Esters are a highly relevant class of compounds in the industrial context, and biocatalysis applied to ester syntheses is already a reality for some chemical companies.

Background: Previous studies on the use of SO₂ and CO₂ as impregnating agent for sugar cane bagasse steam treatment showed comparative and promising results concerning the cellulose enzymatic hydrolysis and the low formation of the inhibitors furfural and hydroxymethylfurfural for the use of CO₂ at 205°C/15 min or SO₂ at 190°C/5 min. In the present study sugar cane bagasse materials pretreated as aforementioned were analyzed by scanning and transmission electron microscopy (SEM and TEM), X-Ray Diffraction (XRD) and Infrared (FTIR spectroscopy) aiming a better understanding of the structural and chemical changes undergone by the pretreated materials. Results: SEM and TEM data showed that the structural modifications undergone by the pretreatment with CO₂ were less pronounced in comparison to that using SO_2, which can be directly related to the combined severity of each pretreatment. According to XRD data, untreated bagasse showed, as expected, a lower crystallinity index (CI = 48.0%) when compared to pretreated samples with SO₂ (CI = 65.5%) or CO₂ (CI = 56.4%), due to the hemicellulose removal of 68.3% and 40.5%, respectively. FTIR spectroscopy supported SEM, TEM and XRD results, revealing a more extensive action of SO₂. Conclusions: The SEM, TEM, XRD and FTIR spectroscopy techniques used in this work contributed to structural and chemical analysis of the untreated and pretreated bagasse. The images from SEM and TEM can be related to the severity of SO₂ pretreatment, which is almost twice higher. The crystallinity index values obtained from XRD showed that pretreated materials have higher values when compared with untreated material, due to the partial removal of hemicellulose after pretreatment. FTIR spectroscopy supported SEM, TEM and XRD results. CO₂ can actually be used as impregnating agent for steam pretreatment, although the present study confirmed a more extensive action of SO₂.

Background: The conditions for steam pretreatment of sugar cane bagasse and leaves were studied using CO₂ as an impregnating agent. The following conditions were investigated: time (5 to 15 min) and temperature (190 to 220°C). The pretreatment was assessed in terms of glucose and xylose yields after enzymatic hydrolysis and inhibitor formation (furfural and hydroxymethylfurfural) in the pretreatment. Results from pretreatment using SO₂ as impregnating agent was used as reference. Results: For sugar cane bagasse, the highest glucose yield (86.6% of theoretical) was obtained after pretreatment at 205°C for 15 min. For sugar cane leaves the highest glucose yield (97.2% of theoretical) was obtained after pretreatment at 220°C for 5 min. The reference pretreatment, using impregnation with SO₂ and performed at 190°C for 5 min, resulted in an overall glucose yield of 79.7% and 91.9% for bagasse and leaves, respectively. Conclusions: Comparable pretreatment performance was obtained with CO₂ as compared to when SO₂ is used, although higher temperature and pressure were needed. The results are encouraging as some characteristics of CO₂ are very attractive, such as high availability, low cost, low toxicity, low corrosivity and low occupational risk.

The establishment of a bioeconomy era requires not only a change of production pattern, but also a deep modernization of the production processes through the implementation of novel methodologies in current industrial units, where waste materials and byproducts can be utilized as starting materials in the production of commodities such as biofuels and other high added value chemicals. The utilization of renewable raw resources and residues from the agro-industries, and their exploitation through various uses and applications through technologies, particularly solid-state fermentation (SSF), are the main focus of this review. The advocacy for biocatalysis in green chemistry and the environmental benefits of bioproduction are very clear, although this kind of industrial process is still an exception and not the rule. Potential and industrial products, such as biocatalysts, animal feed, fermentation medium, biofuels (biodiesel, lignocelulose ethanol, CH₄, and H₂), pharmaceuticals and chemicals are dealt with in this paper. The focus is the utilization of renewable resources and the important role of enzymatic process to support a sustainable green chemical industry.