• Feedstocks Analysed at Celignis

Background on Bark

Bark is a highly heterogeneous and chemically complex section of woody biomass. It is usually divided into the living inner bark and dead outer bark. There are vast differences in the nature and amounts of various chemicals and extractives in the bark that can be found within even a single species, depending on the age and growth site of the trees sampled and the fraction of bark examined.

Celignis founder Daniel Hayes has considerable experience in the chemical and near-infrared analysis of barks and has characterised samples from a variety of different tree species.

Analysis of Bark at Celignis

Celignis Analytical can determine the following properties of Bark samples:

Lignocellulosic Properties of Bark

Cellulose Content of Bark

In barks the cellulose content is significantly less than in the stem wood.

In contrast, the extractives in bark are both much more abundant and more variable than they are in wood with many types being present only in the bark.

Bark extractives can be divided into the lipophilic and hydrophilic fractions with the hydrophilic fraction generally three to five times more abundant. The lipophilic fraction is extractable with nonpolar solvents (e.g. dichloromethane) and consists mainly of fats, waxes, terpenes and terpenoids, and higher aliphatic alcohols. The hydrophilic fraction is extractable with water alone or with polar organic solvents (e.g. ethanol) and contains large amounts of phenolic constituents. Soluble oligosaccharides, such as raffinose and stachyose, tend to be present in minor amounts in bark.

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Hemicellulose Content of Bark

As with cellulose, barks tend to have a lower hemicellulose content than the stem wood of the tree. In addition to the regular hemicelluloses that are present in the stem wood, many barks can also have a highly branched arabinan.

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Lignin Content of Bark

The concentration of lignin is significantly higher in bark than in wood. Some studies indicate that inner bark lignin is similar to wood lignin, whereas the outer bark lignin significantly differs from it.

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Starch Content of Bark

The starch content of bark is typically higher than that of the stem wood and will vary significantly according to species.

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Uronic Acid Content of Bark

Barks can contain more pectin than other parts of the tree and so often have higher uronic acid contents.

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Enzymatic Hydrolysis of Bark

We can undertake tests involving the enzymatic hydrolysis of Bark. In these experiments we can either use a commercial enzyme mix or you can supply your own enzymes. We also offer analysis packages that compare the enzymatic hydrolysis of a pre-treated sample with that of the native original material.

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Bioenergy Properties of Bark

Ash Content of Bark

Bark generally contains a significantly higher concentration of ash than that seen in the wood.

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Heating (Calorific) Value of Bark

Compared against woods, the increased ash, lignin, and extractives contents and decreased polysaccharide contents of barks are unattractive as far as hyrolysis biorefining technologies are concerned. However, the increased lignin and extractives contents suggest barks may be more attractive feedstocks for combustion and thermochemical processes (e.g. gasification) than the wood itself, providing the moisture content is suitable prior to processing.

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Ash Melting Behaviour of Bark

Ash melting, also known as ash fusion and ash softening, can lead to slagging, fouling and corrosion in boilers which may reduce conversion efficiency. We can determine the ash melting behaviour of Bark using our Carbolite CAF G5 BIO ash melting furnace. It can record the following temperatures:

Ash Shrinkage Starting Temperature (SST) - This occurs when the area of the test piece of Bark ash falls below 95% of the original test piece area.

Ash Deformation Temperature (DT) - The temperature at which the first signs of rounding of the edges of the test piece occurs due to melting.

Ash Hemisphere Temperature (HT) - When the test piece of Bark ash forms a hemisphere (i.e. the height becomes equal to half the base diameter).

Ash Flow Temperature (FT) - The temperature at which the Bark ash is spread out over the supporting tile in a layer, the height of which is half of the test piece at the hemisphere temperature.

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Major and Minor Elements in Bark

Examples of major elements that may be present in Bark include potassium and sodium which are present in biomass ash in the forms of oxides. These can lead to fouling, ash deposition in the convective section of the boiler. Alkali chlorides can also lead to slagging, the fusion and sintering of ash particles which can lead to deposits on boiler tubes and walls.

We can also determine the levels of 13 different minor elements (such as arsenic, copper, and zinc) that may be present in Bark.

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Analysis of Bark for Anaerobic Digestion

Biomethane potential (BMP) of Bark

At Celignis we can provide you with crucial data on feedstock suitability for AD as well as on the composition of process residues. For example, we can determine the biomethane potential (BMP) of Bark. The BMP can be considered to be the experimental theoretical maximum amount of methane produced from a feedstock. We moniotor the volume of biogas produced allowing for a cumulative plot over time, accessed via the Celignis Database. Our BMP packages also involve routine analysis of biogas composition (biomethane, carbon dioxide, hydrogen sulphide, ammonia, oxygen). We also provide detailed analysis of the digestate, the residue that remains after a sample has been digested. Our expertise in lignocellulosic analysis can allow for detailed insight regarding the fate of the different biogenic polymers during digestion.

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Physical Properties of Bark

Bulk Density of Bark

At Celignis we can determine the bulk density of biomass samples, including Bark, according to ISO standard 17828 (2015). This method requires the biomass to be in an appropriate form (chips or powder) for density determination.

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Particle Size of Bark

Our lab is equipped with a Retsch AS 400 sieve shaker. It can accommodate sieves of up to 40 cm diameter, corresponding to a surface area of 1256 square centimetres. This allows us to determine the particle size distribution of a range of samples, including Bark, by following European Standard methods EN 15149- 1:2010 and EN 15149-2:2010.

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Publications on Bark By The Celignis Team

Gottumukkala, L. D, Valappi, S. K. (2013) Biobutanol production from rice straw by a non acetone producing Clostridium sporogenes BE01, Bioresource Technology 145: 182-187

Biobutanol from lignocellulosic biomass has gained much attention due to several advantages over bioethanol. Though microbial production of butanol through ABE fermentation is an established technology, the use of lignocellulosic biomass as feedstock presents several challenges. In the present study, biobutanol production from enzymatic hydrolysate of acid pretreated rice straw was evaluated using Clostridium sporogenes BE01. This strain gave a butanol yield of 3.43 g/l and a total solvent yield of 5.32 g/l in rice straw hydrolysate supplemented with calcium carbonate and yeast extract. Hydrolysate was analyzed for the level of inhibitors such as acetic acid, formic acid and furfurals which affect the growth of the organism and in turn ABE fermentation. Methods for preconditioning the hydrolysate to remove toxic end products were done so as to improve the fermentation efficiency. Conditions of ABE fermentation were fine tuned resulting in an enhanced biobutanol reaching 5.52 g/l.

Examples of Other Feedstocks Analysed at Celignis