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This paper is the first illustration of an innovative procedure for studying the dynamics of condensed phases in hydrothermal carbonization of lignocellulosic waste. A novel technique, based on a particular implementation of van Krevelen plots, is shown to be capable of monitoring the compositions precisely during this process. Two fundamental laws describe the system evolution: double-exponential decay and a modified form of the Hill equation. The modeling was tested using batch experiments (200 °C, up to 2 h) performed with three different lignocellulosic materials (silver fir, beech wood, and olive pruning). A high goodness of fit (R2 as high as 0.999) supports the approach and heuristically indicates the way for further research. The method allows for prediction of the time course of solid yield, heating value, atomic ratios, and other relevant process variables. The technique also provides valuable and easy-to-obtain information to address the process optimization of industrial plants.

High yields of nicotinic acid from 3-cyanopyridine bioconversion were obtained by exploiting the in situ nitrile hydratase-amidase enzymatic cascade system of Microbacterium imperiale CBS 498-74. Experiments were carried out in continuously stirred tank UF-membrane bioreactors (CSMRs) arranged in series. This reactor configuration enables both enzymes, involved in the cascade reaction, to work with optimized kinetics, without any purification, exploiting their differing temperature dependences. To this end, the first CSMR, optimized for the properties of the NHase, was operated (i) at low temperature (5°C), limiting inactivation of the more fragile enzyme, nitrile hydratase, (ii) with a high residence time (24 h) to overcome reaction rate limitation. The second CSMR, optimized for the properties of the AMase, was operated (i) at a higher temperature (50°C), (ii) with a lower residence time (6h), and (iii) with a lower substrate (3-cyanopyridine) concentration to control excess substrate inhibition. The appropriate choice of operational conditions enabled total conversion of 3-cyanpyridine (up to 200 mM) into nicotinic acid to be achieved at steady-state and for long periods. Higher substrate concentrations required two CSMRs optimized for the properties of the NHase arranged in series to drive the first reaction to completion.

The bioconversion of benzonitrile to benzamide and benzoic acid catalysed by resting cells of Microbacterium imperiale CBS 498-74 was investigated in batch and UF-membrane reactors. The microorganism converts nitriles through a two-step reaction, catalysed by a nitrile hydratase (NHase)–amidase (AMase) system. The kinetic parameters, Kmappand Vmapp, tested in 50 mM sodium phosphate buffer, pH 7.0, for benzonitrile and benzamide bioconversion were evaluated in batch reactor at 20 °C. Kmapp resulted 1.34 and 0.042 (mM), and Vmapp 1.1 and 0.072 (μmol min−1 mgDCW−1) for NHase and AMase, respectively. Batch and UF-membrane reactors were used to study the effect of operating variables such as enzyme and substrate concentration, temperature and residence time. The appropriate choice of operating conditions allowed to selectively control the NHase/AMase system and consequently the reactor output. A UF-membrane bioreactor operating at 20 °C and a τ of 10.3 h, allowed 96.9% conversion into benzoic acid; in contrast, when operating at 5 °C and a τ of 22.5 h 70.5% benzamide accumulated in the bioreactor.

The enzymatic hydrolysis of wheat straw was carried out in bi-phasic media prepared with acetate esters and Na-acetate buffer. The volume percentage of the organic chemicals was 75%. The biomass was pretreated in a steam explosion plant at 217°C and for 3 min. A cellulase complex from commercial source was utilised and the experiments were run at 45°C and at constant enzyme to biomass weight ratio (0.06). Biomass loadings ranged from 6.25 to 100 g per litre of reactor. The amount of glucose formed per litre of reactor and hour and the glucose yield (grams of product per gram of biomass) were close to the values attained in pure buffer. The glucose concentration in the aqueous phase was in bi-phasic media much higher than in pure buffer and reached the value of 146 g lH2O−1 during 72 h of saccharification. The results were poorly dependent on the physical–chemical properties of the solvents. Nevertheless, butyl acetate could be slightly preferred to propyl and i-amyl acetate. The use of bi-phasic media did not require stirring rate higher than in pure buffer. The presence of acetate ester traces did not alter markedly the production of ethanol in the fermentation stage, but determined the extension of the lag phase.

A method is proposed for the study of enzymatic reactions affected by product inhibition. The use of continuous and stirred ultrafiltration membrane re A mathematical model has been defined which depicts Michaelis-Menten kinetics with a linear-type product inhibition for all competitive, non-competitiv The experimental procedure needed to identify the inhibition pattern and to evaluate the set of kinetic constants is detailed. Two model systems, the h