• Feedstocks Analysed at Celignis
    Miscanthus

Background on Miscanthus

Miscanthus is a perennial C4 grass that originated from Asia but was introduced to Europe in the 1930s when its main use was as an ornamental grass. However, the development of Miscanthus x giganteus, a high-yielding sterile hybrid of the M. sinensis and M. sacchariflorus varieties, led to increased interest in utilizing this variety as an energy crop. Miscanthus is a rare case of a C4 grass that can grow in temperate climates; it can photosynthesise down to a temperature of < 5oC. The crop is also attractive because it has low requirements for fertilizer and pesticides. Miscanthus is closely related to sugar cane, and the two often hybridise in the wild.

There are numerous varieties of Miscanthus that have been grown experimentally but fewer varieties tend to be grown commercially. In Ireland, for example, Miscanthus x giganteus is the only commercial crop that has been established so far, although elsewhere in Europe, particularly in the regions that experience colder winters, M. sinensis has been grown commercially.
Miscanthus_field
Field of Miscanthus in Western Ireland

M. x giganteus is sterile, and so must be propagated vegetatively. This can either involve the planting of rhizome cuttings or plantlets. Crop growth will start in the Spring once daytime temperatures exceed 10oC. Growth is very rapid, in May, June, and July, and results in stems that may reach a height of 3+ metres. Once the canopy closes, the lower layers of leaves begin to senesce. Shoot growth continues through August and September with full senescence occurring following the first frosts of the autumn.

During the end of the growing season, nutrients are translocated from the stems and leaves to the rhizomes for storage and utilisation in the following season. The efficient use of nutrients by Miscanthus varieties means that artificial fertilisation levels need not be high. The low fertiliser and pesticide requirements of Miscanthus mean it is a relatively environmentally friendly crop.

Harvesting of Miscanthus is carried out annually and can occur after crop senescence until just before re-growth in the following spring. It is important that the crop has senesced so that translocation of assimilates to the rhizomes has occurred. Current practices involving Miscanthus seem to be geared towards harvesting the biomass in the spring before the start of the growing season. The reasoning behind this is that the later the harvesting, the lower will be both the moisture content and the inorganic mineral content; these are important qualities in biomass combustion - the primary end use for Miscanthus at this time.

Delaying the point of harvest from the start to the end of the harvest window has been shown to result in a decrease in the amount of standing biomass harvested from the field. That is mostly attributable to the loss of leaf material from the plant.

Analysis of Miscanthus at Celignis



Celignis Analytical can determine the following properties of Miscanthus samples:



Lignocellulosic Properties of Miscanthus

Cellulose Content of Miscanthus

Celignis founder Daniel Hayes has extensive experience in the analysis of Miscanthus samples and has characterised numerous plants and varieties of the species. One research project involved sampling plants each month from the period of senescence until harvest from seven different Miscanthus stands at various locations throughout Ireland. Each plant sampled was separated into the following anatomical fractions: internodes (with a grouping for each metre of height of the stem, e.g. three separate internode samples for a plant three metres in height); nodes (also grouped according to height); live leaf blades; live leaf sheaths; dead leaf blades; dead leaf sheaths; and flowers.

The study found that Miscanthus has a good cellulose content (approx. 40% on a whole plant basis) but that there was significant variability between different parts of the plant and between the different Miscanthus varieties. The cellulose content was found to be greatest in the stem sections and significantly lower in the leaf blades. Smaller plants were also found to typically have a lower cellulose content than taller plants. Due to the loss of leaves over the harvest window the cellulose content of the harvestable plant was found to increase.

Miscanthus_late_harvest
A Miscanthus field late in the harvest window, when most of the leaves have shed from the plant.

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Hemicellulose Content of Miscanthus

Arabinoxylan is the main hemicellulose in Miscanthus. This means that xylose is the principal hemicellulose sugar, with a lower content of arabinose, and galactose typically being the third most abundant sugar. Mannose and rhamnose are usually only present in trace amounts. The hemicellulose content varies significantly between different parts of the plant, with higher contents in the leaves than in the stems and the highest contents observed in the flowers. There are significant differences in hemicellulose content between productive (tall) plants and less productive (smaller) plants. Hemicellulose content also varies between the different varieties, with Miscanthus x giganteus typically having a lower hemicellulose content than other varieties, such as M. x sinensis.

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Lignin Content of Miscanthus

The lignin content of Miscanthus can also vary greatly. It is typically highest in the stem sections, particularly in the lower stem. Lower lignin contents are found in the leaves and flowers. As a result of leaf loss over the harvest window the lignin content of harvestable biomass tends to increase with delayed harvests.

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Starch Content of Miscanthus

The starch content of Miscanthus varies between the different anatomical components of the plant. Typically it is highest in the leaves, where photosynthesis takes place, and lower in the stems. The starch content can also vary according to the maturity of the plant.

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Uronic Acid Content of Miscanthus

Uronic acids are present in the hemicelluloses in Miscanthus and are typically more abundant in the early-stages of growth. Furthermore, the concentrations of uronic acids tends to be greatest in the nodes, lower in the internodes, and at intermediate levels in the leaves.

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Enzymatic Hydrolysis of Miscanthus

We can undertake tests involving the enzymatic hydrolysis of Miscanthus. 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 Miscanthus

Ash Content of Miscanthus

Miscanthus has an ash content typical of grasses. The relative proportion of ash varies between different anatomical fractions of the plant, with higher amounts in the leaves and less in the stem sections. As a result of this, the ash content of harvestable biomass decreases with time along the harvest window, a reflection of the loss of leaves from the standing plant.

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Heating (Calorific) Value of Miscanthus

Miscanthus has a good heating value, meaning that it is suitable for utilisation in boilers for the production of heat and/or electricity. However the effective heating value will depend greatly on the moisture content of the crop. This is highest at the early period of the harvest window but decreases significantly over time. For this reason most Miscanthus is currently harvested at later points in the harvest window (e.g. March/April).

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Ash Melting Behaviour of Miscanthus

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

Ash Flow Temperature (FT) - The temperature at which the Miscanthus 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 Miscanthus

Examples of major elements that may be present in Miscanthus 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 Miscanthus.

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Analysis of Miscanthus for Anaerobic Digestion



Biomethane potential (BMP) of Miscanthus

Due to its high productivity, Miscanthus is considered to be a promising energy crop feedstock for anaerobic digestion. However, when compared with traditional AD feedstocks such as maize (corn), it contains a greater proportion of more recalcitrant lignocellulosic constituents (e.g. lignin) and less of the more labile components such as starch. This can result in biochemical methane potential (BMP) values for Miscanthus (harvested in spring) being around 100-150 litres per kg of volatile solids, whilst they are typically more than twice this for starch.

However, whilst Miscanthus is typically harvested in the spring when the standing biomass is driest (an important property when using this feedstock for combustion), the crop stops growing in the autumn and can potentially be harvested then. At that point the standing biomass in the field will be greater as the majority of the leaves will still be on the plant. These leaves also contain less lignin and more water-soluble carbohydrates than the stems. Experiments have shown that the BMP for autumn-harvested Miscanthus is significantly higher than for spring-harvested Miscanthus and that, coupled with the higher harvestable biomass associated with an autumn crop, the total biomethane yield from a hectare of autumn-harvested Miscanthus can exceed that which could be obtained from a hectare of maize.

Of course, the actual biomethane produced from a Miscanthus crop will depend on the particular conditions of that stand as well as the time of harvest and other factors. For that reason we recommend that a BMP test is undertaken.

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Physical Properties of Miscanthus



Bulk Density of Miscanthus

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

Due to its high productivity, Miscanthus is considered to be a promising energy crop feedstock for anaerobic digestion. However, when compared with traditional AD feedstocks such as maize (corn), it contains a greater proportion of more recalcitrant lignocellulosic constituents (e.g. lignin) and less of the more labile components such as starch. This can result in biochemical methane potential (BMP) values for Miscanthus (harvested in spring) being around 100-150 litres per kg of volatile solids, whilst they are typically more than twice this for starch.

However, whilst Miscanthus is typically harvested in the spring when the standing biomass is driest (an important property when using this feedstock for combustion), the crop stops growing in the autumn and can potentially be harvested then. At that point the standing biomass in the field will be greater as the majority of the leaves will still be on the plant. These leaves also contain less lignin and more water-soluble carbohydrates than the stems. Experiments have shown that the BMP for autumn-harvested Miscanthus is significantly higher than for spring-harvested Miscanthus and that, coupled with the higher harvestable biomass associated with an autumn crop, the total biomethane yield from a hectare of autumn-harvested Miscanthus can exceed that which could be obtained from a hectare of maize.

Of course, the actual biomethane produced from a Miscanthus crop will depend on the particular conditions of that stand as well as the time of harvest and other factors. For that reason we recommend that a BMP test is undertaken.

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Publications on Miscanthus By The Celignis Team

Hayes, D. J. M. (2013) Mass and Compositional Changes, Relevant to Biorefining, in Miscanthus x giganteus Plants over the Harvest Window, Bioresource Technology 142: 591-602

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Miscanthus plants were sampled from several plantations in Ireland over the harvest window (October-April). These were separated into their anatomical components and the loss of leaves monitored. Three distinct phases were apparent: there was minimal loss in the "Early" (October to early December) and "Late" (March and April) phases, and rapid leaf loss in the interim period. Samples were analysed for constituents relevant to biorefining. Changes in whole-plant composition included increases in glucose and Klason lignin contents and decreases in ash and arabinose contents. These changes arose mostly from the loss of leaves, but there were some changes over time within the harvestable plant components. Although leaves yield less biofuel than stems, the added biomass provided by an early harvest (31.9-38.4%) meant that per hectare biofuel yields were significantly greater (up to 29.3%) than in a late harvest. These yields greatly exceed those from first generation feedstocks.

Hayes, D. J. M. (2013) Report on Optimal Use of DIBANET Feedstocks and Technologies, DIBANET WP5 Report84 pages

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The DIBANET process chain, as a result of its patented pre-treatment stage, has significantly increased the yields of levulinic acid, formic acid, and furfural beyond what was considered to be the state of the art. By fractionating lignocellulosic biomass into its three main polymers (cellulose, hemicellulose, lignin) it has also allowed for lignin to be recovered and sold as a higher-value product. These developments have meant that the amount of acid hydrolysis residues (AHRs) that have been produced are significantly (up to 88%) less than in the Biofine process. These AHRs are required to provide process heat for DIBANET. Direct combustion is the most efficient means for doing this. If such combustion does not occur and the AHRs are instead used in other processes, e.g. pyrolysis and gasification, then more biomass will need to be purchased to fuel the core DIBANET process. The AHRs have not been proven to be superior to virgin biomass when put through these thermochemical processes. Indeed, many of the results from DIBANET Work Package 4 indicate the opposite. Hence, given that DIBANET, and the modelling of its optimal configuration, is designed on the basis of an integrated process, centred on the core element of the acid hydrolysis of biomass, then combustion is the only viable end use for the AHRs. Given that realisation, the focus of this modelling Deliverable is on what the optimal configuration of the process chain would be regarding the three core stages (pretreatment, hydrolysis, and the esterification of levulinic acid with ethanol). It has been demonstrated that a scenario incorporating only the first stage can be profitable in its own right and allow for commercial development at much lower capital costs. In this instance bagasse is a much more attractive feedstock, compared with Miscanthus, due to its higher pentose content.

Integrating the second stage increases capital costs but improves the net present value. The esterification step is somewhat capital intensive but an integrated DIBANET biorefinery that incorporates all three stages can still be highly profitable providing the furfural is sold at its current market price and the lignin is sold rather than used as a fuel for process needs. Indeed, the DIBANET process should not be considered only in the context of biofuels but as a true biorefinery that produces lower value fuels (e.g. ethyl-levulinate) in addition to high value chemicals and bio-products (e.g. furfural and lignin).

The energy and carbon balances of the various DIBANET scenarios have been investigated and are highly positive with values significantly superior to those for the energy-intensive Biofine process. A socioeconomic survey has also been carried out and has shown that there can be a positive effect on employment, both direct and indirect, particularly when Miscanthus is used as the feedstock. The DIBANET integrated process also holds up well when its environmental and social performances are ranked for a range of important parameters.

The development of the core DIBANET IP towards commercial deployment appears to be warranted, based on data provided from the models developed. Indeed, these models present possible scenarios whereby even demonstration-scale DIBANET facilities could operate at significant profits and provide healthy returns on the capital invested.

Hayes, D. J. M. (2012) Development of near infrared spectroscopy models for the quantitative prediction of the lignocellulosic components of wet Miscanthus samples, Bioresource Technology 119: 393-405

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Miscanthus samples were scanned over the visible and near infrared wavelengths at several stages of processing (wet-chopped, air-dried, dried and ground, and dried and sieved). Models were developed to predict lignocellulosic and elemental constituents based on these spectra. The dry and sieved scans gave the most accurate models; however the wet-chopped models for glucose, xylose, and Klason lignin provided excellent accuracies with root mean square error of predictions of 1.27%, 0.54%, and 0.93%, respectively. These models can be suitable for most applications. The wet models for arabinose, Klason lignin, acid soluble lignin, ash, extractives, rhamnose, acid insoluble residue, and nitrogen tended to have lower R(2) values (0.80+) for the validation sets and the wet models for galactose, mannose, and acid insoluble ash were less accurate, only having value for rough sample screening. This research shows the potential for online analysis at biorefineries for the major lignocellulosic constituents of interest.

Hayes, D. J. M. (2012) Review of Biomass Feedstocks and Guidelines of Best Practice, DIBANET WP2 Report150 pages

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Shorter Version

This document is the result of the evaluation of biomass feedstocks, from Europe and Latin America, that took place as part of the DIBANET project. That project is co-financed from the 7 th Framework Programme for Research and Technological Demonstration of the European Union. (Title: Enhancing international cooperation between the EU and Latin America in the field of biofuels; Grant Agreement No: 227248-2).

The work in Task 2.1 of Work Package 2 (WP2) at DIBANET partners UL, CTC, and UNICAMP involved evaluating, on a number of levels, potential feedstocks for utilisation in the DIBANET acid-hydrolysis process (WP3). In the early stage of the project a wide number of feedstocks were examined and relevant secondary compositional data were sought from the literature. Selected feedstocks were analysed at the laboratories of UL, CTC, and UNICAMP and, from these, a limited number of feedstocks were subjected to more in-depth analysis/evaluation.

Work at UL focused on Miscanthus, cereal straws, and waste papers. The wet-chemical and spectroscopic analysis that was carried out on a wide number of Miscanthus samples have allowed for in-depth understandings to be reached regarding the changes in lignocellulosic composition, and potential biomass/biofuel yields that could be realised over the harvest window. Straws present much less chemical variation but have enough structural carbohydrates to warrant their processing in the DIBANET technology. Waste papers can have amongst the highest total carbohydrate contents of any of the feedstocks studied.

Work at CTC focused on the residues of the sugarcane industry - sugarcane bagasse and sugarcane trash (field residues from harvesting). A large number of samples were collected from a variety of sugar mills and plantations. It has been seen that there can be a significant variation in the composition of different bagasse samples, particularly with regards to the ash content. Sugarcane trash has lower total carbohydrates contents than bagasse but is still a suitable feedstock for DIBANET.

Work at UNICAMP focused on the evaluation of residues from the banana, coffee, and coconut industries. It was found that these also have potential for utilisation in the DIBANET process, however the value of the residues for this end-use is dependent on which part of the plant is utilised. For instance, coffee husks have sufficient structural carbohydrates to allow for decent yields of levulinic acid, formic acid, and furfural in DIBANET, however the leaves of the coffee plant do not. Leaves from the banana plant are also of less value for DIBANET than the other parts of the plant (e.g. stem).

A major output of this Deliverable is the downloadable electronic database that contains all of the WP2 analytical data obtained during the course of the project. It contains analytical data and predicted biorefining yields for a total of 1,281 samples. It can be obtained, free of charge, from the DIBANET website and will be a valuable tool for stakeholders in biorefining projects.

This document presents the data and evaluations that were made regarding biomass feedstocks, and also puts forward guidelines of best practice in terms of making the best use of these resources. A shortened version of this document can also be downloaded from the DIBANET website.

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)

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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



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