Analysis of Sugarcane Bagasse

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.

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.

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 Ireland’s 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.