Juan García-Serna

Engineering in direct synthesis of hydrogen peroxide: targets, reactors and guidelines for operational conditions

The demand for hydrogen peroxide is booming since it is considered as one of the most environmentally friendly and versatile chemical oxidants available and has a wide range of applications. The annual market, close to 3000 kt per year being produced via the auto-oxidation process (with 2-ethyl anthraquinone (traditional) or amyl anthraquinone for mega-plants), is mostly supplied by the company Solvay (30%), followed by Evonik (20%) and Arkema (13%). Nevertheless, the dream of a direct synthesis process is close to a century old and it has gained momentum in research efforts during the last decade with more than 15 groups active in the world. In this review, we focus the discussion on the targets, e.g. plant tonnage, the reactors and the most feasible industrial operational conditions, based on our experience and point of view using the chemical engineering tools available. Thus, direct synthesis can be competitive when on-site production is required and capacities less than 10 kt per year are demanded. The total investment cost should be approximately 40.3 ± 12.1 MM

Direct synthesis of hydrogen peroxide in methanol and water using scCO2 and N2 as diluents

(in 2012) for a 10 kt per year size process to be comparable to the traditional process in terms of costs. Moreover, all kinds of reactors used are hereby discussed emphasizing the pros and cons; the most common ones are batch and semi-continuous modes of operation. However, at the moment, demonstrations of continuous operations as well as carefully determined kinetics are needed in order to scale up the process. Finally, operational conditions, including the catalyst composition (active metal, oxidation state and support), promoters (halides and acids–pH–isoelectric point), solvents, pressure and temperature need to be carefully analysed. In our opinion, as we try to show here, H2O2 direct synthesis is a competitive process and is ready for larger scale demonstration. Also, more than a hundred patents within the area support this claim, although the barriers of technology demonstration and further licensing are still pending.

Direct synthesis of hydrogen peroxide in water in a continuous trickle bed reactor optimized to maximize productivity

Direct synthesis of hydrogen peroxide is of high importance nowadays due to its improvement over the traditional anthraquinone hydrogenation-oxidation process. In this work we show how H2O2 can be obtained from H2 and O2 in water pressurised with CO2 under supercritical conditions or with N2 at similar conditions without using organic solvents. Pressures up to 16.7 MPa and mild temperatures from 10 to 45 °C using a commercial 5 wt.% Pd/C catalyst lead to yields from 10.8% to 82.6%, concentrations from 0.22 to 4.01 wt.% of H2O2 and Turn Over Frequency at 30 minutes values, TOF30, from 6.0 to 1538 mol·h−1·kgcat−1. The effect of several variables on H2O2 yield has been examined: amount of catalyst, promoters/Pd ratio, amount and nature of solvent and inert gas, reaction temperature, and O2/H2 ratio. Results for methanol and water are compared.

Hydrothermal fractionation of woody biomass: Lignin effect on sugars recovery

Hydrogen peroxide direct synthesis was studied in continuous mode over a 5% wt Pd/C commercial catalyst in a Trickle Bed Reactor. The target of the study was to maximize the hydrogen peroxide production. The catalyst was uniformly diluted in quartz sand at different concentrations to investigate their effects on the direct synthesis. The amount of catalyst and the distribution of the catalyst along the bed were optimized to obtain the highest possible yield. The distribution of the catalyst along the bed gave the possibility to significantly improve the selectivity and production of hydrogen peroxide (up to 0.5% under selected conditions). Higher production rate and selectivity were found when the catalyst concentration was decreased along the bed from the top to the bottom as compared to the uniformly dispersed catalyst. The H2/Pd ratio was found to be an important parameter that has to be investigated in the hydrogen peroxide direct synthesis. The effect of a pretreatment of the catalyst with a solution of sodium bromide and phosphoric acid was studied; the results showed how a catalyst pretreatment can lead to a real green hydrogen peroxide synthesis in water. Some optimization guidelines are also provided.

Modeling of biomass fractionation in a lab-scale biorefinery: Solubilization of hemicellulose and cellulose from holm oak wood using subcritical water.

Subcritical water was employed to fractionate woody biomass into carbohydrates and lignin. Nine urban trees species (hardwood and softwood) from Spain were studied. The experiments were carried out in a semi-continuous reactor at 250 °C for 64 min. The hemicellulose and cellulose recovery yields were between 30%wt. and 80%wt. while the lignin content in the solid product ranged between 32%wt. and 92%wt. It was observed that an increment of solubilized lignin disfavored the hydrolysis of hemicelluloses. It was determined that the maximum extraction of hemicellulose was achieved at 20 min of solid reaction time while the extraction of celluloses not exhibited a maximum value. The hydrolysis of hemicellulose and cellulose would be governed by the hydrolysis kinetic and the polymers accessibility. In addition, the extraction of hemicellulose was negatively affected by the lignin content in the raw material while cellulose hydrolysis was not affected by this parameter.

Green HAZOP analysis: incorporating green engineering into design, assessment and implementation of chemical processes

Lignocellulose fractionation is a key biorefinery process that need to be understood. In this work, a comprehensive study on hydrothermal-fractionation of holm oak in a semi-continuous system was conducted. The aim was to develop a physicochemical model in order to reproduce the role of temperature and water flow over the products composition. The experiments involved two sets: at constant flow (6mL/min) and two different ranges of temperature (140-180 and 240-280°C) and at a constant temperature range (180-260°C) and different flows: 11.0, 15.0 and 27.9mL/min. From the results, temperature has main influence and flow effect was observed only if soluble compounds were produced. The kinetic model was validated against experimental data, reproducing the total organic carbon profile (e.g. deviation of 33%) and the physicochemical phenomena observed in the process. In the model, it was also considered the variations of molecular weight of each biopolymer, successfully reproducing the biomass cleaving.

Simulation and flavor compound analysis of dealcoholized beer via one-step vacuum distillation

The expression ‘sustainable development’ has become a catchphrase in chemical engineering design and operation. There have been several successful attempts for the inherently safer design of processes. There is still a need of guidance tools for design, assessment and implementation of processes using green engineering criteria. Green HAZOP presents a systematic tool based on HAZOP analysis for the incorporation of green engineering criteria within detailed design, commissioning and operation stages. It is aimed at discovering how deviations from the green design intent can occur during the different phases of a project realisation in equipment, actions or materials, and whether the consequences of these deviations can result in a non-green or non-sustainable process. A comprehensive industrial example about Bhopals pesticide plant and the dramatic accident is presented in text.

Hydrothermal hydrolysis of grape seeds to produce bio-oil

The coupled operation of vacuum distillation process to produce alcohol free beer at laboratory scale and Aspen HYSYS simulation software was studied to define the chemical changes during the dealcoholization process in the aroma profiles of 2 different lager beers. At the lab-scale process, 2 different parameters were chosen to dealcoholize beer samples, 102mbar at 50°C and 200mbar at 67°C. Samples taken at different steps of the process were analyzed by HS-SPME-GC-MS focusing on the concentration of 7 flavor compounds, 5 alcohols and 2 esters. For simulation process, the EoS parameters of the Wilson-2 property package were adjusted to the experimental data and one more pressure was tested (60mbar). Simulation methods represent a viable alternative to predict results of the volatile compound composition of a final dealcoholized beer.

Understanding bottom-up continuous hydrothermal synthesis of nanoparticles using empirical measurement and computational simulation

In the present work, the hydrothermal hydrolysis of grape seeds focused on the production of bio-oil was studied. The grape seeds composition in terms of lignin, sugars, ash, extractives and bio-oil was determined. The composition of grape seeds was: 17.0 wt% of extractives; 36.8 wt% of sugars (hemicellulose and cellulose); 43.8 wt% of lignin and 2.4 wt% of ash. The grape seeds were hydrothermally treated using three different temperatures: 250 °C, 300 °C and 340 °C employing a semi-continuous reactor. The solid residue varied from 25.6–35.8 wt% depending on the hydrolysis temperature. The maximum yields of light (15.7 wt%) and heavy bio-oil (16.2 wt%) were achieved at 340 °C. The Arrhenius parameters for the kinetics of grape seeds hydrolysis in our system were k0 = 0.995 g min−1 and Ea = 13.8 kJ mol−1. The increment of the flow rate favoured the mass transfer in the system and so, the hydrolysis rate. However, the maximum hydrolysis rate was found at a water surface velocity of 2.3 cm min−1.

Continuous H2O2 direct synthesis process : an analysis of the process conditions that make the difference

Continuous hydrothermal synthesis was highlighted in a recent review as an enabling technology for the production of nanoparticles. In recent years, it has been shown to be a suitable reaction medium for the synthesis of a wide range of nanomaterials. Many single and complex nanomaterials such as metals, metal oxides, doped oxides, carbonates, sulfides, hydroxides, phosphates, and metal organic frameworks can be formed using continuous hydrothermal synthesis techniques. This work presents a methodology to characterize continuous hydrothermal flow systems both experimentally and numerically, and to determine the scalability of a counter current supercritical water reactor for the large scale production (>1,000 T·year–1) of nanomaterials. Experiments were performed using a purpose-built continuous flow rig, featuring an injection loop on a metal salt feed line, which allowed the injection of a chromophoric tracer. At the system outlet, the tracer was detected using UV/Vis absorption, which could be used to measure the residence time distribution within the reactor volume. Computational fluid dynamics (CFD) calculations were also conducted using a modeled geometry to represent the experimental apparatus. The performance of the CFD model was tested against experimental data, verifying that the CFD model accurately predicted the nucleation and growth of the nanomaterials inside the reactor.