434
Milli- and micro-scale reactors have been a focal interest in process modularization, as they allow better control of the reaction and product distribution by enhancing transport, increasing residence time, and mixing for continuous reactions and
allow for inherently safe operations [17, 18]. The fundamental advantage of microreactors is the significant enhancement of heat and mass transfer rates per unit volume when compared to traditional chemical reactors. Typically, microreactor has a
minimum feature size in the range of 50–500 μm, which enhances heat transfer
coefficients by orders of magnitude, up to 25 kW/m
2
K [19]. Such reactors are typically designed to include parallel arrays of vertical channels that are packed or
coated with a catalyst, and cross-flow horizontal cooling channels, which enables
the significant reduction of the overall reactor volume and an increase in the overall
productivity [20].
From a commercial perspective, a major motivation for utilizing micro-reactor
technology for FT synthesis is that it enables the utilization of smaller point sources,
without significant commercial or operational risk. The conventional FT technology
requires about 50 MMSCF/d of the feed gas over a 30-year period in order to achieve
the minimal acceptable production capacity of 50,000 barrels per day, in order to
lower the capital cost per barrel to an acceptable level [21].
2.1 Microreactor Fabrication Methods and Materials
Microreactors are typically fabricated using conventional techniques in micro−/
nanotechnology and precision engineering. The internal structure of the microreactor, such as channels (referred to as reaction zone), has characteristic dimensions
ranging from sub-millimeter to micrometer range. These internal microstructures
are constructed hierarchically, usually parallel channels in an array system (reaction
or mixing zone) containing an inlet and an outlet. In this chapter, we use the term
“microreactor” for all the devices where the characteristic dimension will be in the
range of nanometers-sub-micrometer to sub-millimeter.
The design and configuration of microreactors are based on its applications.
Structural hierarchy varies based on the type of reactor and unit operation, in addition to the operation mode (continuous flow or batch type processes). Some of the
microdevices investigated, previously, are micromixers [22, 23], microreactors [24,
25], micro heat exchangers [26, 27], micro separators [28], and microturbines [29].
The main focus of this chapter is the application of microreactors for FTS.
Microreactors can be fabricated using a variety of materials, the most common
of which are silicon, glass, polymer, and metals (316 stainless steel). The selection
of the materials depends on the intended application, reaction type, operating conditions, the physical and chemical properties of reactants, reaction complexity, and
cost. Table 1 highlights the advantages and disadvantages of common fabrication
materials for microreactor applications.
The limitations of polymer and glass materials make them unsuitable to fabricate
microreactors for high-temperature and high-pressure reaction systems. The section
N. Mohammad et al.
Milli- and micro-scale reactors have been a focal interest in process modularization, as they allow better control of the reaction and product distribution by enhancing transport, increasing residence time, and mixing for continuous reactions and
allow for inherently safe operations [17, 18]. The fundamental advantage of microreactors is the significant enhancement of heat and mass transfer rates per unit volume when compared to traditional chemical reactors. Typically, microreactor has a
minimum feature size in the range of 50–500 μm, which enhances heat transfer
coefficients by orders of magnitude, up to 25 kW/m
2
K [19]. Such reactors are typically designed to include parallel arrays of vertical channels that are packed or
coated with a catalyst, and cross-flow horizontal cooling channels, which enables
the significant reduction of the overall reactor volume and an increase in the overall
productivity [20].
From a commercial perspective, a major motivation for utilizing micro-reactor
technology for FT synthesis is that it enables the utilization of smaller point sources,
without significant commercial or operational risk. The conventional FT technology
requires about 50 MMSCF/d of the feed gas over a 30-year period in order to achieve
the minimal acceptable production capacity of 50,000 barrels per day, in order to
lower the capital cost per barrel to an acceptable level [21].
2.1 Microreactor Fabrication Methods and Materials
Microreactors are typically fabricated using conventional techniques in micro−/
nanotechnology and precision engineering. The internal structure of the microreactor, such as channels (referred to as reaction zone), has characteristic dimensions
ranging from sub-millimeter to micrometer range. These internal microstructures
are constructed hierarchically, usually parallel channels in an array system (reaction
or mixing zone) containing an inlet and an outlet. In this chapter, we use the term
“microreactor” for all the devices where the characteristic dimension will be in the
range of nanometers-sub-micrometer to sub-millimeter.
The design and configuration of microreactors are based on its applications.
Structural hierarchy varies based on the type of reactor and unit operation, in addition to the operation mode (continuous flow or batch type processes). Some of the
microdevices investigated, previously, are micromixers [22, 23], microreactors [24,
25], micro heat exchangers [26, 27], micro separators [28], and microturbines [29].
The main focus of this chapter is the application of microreactors for FTS.
Microreactors can be fabricated using a variety of materials, the most common
of which are silicon, glass, polymer, and metals (316 stainless steel). The selection
of the materials depends on the intended application, reaction type, operating conditions, the physical and chemical properties of reactants, reaction complexity, and
cost. Table 1 highlights the advantages and disadvantages of common fabrication
materials for microreactor applications.
The limitations of polymer and glass materials make them unsuitable to fabricate
microreactors for high-temperature and high-pressure reaction systems. The section
N. Mohammad et al.