Patent Description:
The use of microwave radiation for microwave-assisted chemistry methods, such as acid digestion, solvent extraction, and synthesis, is generally well known to those skilled in the art.

The term "digestion" refers to several well-understood processes which reduce the compounds that make up the material into its constituent elements or more basic compounds. Commonly, the process is carried out by use of a solvent. At the end of digestion, the result is usually a colorless or nearly colorless solution that can be diluted and then tested using one or more quantitative analysis techniques. When using pressurized digestion techniques, the temperature of the process is elevated by carrying out the digestion in a sealed, heated container. This allows the reaction to reach temperatures above the atmospheric boiling point of the digestion solvent. This in turn also increases the rate of the chemical reactions that accomplish the digestion.

To attack the structure or matrix of a sample and reduce it to its elements or more basic compounds, acid digestion uses one or more strong acids, frequently at an elevated temperature, pressure, or both. In microwave-assisted acid digestion, microwave radiation is used to add energy to materials that are responsive to microwave radiation. Microwaves can assist in carrying out acid digestion faster, using less solvent, and at higher temperatures and pressures than more conventional heating methods. Because of the frequency and corresponding wavelength of microwave radiation assigned to laboratory use e.g., <NUM> or about <NUM>, microwave-assisted techniques are often carried out in closed vessels which are in turn placed inside a device that bears a superficial relation to a consumer microwave oven, but that is more sophisticated in its source, waveguide, cavity, and control elements.

The term "extraction" refers to the process of separating a desired substance (often an organic compound) when it is mixed with others often as sample preparation in advance of an analytical tool. Solvent extraction by traditional techniques consumes significant amounts of time and solvent and leaves open the possibility of contamination. Microwave-assisted, closed-vessel extraction can be used to prepare a number of samples concurrently using less time and smaller amounts of solvent than that required for conventional solvent extractions.

The term "synthesis" refers to the process of the execution of chemical reactions to obtain one or more products. Microwave-assisted, closed-vessel synthesis allows for rapid heating of reactants to high pressures and temperatures. The skilled person understands that, based on the Arrhenius Law, the rates of most chemical reactions are increased by heating the reaction mixture. Because most synthesis reactions require heating at some point, microwave heating can significantly reduce the reaction time and therefore overall production time. Using closed vessels together with microwave-assisted heating can reduce reaction time from days and hours to minutes or seconds.

At the temperatures commonly used for microwave assisted chemistry methods, the pressure in the vessel used is generated from two components. The first is the vapor pressure generated by a digestion or the synthesis components, or other gas-generating reactions. Such vapor pressures are generally predictable because they are based on the temperature of a known amount of a known composition. The second is the pressure of the gaseous by-products generated during the reaction process, which is generally less predictable, particularly in digestion or extraction, because it will be based on the size and composition of the sample. Consequently, the vessels used for microwave-assisted chemistry methods must be microwave transparent but offer the structural capabilities required to withstand unpredictable high pressures.

The skilled person will be familiar with the available methods for conducting microwave-assisted digestion, extraction, and synthesis. For example, one method for conducting digestion reactions inserts multiple reaction vessels inside of a large metal cavity reaction chamber secured with metal clamps, subjects them to high pressure from a gas such as nitrogen to seal the vessels, and then uses microwaves to heat the vessels to speed the chemical reactions. Recent example includes the Ultrawave Microwave Acid Digestion System (Milestone Inc. , <NUM> Controls Drive, Shelton, CT <NUM>, https://milestonesci. com/ultrawave-microwave-acid-digestion-system/(accessed January <NUM>, <NUM>)); and the Multiwave <NUM> (Anton Paar, <NUM> World Houston Parkway, Suite <NUM>, Houston, TX <NUM>, https://www. anton-paar. com/us-en/products/details/microwave-digestion-system-multiwave-<NUM>/ (accessed January <NUM>, <NUM>)) have reasonably-sized footprints, but likewise use a metal cavity reaction chamber, high pressure gas to seal the reaction vessels, and microwaves to heat the vessels to speed the reactions. Thus, the user faces the same concerns and inconveniences and the same sample size or sample number constraints as with larger footprint instruments.

The structure and operation of devices such as the UltraWave or MultiWave demonstrate their weaknesses. The professed goal is, of course, to provide the user with a reaction vessel that is disposable, which in reality means that the vessel can be formed of the types and amounts of materials that can produce an inexpensive vessel so that the user finds it economically advantageous to use the vessel only once.

In order to accomplish this objective, these devices place the fragile vessels with their unsecured or lightly secured closures in a liquid bath (with water or a dilute acid being typical) inside of a metal bomb that is highly pressurized (e.g., <NUM> to <NUM> psi) with nitrogen. This high pressure holds the closures on the vessels while the microwaves heat the water. As a result, the compositions in the vessels are heated in a conventional conduction manner by the hot water rather than by any dipole interaction with the microwaves.

The high pressure creates a number of secondary issues. First the nitrogen pressure-a safety issue in and of itself-must be high enough to force and keep the vessels closed throughout the intended reaction without any venting whatsoever, because venting will cross-contaminate the vessels in the bomb.

As another disadvantage, the reaction vessel sizes must be relatively small. For example, a bomb with a volume of about <NUM> liter, can hold about <NUM><NUM> vessels or about <NUM><NUM> vessels. These small vessel sizes, however, exacerbate the pressure problems because of the inverse relationship between gas volume and gas pressure. Stated differently, as vessel size decreases, the pressure generated by any given reaction in the vessel will increase compared to a larger vessel under the same temperature conditions.

As yet another problem, because nitrogen pressure rather than mechanical pressure is used to close the fragile vessels, an extended cooling ramp time is required before the pressure can be released and the caps or closures removed from the vessels without cross contamination.

Other systems avoid the use of the high pressure, single reaction chamber and use an individual microwave-transparent pressure vessel for each sample. Microwave-transparent pressure vessels are commonly made from engineered plastics that can withstand relatively high pressures before failing. The nature of many engineered polymers is such, however, that if the vessel fails under pressure, it will tend to fail catastrophically. In order to avoid catastrophic failure, vessels for microwave digestion have been developed that include some means for pressure release. In some cases, the pressure release is provided by a small pathway leading from the interior to the exterior of the vessel with a small portion of the pathway blocked by a diaphragm that will fail at a predetermined pressure. When the pressure in such a vessel exceeds the predetermined limit, the diaphragm will burst and the gases will vent from the vessel without any catastrophic or near-catastrophic failure. Commonly assigned <CIT>; <CIT>; <CIT>; <CIT> and <CIT> are representative of the diaphragm type of release system.

Vessels in which the pressure release is temporary rather than complete and which allow the reaction to continue during and after the pressure release have been developed. When the pressure in the vessel exceeds predetermined limits, such vessels vent a small amount of gas and reseal themselves once the pressure drops below the predetermined limit. Examples include commonly assigned <CIT>; <CIT> and <CIT>.

As a further improvement, commonly owned <CIT>; <CIT> and <CIT> describe a fluoropolymer reaction vessel with a floating cap that allows for limited release of excessive pressure from the reaction vessel followed by resealing without permanent vessel damage or distortion. Each fluoropolymer reaction vessel is inserted in a reinforcing sleeve that provides the radial strength required to keep the reaction vessel intact under the high pressure created by the digestion reaction. The use of the sleeves with the reaction vessels eliminates the problems created by the large volume of the metal cavities used in some other methods.

The fluoropolymer reaction vessel needs to be cleaned, however, between uses because any chemical reaction will leave residual contamination in the vessel after completing the microwave-assisted method. This cleaning is time-consuming regardless of the corresponding advantages of the systems described in the <NUM>, <NUM>, and <NUM> patents. This results in the loss of efficiency in processing numerous samples daily. Microwave transparent, flexible film fluoropolymer liners (e.g., commonly assigned Application Number <CIT>, for Vessel and Disposable Inner Sleeve for Microwave Assisted Reactions) having a size and shape that generally conform to the inner walls of the fluoropolymer reaction vessel, can eliminate the need to clean the reaction vessels. Introducing small or powder-like samples into a flexible liner, however, can prove cumbersome. Thicker-walled liners made of, e.g., glass simplify the introduction of a sample but increase expense and can be susceptible to break under the high pressure conditions created by digestion reactions. Furthermore, open-top liners allow the possibility that, as pressure inside the liner increases, the contents of the liner will escape the liner and will contaminate the reaction vessel. <CIT> and <CIT> disclose microwave synthesis vessels with closure means.

Thus, a need continues to exist for high pressure, microwave-assisted chemistry methods that can use cost-effective rigid liners while avoiding breaking during high pressure reactions.

In one aspect, the invention is a method of microwave-assisted high temperature high pressure chemistry that comprises adding a microwave-absorbing liquid to an interstitial space between two coaxially aligned and nested microwave-transparent reaction vessels in which the inner nested vessel contains one or more reaction compositions. The amount of microwave-absorbing liquid in the interstitial space is sufficient to generate a vapor pressure under microwave radiation that starts as being the same or greater (to a defined extent) than the vapor pressure of the reacting compositions under the same application of microwave radiation. The microwave-absorbing liquid does not otherwise interfere with the relevant compositions, starting materials, or end products, or with the reactions between or among them.

Methods of the present invention may be carried out in a vessel system for microwave-assisted high temperature high-pressure chemistry comprising a cylindrical reaction vessel formed of a polymer that is resistant to strong mineral acids at high temperatures and that is transparent to microwave radiation. The cylindrical reaction vessel has one closed end and one open end defining a mouth for cylindrical reaction vessel. The reaction vessel has a rigid liner cylinder positioned coaxially inside of the cylindrical reaction vessel. The rigid liner cylinder includes one closed end positioned adjacent the closed end of the cylindrical reaction vessel and one open end defining a rigid liner cylinder mouth below the cylindrical reaction vessel mouth. The outer diameter of the rigid liner cylinder together with the inner diameter of the cylindrical reaction vessel define an interstitial space between the cylindrical reaction vessel and the rigid liner cylinder. A cylindrical liner cap, formed of a microwave-transparent material, rests in the mouth of the rigid liner cylinder for closing the rigid liner cylinder. The cylindrical liner cap includes a depending cylindrical column that has a circumference that closely matches the inside diameter of said rigid liner cylinder and a passage along the cylindrical column to provide a gas venting space between the cylindrical column of the liner cap and the rigid liner cylinder. A disk at one end of the depending cylindrical column has a diameter larger than the outer diameter of said rigid liner cylinder and smaller than the inner diameter of said cylindrical reaction vessel so that the cylindrical liner cap can rest in a defined position at the mouth of the rigid liner cylinder. A microwave-transparent reaction vessel plug rests in the mouth of the cylindrical reaction vessel and above the mouth of the rigid liner cylinder and coaxially against the cylindrical liner cap. A female threaded cap engages male threads on the cylindrical reaction vessel at the mouth of the cylindrical reaction vessel and bears against the reaction vessel plug to exert an axial closing force and provide a pressure resistant closure for the vessel system. A microwave-transparent cylindrical reinforcing sleeve surrounds the cylindrical reaction vessel coaxially with both the cylindrical reaction vessel and the rigid liner cylinder for increasing the radial pressure resistance strength of the vessel system.

In another aspect, the invention is a method of microwave-assisted high temperature high pressure chemistry that comprises adding a microwave-absorbing liquid to an interstitial space between two coaxially aligned and nested microwave-transparent reaction vessels in which the inner nested vessel contains a digestion sample and an amount of mineral acid sufficient to digest the sample; closing the inner nested reaction vessel with a microwave-transparent cap that slides into the inner nested reaction vessel and that includes at least one pressure-activated dynamic passage from the inner nested vessel to the interstitial space; closing the outer nested reaction vessel with a pressure resistant cap connection to thereby increase the pressure capacity of the interstitial space; applying a closing force against the sliding cap in an amount sufficient to sufficient to withstand some vapor pressure created by the compositions in the inner nested reaction vessel under the application of microwave radiation while allowing venting at higher vapor pressures generated by the reaction compositions (e.g., a strong mineral acid and a digestion sample; an organic solvent for synthesis) at reaction temperatures; and applying microwave radiation to the reaction compositions inside of the inner nested reaction vessel and to the microwave-absorbing liquid in the interstitial space to thereby encourage the digestion of the sample in the acid while concurrently increasing the pressure in the interstitial space based on the increased vapor pressure or gaseous state of the microwave-absorbing liquid under the application of the microwave radiation. The amount of microwave-absorbing liquid in the interstitial space is sufficient to generate a vapor pressure under microwave radiation that bears against the sliding cap to exert an axial closing force under the same application of microwave radiation. The microwave-absorbing liquid does not otherwise interfere with the relevant compositions, starting materials, or end products, or with the reactions between or among them.

Methods of the present invention may also be carried out in a vessel system for high-temperature high-pressure microwave assisted chemistry comprising a microwave transparent pressure releasing and resealing cylindrical reaction vessel nested coaxially inside of a microwave transparent pressure releasing cylindrical containment vessel with a small annular interstitial space between and defined by the nested reaction vessel and the nested containment vessel.

As used herein the term "nest" and its past tense "nested" are used in their dictionary sense which can be variously understood as, "an assemblage of things lying or set close together or within one another,. to fit or place one within another,. to fit together or within one another as boxes, pots, and pans, dishes, small tables or the like.

The foregoing and other objects and advantages of the invention will become clearer based on the following detailed description in conjunction with the accompanying drawings.

The invention is a method for microwave-assisted, high temperature, high-pressure chemistry.

In contrast to the small numbers of small vessels used in the bomb-type instruments, the invention typically uses sets of <NUM> vessels that are each between <NUM> and <NUM> in volume, or up to <NUM> vessels that are <NUM> in volume.

<FIG> is a cross-sectional view, and <FIG> is an exploded elevational view, of a vessel system suitable for use in methods according to the present invention. As illustrated in <FIG>, the vessel system is broadly designated at <NUM> and includes a cylindrical reaction vessel <NUM> formed of a polymer that is resistant to relevant solvents such as strong mineral acids for digestion reactions or organic solvents for extraction and synthesis reactions at high temperatures and that is transparent to microwave radiation and infrared radiation. Typical embodiments will be of fluoropolymers such as polytetrafluoroethylene ("PTFE") and equivalents. "High temperature" generally refers to a temperature above room temperature that will successfully drive the intended reaction more rapidly in the selected solvent and under an increased pressure (i.e., above atmospheric pressure) generated by the heated solvent. In general, no need exists to raise the temperature in some unlimited fashion.

The cylindrical reaction vessel <NUM> has a closed end <NUM> and an open end <NUM>. In the illustrated embodiment at the closed end of the cylindrical reaction vessel <NUM>, the outer surface of the cylindrical reaction vessel <NUM> is longer than the inner surface of the cylindrical reaction vessel <NUM>. Consequently, if the cylindrical reaction vessel <NUM> is resting on a flat surface on its closed end, only the outer circumferential edges of the closed end of the cylindrical reaction vessel <NUM> touch the surface on which the cylindrical reaction vessel <NUM> rests while the center of the cylinder does not touch the surface. The recess <NUM> at the bottom of the cylindrical reaction vessel <NUM> serves as an infrared window so that an infrared device (not shown) can read the temperature of the reaction taking place in the cylindrical reaction vessel <NUM>. The open end <NUM> defines a mouth for the reaction vessel <NUM>.

A rigid liner cylinder <NUM>, which in the illustrated embodiment broadly resembles a test tube, nests coaxially inside the cylindrical reaction vessel <NUM>. The rigid liner cylinder <NUM> has an outer diameter that together with the inner diameter of the cylindrical reaction vessel <NUM> defines an interstitial space <NUM> between the cylindrical reaction vessel <NUM> and the rigid liner cylinder <NUM>. The rigid liner cylinder will be typically formed of a material that is rigid, transparent to microwave radiation and infrared radiation, chemically inert, and optically clear. It will be typically selected from the group consisting of glass, quartz, and equivalents.

The rigid liner cylinder <NUM> has one closed end <NUM> positioned adjacent to the closed end <NUM> of the cylindrical reaction vessel <NUM> when the rigid liner cylinder <NUM> is nested in the cylindrical reaction vessel <NUM>. The rigid liner cylinder <NUM> has one open end <NUM> that defines a mouth positioned below the mouth of the cylindrical reaction vessel <NUM> when the rigid liner cylinder <NUM> is nested in the cylindrical reaction vessel <NUM>. A cylindrical liner cap <NUM> fits in the mouth of the rigid liner cylinder <NUM> and closes the rigid liner cylinder <NUM>. The cylindrical liner cap <NUM> is formed of a polymer that is resistant to strong mineral acids at high temperatures and that is transparent to microwave radiation.

<FIG> offers a perspective view of the liner cap <NUM>. As depicted in <FIG>, the liner cap <NUM> includes a disk <NUM>, a depending cylindrical column <NUM>, and a cylindrical knob <NUM>. The depending cylindrical column <NUM> on the bottom face <NUM> of the disk <NUM> has a circumference that closely matches the inside circumference of the rigid liner cylinder <NUM> so that the depending cylindrical column <NUM> engages the inside of the rigid liner cylinder <NUM>, but can still slide into the rigid liner cylinder <NUM>. The disk <NUM> has a diameter larger than the outer diameter of the rigid liner cylinder <NUM> and smaller than the inner diameter of the cylindrical reaction vessel <NUM> so that the liner cap <NUM> can rest in a defined position in the rigid liner cylinder <NUM> at the mouth of the rigid liner cylinder <NUM>. In the illustrated embodiment, the disk <NUM> rests on the circumferential edge of the rigid liner cylinder <NUM> and the depending cylindrical column <NUM> slides into and rests at the mouth of the rigid liner cylinder <NUM>. A cylindrical knob <NUM> extends from the top face <NUM> of the disk <NUM> and is oriented coaxial with the depending cylindrical column <NUM>. The cylindrical knob <NUM> has a diameter smaller than that of the disk <NUM> and the depending cylindrical column <NUM> and facilitates digital removal of the cylindrical liner cap <NUM> from the rigid liner cylinder <NUM>.

The liner cap <NUM> includes a passage <NUM> that in the illustrated embodiment is oriented axially along the circumferential edge of the depending cylindrical column <NUM>, and as further illustrated in the embodiment depicted in <FIG>, is a flat oblique chamfered portion along the depending cylindrical column <NUM>. The passage <NUM> provides a space for gases emitted from a chemical reaction in the rigid liner cylinder <NUM> to vent between the depending cylindrical column <NUM> and the rigid liner cylinder <NUM>.

Above and coaxially with the cylindrical liner cap <NUM> and the rigid liner cylinder <NUM>, a microwave-transparent reaction vessel floating plug <NUM> rests in the mouth of the cylindrical reaction vessel <NUM>. In the embodiment illustrated in <FIG>, the reaction vessel floating plug <NUM> has a cylindrical portion <NUM> that has a diameter equal to or slightly larger than the interior diameter of the mouth of the cylindrical reaction vessel <NUM>. Consequently, the cylindrical portion of the reaction vessel floating plug <NUM> rests on the circumferential edge of the cylindrical reaction vessel <NUM> at the mouth of the cylindrical reaction vessel <NUM>. In the embodiment illustrated in <FIG>, the reaction vessel floating plug <NUM> has a lower frustoconical portion <NUM>. The cylindrical reaction vessel <NUM> has a beveled lip <NUM> at its open end <NUM> to allow the frustoconical portion <NUM> of the reaction vessel floating plug <NUM> to rest in the mouth of the cylindrical reaction vessel <NUM> above the cylindrical liner cap <NUM> and which, in the embodiment illustrated in <FIG>, leaves a small interstitial space <NUM> between the reaction vessel floating plug <NUM> and the cylindrical liner cap <NUM>. The function of this interstitial space <NUM> will be described and clarified with respect to the method embodiments and other drawings. As used herein and as set forth in <CIT>, the word "floating" means that the plug <NUM> is placed in a resting relationship with respect to the reaction vessel <NUM> and the beveled lip <NUM> without any direct mechanical advantage between and among the reaction vessel floating plug <NUM> and any other part of the vessel system <NUM>.

The bottom of the frustoconical portion <NUM> of the reaction vessel floating plug <NUM> includes a small cylindrical notch <NUM> that is coaxial with the reaction vessel floating plug <NUM>. This cylindrical notch <NUM> allows the cylindrical knob <NUM> on the cylindrical liner cap <NUM> to nest inside the notch <NUM>.

Above the reaction vessel floating plug <NUM>, a reaction vessel cap <NUM> has female threads <NUM> that engage male threads <NUM> on the outside of the top portion of the cylindrical reaction vessel <NUM>. When the female threads <NUM> and the male threads <NUM> are fully engaged, the reaction vessel cap <NUM> bears against the reaction vessel floating plug <NUM> to provide a pressure resistant closure for the vessel system <NUM> illustrated in <FIG>. As set forth in <CIT>, the reaction vessel floating plug <NUM> is held in place by the response of the reaction vessel cap <NUM>. The top <NUM> of the reaction vessel cap <NUM> contains a vent opening <NUM>, the operation of which will be described and clarified in respect to other elements of the vessel system <NUM>.

<FIG> illustrates that the vessel system <NUM> is inserted coaxially into a microwave- transparent cylindrical reinforcing sleeve <NUM> in order to provide additional radial pressure resistance strength of the vessel system <NUM>. Because the reinforcing sleeve touches neither the sample nor the mineral acids, it can be selected and formed from materials that offer the best combination of weight, strength, and cost factors. As set forth in (for example) commonly assigned <CIT>, multiple layers of high strength fibers molded into a high strength polymer provides a composite structure that has both the strength of the molded polymer, together with the flexibility and break resistance of the high strength fibers.

In the embodiment illustrated in <FIG>, the rigid liner cylinder <NUM> is nested in a plugged polymer cylinder reaction vessel <NUM> which is described in commonly owned Application Number <CIT>, published as <CIT> for High Temperature Pressure Digestion Vessel System with Dual Action Seal. As in the reaction vessel <NUM>, the rigid liner cylinder <NUM> has a diameter that together with the inner diameter of the reaction vessel <NUM> defines an interstitial space <NUM> between the reaction vessel <NUM> and the rigid liner cylinder <NUM>. A closure plug <NUM> rests over the liner cap <NUM>. The closure plug <NUM> rests in the mouth <NUM> of the reaction vessel <NUM>. A small cylindrical notch <NUM>, in and coaxial with the closure plug <NUM>, allows the cylindrical knob <NUM> on the liner cap <NUM> to nest in the closure plug <NUM>. A cap <NUM>, fits over the closure plug <NUM>, and the sides of the cap <NUM> girdle the outside of the upper rim of the mouth <NUM> of the reaction vessel <NUM>. <FIG> illustrates that the entire vessel system <NUM> is, in turn, nested in a reinforcing sleeve <NUM>. The entire vessel assembly <NUM>, inside its reinforcing sleeve <NUM>, fits inside a flexible frame <NUM> that includes a vertically oriented bolt <NUM> that is threaded and turned through the top of the frame to exert an axial force against the cap <NUM>.

The reaction vessel <NUM> has a circumferential tapered portion <NUM>, near but not at the vessel mouth, which matches the circumferential tapered portion of the closure plug <NUM> when the closure plug <NUM> rests in the mouth of the reaction vessel <NUM>. The mouth of the liner cylinder <NUM> rests at the base of this tapered portion. Similar to the floating plug <NUM> in reaction vessel <NUM>, the closure plug <NUM> rests in the mouth of the reaction vessel <NUM> leaving a small interstitial space <NUM> above the liner cap <NUM>. As set forth in detail in the <NUM> application, at excess pressure the closure plug <NUM> will push axially in the reaction vessel <NUM>. This causes the frame <NUM> to flex and in turn creates a small gap between the tapered sections of the plug and the upper portion of the reaction vessel <NUM>. The upper portion of the plug remains in contact with the upper portion of the reaction vessel <NUM> above the tapered portion <NUM> of the reaction vessel <NUM>. This allows venting to take place through the radial vessel vent opening <NUM> just below the mouth <NUM> of the reaction vessel <NUM>. This vent opening <NUM> is oriented to coincide with the radial frame vent tube <NUM> to allow excess gas to be released into the atmosphere. The function of the interstitial space <NUM> will be described and clarified with respect to the method embodiments and other drawings.

The skilled person will understand that shapes other than cylinders can serve for the reaction vessels and liners. Such different shapes, however, will add complexity, and thus cost, and as a result will tend to reduce the possibility that the liner can be used for a single test and then disposed of. Cylindrical vessels and liners also have certain strength advantages. Nevertheless, it will be understood that picking a different shape (e.g., cross section) for one or both vessels (e.g., hexagon, octagon, decahedron, dodecahedron) could be made to work.

In the figures, the liner cap <NUM> is illustrated as having a depending cylindrical column with the passage likewise being illustrated as a flat chamfered portion <NUM> that replaces an arc along the circumference of the depending cylindrical column.

A cylinder is a straightforward shape for the depending column, but other shapes can be incorporated provided they eliminate axial degrees of freedom when the cap is inserted into the rigid liner cylinder. Typically, eliminating the axial degrees of freedom will require at least three points of contact between the depending column and the inner circumference of the rigid liner cylinder, and obviously could include more than three points of contact depending upon design choices. In exemplary embodiments the points of contact will self-center the depending column.

Similarly, the oblique chamfered edge is a highly efficient venting passage for purposes of manufacture, pressure release, and cleaning. Nevertheless, the skilled person will understand that the passage could have a more complex design, such as a bore hole through portions of the cap to provide a gas passage from the reaction space to the interstitial space. Again, although possible and within the invention, such complexities add in turn to the complexities of manufacture and use, and, perhaps most importantly, the ease of cleaning.

In one aspect, the invention is a method of microwave-assisted high temperature high pressure strong mineral acid digestion. In this embodiment, the invention includes the steps of placing a digestion sample and an amount of mineral acid sufficient to digest the sample in the rigid liner cylinder <NUM>, nesting the rigid liner cylinder <NUM> coaxially in the cylindrical reaction vessel <NUM>, introducing a microwave-absorbing liquid, for example, hydrogen peroxide, to the interstitial space <NUM>, closing the rigid liner cylinder <NUM> by sliding the cylindrical liner cap <NUM> into the rigid liner cylinder <NUM>, closing the cylindrical reaction vessel <NUM> with the reaction vessel floating plug <NUM>, placing the reaction vessel cap <NUM> on the reaction vessel <NUM> and engaging the female threads <NUM> of the reaction vessel cap <NUM> with the male threads <NUM> of the reaction vessel until the reaction vessel cap <NUM> bears against the reaction vessel floating plug <NUM>, placing the vessel system <NUM> into the reinforcing sleeve <NUM>, applying microwave radiation to the contents of the vessel system <NUM> including the digestion sample, the strong mineral acid inside the rigid liner cylinder <NUM>, and the microwave-absorbing liquid in the interstitial space <NUM>, measuring the temperature of the digestion reaction inside the rigid liner cylinder <NUM> based on the infrared radiation emitted from the reaction and through the rigid liner cylinder <NUM> and the reaction vessel <NUM>, and moderating the application of microwaves to the contents of the vessel system <NUM> based on the measured temperature.

The floating plug <NUM>, the male threads <NUM> and the female-threaded reaction vessel cap <NUM> thus form a pressure-resistant closure connection.

The microwave-absorbing liquid added to the interstitial space <NUM> does not otherwise interfere with the composition in the rigid liner cylinder <NUM>.

The amount of microwave-absorbing liquid in the interstitial space is sufficient to generate a vapor pressure under microwave radiation that at reaction temperatures defines a pressure in the interstitial space that bears against the sliding cap while the same microwave radiation drives a reaction within the inner nested rigid liner cylinder <NUM>. As the skilled person will recognize, knowing the composition in the rigid liner cylinder, the skilled person can closely estimate the amount of pressure the chemistry method will generate. The skilled person can then calculate or at least safely estimate the amount of microwave-absorbing liquid required to raise the pressure in the interstitial space <NUM> to initially exceed the pressure in the rigid liner cylinder <NUM> based upon well-understood relationships of the ideal gas law or (if desired) those versions of the gas law that are somewhat more refined.

For example, typically, for digestion, the method is carried out by adding between about <NUM> and <NUM> grams of the digestion sample and between about <NUM> and <NUM> of the strong mineral acid to the liner cylinder <NUM> with a volume of between about <NUM> and <NUM> and adding between about <NUM> and <NUM> of hydrogen peroxide to the interstitial space.

The vapor pressure exerted in the interstitial spaces <NUM> and <NUM> by the hydrogen peroxide or other microwave-absorbing liquid serves purposes which the skilled person understands. First, it increases the overall pressure in the reaction vessel <NUM> outside of the rigid liner cylinder <NUM>, thereby raising the boiling point of the digestion acid and maintaining a liquid phase for digestion, and thereby speeding the digestion of the sample. Second, the vapor pressure pushes down axially on the cylindrical liner cap <NUM> allowing the internal liner pressure to increase and preventing vaporized acid and sample from escaping into the interstitial spaces <NUM> or <NUM> until the pressure inside the liner cylinder <NUM> exceeds the pressure in the interstitial spaces <NUM> and <NUM> allowing the liner cylinder <NUM> to burp, releasing that pressure into the interstitial space. Third, because the cylindrical liner cap <NUM> is at a somewhat lower temperature than the reaction mixture, acid vapor condenses on the surface of the cylindrical liner cap <NUM> inside the rigid liner cylinder <NUM> and drips back down into the rigid liner <NUM> to rejoin and encourage the digestion.

The cylindrical liner cap <NUM>, like the plug <NUM>, is "floating" meaning that it is placed in a resting relationship with respect to the rigid liner cylinder without any direct mechanical advantage between and among the cylindrical liner cap <NUM> and any other part of the vessel system <NUM>.

As an advantage over (for example) nitrogen pressurized chambers, the hydrostatic pressure in the interstitial spaces <NUM> helps maintain the liner cap <NUM> in place on the liner cylinder <NUM> where the chemical reaction is taking place, eliminates the risk of cross contamination, and eliminates the need for the nitrogen overpressure and all the associated fittings and supplies. As an additional advantage, the cylindrical shape of the liner cylinder <NUM> is particularly well suited to withstand the external pressure exerted by the hydrostatic pressure in the interstitial space <NUM>. Furthermore, because of its high compressive strength both radially and axially, even thin glass can be used to form the liner cylinders <NUM> which minimizes the cost of the liner cylinders <NUM> and allows them to be consumable.

While the digestion reaction is ongoing, because the cylindrical liner cap <NUM> provides at least one pressure-activated dynamic passage from the rigid liner cylinder <NUM> to the interstitial space (in the present embodiment, the chamfered portion <NUM> of the depending cylindrical column <NUM>), if the vapor pressure inside the rigid liner cylinder <NUM> exceeds the vapor pressure exerted on the cylindrical liner cap <NUM> by the vapor pressure of the microwave-absorbing liquid in the interstitial space <NUM>, the disk <NUM> of the cylindrical liner cap <NUM> will lift off the circumferential edge of the rigid liner cylinder <NUM> and allow some gases to escape the rigid liner cylinder <NUM> thereby reducing the pressure inside of the rigid liner cylinder <NUM>. Thereafter, while the digestion reaction is continuing to progress, the vapor pressure of the microwave-absorbing liquid bearing against the cylindrical liner cap <NUM> will reseat the cap <NUM> and the disk <NUM> will again rest on the circumferential edge of the rigid liner cylinder <NUM>.

The reaction vessel cap <NUM>, when threaded, applies a closing force against the reaction vessel floating plug <NUM> sufficient to withstand the vapor pressure of the strong mineral acid at digestion temperatures. It thereby provides a pressure resistant cap connection to increase the pressure capacity of the interstitial space. When the pressure inside the reaction vessel <NUM> exceeds a mechanically defined set point, the top <NUM> of the reaction vessel cap <NUM> can flex to allow the reaction vessel floating plug <NUM> to move slightly and release gas pressure from the reaction vessel <NUM> while the digestion reaction continues. The excess gas can then vent through the vent opening <NUM>. In some embodiments the flexibility of the top <NUM> of the reaction vessel cap <NUM> defines the pressure release set point, while in other embodiments (e.g. <CIT>), the vessel system <NUM> is clamped inside of a slightly flexible frame, and a bolt or other clamp bears down (to an amount desired by the user) on the flexible portion <NUM> of the reaction vessel cap <NUM> to define the pressure exerted and thus the pressure at which gas will escape. In the embodiment illustrated in <FIG>, the bolt <NUM> bears on the cap <NUM> to keep the reaction vessel <NUM> sealed so that excess gas vents through the vessel vent opening <NUM> and the frame vent tube <NUM>. In any case, the reaction vessel remains closed during the entire digestion reaction and is vented without otherwise opening the reaction vessel.

As a point of confirming clarification, when the vessel is used in a frame, the frame may exert force against the plug, but this force is not exerted against the liner cap in the rigid liner cylinder.

The skilled person will understand that the cylinder liner <NUM>, the liner cap <NUM>, and the interstitial space <NUM> and <NUM> will serve the same or similar purposes in reaction vessels <NUM> or <NUM> and in other high temperature, high pressure chemistry methods such as extraction or synthesis.

As an advantage over, e.g., nitrogen-pressurized chambers, each reaction vessel <NUM> or reaction vessel <NUM> used in the present claimed invention vents to the atmosphere through vent opening <NUM> or vent opening <NUM> rather than to a common pressurized chamber. Thus, the present claimed invention eliminates the risk of cross contamination associated with systems such as the Multiwave <NUM> or the Ultrawave which use a common pressurized chamber.

As a further advantage over, e.g., nitrogen-pressurized chambers, the claimed invention creates pressure by heating the liquid in the interstitial space <NUM> and <NUM> in each reaction vessel <NUM> or reaction vessel <NUM> and thus eliminates the need for a pressurized gas source to pre-pressurize a common chamber. This reduces the costs associated with putting a large volume chamber under high pressure.

Moreover, the claimed invention eliminates the risk associated with a large chamber under high pressure. Because the risk associated with high pressure increases as volume increases, the present invention's use of the interstitial space <NUM> and <NUM> to create pressure rather than a large common chamber effectively eliminates the risk.

As a result of eliminating the hazards associated with a large chamber under high pressure, the claimed invention eliminates the concomitant limit on the number of samples that can be run simultaneously. Because each reaction vessel <NUM> or reaction vessel <NUM> is only, for example, <NUM> in volume, over <NUM> samples can be safely run simultaneously.

The invention can also be performed in a microwave transparent pressure releasing and resealing cylindrical reaction vessel <NUM>, for which glass or quartz are particularly appropriate, nested coaxially inside of a microwave transparent pressure releasing and resealing cylindrical containment vessel <NUM>, for which a fluoropolymer is particularly appropriate, with a small annular interstitial space <NUM> between and defined by the reaction vessel <NUM> and the containment vessel <NUM>.

Considered in this aspect, the coaxially nested cylindrical reaction vessel <NUM> is closed by the sliding cap <NUM>, and the coaxially nested cylindrical containment vessel <NUM> is closed by the floating plug <NUM> and the threaded flexible cap <NUM> on the containment vessel <NUM> that bears against the floating plug <NUM>, and with the floating plug <NUM> bearing coaxially against the sliding cap <NUM>.

In operation, and with or without the microwave absorbing liquid in the interstitial space <NUM>, this arrangement defines both the force magnitude with which the vessels are closed, and in turn the pressures at which they will vent and reseal. Thus, excess pressure in the reaction vessel <NUM> will drive the sliding cap against the floating plug <NUM> with a force greater than the mechanical force originally applied, in turn allowing venting to take place until the forces equilibrate and the sliding cap <NUM> recloses the reaction vessel <NUM>.

In an analogous manner, when the pressure outside of the reaction vessel <NUM>, but inside of the containment vessel <NUM>, exceeds the mechanical force applied by the threaded cap <NUM> against the floating plug <NUM>, the floating plug will open the containment vessel to allow pressure to escape until the system again reaches a state of equalized forces.

<FIG> is a schematic of the method embodiment. As set forth in the commonly owned Application Number <CIT>, published as <CIT>, for Vessel and Disposable Inner Sleeve for Microwave Assisted Reactions, a strong mineral acid and the digestion sample along with the microwave-absorbing liquid in the interstitial space are heated in a vessel liner with microwave radiation from the microwave source <NUM>. The microwave source <NUM> is typically a magnetron, but could include a klystron or an IMPATT diode. The infrared (IR) detector <NUM> measures the temperature of a digestion reaction in the rigid liner cylinder <NUM> based on infrared radiation emitted from the digestion reaction in the rigid liner cylinder <NUM> and through the recess <NUM>. As depicted in <FIG>, the IR detector measures the temperature of a plurality of reactions inside a plurality of vessel systems <NUM> as the vessel systems <NUM> are moved successively over the IR detector <NUM>.

The IR detector <NUM> measures wavelengths (frequencies) to which both the rigid liner cylinder <NUM> and the cylindrical reaction vessel <NUM> are transparent. For example, fluorinated polymers are transparent within the region (approximately) of <NUM> - <NUM> micron. Thus, the IR detector measures wavelengths within some or all of the <NUM> - <NUM> range. By using the infrared radiation emitted by the digestion reaction to which the rigid liner cylinder <NUM> and the cylindrical reaction vessel <NUM> are transparent, the IR detector measures the temperature of the reaction solution itself instead of reading the temperature of the cylindrical reaction vessel <NUM> or the rigid liner cylinder <NUM>.

The method further comprises employing the processor (CPU) <NUM>, in communication with the microwave source <NUM> and the IR detector <NUM>, to moderate the application of microwaves from the microwave source <NUM> to the rigid liner cylinder <NUM> nested in the cylindrical reaction vessel <NUM> based on the temperature of the digestion reaction in the rigid liner cylinder <NUM> measured using the IR detector <NUM>.

The method can further comprise the steps of opening the reaction vessel, typically after cooling to near ambient temperature (to allow the interior pressure to subside), removing the acid and the digestive sample from the rigid liner cylinder <NUM> and removing the rigid liner cylinder from the reaction vessel <NUM>, and thereafter adding a new rigid liner <NUM> to the reaction vessel <NUM> without any intervening step or otherwise cleaning the reaction vessel <NUM>.

The method further comprises the steps of repeating the entire digestion process with microwaves and temperature measurement for a new sample in the new liner.

As set forth in commonly owned Application Number <CIT>, the strong mineral acids are typically selected from the group consisting of nitric, sulfuric, hydrofluoric, and hydrochloric, as well as mixtures of two or more of these acids.

In order to work with these acids, the reaction vessel <NUM> can be formed from PFA, FEP or PVDF, or additionally from PTFE, or from any other polymer that otherwise can withstand the expected pressure and temperatures, and the corrosive aspects of the strong mineral acids.

The cylindrical liner cap <NUM> is formed of a polymer that is resistant to strong mineral acids at high temperatures and transparent to microwave radiation selected from the group consisting of polytetrafluoroethylene (PTFE, TEFLON®), polychlorortrifluoroethylene (PCTFE, KEL-F®), polyvinylidene fluoride (PVDF, KYNAR®, SYMALIT®), poly(ethylene chlorotrifluoroethylene) (ECTFE, HALAR®), chlorinated Polyvinyl Chloride (CPVC), polyethylene terephalate G copolymer (PETG/PET), polycarbonate (PC), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), and ethylene-tetrafluoroethylene (ETFE), and equivalents.

<FIG> is a perspective view of a plurality of vessel systems <NUM> positioned in a turntable <NUM> defined by upper <NUM> and lower <NUM> racks. As set forth in commonly owned <CIT>, the vessel systems <NUM> are placed in openings <NUM>, <NUM> in the racks <NUM>, <NUM> and move in an orbital path around the center of the turntable <NUM> as the turntable rotates within a microwave cavity during the digestion process.

The rotation of the turntable <NUM> containing the vessel systems <NUM> provides the advantage of being able to carry out a number of digestions at the same time in the same cavity while also accommodating the standing node nature of microwaves in cavities of the size and shape into which the turntable <NUM> and the vessel systems <NUM> will fit.

The openings <NUM>, into which the vessel systems fit in the lower rack <NUM>, allow the lower part of each vessel system <NUM> to be exposed. Applying the method as depicted in <FIG>, rotating of the turntable allows the vessel systems <NUM> to move across the IR detector <NUM> successively to obtain frequent temperature measurements and allows the processor <NUM> to adjust the microwave source <NUM> accordingly as previously described.

<FIG> is a perspective view of a plurality of vessel assemblies <NUM> in frames <NUM> on a turntable for being placed in a common microwave cavity as set forth in the <NUM> application. Like the turntable <NUM>, the rotating of the turntable <NUM> provides the advantage of being able to carry out a number of reactions at the same time in the same cavity while accommodating the standing node nature of microwaves in cavities of the size and shape into which the turntable <NUM> will fit.

Table <NUM> (Milk Powder; a certified reference material) and Table <NUM> (Rice Flour) demonstrates the results of the vessel method according to the invention. The experiments were carried out as follows.

A sample was added to each <NUM> vessel in an amount of <NUM> grams. A combination of nitric acid and hydrochloric acid was added to each vessel in a <NUM>:<NUM> ratio (HNO<NUM> to HCl) by volume, and specifically as <NUM> of HNO<NUM> and <NUM> of HCl. The vessels were placed in a CEM MARS <NUM>™ instrument which was used to carry out a <NUM>-minute ramp to <NUM> followed by a <NUM> minute hold.

After cooling, the results were analyzed in a Thermo-iCap Q™ inductively coupled plasma mass spectroscopy (ICP-MS) instrument (ThermoFisher Scientific, www. thermofisher. com; accessed February <NUM>, <NUM>).

Claim 1:
A method of microwave-assisted, high-temperature, high-pressure chemistry comprising adding a microwave-absorbing liquid to an interstitial space between two coaxially aligned and nested microwave-transparent reaction vessels in which the inner nested vessel contains one or more reaction compositions,
wherein the amount of microwave-absorbing liquid in the interstitial space is sufficient to generate a vapor pressure under microwave radiation that starts as being the same or greater than the vapor pressure of the reacting compositions under the same application of microwave radiation and that, at reaction temperatures, defines a pressure in the interstitial space that is greater than the vapor pressure of the reacting compositions in the inner nested vessel and bears against a sliding cap in the mouth of the inner nested vessel; and
wherein the microwave-absorbing liquid does not otherwise interfere with the relevant compositions, starting materials, or end products, or with the reactions between or among them.