• Feedstocks Analysed at Celignis
    Hydrolysis Residues

Background on Hydrolysis Residues

Hydrolysis technologies usually target the production of fuels/chemicals from the cellulose and hemicellulose polysaccharides in the biomass. The solid residue of the process will contain lignin, the portion of the ash that has not been solubilised, and any un-hydrolysed cellulose and hemicellulose.

Our Recommendations for Evaluating Hydrolysis Processes
We have a lot of experience in analysing many products (both liquid and solid) from biomass hydrolysis processes. These samples have covered a wide variety of starting feedstocks and hydrolysis processes and conditions. Below we recommend a set of Celignis analysis packages for getting the most detailed data about the whole conversion process:

(1) The Starting Feedstock
We recommend that analysis package P10 - Sugars, Lignin, Extractives, and Ash is used as this will fully remove the extractives prior to the hydrolysis stage meaning that you can be confident that the sugars reported in this package come from lignocellulose.

We would also recommend analysis package P12 - Sugars in Solvent Extract as this will report the amount of water-soluble carbohydrates in the sample. It is likely that water-soluble carbohydrates will be present in the liquid output of many hydrolysis processes and, if their concentrations are not known, it may be incorrectly inferred that such sugars present in the liquid must come from lignocellulose. However, if the water-soluble carbohydrate composition is known then these values can be substracted from the amounts of sugars in the hydrolysis liquid to determine the amount of true lignocellulosic sugars that are present.

Similarly, if you expect that there will be some starch in your sample then we also recommend that analysis package P14 - Starch Content is also undertaken as starch may also be removed and hydrolysed in many hydrolysis processes.

Additionally, if you are interested in the uronic acid composition of the biomass then we recommend analysis package P15 - Uronic Acids is also undertaken.

(2) The Liquid Product from Hydrolysis
For the most detailed results, we would recommend that the liquid output is analysed using analysis packages P13 - Sugars and Oligosaccharides in Solution, P22 - Organic Acids and Furans, and P15 - Uronic Acids. However, if uronic acids are expected to be very low in your original biomass sample then that analysis package may not need to be undertaken.

(3) The Solid Residue from Hydrolysis
As it is likely that most of the extractives will have been removed in the hydrolysis, it may not be necessary to remove or characterise these. Instead, we recommend that analysis package P9 - Lignocelullosic Sugars and Lignin is undertaken to determine the lignocellulosic composition of the residue. We would also recommend that analysis package P3 - Ash Content is also undertaken to see whether the hydrolysis process significantly changes the ash content of the sample. Also, if the fate of the uronic acids is of interest then analysis package P15 - Uronic Acids could be undertaken.

Celignis founder Daniel Hayes has considerable experience in the chemical and near-infrared analysis of residues from hydrolysis processes, in large part due to his participation in the DIBANET research project, funded by the European Union's 7th Framework Programme. That project involved the development of advanced technologies for the production of biofuels and valuable chemicals (including levuinic acid, formic acid, and furfural) from biomass.

Analysis of Hydrolysis Residues at Celignis

Celignis Analytical can determine the following properties of Hydrolysis Residues samples:

Lignocellulosic Properties of Hydrolysis Residues

Cellulose Content of Hydrolysis Residues

An efficient hydrolysis biorefinery will hydrolyse most of the cellulose present in the biomass, meaning that the cellulose content of the solid residue should be low.

Click here to see the Celignis Analysis Packages that determine Cellulose Content

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Hemicellulose Content of Hydrolysis Residues

In most hydrolysis biorefineries the hemicellulose fraction is hydrolysed from the biomass, either in the pre-treatment stage or in the main hydrolysis reactor. Hence, hemicellulose content in the hydrolysis residue should be low.

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Lignin Content of Hydrolysis Residues

If the cellulose and hemicellulsoe contents of the hydrolysis residue are lower than in the original biomass sample then it would be expected that the lignin content should be increased. This is because the majority of lignin is typically not hydrolysed in the main hydrolysis reactor, however it may have been removed in the earlier pre-treatment.

Click here to see the Celignis Analysis Packages that determine Lignin Content

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Starch Content of Hydrolysis Residues

It would typically be expected that the starch content of hydrolysis residues should be very low as this polysaccharide would have been hydrolysed in the process.

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Uronic Acid Content of Hydrolysis Residues

Depending on the severity of the hydrolysis conditions, the uronic acids that were present in the original biomass may either have been hydrolysed or retained within the acid hydrolysis residue. We can determine uronic acid content of liquid output streams from biomass processes as well as the uronic acid content of biomass and solid process residues.

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Enzymatic Hydrolysis of Hydrolysis Residues

We can undertake tests involving the enzymatic hydrolysis of Hydrolysis Residues. 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 Hydrolysis Residues

Ash Content of Hydrolysis Residues

Providing that a large proportion of the ash present in the virgin biomass has not been solibilised in either the pre-treatment or hydrolysis processes, it can be expected that the ash content of the hydrolysis residue should be greater than in the original biomass sample.

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Heating (Calorific) Value of Hydrolysis Residues

Lignin has a greater heating value than cellulose and hemicellulose, therefore a hydrolysis residue that contains an increased lignin content, and lesser cellulose and hemicellulose contents, should be expected to have a greater heating value (on a dry mass basis) than the original biomass.

However, the moisture content of the residue will be of key importance in determining the effective heating value of the sample.

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Ash Melting Behaviour of Hydrolysis Residues

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 Hydrolysis Residues 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 Hydrolysis Residues 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 Hydrolysis Residues ash forms a hemisphere (i.e. the height becomes equal to half the base diameter).

Ash Flow Temperature (FT) - The temperature at which the Hydrolysis Residues 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.

Click here to see the Celignis Analysis Packages that determine Ash Melting Behaviour

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Major and Minor Elements in Hydrolysis Residues

Examples of major elements that may be present in Hydrolysis Residues 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 Hydrolysis Residues.

Click here to see the Celignis Analysis Packages that determine Major and Minor Elements

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Analysis of Hydrolysis Residues for Anaerobic Digestion

Biomethane potential (BMP) of Hydrolysis Residues

As hydrolysis residues are typically primarily composed of lignin, as well as any residual ash, they are not considered to be suitable feedstocks for anaerobic digestion.

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Physical Properties of Hydrolysis Residues

Bulk Density of Hydrolysis Residues

At Celignis we can determine the bulk density of biomass samples, including Hydrolysis Residues, 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 Hydrolysis Residues

As hydrolysis residues are typically primarily composed of lignin, as well as any residual ash, they are not considered to be suitable feedstocks for anaerobic digestion.

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Publications on Hydrolysis Residues By The Celignis Team

Hayes, D. J. M. (2011) Analysis of Lignocellulosic Feedstocks for Biorefineries with a Focus on The Development of Near Infrared Spectroscopy as a Primary Analytical Tool, PhD Thesis832 pages (over 2 volumes)


The processing of lignocellulosic materials in modern biorefineries will allow for the production of transport fuels and platform chemicals that could replace petroleum-derived products. However, there is a critical lack of relevant detailed compositional information regarding feedstocks relevant to Ireland and Irish conditions. This research has involved the collection, preparation, and the analysis, with a high level of precision and accuracy, of a large number of biomass samples from the waste and agricultural sectors. Not all of the waste materials analysed are considered suitable for biorefining; for example the total sugar contents of spent mushroom composts are too low. However, the waste paper/cardboard that is currently exported from Ireland has a chemical composition that could result in high biorefinery yields and so could make a significant contribution to Irelandís biofuel demands.

Miscanthus was focussed on as a major agricultural feedstock. A large number of plants have been sampled over the course of the harvest window (October to April) from several sites. These have been separated into their anatomical fractions and analysed. This has allowed observations to be made regarding the compositional trends observed within plants, between plants, and between harvest dates. Projections are made regarding the extents to which potential chemical yields may vary. For the DIBANET hydrolysis process that is being developed at the University of Limerick, per hectare yields of levulinic acid from Miscanthus could be 20% greater when harvested early compared with a late harvest.

The wet-chemical analysis of biomass is time-consuming. Near infrared spectroscopy (NIRS) has been developed as a rapid primary analytical tool with separate quantitative models developed for the important constituents of Miscanthus, peat, and (Australian) sugarcane bagasse. The work has demonstrated that accurate models are possible, not only for dry homogenous samples, but also for wet heterogeneous samples. For glucose (cellulose) the root mean square error of prediction (RMSEP) for wet samples is 1.24% and the R2 for the validation set ( ) is 0.931. High accuracies are even possible for minor analytes; e.g. for the rhamnose content of wet Miscanthus samples the RMSEP is 0.03% and the is 0.845. Accurate models have also been developed for pre-treated Miscanthus samples and are discussed. In addition, qualitative models have been developed. These allow for samples to be discriminated for on the basis of plant fraction, plant variety (giganteus/non-giganteus), harvest-period (early/late), and stand-age (one-year/older).

Quantitative NIRS models have also been developed for peat, although the heterogeneity of this feedstock means that the accuracies tend to be lower than for Miscanthus. The development of models for sugarcane bagasse has been hindered, in some cases, by the limited chemical variability between the samples in the calibration set. Good models are possible for the glucose and total sugars content, but the accuracy of other models is poorer. NIRS spectra of Brazilian bagasse samples have been projected onto these models, and onto those developed for Miscanthus, and the Miscanthus models appear to provide a better fit than the Australian bagasse models.

Examples of Other Feedstocks Analysed at Celignis