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A techno-economic study of different pretreatments of lignocellulosic biomass (LCB) has been carried out: diluted sulfuric acid (DSA) pretreatment, fractionation of LCB with an ethanol-water mixture (EW), and the same process with liquor reuse (EWR). A simplified analysis was performed considering selected equipment, utilities, and supplies consumption, while also considering the influence of the liquid to solid (L/S) ratio. The equipment cost was found to be similar for the three alternatives, although selected operating costs were somewhat lower for the DSA pretreatment than for the EW. When liquor reuse was considered, EWR costs were significantly reduced. For the case study of L/S of 10, costs were halved under the tested conditions. The influence of the L/S ratio was found to be approximately linear, and correlations were obtained to estimate steam and utilities consumption for different L/S ratios.

The evolution of lignocellulosic biorefineries increasing the process complexity and integration through the processing of multiple raw biomass-based materials into several products is described. This critical overview deals with available lignocellulosic feedstocks, pretreatment operations, enzymatic saccharification to monosaccharides and their final transformation into bioethanol and other bio-based products. Aspects as process operating conditions, modes of operation, underlying physical and chemical phenomena, and mathematical modelling are addressed. Pretreatment stage is a key step for any further processing, specially when using multifeedstock. The use of ethanol-water mixtures for biomass fractionation is a promising treatment able to compete with the nowadays more employed pretreatment such as steam explotion and diluted acid processes. Enzymatic saccharification of pretreated biomass has been analysed considering its complexity and selectivity. Its mathematical modelling is described in detail, together with the underlying phenomena, highlighting the importance of mass transfer in a biphasic system. An adequate operation unit design, scale-up and control, and process design and integration can be ensured in this way. Finally, biotransformations of monosaccharides to biofuels and platform chemicals is analysed as they are becoming key processes within bioeconomy, in the framework of integrated biorefinery to fuels, chemicals and materials.

Enzymatic hydrolysis of pre-treated wheat straw has been studied. Several additives have been checked as potential improvers of glucose yield in the enzymatic hydrolysis, trying to avoid the cellulases inhibition by the lignin as a cause of the decrease of the saccharification rate of lignocellulosic biomass. Non-ionic surfactants, such as Tween 80 (poly(oxyethylene)20-sorbitan-monooleate) and polyethylene glycol-6000, and proteins, as bovine serum albumin, casein and skimmed milk powder, have been used to improve the sugars yield in the enzymatic hydrolysis. Two pre-treated wheat straw materials, one with high delignification and another with low delignification, have been tested. Three concentrations of each additive have been considered. The results obtained point out that the lignin content of the pre-treated lignocellulosic biomass has a decisive influence in reaching a high yield in the enzymatic saccharification. The additives checked have a moderate effect on the cellulose hydrolysis rate. The more favorable option combines high delignification with the use of a cheap protein such as casein, reaching a glucose yield of 88.6% when the best conditions are employed.

Background: Isobutanol is a candidate to replace gasoline from fossil resources. This higher alcohol can be produced from sugars using genetically modified microorganisms. Shimwellia blattae (p424IbPSO) is a robust strain resistant to high concentration of isobutanol that can achieve a high production rate of this alcohol. Nevertheless, this strain, like most strains developed for isobutanol production, has some limitations in its metabolic pathway. Isobutanol production under anaerobic conditions leads to a depletion of NADPH, which is necessary for two enzymes in the metabolic pathway. In this work, two independent approaches have been studied to mitigate the co-substrates imbalance: (i) using a NADH-dependent alcohol dehydrogenase to reduce the NADPH dependence of the pathway and (ii) using a transhydrogenase to increase NADPH level., Results: The addition of the NADH-dependent alcohol dehydrogenase from Lactococcus lactis (AdhA) to S. blattae (p424IbPSO) resulted in a 19.3% higher isobutanol production. The recombinant strain S. blattae (p424IbPSO, pIZpntAB) harboring the PntAB transhydrogenase produced 39.0% more isobutanol than the original strain, reaching 5.98 g L−1 of isobutanol. In both strains, we observed a significant decrease in the yields of by-products such as lactic acid or ethanol., Conclusions: The isobutanol biosynthesis pathway in S. blattae (p424IbPSO) uses the endogenous NADPH-dependent alcohol dehydrogenase YqhD to complete the pathway. The addition of NADH-dependent AdhA leads to a reduction in the consumption of NADPH that is a bottleneck of the pathway. The higher consumption of NADH by AdhA reduces the availability of NADH required for the transformation of pyruvate into lactic acid and ethanol. On the other hand, the expression of PntAB from E. coli increases the availability of NADPH for IlvC and YqhD and at the same time reduces the availability of NADH and thus, the production of lactic acid and ethanol. In this work it is shown how the expression of AdhA and PntAB enzymes in Shimwellia blattae increases yield from 11.9% to 14.4% and 16.4%, respectively.

Enzymatic hydrolysis of three pre-treated lignocellulosic biomasses -LCB- (wheat straw-WS-, corn stover-CSV- and cardoon stems -CS-) is studied. These biomasses were pre-treated by two methods: diluted sulfuric acid and acid ethanol-water extraction at six severity levels (H values). Pretreated solid fractions were hydrolyzed with commercial enzyme cocktails at standard conditions. A first-order kinetic fractal model was fitted to the experimental results. This model accurately describes the hydrolysis of all biomasses at all pre-treatment conditions studied. The results show that the formal first-order kinetic constant k depends on the biomass nature. The hydrolysis rate increases as the pre-treatment severity does, while the fractal exponent value h decreases. With these pre-treatments, and in terms of k and h, WS is highly reactive and, at medium H with EW pretreatment, highly accessible; CSV has a low reactivity and high accessibility and CS has the lowest reactivity and an increasing accessibility as severity rises.

As a way to valorise glycerol, the main by-product of biodiesel, this study is focused on the production of esters of p-methoxycinnamic acid and glycerol. These esters can replace hazardous octylmethoxycinnamate in the cosmetic industry, which is thought to act as an endocrine disruptor and can interfere with thyroid function. Several sulfonated mesoporous catalysts, with and without endcapping, were easily synthetized using several alcohols as porogens. These catalysts were characterized for structure and surface area, chemical composition and acidity, and tested under solventless conditions for the esterification of glycerol with p-methoxycinnamic acid. Their activity was similar to that of p-toluenesulfonic acid. The best catalysts for the reaction under study was the end-capped mesoporous solid prepared in isopropanol. Finally, the selected catalyst was tested in 9 runs conducted at 150–170 °C and at molar ratios glycerol:p-methoxycinnamic acid ranging from 3:1 to 9:1. The kinetic model that better fits to the experimental data comprises two esterification reactions in-series and a first-order catalyst deactivation. The activation energies were 87.33 ± 5.67 kJ mol for the average esterification to the monoglycerides, 69.17 ± 9.84 kJ mol in average for the reactions yielding the diglycerides, and 104.00 ± 15.30 kJ mol for the catalyst deactivation.

The fractionation of wheat straw by ethanol-water (EW) pre-treatment was studied regarding its main operating conditions: time, temperature, L/S ratio and ethanol percentage were optimized by using an orthogonal experimental design (Taguchi). Afterwards, diluted sulfuric acid (DSA) hydrolysis and EW treatments have been compared in terms of energy consumption and yield of a cellulosic solid residue able to be enzymatically hydrolyzed to glucose. Experimental results show that temperature is the only variable of EW with a significant effect on the quality of the pretreated solids. EW pre-treatment of wheat straw is more effective than DSA hydrolysis due to its higher capacity of delignification. Moreover, a high glucose yield (80%) can be obtained by enzymatic hydrolysis of a solid pretreated with a moderate energy input EW (160 °C, 45 min) while wheat straw needs of a higher energy input during DSA to produce a similar yield of glucose after saccharification.

Ethanol-water (EW) process, an efficient and low energy consumption method for lignocellulose fractionation, has been applied to the valorization of Cynara cardunculus (cardoon) as an integrated biorefinery raw material. Cardoon is a perennial plant fully adapted to low fertility soils and could be a solution to improve the biomass supply in rural areas with marginal lands. The purpose of this study is to optimize the fractionation of cardoon biomass, maximizing glucose yield in the subsequent enzymatic saccharification. Operational conditions have been optimized using Taguchi statistical approach, being the responses: recovery of glucans, hydrolysis yield of xylans, delignification yield and enzymatic hydrolysis rate. The variables studied have been: time, temperature, liquid/solid (L/S) ratio and ethanol concentration; each variable was studied at three levels. The best treatment conditions are achieved at the maximum tested values for time, temperature and L/S ratio (120 min, 190 °C and 30 L/kg, respectively), and the intermediate level for the ethanol concentration (33%). Nevertheless, temperature is the most influential variable and, with a moderate energy input (60 min, 190 °C, 20 L/kg and 25% of ethanol), cardoon retains most of the glucans (> 97%), while significant amounts of xylans (> 68%) and lignin (> 58%) are removed, resulting in a a high glucose yield (c.a. 72%) in the subsequent enzymatic saccharification process. Therefore, EW treatment leads to similar glucose yields if compared to other pre-treatments, but at a fraction of the energy input.

Ethanol-water (EW) and diluted sulfuric acid (DSA) pre-treatment have been studied for lignocellulosic biomass (corn stover, Cynara cardunculus L. stems and wheat straw). Both pre-treatments have been compared taken into account: solids recovery, glucans recovery, xylans removed, delignification and glucose yield. In all cases, the amount of energy involved has been taken as a criterion for sustainability. In general terms, EW is more efficient to remove lignin and DSA more appropriate to hydrolysate xylans. The combined effect of delignification and xylans removal is responsible for the improvement in the enzymatic cellulose hydrolysis. Under conditions of moderate-low energy inputs, EW pre-treatment yields better results than DSA with glucose yields in the range of 50–60% for EW pre-treated corn stover and cardoon stems; while wheat straw pulps reach up to 80%. So, multiple raw materials biorefinery needs a previous study to fit the type and conditions of the pre-treatment to each feedstock.

Dihydroxyacetone production from glycerol has been studied. Cultures of Gluconobacter oxydans ATCC 621, a promising microorganism that is able to convert glycerol into dihydroxyacetone, has been employed. In this work, the influence of oxygen transport rate and the fluid dynamic conditions have been studied working with resting cells cultures. Several experiments were carried out at two different scales: 250 mL Erlenmeyer flasks and a 2 L stirred tank bioreactor, varying the agitation speed. Product and substrate concentration were determined employing high-performance liquid chromatography. Additionally, oxygen concentration was measured in the runs carried out in stirred tank reactors. Taking into account the results obtained in these experiments, three different behaviors were observed, depending on the mass transfer and chemical reactions rates. For experiments with low stirring speed (below 200 rpm for shake flasks and 300 rpm for reactors), the oxygen transport rate is the controlling step, while at high stirring speed (over 300 rpm in shake flasks and 560 rpm in the bioreactor), the chemical reaction is controlling the overall process rate. In some runs conducted at medium agitation, a mix control was found. All the kinetic models were able to reproduce experimental data and fulfill thermodynamic and statistical criteria, highlighting the importance of the mass transfer rate upon this system., Ministerio de Economía y Competitividad (MINECO), Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

RESEARCH ID L-2854-2014 (Rafael Castillo Romero) ORCID 0000-0003-1957-3098 (Rafael Castillo Romero) RESEARCHER ID M-3378-2014 (María Vallet Regí) ORCID 0000-0002-6104-4889 (María Vallet Regí), The synthesis of MCM-41mesoporous silica nanoparticles (MSNs) of controlled sizes and porous structure has been performed at laboratory and pilot plant scales. Firstly, the effects of the main operating conditions (TEOS addition rate, nanoparticle maturation time, temperature, and CTAB concentration) on the synthesis at laboratory scale (1 L round-bottom flask) were studied via a Taguchi experimental design. Subsequently, a profound one-by-one study of the effects of temperature and CTAB to TEOS molar ratio allowed to set these variables in 60 ºC and 8, avoiding particle enlargement and deformation of the internal structure. The final runs were performed at pilot plant scale (5 L cylindrical thermostated reactor) to analyze stirring speed, type of impeller, TEOS addition rate and nanoparticle maturation time effects, confirming results at laboratory scale. Despite slight variations on the morphology of the nanoparticles, this methodology provided MSNs with adequate sizes and porosities for biomedical applications regardless of the reactor/scale. The process showed to be robust and reproducible using mild synthesis conditions (2 mLmin-1 TEOS addition rate, 400 rpm stirred by a Rushton turbine, 60 minutes maturation time, 60 ºC, 2 gL-1 CTAB, molar ratio TEOS/CTAB=8), providing prismatic short mesoporous 100-200 nm nanorods with non-connected 3 nm parallel mesopores., Unión Europea. Horizonte 2020, Depto. de Química en Ciencias Farmacéuticas, Fac. de Farmacia, TRUE, pub

The inhibition of the enzymatic saccharification of acid pretreated corn stover (PCS) biomass due to several compounds either present in PCS or produced during saccharification has been studied. The prospective inhibitors tested were glucose (≤110 g L-1), celobiose (≤24 g L-1), xylose (≤50 g L-1), arabinose (≤1.5 g L-1), furfural (≤2 g L-1), hydroxymethylfurfural (≤1 g L-1), acetic acid (≤4 g L-1), and lignin (≤50 g L-1). Each of these compounds was added at three different concentrations, being the concentration intervals different according to standard maximum concentrations of such compounds in the reaction medium, previously measured and described in literature. In addition, these experiments were employed to evaluate the standard error present during the evaluation of the results obtained in the inhibition reactions. Those results show that significant inhibition was only detected for lignin (more than 25 g L-1) and it was also appreciable for glucose at high concentrations (above 75 g L-1), although it was not remarkable at medium concentrations (40 g L-1). On the other hand, neither of the remaining compounds tested presented any significant inhibitory effect at the usual process concentration range.