially toxic elements, such as heavy metals, which can accumulate in soil and pose a risk to plant and human health. Hence, it is important that the composition of ash and the potential presence of toxic elements should be considered when selecting biomass feedstocks for biochar production.

Relevant Feedstock Analyses Offered by Celignis

Lignocellulosic Composition

For lignocellulosic feedstocks, detailed compositional data on the relative amounts of cellulose, hemicellulose, and lignin (along with data on other components such as extractives and ash) will help to inform which types of biomass would be most suitable for producing biochar for your desired application(s).

At Celignis we offer a wide range of lignocellulose analysis packages (as detailed here), however for the evaluation of candidate feedstocks for biochar production we would recommend packages P10 or P19, as detailed here.

Major and Minor Elements

We can determine the major and minor elements present within the biomass. These will be concentrated in the biochar that is produced from the feedstock and so are important to consider when examining whether a feedstock can be suitable for producing biochar for a particular end-use.

For example, the European Biochar Certificate (EBC), an organisation set up to ensure the quality and safety of biochar produced in Europe, sets thresholds for the upper limits for the amounts of certain heavy metals in biochar. These threshold values vary according to the planned end-use of the biochar. For example, the limit for the arsenic content of biochar to be used in animal feed applications is 2ppm whilst this limit rises to 13ppm if the biochar is to be used in consumer biomaterials.

At Celignis we can profile your potential biochar feedstocks for their major and minor elements and then, based on an estimate of the expected biochar yield, the expected amount of each element in the resulting biochar can be calculated. For example, if your feedstock has a zinc content of 20ppm and it is expected that the biochar yield would be 20%, then the zinc content of the final biochar can be estimated to be 100pm.

Such expected values can then be compared against threshold upper limits, from EBC or other institutions, to see if the resulting biochar would qualify for the desired end-use.

Such a pre-screening approach would be much more cost-effective than producing a biochar sample and then analysing it for its heavy metals contents.

Ultimate Analysis and Protein Content

It is a general rule that constituents and feedstocks that have higher carbon contents tend to lead to higher yields of biochar (on an ash-free basis) than materials that have higher oxygen contents.

We have a number of analysis packages that can determine the carbon content of a feedstock using the Dumas analysis method. This method also allows for the determination of the hydrogen, nitrogen, and sulphur contents, with the oxygen content calculated by difference (considering the ash also present).

The determination of nitrogen content of the feedstock is also important when considering the targetted end-use for the biochar, particularly if soil-amendment is being considered. Protein content can be estimated from the nitrogen content by multiplying it by a conversion factor relevant to the type of feedstock (for example a factor of 6.25 is used for many types of biomass). However, if a greater understanding of the protein composition of the feedstock is required then we can analyse the sample for its amino acid composition (package P17).

Thermogravimetric Analysis (TGA) of the Feedstock

Thermogravimetric analysis (TGA) is a useful means of evaluating the thermal behaviour of a material over a wide temperature range. It involves the weight of a sample being recorded as the temperature it is exposed to increases. We can undertake this analysis in a range of different atmospheres, with nitrogen and air being the most commonly used.

If nitrogen is used then the sample will be heated under pyrolysis conditions (i.e. with no oxygen). This means that estimates can be made for the potential biochar yield at a given temperature or that a pyrolysis temperature can be selected for a particular yield of biochar.

TGA is a cost-effective method for screening potential biochar feedstocks for their behaviours under pyrolysis conditions without having to produce biochar in a pyrolysis reactor.

Relevant packages for the thermogravimetric analysis of feedstocks are listed below:

Click here to read more about the thermogravimetric analysis of biomass.

Additional Information on Biochar Feedstock Evaluations

Feel free to get in touch with us if you have any questions about our analytical services for potential feedstocks for biochar production. Relevant members of the Celignis biochar team will be happy to assist. Those team members with the most experience with undertaking these tests and interpreting the resulting data are listed below.

Sajna KV

Bioanalysis Developer


Our Biomass Detective! Designs, tests, optimizes and validates robust analytical methods for properties of relevance to the various biochar market applications.

Dan Hayes

Celignis CEO And Founder

PhD (Analytical Chemistry)

Dreamer and achiever. Took Celignis from a concept in a research project to being the bioeconomy's premier provider of analytical and bioprocessing expertise.

Edgar Ramirez Huerta

Biochar Project Developer


Has taken a major role in developing Celignis's capabilities for biochar analysis and project development. His thesis covered the evaluation of high value applications for high-carbon materials.

Other Celignis Tests and Services for Biochar

Global Recognition as Biomass and Biochar Experts

Celignis provides valued services to over 1000 clients. We understand how the focus of biochar projects can differ between countries and have advised a global network of clients. We also have customs-exemptions for samples sent to us allowing us to quickly get to work no matter where our clients are based.

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Biochar Production

We can produce biochar samples from your feedstocks using a wide range of temperatures, heating rates, and residence times. We can formulate a Design of Experiments (DoE) to study the effects of varying process parameters on biochar yield and quality and can optimise these outputs according to your desired biochar market applications.

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Biochar Analysis

We have an extensive array of analysis packages to evaluate the suitability of biochar for a range of applications. These analyses cover properties relevant to combustion, soil amendment, feed, and biomaterials. Our reports compare the results against internationally-recognised limits for using the biochar in specific end-products.

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Biochar Combustion Properties

Biochar can be a superior fuel versus virgin biomass due to its greater carbon content and energy density. We offer a wide array of analysis packages to fully evaluate biochar as a fuel. For example, we can determine both organic and inorganic carbon and can monitor the behaviour of the biochar ash over wide temperature ranges.

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Soil Amendment & Plant Growth Trials

We can test biochar for several properties (e.g. water holding capacity, electrical conductivity etc.) relevant to its use in soil amendment. We can also grow plants in biochar-amended soils and assess the impacts of this approach on germination, plant growth, plant health, and soil biology.

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Analysis of PAHs in Biochar

Polycyclic aromatic hydrocarbons can be formed during the pyrolysis of biomass and accumulate in biochar, leading to potential risks to the environment. We can accurately quantify a range of different PAHs and determine if their concentrations exceed regulatory limits. We can also develop strategies to reduce the amount of PAHs in biochar.

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Surface Area and Porosity of Biochar

The suitable markets for a biochar are often greatly dependent on its surface area and pore size-distrubtion. We provide detailed reports on biochar surface area and porosity and can provide guidance on the implications of the results. We can also work on strategies to increase the surface area and modify the pore-size distribution of biochar.

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Thermogravimetric Analysis of Biochar

TGA is a powerful analytical technique for the study of biochars because it allows us to examine the thermal stability of the material as a function of temperature. The thermal stability of biochars is an important factor to consider when evaluating their potential use as a soil amendment or for carbon sequestration.

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Biochar Upgrading

There are several different methods (covering physical, chemical and biologial routes) by which we can upgrade your biochar in order to increase its value and make it more suitable for the desired market applications. We are able to fully characterise the changes in physicochemical properties associated with upgrading.

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Biochar for Carbon Sequestration

Biochar's efficacy as a means for sequestering carbon depends on a range of factors (e.g. feedstock and pyrolysis conditions). We can undertake a range of analytical tests to help you determine the stability of your biochar's carbon. We can also suggest alternative approaches to improve carbon sequestration potential.

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Technoeconomic Analyses of Biochar Projects

Our TEA experts work with you to evaluate the economic prospects of your biochar facility, considering various scale, technology, and feedstock options. We apply accurate costing models to determine CAPEX/OPEX of simulated and pilot scale processes which are then used to determine key economic indicators (e.g. IRR, NPV).

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Research Project Collaborations

Celignis is active in a number of important research projects focused on biomass valorisation. Biochar is a key component in some of these ongoing projects as well as in several prior projects. We are open to participating in future collaborative research projects where our extensive infrastructure and expertise in biochar can be leveraged.

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