Flow Chemistry with DART-DM Flow Reactors

Advantages of flow chemistry 

There are well-defined key advantages using flow technologies as compared to standard batch chemistry methods:

  • Improved heat transfer
  • Improved mass transfer/mixing
  • Reproducibility
  • Scale-up
  • Extreme reaction conditions (high/low temperature, high pressure)
  • Multistep (telescoping)
  • In-line downstream processing
  • Automation
  • Improved Safety (managing hazardous reagents and intermediates)

Parameters in flow chemistry

Beyond the aforementioned advantages, running a reaction under flow conditions requires knowledge of many reaction parameters (e.g. stoichiometry, reaction time, concept of steady state, etc).

a.     Stoichiometry

Whilst under batch conditions the stoichiometry is set by the molar ratio of the reagents used, in a flow process the ratio of parameters such as flow rate and molarity is used to set the specific stoichiometry.

b.     Residence time as "reaction time"

In batch mode synthesis the reaction time is determined by the time a vessel is stirred under fixed conditions, whereas the concept of reaction time in a flow process is expressed by the residence time, i.e., the time reagents spend in the reactor zone. Residence time is given by the ratio of the reactor volume and the reaction flow rate (overall flow rate).

τ = V/q

Where τ is the variable corresponding to the residence time, V is the volume of the system, and q is the flow rate for the system

c.     Flow rates

While in batch mode, the reaction kinetics are controlled essentially by the reagent exposure time under the specified reactions conditions, under flow conditions reactions kinetics are controlled by the flow rates of the reagents streams. The flow rates of the reagents indeed will influence the residence time of the reaction and have an impact on the outcome of the transformation.

q = dV/dt

q is usually expressed in units such as mL min-1

d.     Volume vs space (steady state)

When considering a batch reaction, the reagent and product concentrations vary over the time, and mixing becomes a relevant aspect (especially when increasing the scale of the reaction) in order to reduce concentration gradients that affect the kinetics of a reaction. Under flow conditions, each portion of the reactor is defined by specific concentrations of the starting material(s) and product(s): in this sense, the reaction profile within a flow reactor can be defined within space rather than time. A very important parameter in flow chemistry is the steady state that defines a condition where all the parameters are defined and remain unchanged (steady) at a particular point in time.

e.     Mixing and mass transfer

Mixing in a flow process is highly advantageous, compared to batch mode, as it is determined by diffusion within very small volumes of reagents. A high degree of mixing translates into better reaction profiles. Under flow conditions, indeed, mass transfer is considered very effective and determines the specific and enhanced kinetics observed. There are specific aspects of mixing that should be considered (e.g. axial vs. vortex mixing) and are dependent on specific fluid behaviours, namely plug or laminar flow patterns.

f.       Temperature control and heat transfer

The control of temperature in flow processes can be achieved very accurately, due to the high surface area-to-volume ratio.

Accordingly, heat transfer can be very efficient although this parameter depends on the specific aforementioned aspects of the fluid behaviour. Indeed, depending on whether the flow is laminar or turbulent, heat transfer can follow different patterns.

Reaction Types

DART-DM reactors can be configured to meet the needs of many different synthetic and biological processes.

DART-DM reactors can process reactions involving gases, liquids and suspended solids, (slurries). Photochemistry versions of DART-DM are now also available opening up new areas of processing and manufacturing where catalysts are used in photochemistry.

With the kind permission of our customers; below are just a few examples of the types of reactions that can be undertaken in DART.

Project Example:- Ester Reduction

Reactions typically complete after 2 h with above conditions in batch.
Alcohols tend to precipitate out of solution as reaction progresses.
Catalyst sensitive to oxygen when in solution state.
12minute residence time in DART-DM7 Flow Reactor.
DART-DM7 Flow Reactor Ester Reduction 12min residance Timepng
54 minute residence time DART-DM7 Flow Reactor.
DART-DM7 Flow Reactor Ester Reduction 54min residance Timepng

Project Example:- NO2 Reduction

30min Residence Time in DART-DM7x7 Flow Reactor
DART-DM7 Flow Reactor NO2 Reduction 30min residence Timepng
60min Residence Time in DART-DM7x7 Flow Reactor DART-DM7 Flow Reactor NO2 Reduction 60min residence Timepng

CO2 Capture CO2 capture

Project Example:- Bio-processsing

It is widely known that that a high CO2 mass transfer rate is vital to the design of better bioreactors for CO2 mitigation.  By comparison with traditional sparging methodologies, the use of a DART reactor greatly increases the  residence time of the gas in the algae culture.

Flow Chemistry | DART-DM