Enzymatische Hydrolyse von Lignocellulose im Festbettreaktor

There are still severe problems with high solid concentrations during the enzymatic hydrolysis of lignocellulosic biomass in stirred tank reactors. Thus, the integration of the thermal pretreatment and the enzymatic hydrolysis of the biomass in the same fixed bed reactor is investigated in this work. The influence of pumps on the enzyme activity is shown to be negligible for later applications although sharp pressure drops in valves decrease enzymatic activity. Mechanical treatment upfront to the thermal hydrolysis shows good results during the enzymatic reaction (yield > 95 % after 48 h for pelletized straw). Finally the success of the enzymatic reaction in a fixed bed reactor with different solid contents (7 – 20 %) is presented.     

Odor‐Free Lignin from Lignocellulose by Means of High Pressure Unit Operations: Process Design,Assessment and Validation

In this work a process for the production of odor‐free lignin from wheat straw using solely water, enzymes and CO₂ is described. Wheat straw pellets are pretreated by liquid hot water and enzymatic hydrolysis in a pilot plant with a capacity of 40 L, which enables the production of 3 – 4 kg of Aquasolv lignin per batch. Dried lignin samples are further treated using supercritical CO₂, resulting into extraction of a large number of odorous free fatty acids and volatile organic compounds. All process steps can be sequentially conducted in a fixed‐bed via different sustainable solvents in a throughput regime.     

Chemoselective hydrolysis of methyl 2‐acetoxybenzoate using free and entrapped esterase in K‐carrageenan beads

Porcine liver esterase was entrapped in natural polysaccharides K‐carrageenan and retention of its activity was determined using p‐nitrophenyl acetate as the substrate. The optimum pH for esterase activity of entrapped enzyme showed a little shift towards acidic side. Immobilized enzyme showed improved thermal and storage stability. The entrapped esterase retained 50% of its activity after eight repetitive cycles. Michaelis constant K_m for the free and entrapped enzymes was almost same indicting no conformational change during immobilization. Maximum velocity V_max was observed to decrease on immobilization. The free and entrapped esterase was used for selective hydrolysis of methyl 2‐acetoxybenzoate to methyl 2‐hydroxybenzoate in batch process as well as in a fixed bed reactor. The hydrolysis was observed to be 99% within 2 h for free as well as immobilized enzyme in batch process. The rate of hydrolysis was found to depend on pH. The turn over number of selective hydrolysis in batch and fixed bed reactor was 3.08 × 10⁶ and 1.19 × 10⁷, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

CO2 methanation: Optimal start‐up control of a fixed‐bed reactor for power‐to‐gas applications

Utilizing volatile renewable energy sources (e.g., solar, wind) for chemical production systems requires a deeper understanding of their dynamic operation modes. Taking the example of a methanation reactor in the context of power‐to‐gas applications, a dynamic optimization approach is used to identify control trajectories for a time optimal reactor start‐up avoiding distinct hot spot formation. For the optimization, we develop a dynamic, two‐dimensional model of a fixed‐bed tube reactor for carbon dioxide methanation which is based on the reaction scheme of the underlying exothermic Sabatier reaction mechanism. While controlling dynamic hot spot formation inside the catalyst bed, we prove the applicability of our methodology and investigate the feasibility of dynamic carbon dioxide methanation. © 2016 American Institute of Chemical Engineers AIChE J, 63: 23–31, 2017     

Fischer‐Tropsch Synthesis: Modeling and Performance Study for Fe‐HZSM5 Bifunctional Catalyst

A water‐cooled fixed bed Fischer‐Tropsch reactor packed with Fe‐HZSM5 catalyst has been modeled in two dimensions (radial and axial) using the intrinsic reaction rates previously developed at RIPI. The reactor is used for production of high‐octane gasoline from synthesis gas. The Fischer‐Tropsch synthesis reactor was a shell and tube type with high pressure boiling water circulating on the shell side. By the use of a two‐dimensional model, the effects of some important operating parameters such as cooling temperature, H₂/CO ratio in syngas and reactor tube diameter on the performance capability of the reactor were investigated. Based on these results, the optimum operating conditions and the tube specification were determined. The model has been used to estimate the optimum operating conditions for the pilot plant to be operated in RIPI.     

Immobilization of α‐chymotrypsin for use in batch and continuous reactors

α‐Chymotrypsin from bovine pancrease (EC 3.4.21.1) was entrapped in Ca‐alginate gel particles to carry out hydrolysis of N‐acetyl‐L ‐phenylalanine methyl ester (APME) in batch as well as continuous fixed bed reactor. The enzyme was covalently modified with homo‐bifunctional polyethylene glycol derivatives in order to reduce its leakage from the beads; 85% modification of the ∈‐NH₂ groups of lysine residues caused reduction in the enzyme activity by 50%. However, this modification was helpful in a long run because it reduced both enzyme leakage and deactivation. Effective diffusivities and the distribution coefficients of the substrate and the product were determined experimentally, and later used in simulation of a batch experiment employing the beads. A continuous fixed bed reactor with the gel beads was operated to study the deactivation of the enzyme. During a 15‐day period, the enzyme showed about 15% loss in the conversion which occurred only during the first 5 days. After that the enzyme did not deactivate further which demonstrates that this method can be applied for continuous reactions. © 2000 Society of Chemical Industry     

Synthesis of the Biofuel Additive 1,1‐Diethoxybutane in a Fixed‐Bed Column with Amberlyst‐15 Wet

The synthesis of 1,1‐diethoxybutane (DEB) through the acetalization reaction between ethanol and butyraldehyde was studied in a fixed‐bed adsorptive reactor packed with Amberlyst‐15 wet. The miscibilities of reactants and water were evaluated and breakthrough experiments with nonreactive pairs of ethanol‐water and ethanol‐DEB were performed. The parameters of the isotherms were fitted by a Langmuir competitive model. Synthesis of the acetal was carried out with mixtures of ethanol and butyraldehyde at different molar ratios. The dynamic behavior of the fixed‐bed adsorptive reactor was described by a mathematical model developed taking into account the reaction kinetics, adsorption mechanisms, mass transfer resistances, and velocity variations.     

A Two‐Compartment Fluidized Bed Reactor for CO2 Capture by Chemical‐Looping Combustion

Chemical‐looping combustion (CLC) is a combustion method for a gaseous fuel with inherent separation of the greenhouse gas carbon dioxide. A CLC system consists of two reactors, an air reactor and a fuel reactor, and an oxygen carrier circulating between the two reactors. The oxygen carrier transfers the oxygen from the air to the fuel. The flue gas from the fuel reactor consists of carbon dioxide and water, while the flue gas from the air reactor is nitrogen from the air. A two‐compartment fluidized bed CLC system was designed and tested using a flow model in order to find critical design parameters. Gas velocities and slot design were varied, and the solids circulation rate and gas leakage between the reactors were measured. The solids circulation rate was found to be sufficient. The gas leakage was somewhat high but could be reduced by altering the slot design. Finally, a hot laboratory CLC system is presented with an advanced design for the slot and also with the possibility for inert gas addition into the downcomer for solids flow increase.     

Optimizing ethanolic hot compressed water (EHCW) cooking as a pretreatment to glucose recovery for the production of fuel ethanol from oil palm frond (OPF)

The objective of this work is to study the effects of reaction temperature, reaction time and ethanol percentage on the pretreatment of oil palm fronds (OPF) using ethanolic hot compressed water (EHCW) to enhance sugar recovery in enzymatic hydrolysis. A central composite rotatable design was used to optimize the pretreatment process conditions. All variables (individual and interactive) were found to affect glucose recovery significantly. A quadratic polynomial equation was modelled for glucose recovery by multiple regression analysis using response surface methodology (RSM). Using a 10 bar pressurized reactor, the optimum conditions for pretreatment of OPF were obtained at 180 °C, 42 min and EtOH wt.% of 26.4%. At the optimum conditions, the predicted glucose recovery was 88.48%. Experimental verification of the optimum conditions gave glucose recovery well within the estimated value of the model.     

Production of low methoxyl pectin using immobilized pectinmethylesterase silica from acerola (Malpighia glabra L.)

The aim of this work was to develop an efficient reactor for the production of low methoxyl pectin, using pectinmethylesterase (PME, EC 3.1.1.11) from acerola immobilized on silica. The immobilized enzyme was used in up to 50 successive bioconversion runs at 50 °C with an efficiency loss of less than 20%. The fixed‐bed reactor (6.0 × 1.5 cm) was prepared using PME immobilized in glutaraldehyde‐activated silica operated at 50 °C with an optimum flow rate of 10 mL h^?1. The bioconversion yield was shown to strongly depend on the nature of the enzymatic preparation. An efficiency of 44% was achieved when concentrated PME was used, compared with only 30% with purified PME, both after an 8‐h run. The process described could provide the basis for the development of a commercial‐scale process. Copyright © 2006 Society of Chemical Industry     

Liquid‐Solid Mass Transfer Behavior of a Stirred‐Tank Reactor with a Fixed Bed at Its Bottom

The mass transfer behavior of a new batch stirred tank with a fixed bed of Raschig rings at the bottom was studied using diffusion‐controlled dissolution of copper in acidified dichromate. Variables studied, amongst others, were the impeller rotation speed, Raschig ring diameter, fixed‐bed height, and impeller geometry. The rate of mass transfer from the fixed bed to the solution increased with increasing impeller rotation speed, decreasing particle size, and decreasing bed height. The axial‐flow turbine is more efficient in increasing the rate of mass transfer than the radial‐flow turbine. The presented reactor is especially useful for conducting diffusion‐controlled liquid‐solid catalytic reactions involving reactants that need to be dispersed first, such as sparingly soluble solid particles.     

纸浆蔗渣酶法水解反应过程的考察

以蒸煮时间5．5小时,温度为155－160℃,P=0.6MPa,pH为4．5的40目的纸浆渣为底物,日本Yakult生物化学试剂公司的Onozuka-R-10纤维素酶为催化剂,在50℃,PH为4．8（乙酸－乙酸钠缓冲液）的条件下,考察了釜式和固定床反应器对酶解反应过程的影响,测定了在不同底物浓度时的酶解反应还原糖得率,探讨了酶的吸附以及酶活性在酶解反应过程的变化情况。实验结果表明,在本实验条件下,底物浓度高,转化率则低,固定床反应器对酶的吸附比釜式反应器略多;酶的活性变化在两种反应器中几乎没多大差别。     

Mathematical modeling and simulation of steady state plug flow for lactose-lactase hydrolysis in fixed bed

A detailed mathematical model for evaluating lactose hydrolysis with immobilized enzyme in a packed bed tubular reactor is presented. The model accounts for axial and radial dispersion effects, chemical reaction and external mass transfer resistances but is void of significant internal diffusion resistances of the particles. The comprehensive model was then simplified to a plug flow model for lactose-lactose hydrolysis in fixed bed. The resulting plug flow model was solved by using Runge-Kutta-Gill method via employing different kinetics for lactose hydrolysis. The reliability of model simulations was tested using experimental data from a laboratory packed bed column, where the β-galactosidase of Kluyveromyces fragilis was immobilized on spherical chitosan beads. Comparison of the simulated results with experimental exit conversion show that the plug flow model incorporating Michaelis-Menten kinetics with competitive product (galactose) inhibition are appropriate to interpret the experimental results and simulate the process of lactose hydrolysis in a fixed bed when the mass transfer resistance was reduced by a factor of 34.5.     

Catalytic dehydration of glucose to 5‐hydroxymethylfurfural with a bifunctional metal‐organic framework

Glucose conversion to 5‐hydroxymethylfurfural (HMF) generally undergoes catalytic isomerization reaction by Lewis acids followed by the catalytical dehydration to HMF with Brönsted acid. In this work, a sulfonic acid functionalized metal‐organic framework MIL‐101(Cr)‐SO₃H containing both Lewis acid and Brönsted acid sites, was examined as the catalyst for γ‐valerolactone‐mediated cascade reaction of glucose dehydration into HMF. Under the optimal reaction conditions, the batch heterogeneous reaction gave a HMF yield of 44.9% and selectivity of 45.8%. Reaction kinetics suggested that the glucose isomerization in GVL with 10 wt % water follows the second‐order kinetics with an apparent activation energy of 100.9 kJ mol^?1. Continuous reaction in the fixed‐bed reactor showed that the catalyst is highly stable and able to provide a steady HMF yield. This work presents a sustainable and green process for catalytic dehydration of biomass‐derived carbohydrate to HMF with a bifunctional metal‐organic framework. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4403–4417, 2016     

Development of a fixed‐bed column with cellulose/chitin beads to remove heavy‐metal ions

Environmental friendly cellulose/chitin beads, having relatively high mechanical properties, were successfully prepared from a blend of cellulose and chitin in 6 wt % NaOH/5 wt % thiourea aqueous solution by coagulating with 5% H₂SO₄ aqueous solution. The ability of the beads to adsorb Pb²⁺ in an aqueous solution was measured with a fixed‐bed column. The effects of important parameters, to design an adsorption column of the cellulose/chitin beads for fixed‐bed columns, were investigated. The breakthrough curves for the adsorption behavior indicated that the column performance was improved with decreasing initial lead concentration, ionic strength, flow velocity or bead size, as well as increasing pH dependence and bed height. Column studies showed that constants, calculated from the experimental data, and the Bed Depth Service Time (BDST) model had a good correlation. The columns were easily regenerated by treating with 0.1 mol/L HCl aqueous solution after the adsorption of metals, providing a simple and economical method for removal and recovery of heavy metals. After four adsorption–desorption cycles, the efficiency of column for the removal of lead was not significantly reduced (not more than 5%). It is shown that heavy‐metal biosorption processes in fixed‐bed columns could give a broad range of potential industrial applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 684–691, 2004     

Fluidized‐bed reactor modeling for polyethylene production

Gas‐phase technology for polyethylene production has been widely used by industries around the world. A good model for the reactor fluid dynamics is essential to properly set the operating conditions of the fluidized‐bed reactor. The fluidized‐bed model developed in this work is based on a steady‐state model, incorporating interactions between separate bubble, emulsion gas phase, and emulsion solid polymer particles. The model is capable not only of computing temperature and concentration gradients for bubble and emulsion phases, calculating polymer particle mean diameter throughout the bed and polyethylene production rate, but also of pinpointing the appearance of hot spots and polymer meltdown. The model differs from conventional well‐mixed fluidized‐bed models by assuming that the particles segregate within the bed according to size and weight differences. The model was validated using literature and patent data, presenting good representation of the behavior of the fluidized‐bed reactor used in ethylene polymerization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 321–332, 2001     

Different process configurations for bioethanol production from pretreated olive pruning biomass

BACKGROUND: In Mediterranean countries, olive tree pruning provides a widely available renewable agricultural residue with, currently, no industrial application. This residue could provide feedstock for the bioethanol industry. In the present study, olive tree pruning biomass pretreated with both ‘liquid hot water’ and ‘dilute‐sulfuric acid’ was tested as a substrate for ethanol production. Three different process configurations, separate hydrolysis and fermentation (SHF), simultaneous saccharification, fermentation and prehydrolysis (PSSF), and simultaneous saccharification and fermentation (SSF), were compared at different water‐insoluble solids concentrations. RESULTS: High ethanol concentration of about 3.7% (v/v) was obtained by separate hydrolysis and fermentation or prehydrolysis and simultaneous saccharification and fermentation of liquid hot water pretreated at 23% (w/w) substrate loading. CONCLUSION: The nature of the pretreated residue allows high substrate concentration (≥17% w/w) to be used in the enzymatic hydrolysis step. Substrate loading of 17% DM has been shown to provide a compromise between hydrolysis efficiency and glucose concentrations for the same enzyme/substrate ratio. Prehydrolysis prior to simultaneous saccharification and fermentation facilitated SSF performance at high substrate loading on liquid hot water pretreated olive pruning residue. This effect was not observed with dilute‐acid pretreated substrate. Copyright © 2011 Society of Chemical Industry     

Modeling of Multi‐Tubular Reactors for Fischer‐Tropsch Synthesis

The results of the simulation of multi‐tubular Fischer‐Tropsch reactors based on a two‐dimensional pseudo‐homogeneous model are presented. The model takes into account the intrinsic kinetics of two commercial iron and cobalt catalysts, intraparticle mass transfer limitations, and the radial heat transfer within the fixed bed and to the cooling medium (boiling water). The effective rate with Co is slightly higher than with Fe. Hence, a temperature level can be used for Co that is 20 °C lower compared to Fe. The conversion and product selectivies are then almost the same and the reactor can be operated safely without a temperature runaway. The results of the simulations are consistent with literature data and show that there is still room for improvement of fixed bed FT reactors, e.g., by an enhanced heat transfer.     

Entwicklung eines optisch zugänglichen Reaktors zur Thermographiemessung in einer Katalysatorschüttung

To measure the microkinetics in heterogeneously catalyzed strongly exothermic gas phase reaction heat and mass transfer limitations should be excluded. Also an unequal distribution of temperature in the catalyst fixed bed, like a hot spot, distorts the results of microkinetic investigations. A promising approach to measure the temperature contactless is thermography. For this work, an optically accessible reactor is developed to measure the temperature in a catalytically powder fixed bed. In the scope of this work, this technique is used to investigate the temperature development and distribution during the exothermal CO₂ methanation depending on the bed and gas dilution and the reactor performance.