Glycerol carbonate as green solvent for pretreatment of sugarcane bagasse

Background\ud Pretreatment of lignocellulosic biomass is a prerequisite for effective saccharification to produce fermentable sugars. We have previously reported an effective low temperature (90 °C) process at atmospheric pressure for pretreatment of sugarcane bagasse with acidified mixtures of ethylene carbonate (EC) and ethylene glycol (EG). In this study, “greener” solvent systems based on acidified mixtures of glycerol carbonate (GC) and glycerol were used to treat sugarcane bagasse and the roles of each solvent in deconstructing biomass were determined. \ud \ud Results\ud Pretreatment of sugarcane bagasse at 90 °C for only 30 min with acidified GC produced a solid residue having a glucan digestibility of 90% and a glucose yield of 80%, which were significantly higher than a glucan digestibility of 16% and a glucose yield of 15% obtained for bagasse pretreated with acidified EC. Biomass compositional analyses showed that GC pretreatment removed more lignin than EC pretreatment (84% vs 54%). Scanning electron microscopy (SEM) showed that fluffy and size-reduced fibres were produced from GC pretreatment whereas EC pretreatment produced compact particles of reduced size. The maximal glucan digestibility and glucose yield of GC/glycerol systems were about 7% lower than those of EC/ethylene glycol (EG) systems. Replacing up to 50 wt% of GC with glycerol did not negatively affect glucan digestibility and glucose yield. The results from pretreatment of microcrystalline cellulose (MCC) showed that (1) pretreatment with acidified alkylene glycol (AG) alone increased enzymatic digestibility compared to pretreatments with acidified alkylene carbonate (AC) alone and acidified mixtures of AC and AG, (2) pretreatment with acidified GC alone slightly increased, but with acidified EC alone significantly decreased, enzymatic digestibility compared to untreated MCC, and (3) there was a good positive linear correlation of enzymatic digestibility of treated and untreated MCC samples with congo red (CR) adsorption capacity.\ud \ud Conclusions\ud Acidified GC alone was a more effective solvent for pretreatment of sugarcane bagasse than acidified EC alone. The higher glucose yield obtained with GC-pretreated bagasse is possibly due to the presence of one hydroxyl group in the GC molecular structure, resulting in more significant biomass delignification and defibrillation, though both solvent pretreatments reduced bagasse particles to a similar extent. The maximum glucan digestibility of GC/glycerol systems was less than that of EC/EG systems, which is likely attributed to glycerol being less effective than EG in biomass delignification and defibrillation. Acidified AC/AG solvent systems were more effective for pretreatment of lignin-containing biomass than MCC

Production of levulinic acid and other chemicals from sugarcane fibre

Lignocellulosics represent a renewable resource for producing fuels and chemicals as an alternative to fossil resources. This study utilised an organic acid catalyst and a co-solvent to develop an environmentally friendly processing technology for the production of levulinic acid and furfural from a waste material, sugarcane fibre

Membrane filtration of clarified juice

A membrane filtration plant using suitable micro or ultra-filtration membranes has the potential to significantly increase pan stage capacity and improve sugar quality. Previous investigations by SRI and others have shown that membranes will remove polysaccharides, turbidity and colloidal impurities and result in lower viscosity syrups and molasses. However, the conclusion from those investigations was that membrane filtration was not economically viable. A comprehensive assessment of current generation membrane technology was undertaken by SRI. With the aid of two pilot plants provided by Applexion and Koch Membrane Systems, extensive trials were conducted at an Australian factory using clarified juice at 80–98°C as feed to each pilot plant. Conditions were varied during the trials to examine the effect of a range of operating parameters on the filtering characteristics of each of the membranes. These parameters included feed temperature and pressure, flow velocity, soluble solids and impurity concentrations. The data were then combined to develop models to predict the filtration rate (or flux) that could be expected for nominated operating conditions. The models demonstrated very good agreement with the data collected during the trials. The trials also identified those membranes that provided the highest flux levels per unit area of membrane surface for a nominated set of conditions. Cleaning procedures were developed that ensured the water flux level was recovered following a clean-in-place process. Bulk samples of clarified juice and membrane filtered juice from each pilot were evaporated to syrup to quantify the gain in pan stage productivity that results from the removal of high molecular weight impurities by membrane filtration. The results are in general agreement with those published by other research groups

A new design of jigger system to improve pan performance

A new jigger system has been designed by SRI to boost circulation and heat transfer rates in vacuum pans. The jigger system injects and distributes numerous small bubbles of steam/incondensible gases at controllable rates into the base of the pan. Circulation is improved through a combination of the rising bubbles and the increased heat transfer that results from the increased velocity of massecuite through the tubes. The jigger system offers benefits to the pan’s performance throughout the entire pan cycle. \ud \ud Trials were undertaken during the 2004 and 2005 seasons on batch and continuous pans in Australia to determine the performance during operation with and without the jigger system. The performance was assessed by taking circulation measurements using anemometer probes, measuring heat transfer from the calandria section of the pan, monitoring the calandria pressure and steam flow rate during operation and monitoring the production rate of massecuite. \ud \ud The installation of the jigger system shows substantial performance improvements including:\ud • Reduced calandria pressure; \ud • Improved heat transfer coefficients; \ud • Increased circulation velocities; \ud • Shorter batch pan cycle times; and\ud • Production of massecuites at higher brix. \ud \ud Additional advantages of the jigger system include:\ud • Relatively cheap and low maintenance;\ud • Reduced need for balance water and the use of surfactants; and\ud • The pipework system does not block with massecuite so non-return valves are not required.\ud \ud The jigger system can be retrofitted to existing batch and continuous pans of any design

Stability of sugarcane juice – a preliminary assessment\ud of the colorimetric method used for phosphate analysis

This paper reviews the properties of sugarcane juice by summarizing\ud the main chemical and physical reaction processes that occur\ud during the clarification process. As the phosphate content in sugarcane\ud juice is an important parameter in the clarification process,\ud this paper also examines the current colorimetric method used for\ud the determination of phosphate in sugarcane juice. In this method\ud a phosphomolybdate blue complex is measured at 660 nm. At this\ud wavelength the soluble inorganic phosphate content of juice can be\ud underestimated by as much as 30%, due to interference of color in\ud juice. It is recommended that the measurement should be carried\ud out at the higher wavelength of 875 nm

Some aspects of calcium phosphate chemistry in sugarcane clarification

This paper reviews some aspects of calcium phosphate chemistry since phosphate in juice is an important\ud parameter in all sugar juice clarification systems. It uses basic concepts to try and explain the observed differences\ud in clarification performance obtained with various liming techniques. The paper also examines the current\ud colorimetric method used for the determination of phosphate in sugar juice. In this method, a phosphomolybdate\ud blue complex formed due to the addition of a dye is measured at 660 nm. Unfortunately, at this wavelength there is interference of the colour arising from within the juice and results in the underestimation of the amount of soluble\ud inorganic phosphate content of juice. It is suggested that phosphate analysis be conducted at the higher\ud wavelength of 875 nm where the interference of the juice colour is minimised

Steam side calandria modelling of vacuum pans and evaporators

The heat transfer and condensation of steam within the steam belt and the steam chest surrounding the calandria tubes of vacuum pans and evaporators were investigated using computational fluid dynamics (CFD) modelling techniques. The flow of steam in evaporators and vacuum pans is an aspect that is not usually given much attention but it can influence the productivity of these vessels. The latent heat of the steam provides the heat to the juice or massecuite which induces the formation of vapour bubbles and drives the circulation of the fluid within the vessel. Strong and uniform circulation of the massecuite in vacuum pans increases the production capacity and improves the quality of the sugar produced. \ud \ud Non-uniform heating by the steam on the outside of the calandria tubes can contribute to uneven and inconsistent heat transfer to the juice or massecuite within the vessel. As a consequence under these circumstances the installed heating surface is not effectively utilised. Inconsistent heating can affect the performance of vacuum pans since it influences the circulation of massecuite and the crystallisation rate of sugar.\ud \ud The CFD modelling investigation into the steam side operation of the calandria of vacuum pans and evaporators was preliminary in nature but has shown promising results. The results of the CFD simulations were compared against measured data to determine the applicability of the CFD model. The condensation physics of the CFD model currently has limitations, yet despite these, the CFD model has identified some deficiencies in the flow of steam within the calandria. The investigations into different geometries for steam flow into evaporators and vacuum pans and the results of CFD simulations are detailed and discussed. Some of the proposed modifications resulted in predicted improvements to the distribution of steam within the calandria

Degradation of phenethoxybenzene in sodium hydroxide

Simple lignin model compounds containing <i>β-O-4</i> aryl ether linkages have been utilized as a means to understand lignin depolymerisation. The effects of, reaction temperature and time, catalyst concentration, initial phenethoxybenzene (PEB) on the degradation of PEB in <i>NaOH</i> was investigated. Operating at 300 ^oC for 1 h resulted in the highest combined yield of the primary products, phenol and styrene, and also resulted in the reduced amount of degradation products formed. The proportion of oligomeric and polymeric materials formed depended on the <i>NaOH</i> concentration, but not on the initial PEB concentration for equal reaction time. The results were used to propose reaction pathways for PEB degradation