Patent Application
20160001199
This invention is generally related to chemical reactors. More specifically, the present invention relates to chemical reactors based on a system with elongated pillar structures with a high width-to-length aspect ratio, such as, for example, a liquid chromatography system.
Chemical reactor devices that make use of liquid propagation have a large number of applications, including the production of chemical components, synthesis of nanoparticles, separation and/or extraction of components, etc. Chromatography is a specific example of an accurate way to analyze a separation technique for the separation of mixtures, for instance. There is a variety of forms of chromatography such as gas chromatography, gel chromatography, thin layer chromatography, adsorption chromatography, affinity chromatography, liquid chromatography, etc. Liquid chromatography is typically used in pharmacy and chemistry, both for analytical applications, as well as for production applications. In liquid chromatography use is made of the difference in affinity of different substances with a mobile phase and a stationary phase. Because each substance has its own “adhesive force” to the stationary phase they are transported faster or slower along with the mobile phase and this allows certain substances to be separated. It is in principle applicable to any compound, it has the advantage that no evaporation of the material is necessary and it has the advantage that variations in temperature only have a negligible effect.
An efficient form of liquid chromatography, high-pressure liquid chromatography (also known as high-performance liquid chromatography) or HPLC, where high pressure is used in the separation process. A specific example of a technique to perform HPLC is based on chromatography columns on the basis of pillars. Since their introduction in liquid chromatography, chromatography columns based on pillars proved a worthy alternative for systems based on packed bed structures and monolithic systems. Because of the possibility of applying pillars with a high degree of uniformity and to arrange them perfectly, the dispersion originating from differences in flow paths or “eddy dispersion” can be almost completely avoided. This principle is more generally applicable in chemical reactors which are based on liquid plug flow propagation.
A known problem in liquid chromatography is the occurrence of edge effects. Edge effects originate from the difference in flow rate at the wall of the column and in the middle of the column. The latter can be understood as follows, whereby reference is made to
The problem of edge effects is set out in Vervoort et al., Anal. Chem. (2004) 76 pp 4501-4507. This indicates that small structural variations of the column structures at the wall at a magnitude of only 5% in diameter of the particles can cause a fourfold increase of the band broadening (expressed as plate height) for the result, which results in a dramatic loss in performance.
One way to compensate for this is to adjust the wall of the column. Another—often deployed—way to compensate for this is to adjust the width of the passage at the edge of the column, in relation to the width between pillars in the column, away from the edge. A typical ratio then being implemented is
B=1.25×W
whereby W is the width of the passage at the edge of the column (as shown in
As one often strives for an as small as possible interpillar distance B with the manufacturing method available, this lower limit imposed by wall conditions is not an optimal situation.
It is an objective of the embodiments of the present invention to provide for good chemical reactor system and methods on the basis of fluid channels with pillar structures, for instance micro-fabricated pillar structures. Chemical reactor systems encompass among others liquid chromatography systems, although the invention is not limited to this.
It was surprisingly found that the embodiments in accordance with the present invention provide chemical reactor devices based on liquid plug flows, whereby the edge effects are reduced or are even negligible without this in itself being a limitation on the pillar distance in the fluid channel at positions away from the edge.
It is an advantage of at least some of the embodiments in accordance with the present invention that in addition to a solution for the edge problem, the provided chemical reactor devices also have a very good separation ability.
It is an advantage of at least some of the embodiments in accordance with the present invention that in addition to a solution for the edge problem, the provided chemical reactor devices can also generate a uniform retention time for various parts of a fluid flow.
It is an advantage of at least some embodiments in accordance with the present invention that in addition to a solution for the edge problem, the provided chemical reactor devices also imply a limited column length because of the advantageous width—length aspect ratio of the pillar structures, allowing compact devices to be obtained.
It is an advantage of at least some of the embodiments in accordance with the present invention that the edge effects can both be reduced or be negligible for components that interact with the structures and walls in the reactor as well as for components that do not interact with the structures and walls in the reactor.
It is an advantage of at least some of the embodiments in accordance with the present invention that devices are obtained in which unwanted dispersion can be reduced and in some cases can even be made negligible.
The above objective is achieved by an apparatus and a method in accordance with the embodiments in accordance with the present invention.
The present invention relates to a chemical reactor device based on a fluid flow, the chemical reactor apparatus comprising a substrate with a fluid channel defined by a channel wall, whereby the channel has an inlet and an outlet and whereby the channel has a longitudinal axis, in accordance with the average direction of a fluid flow in the channel from inlet to outlet, an ordered set of pillar structures positioned in the channel, whereby the individual pillar structures have a length in the direction of the longitudinal axis of the channel and a width in a direction perpendicular to the longitudinal axis, and in which the individual pillar structures have a width to length ratio of at least 7.
The individual pillar structures can have a width to length ratio (aspect ratio) of at least 10.
The smallest distance (W) between the channel wall and a wall of a neighboring, non-touching, pillar structure can be greater than 0.9 times, greater than, for example, the smallest distance (B) between two neighboring pillar structures themselves.
It is an advantage of the present invention that by making use of pillar structures with a large width to length ratio, the edge effects in a fluid channel be reduced and possibly even are negligible.
The smallest distance (W) between the channel wall and a wall of an adjoining, non-touching pillar structure, and the smallest distance (B) between two adjoining pillar structures themselves, may be measured in the width direction of the channel, perpendicular on the longitudinal axis.
The wall can at least for some portion be flat, also called straight, in the longitudinal direction of the channel.
The pillar structures can be positioned in such a way that they determine a set of bound longitudinal and transversal micro-channels, whereby a first subset of longitudinal micro-channels is extending in the direction of the longitudinal axis and is defined through the wall of two pillar structures and a second subset of longitudinal micro-channels is extending in the direction of longitudinal axis and defined through the channel wall and a wall of a pillar structure, and wherein the smallest width (B) of the first subset can be smaller than or equal to the smallest width (W) of the second subset.
It is an advantage of the embodiments in accordance with the present invention that a low interpillar distance can be achieved, resulting in a high pressure in the system, while the edge effects can be limited, negligible or absent.
The pillar structures can be micro-fabricated pillar structures.
The pillar structures can have a width to length ratio of more than 12.
The smallest distance (B) between two neighbouring pillar structures can be between 0.5 and 0.8 times the smallest distance (W) between the channel wall and a wall of a neighbouring, non-touching, pillar structure.
The individual pillar structures can have a polygonal cross-section.
The individual pillar structures can have a substantial hexagonal cross-section.
The individual pillar structures may be limited in width by side walls of the pillar structures situated along the longitudinal axis of the channel and the length of the side walls may be at least 0.02, preferably 0.1 times the length of the pillar structures.
The channel and the micro-channels formed by the pillar structures may furthermore be limited on two sides by substrates.
The chemical reactor can be a liquid chromatography separation apparatus.
The channel wall can be formed by a membrane.
The present invention also relates to a mask for the lithographic application of a structure in a substrate for the making of a chemical reactor device, the mask comprising design elements for defining of an ordered set of pillar structures positioned in a channel of the chemical reactor device, whereby the individual pillar structures have a length in the direction of the longitudinal axis of the channel and a width in a direction perpendicular on the longitudinal axis, whereby the design elements are provided in the mask such that the resulting individual pillar structures have a width to length proportion of at least 7.
The design elements can be so defined such that the resulting pillar structures are positioned in the channel so that the smallest distance (W) between the channel wall defining the channel and a wall of a neighbouring, non-touching, pillar structure is greater than 0.9 times, for instance larger than, the smallest distance (B) between two neighbouring pillar structures themselves. The smallest distance (W) between the channel wall which defines the channel and a wall of a neighboring, non-touching, pillar structure can be greater than or equal to the smallest distance (B) between two neighboring pillar structures themselves. The smallest distance (W) between the channel wall which defines the channel and a wall of a neighboring, non-touching, pillar structure can be greater than the smallest distance (B) between two neighboring pillar structures themselves.
The design elements can be adapted so that the resulting pillar structures are bounded in width by pillar structure side walls situated according to the longitudinal axis of the channel and, wherein the length of the side walls is at least 0.02 times, preferably 0.1 times, even more by preference 0.2 times, of the length of the pillar structures.
The mask may be such that the formed wall of the channel be at least flat for some portion, also called the right section, in the longitudinal direction of the channel. The present invention also relates to a method for the manufacture of a chemical reactor system, the method comprising lithographically implementing a channel with pillar structures including using a mask as described above.
Specific and preferential aspects of the invention are included in the attached independent and dependent claims. Characteristics of the dependent claims can be combined with characteristics of the independent claims and with the characteristics of other dependent claims as appropriate and not only as expressly stated in the claims to be brought forth.
The figures are only schematic and not limiting. In the figures, the dimensions of some parts may be exaggerated and may not be to scale and are proposed for illustrative purposes. The dimensions and relative dimensions do not necessarily correspond to those of practical embodiments of the invention. Reference numbers in the claims should not be interpreted to limit the scope of the protection.
The present invention will be described referring to specific embodiments and to certain drawings but the invention is not limited thereto and is only limited by the claims.
It should be noted that the term “contains” and “comprises”, as used in the claims, should not be interpreted as restricted to the means listed thereafter; this term does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, values, steps or components as referred to, but this does not preclude the presence or addition of one or more other features, values, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising components A and B” should not be limited to devices existing only of components A and B. It means that with regard to the present invention, A and B are the only relevant components of the device.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Therefore, appearances of the expressions “in one embodiment” or “in an embodiment” at various locations throughout this specification do not all necessarily refer to the same embodiment, but may do so. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one skilled in the art on the basis of this disclosure, in one or more embodiments.
Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than explicitly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of one single foregoing disclosed embodiment. Therefore, the claims following the detailed description are hereby explicitly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
Furthermore, while some embodiments of the invention described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by one skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.
It should be noted that the use of certain terminology in describing certain features or aspects of the invention should not be understood to imply that the terminology herein is being redefined to be limited to particular characteristics of the features or aspects of the invention to which this terminology is linked.
Where in the present description and claims reference is made to micro-channels, reference is made to channels wherein at least one of the dimensions lies in the range of 50 μm to 1 μm.
Where in the present description and claims reference is made to an ordered set, reference is made to a set of elements which are not randomly positioned, but where a specific relationship exists between the distances of the elements to each other.
Where in the present description and claims reference is made to distribution or dispersion, reference is made to the spatial spread over an area or volume.
Where in the present description and claims reference is made to the permeability, reference is made to the flow rate at which a liquid can flow through the liquid channel with pillar structures.
In a first aspect the present invention relates to a chemical reactor device based on a fluid flow. Such a chemical reactor device is typically suitable for the propagation of a fluid plug, for example a liquid plug. The chemical reactor device according to embodiments of the present invention may be a liquid chromatography device, although embodiments are not restricted thereto. Another specific example is a gas chromatography device. The chemical reactor can more generally be suitable for producing certain components, such as intermediaries, for the synthesis of components such as synthesis of nanoparticles, for the separation and/or extraction of components, etc.
According to embodiments of the present invention the chemical reactor device comprises a substrate with a fluid channel. The substrate can be any suitable substrate, such as for example a polymer substrate, semiconductor substrate, a metal substrate, a ceramic substrate, or a glass or vitreous substrate. The substrate can, for example, be a typical microfluidic substrate. The fluid channel can be a channel that is formed in the substrate or can be a channel that is formed on the substrate. In a specific embodiment, the invention not being limited hereto, the fluid channel is provided as a recess in the substrate and a second substrate is provided on top of the first substrate so as to obtain a fluid channel that is closed at the top, side and bottom. Such a second substrate can be a membrane. In such an embodiment the channel is typically rectangular in cross-section. According to embodiments of the present invention the fluid channel also has an inlet and an outlet for the supply and the removal of the fluid, for example, the liquid. In the specific embodiment described above such an inlet and outlet can be provided by means of perforations in the first and/or the second substrate.
The fluid channel can have a length depending on the application. By the use of particular inlet structures and/or outlet structures, for example distributors, the necessary length can moreover be influenced. A typical width of the fluid channel can be chosen as necessary. The necessary width will typically depend on the selected length and vice versa. In one set of examples the width of the fluid channel Bk may be selected in the range of 0.1 mm to 250 mm.
For the fluid channel a longitudinal axis can typically be defined, whereby the longitudinal axis is situated according to the direction of the average flow direction of the fluid in the channel, from inlet to outlet. By way of illustration the longitudinal axis in the schematic example of the chemical reactor 100 is shown in
According to embodiment of the present invention an ordered set of pillar structures 130 is also provided in the fluid channel 120. These pillar structures can be micro-fabricated pillar structures, although embodiments are not limited thereto. The pillar structures may be based on precision manufacturing techniques. According to embodiments of the present invention, the pillar structures 130 have an elongated shape. The specific geometric elongated shape of the pillar structures can be any appropriate shape. A cross-section of the pillar structure may for example be diamond-shaped, elliptical, oval, polygonal, etc. As an illustration, a magnified image of an exemplary pillar structure 130 is shown in
The number of pillars provided in the channel can be chosen depending on the objective (for example the separation capability) that is to be obtained. The number of pillars which can be provided on a particular row in the fluid channel is dependent on the width of the channel. There may, for example, be provided between 3000 and 3 pillars per mm width of the channel. The absolute width of the pillars may have been chosen in a range between 0.3 μm and 50000 μm. The absolute distance between the pillars in the channel remote from the wall can for example be chosen in a range between 0.05 μm and 2000 μm. In preferred embodiments of the present invention, the interpillar distance may be chosen from the range between 0.1 μm and 1000 μm, preferably between 0.3 μm and 3 μm. In addition, the size and shape of the pillars may vary, for example along the longitudinal axis of the channel.
In some specific embodiments of the present invention the pillar structures are positioned in the channel in such a way that the smallest distance (W) between the channel wall and a wall of a neighboring but not-touching, pillar structure is larger than 0.9 times, for example larger than, the smallest distance (B) between two neighboring pillar structures. It was surprisingly found that, although the width of the micro channels formed by the wall and the pillar structures is larger than the width of the micro channels formed by pillars remote from the channel wall, this actually does not cause edge effects when pillars are used as defined above. This surprising conclusion results from the fact that—apart from technological restrictions for the manufacture of the structures—the interpillar distance is no longer defined by the dimensions of the channels against the wall. This allows the interpillar distance to be chosen smaller than expected, which allows very efficient fluid channels to be made, for example, columns. It should be noted in this respect that this implementation can occur without loss of resolution or without introduction of additional dispersion.
In a specific embodiment of the present invention the chemical reactor is a liquid chromatography apparatus and the fluid channel is a separation column. It is an advantage that the separation efficiency of the system can be high due to the large lateral migration that occurs, while furthermore no edge effects occur or that these are negligible. In addition, because of the specific width-to-length ratio of the pillars, the necessary length of the column to obtain a certain degree of separation can be reduced.
It is an advantage of some embodiments of the present invention that they are based on sets of organized pillar structures, through which a low dispersion can be obtained. When the band dispersion is described by means of the Van Deemter equation, i.e.
H=A+B/u+C·u
whereby A, B, C are constants and u is the linear velocity of the mobile phase, structures according to the present invention also result in an exceptional low A value (representative for the dispersion due to flow differences in the paths) and a low B value (representative for the dispersion due to the longitudinal diffusion).
One or more additional components may also be present in the chemical reactor according to embodiments of the present invention, depending on the functionality of the chemical reactor, as known by one skilled in the art. In some embodiments of the present invention for example one or more distributors may be present, a detector may be present, which may be integrated or not in one of the substrates of the chemical reactor, a further micro-fluidized network may be present, electrodes may be present (for example in a chemical reactor based on electrophoresis or an electrochemical reactor), a membrane or a filter, a catalytic bed, a heat exchanger, a radiation source, etc.
In a specific embodiment of the present invention the pillar structures can also have a form as further described in a further aspect of the present invention.
By way of illustration
In another aspect, the present invention also relates to a mask with a design for forming the pillar structures as described above. The mask can comprise typical design elements for defining an ordered set of pillar structures positioned in a fluid channel of a chemical reactor, whereby the pillar structures have a length in the direction of the longitudinal axis of the channel and a width in a direction perpendicular to the longitudinal axis, and whereby the design elements are provided in the mask in such a way that the resulting pillar structures have a width-to-length ratio of at least 7. In some embodiments of the present invention the design elements of the mask are optionally further provided such that the pillar structures produced in the channel on the basis of the mask have a smallest distance (W) between the channel wall and a wall of a neighboring, non-touching, pillar structure which is larger than 0.9 times, for example larger than, the smallest distance (B) between two neighboring pillar structures among themselves. The mask may furthermore comprise additional design features characteristic for a channel wall for defining a fluid channel in a substrate. Further designs elements from the mask may also be provided in such a manner that characteristics of the pillar structures and their relation to the channel as described in the first aspect, are obtained. Moreover the mask may also be adapted with design features to define characteristics of pillar structures for the chemical reactor as further described in the further aspect.
The present invention also relates to a method for manufacturing a chemical reactor, such as for example a chromatography device with a chromatography column, where the method comprises the use of a mask as defined above. The method may comprise the step of lithographic printing of a mask on a substrate to generate substrate features, and the etching of the substrate features to generate pillar structures. Other characteristics of the manufacturing process of the chemical reactor can be as known by one skilled in the art and are therefore not described in further detail here.
By way of illustration, embodiments of the present invention not being limited thereby, a comparative study is discussed below wherein the flow behavior and the occurrence or not of edge effects is studied in function of the use of pillar structures with a large width-to-length ratio.
Columns with a length of 1 cm and a width of 1 mm were produced, whereby pillar structures with a different width-to-length aspect ratio were used for different columns, in order to evaluate the effect of this aspect ratio. The interpillar distance as well as the length of the pillars (in the direction of the longitudinal axis of the column) was kept constant, in the present example 2.5 μm and 5 μm respectively, while the width of the pillar structures varied per column, from 10 μm (resulting in an aspect ratio of 2) to 125 μm (resulting in an aspect ratio of 25). The pillar structures, the inlet and the outlet were manufactured with the use of mid-UV photo-lithography on a (100) silicon wafer substrate. After the photo-lithographic process, the pillar structures were etched on the basis of a Bosch etching process, so that a depth of 8 micrometers was obtained. The photoresist was then removed, using an oxygen plasma etching and nitric acid. The inlet and outlet were further defined by a 800 μm etching using a Bosch etching process via the back side of the substrate. The reactor was closed by making use of a Pyrex substrate which was anodically bonded to the silicon substrate.
For measurement of the results the following experimental setup was used. An automatic valve system was used to inject the sample into the structure. For obtaining the propagation of the liquid phase a nitrogen pressure supply was used. During the injection step the inlet and the outlet of the circuit in which the mobile phase moves was closed, while during the subsequent sample preparation, the inlet and the outlet of the sample injection circuit was redirected to a capillary tube with high flow resistance so that a small leakage flow was created so as to avoid tail formation. In order to follow the flow behavior use was made of fluorescent dyes which were excited during registration by means of a mercury-vapor UV source. Visualization of the fluorescence was performed using an air-cooled CCD camera.
It was possible to determine that for pillar structures with an aspect ratio varying from 2 to 25, the plate height could be reduced from 2.6 μm to 0.5 μm, because a reduction in longitudinal dispersion could be obtained. When the Van Deemter equation was considered, a reduction of the B term (representative for the longitudinal dispersion) with a factor of 15 could be established for the use of an aspect ratio of 25 in relation to an aspect ratio of 2. A good separation behavior could therefore be established.
In addition to this result it could also be determined that edge effects which occur in systems with pillars having a small aspect ratio, were greatly reduced or even negligible in the structures according to the present invention. This could be established on the basis of the CCD images recorded on the chemical reactor on the chip.
The same is illustrated in
Further by way of illustration a test is also reported here in which 4 fluorescent marker dyes (c440, c450, c460 and c480 in a 70/30 proportion of water/methanol) are separated in the first millimeter of a separation column wherein pillar structures having a width-to-length aspect ratio of 25 are provided. The column was functionalized with C8. The detection of the four bands as straight bands clearly indicates the absence of substantially contributing edge effects. An image of this detection is shown in
In a further specific aspect of the present invention, embodiments of a chemical reactor device are provided, based on a fluid flow, wherein the chemical reactor device also comprises a substrate with a fluid channel. This channel is also defined by a channel wall and also has an inlet and an outlet. For the channel also a longitudinal axis can be defined in accordance with the average flow direction of the fluid when it moves in the channel from the inlet to the outlet. The chemical reactor thereby also comprises an ordered set of pillar structures positioned in the channel, whereby the pillar structures have a length in the direction of the longitudinal axis of the channel and a width in a direction perpendicular to the longitudinal axis, and wherein the pillar structures have a width-to-length ratio of at least 7. According to embodiments of this aspect, the pillar structures are furthermore bounded in the width direction by side walls situated in accordance with the longitudinal axis of the channel, whereby the length of these side walls is at least 0.02 times, preferably at least 0.1 times, preferably at least 0.2 times, the length of the pillar structures. In other words, the sides of the pillar structures do not end in a tip, but end in a wall parallel with the wall of the channel. By way of example, the pillar structure may have in such a case a hexagonal cross-section. An illustration of such an exemplary pillar structure is shown in
The present invention also relates to a mask with a design for forming the pillar structures as described above. The mask can typically comprise design elements for defining an ordered set of pillar structures positioned in a fluid channel of a chemical reactor, whereby the pillar structures have a length in the direction of the longitudinal axis of the channel and a width in a direction perpendicular to the longitudinal axis, and whereby the design elements are provided in the mask in such a way that the resulting pillar structures have a width-to-length ratio of at least 7 and the pillar structures moreover are bounded in the width direction by side walls situated according to the longitudinal axis of the channel, whereby the length of the side walls is at least 0.02 times, preferably at least 0.1 times, preferably at least 0.2 times, the length of the pillar structures. Further designs elements of the mask may also be provided in such a manner that characteristics of the pillar structures as described in the first aspect are obtained.
The present invention also relates to a method of manufacturing a chemical reactor, such as for example a chromatography device with a chromatography column, whereby the method comprises the use of a mask as defined above. The method may comprise the step of lithographic printing of a mask on a substrate to generate substrate features, and the etching of the substrate features to generate pillar structures. Other characteristics of the manufacturing process of the chemical reactor can be as known to the skilled person, and are therefore not described in further detail here.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013/0078 | Feb 2013 | BE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2014/058808 | 2/5/2014 | WO | 00 |
