Reactor and membrane module

Membrane Reactor Technologies Ltd (MRT) has experimentally verified the permeative-stage membrane reactor concept. With the membranes outside the reaetor, operation at more favorable conditions for both reaction (750 °C) and membrane separation (450 °C or lower) is possible. A decrease in the metal cost of palladium-based membranes by 86.5% and membrane area by >70% to aehieve equal hydrogen production capacity was reported. The volume of reformer decreases accordingly, thus, the costs of both the reactor and membrane module are reduced. 

Methane content at the outlet of first and second reforming reactors and membrane modules. 

Staged membrane reactor (SMR) or reactor and membrane module (RMM), where the selective membrane is placed outside the reactor, in a proper unit located downstream (Fig. 12.2). 

Today, annual market membrane of ca. U.S. 4.5 x 10 for membranes and membrane modules (mostly polymeric ones) indicates that separation processes seem to be the largest application field, whereas membrane reactors are just on the verge of being considered as a competitive tool [274]. 

Industrial interest in soluble polymer-bound catalysts has been closely linked to the development of ultrafiltration membranes with sufficient long-term stability in organic solvents. Membranes fulfilling these requirements were prepared first in the late 1980s. Today, solvent-stable flat sheet membranes and membrane modules are available from several suppliers. As for the viability of ultrafiltration in organic solvents, rhodium-catalyzed hydroformylation of dicydopentadiene with continuous catalyst recovery and recycling has been demonstrated successfully on a pilot plant scale over an extended period of time [5]. The synthesis of other fine chemicals by asymmetric reduction and other reactions has also been carried out in continuously operated membrane reactors (also cf Section 7.5) [6-9]. The extent of commercial interest in catalysts bound to soluble polymers appears to fluctuate at intervals. Amongst other factors, the price of precious metals can be a driver. 

Due to these main reasons, new configurations called Staged Membrane Reactor (SMR) or Reformer and Membrane Modules (RMMs) have been proposed in the teehnieal literature [25-29]. 

De Falco M, Barba D, Cosenza S, laquaniello G, Marrelli L (2008) Reformer and membrane modules plant powered by a nuclear reactor or by a solar heated molten salts assessment of the design variables and production cost evaluation. Int J Hydrogen Energy 33 5326-5334... 

In order to avoid the conflict of catalyst and membrane operating parameters, the selective membrane can be placed outside the reactor, in proper units located downstream. This is the concept of Reformer and Membrane Modules (RMM) steam reforming plant [3, 6, 16], shown in Fig. 5.9. 

Recently, the first membrane reactor pilot plant has been realized. A staged membrane reactor for natural gas steam reforming, also called reformer and membrane modules (RMM) test plant, having the capacity of 20 Nm /h of hydrogen, has been designed and constructed to investigate at an industrial scale level the performance of such innovative architecture. 

A reformer and membrane module system (RMM) (permeative-stage membrane reactor) with 20 N m h of hydrogen capacity has been designed... 

In configuration 1, the reformer and membrane module (RMM) where hydrogen selective membrane is assembled in separation modules applied downstream to reaction units so that the process scheme is composed by a series of reaction-separation units (staged membrane reactor architecture)... 

De Falco M., Salladini A., Palo E. and laquaniello G., (2011b), Reformer and membrane modules (RMM) for methane conversion powered by a nuclear reactor experimental assessment and perspectives of such novel architecture , in Editor Pavel Tsvetkov Nuclear Power, InTech Open Access Publisher. 

In this case study, an enzymatic hydrolysis reaction, the racemic ibuprofen ester, i.e. (R)-and (S)-ibuprofen esters in equimolar mixture, undergoes a kinetic resolution in a biphasic enzymatic membrane reactor (EMR). In kinetic resolution, the two enantiomers react at different rates lipase originated from Candida rugosa shows a greater stereopreference towards the (S)-enantiomer. The membrane module consisted of multiple bundles of polymeric hydrophilic hollow fibre. The membrane separated the two immiscible phases, i.e. organic in the shell side and aqueous in the lumen. Racemic substrate in the organic phase reacted with immobilised enzyme on the membrane where the hydrolysis reaction took place, and the product (S)-ibuprofen acid was extracted into the aqueous phase. 

An integrated proof-of-concept (POC) size fluidized-bed methane reformer with embedded palladium membrane modules for simultaneous hydrogen separation is being developed for demonstration (Tamhankar et al., 2007). The membrane modules will use two 6 in. X 11 in. Pd-alloy membrane foils, 25-pm thick, supported on a porous support. The developmental fluidized-bed reactor will house a total of five (5) membrane modules with a total membrane area of about 0.43 m2 and is scheduled for demonstration by September 2007. 

A continuous cross-flow filtration process has been utilized to investigate the effectiveness in the separation of nano sized (3-5 nm) iron-based catalyst particles from simulated Fischer-Tropsch (FT) catalyst/wax slurry in a pilot-scale slurry bubble column reactor (SBCR). A prototype stainless steel cross-flow filtration module (nominal pore opening of 0.1 pm) was used. A series of cross-flow filtration experiments were initiated to study the effect of mono-olefins and aliphatic alcohol on the filtration flux and membrane performance. 1-hexadecene and 1-dodecanol were doped into activated iron catalyst slurry (with Polywax 500 and 655 as simulated FT wax) to evaluate the effect of their presence on filtration performance. The 1-hexadecene concentrations were varied from 5 to 25 wt% and 1-dodecanol concentrations were varied from 6 to 17 wt% to simulate a range of FT reactor slurries reported in literature. The addition of 1-dodecanol was found to decrease the permeation rate, while the addition of 1-hexadecene was found to have an insignificant or no effect on the permeation rate. 

Cabral and coworkers [253] have investigated the batch mode synthesis of a dipeptide acetyl phenylalanine leucinamide (AcPhe-Leu-NH2) catalyzed by a-chymotrypsin in a ceramic ultrafiltration membrane reactor using a TTAB/oc-tanol/heptane reverse micellar system. Separation of the dipeptide was achieved by selective precipitation. Later on the same group successfully synthesized the same dipeptide in the same reactor system in a continuous mode [254] with high yields (70-80%) and recovery (75-90%). The volumetric production was as high as 4.3 mmol peptide/l/day with a purity of 92%. The reactor was operated for seven days continuously without any loss of enzyme activity. Hakoda et al. [255] proposed an electro-ultrafiltration bioreactor for separation of RMs containing enzyme from the product stream. A ceramic membrane module was used to separate AOT-RMs containing lipase from isooctane. Application of an electric field enhanced the ultrafiltration efficiency (flux) and it further improved when the anode and cathode were placed in the permeate and the reten-tate side respectively. 

The first step in downstream processing is the separation of the product-rich phase from the second phase and the biocatalyst. This may be simplified if the enzyme is immobilized or if a membrane module is included in the experimental set-up. In the case of emulsion reactors, centrifugation for liquid phase separation is a likely separation process [58], although the small size of droplets, the possibility of stable emulsion formation during the reaction, particularly if surface-active... 

Figure 13.18 Continuous recycle fermentor membrane reactor. An ultrafiltration module removes the liquid products of fermentation as a clean product. This system is being developed for production of ethanol, acetone and butanol by fermentation of food processing waste streams...

Figure 13.19 A hollow fiber membrane reactor. Nutrients (S) diffuse to the microbial cells on the shell side of the reactor and undergo reaction to form products (P) such as monoclonal antibodies [31]. Reprinted from J. Membr. Sci. 39, K. Schneider, W. Holz, R. Wollbeck and S. Ripperger, Membranes and Modules for Transmembrane Distillation,...

Membrane bioreactors are composed of two fundamentals parts, the biological reactor in which the reaction occurs (active sludge containing purifying bacteria) and the membrane module for the separation of the different compounds. 

In this case the fluid phase is aerated (in the case of aerobic bioreactor) that maintains the turbulent hydrodynamic conditions on the one hand, and prevents the forming of the cake layer on the immersed membrane module, on the other hand. The reactor description is also well known [67], and is not discussed here. 

In recent years, membrane bioreactors, bioreactors combined with membrane separation unit have established themselves as an alternative configuration for traditional bioreactors. The important advantages offered by membrane bioreactors are the several different types of membrane modules, membrane structures, materials commercially available. Membrane bioreactors seem particularly suited to carry out complex enzymatic/microbial reactions and/or to separate, in situ, the product in order to increase the reaction efficiency. The membrane bioreactor is a new generation of the biochemical/chemical reactors that offer a wide variety of applications for producing new chemical compounds, for treatment of wastewater, and so on. 

The obtained results have shown that the configuration where the recirculation tank was irradiated and the catalyst was used in suspension appeared to be the most interesting for industrial applications [73]. Moreover, it was observed that the degradation rate was higher when an immersed lamp was used compared to a system with an external lamp [81]. Therefore, actually the studies in progress are realized in the system described elsewhere [39] consisting of a Pyrex annular photoreactor with a 125-W medium-pressure Hg lamp axially positioned inside the reactor. The separation module containing the flat-sheet membrane was connected to the photoreactor in a recirculation loop. 

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