• Biochar
    Important Analysis Methods

Numerous strategies are being implemented to achieve a neutral carbon footprint, but biomass is one of the few alternatives that have the potential to sustainably meet energy and material needs while being, potentially, carbon-negative.

One route for this is by transforming biomass through pyrolysis, a thermochemical modification process where biomass is broken down in an oxygen-free atmosphere into biochar, bio-oil, and combustible gases. Biochar is a carbon-rich material with typically 70 to 80% of fixed carbon (on an ash-free basis) that has a extensive array of potential applications, whereas the combustible gases are commonly used to fuel the pyrolysis process.

During pyrolysis the release of volatiles components present in biomass provides biochar with a characteristic honeycomb structure with, what can be, a relatively high surface area. This porous nature potentially allows biochar to be suitable for a range of applications such as: a soil supplement for improving plant growth; an adsorbent to decontaminate air and water; and as a catalyst during the production of biodiesel.

Additionally, biochar can be used as: a water filter for domestic use; a clean-burning source of bioenergy; an additive for upgrading biogas production; a stabilizer in composting; a carbon sequestration instrument in the building sector; and even for producing engineering parts for electrical devices.

The pyrolysis process is carried out by optimizing parameters such as residence time, temperature, heating rate, inert gas flow rate, and particle size. For example, a particle size of 0.8 mm and a heating rate of 10 °C/min can improve the biochar yield. In contrast, smaller particles and faster heating rates prompts the release of more volatiles, which results in higher bio-oil and gas yields. However, the temperature is considered to be the most critical parameter because this influences biochar porous configuration and yield. For instance, biochar surface area can decrease when the reaction temperature increases (i.e., 400 to 600 °C) due to the melting of its porous structure. Moreover, high temperatures (greater than 400 °C) also lead to thermal cracking, increasing liquid and gas components and decreasing biochar yield

Nevertheless, the most porous biochar is derived from physical or chemical activation using high temperatures (450–900 °C). Physical activation releases volatiles trapped in the biochar pores meaning that the surface area of physically activated biochar is larger and more microporous (less than 2 nm) rather than mesoporous (2–50 nm). Air is one of the most common activation methods because the activation energy is less compared to carbon dioxide or steam, which improves the economics of the process. However, physical activation using air can result in partial combustion, leading to a high ash content and a lower biochar yield if the method is not properly controlled.

During chemical activation biochar reacts with the chosen set of chemicals at temperatures of around 450 to 900 °C. While chemical activation is less common than physical activation, it has several advantages like lower energy input, a better carbon yield, higher microporosity and significantly increased surface area (over 3,000 m2/g). Nevertheless, chemical activation requires regular equipment maintenance because the methods can lead to chemical corrosion.

Important Parameters for Biochar

The key analytes and properties related to biochar, and the analysis packages that Celignis offers for these, are listed below. Click on an a package for further details on it.

Surface Area and Porosity

The surface area of biochar can vary significantly and, with it, the potential range of applications for the biochar. This is because there are numerous variables that can impact the porosity of the sample. These include: the type of feedstock, the pretreatment, process conditions, the presence of ash or condensates clogging the pores, and the selected activation method. Therefore, a sample obtained after pyrolysis-like processes needs to be analysed to determine its surface area and pore size distribution in order to reveal the true porous nature of the sample and its most suitable application.

We determine the surface area and pore size distribution of carbonaceous samples using a Quantachrome NOVA-e Series 2200e analyser which has been designed to satisfy the procedures outlined in EBC (2012-2022) 'European Biochar Certificate - Guidelines for a Sustainable Production of Biochar.' European Biochar Foundation (EBC), Arbaz, Switzerland. Version 10.1 from 10th Jan 2022.

Our analysis packages for surface area and porosity are listed below. Our reports are comprehensive assessments and provide a user-friendly interpretation of the pore analysis results. What´s more, Celignis offers the same quality of data for all the EBC/IBI Analytical Methods, so you can have an exhaustive characterization of your sample. We also provide application tests and consultation services based on the analysis data to enable clients to determine the most suitable application of their biochar samples.

Click here to read in more detail about the techniques we use for surface area and porosity analysis and to see the types of data that our reports provide.

Analysis Packages for Surface Area and Porosity


Suitability for Soil Amendment

The amendment of soil with biochar has attrached attention for two main reasons. Firstly, biochar is an inert form of carbon that is highly recalcitrant to microbial degradation, particularly when compared against the feedstocks it has been produced from. Hence, carbon, initially taken from the atmosphere to grow the feedstock used for biochar production, then becomes locked into biochar which is then added to the soil - a form of carbon sequestration.

Additionally, biochar can help improve the fertility of the soils, allowing for enhanced plant growth and resiliance. Biochar can benefit plant growth as a result of several complementary effects including: increasing carbon stocks, increasing nutrient availability, and allowing for an improved environment for Arbuscular mycorrhizal fungi to proliferate. These fungi exist in a symbiotic relationship with plant roots, allowing for the update of increased amounts of nutrients by the plants.

Celignis personnel have prior experience in the evaluation of biochar as a plant growth promoter. Images are provided of a prior nationally-funded research project which looked at the effects of soil amendement using biochars from different feedstocks. It was found that the production over an initial 21 day period was significantly greater than the no-biochar control and that the size of the increase depended on the feedstock from which the biochar was produced. There was also evidence that the plant roots orientated towards the biochar, as shown in the photos here.

At Celignis we can undertake such plant-growth pot trials and we can measure various important productivity parameters, including Time to Germination, Mean Shoot Length, Shoot Weight and Root Weight. We can also measure a range of other properties relevant to soil amendment, including: Electrical Conductivity, Water Holding Capacity, Cation-Exchange Capacity, Liming, and the contents of 18-different Polyscyclic Aromatic Hydrocarbons (PAHs).

We can also take Scanning Electron Microscopy (SEM) images to evaluate the ultrastructure of the biochar, a useful companion piece of data alongside surface area analysis, to see how suitable the biochar can be as a substrate within which Arbuscular mycorrhizal fungi can proliferate.

Relevant Analysis Packages for Soil Amendment


Thermal Properties

Biochar has several advantages as a fuel over the original biomass feedstocks. For example, the carbon and hydrogen contents are greater whilst the oxygen contents are lower, leading to increased calorific values. The loss of highly volatile components during the pyrolysis process also allows for biochar to be a cleaner burning fuel.

Many of Celignis's analysis methods and packages designed to evaluate biomass as a combustion feedstock are also relevant for biochar. Click here to read more about these methods.

Additionally, there are number of other analyses that may be of particular interest for biochars. These include the determination of the inorganic carbon content, the ash content at 815 °C (compared with the 550 °C traditionally used for biomass), the inherent moisture content and the thermogravimetric analysis (TGA) of the sample. An example TGA thermogram and differential thermogram are provided in the interactive image displayed here. Click here to read more about TGA analysis at Celignis.

Relevant Analysis Packages for Biochar Thermal Properties


Additional Information on Biochar Analysis

Feel free to get in touch with us if you have any questions about our analysis methods for biochar. Relevant members of the Celignis biochar team will be happy to assist. Those team members with the most experience in biochar analysis analyses 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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Feedstock Evaluation

Our analysis packages can screen biochar feedstocks. We can estimate biochar yield and quality using feedstock chemical composition and can estimate biochar composition using the ultimate and major/minor elements analyses of the feedstock. With TGA analysis we can also monitor feedstock behaviour under pyrolysis conditions.

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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 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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