KR20040029388A - Chemical processing using non-thermal discharge plasma - Google Patents

Abstract

A method of activating a chemical reaction using a non-thermal capillary discharge plasma (NT-CDP) unit or a non-thermal slot discharge plasma (NT-SPD) unit (collectively referred to as "NT-CDP / SDP"). The NT-CDP / SDP unit includes a first electrode disposed between two dielectric layers 8, 9, where the first electrode and the dielectric layer have one or more openings (eg, capillaries or slots) defined therethrough. . The dielectric sleeve 3 is inserted into the opening and one or more second electrodes 2 (eg, in the form of pins, rings, metal wires or tapered metal blisters) are placed in fluid communication with a combination opening. When a voltage difference is applied between the first electrode and the second electrode, the nonthermal plasma discharge is released from the opening. The chemical feedstock to be treated is then exposed to non-thermal plasma. This process is suitable for the following exemplary chemical reactions; (i) partial oxidation of hydrocarbon feedstocks to produce functional organic compounds; (ii) chemical stabilization of polycer fibers (eg, PAN fiber precursors in carbon fiber production processes); (iii) pre-reforming longer chain length petroleum hydrocarbons to generate feedstocks suitable for reforming. ); (iv) natural gas reforming in a chemically reducing atmosphere (eg, ammonia or urea) to produce carbon monoxide and hydrogen gas; Or (v) plasma enhanced water gas shifting.

Description

Chemical process using non-thermal discharge plasma {CHEMICAL PROCESSING USING NON-THERMAL DISCHARGE PLASMA}

The use of electrical discharges to produce industrially important chemical reactions is known and has been used for a long time. One of the oldest and most effective chemical transformations that occur in the presence of electrical discharges is ozone generation. The generated ozone can react with unsaturated hydrocarbons to synthesize ozones, aldehydes and ketones. Knight, Henry de Boyne, The arc discharge ; As described in its application to power control , London, Chapman & Hall (1960), conventional early gas discharge devices are operated by exposing a reactant gas to an electric arc (thermal plasma).

Recent chemical processes have been carried out using both thermal and nonthermal plasmas. US Pat. No. 6,372,192 to Paulauskas et al describes a carbon fiber manufacturing process using plasma. In this patented process, as a first step in the carbon fiber process, stabilized polyacrylonitrile (PAN) fibers are converted to carbon graphite fibers using a GHz frequency plasma under low pressure oxygen free atmosphere. However, this patent does not disclose or suggest the use of oxygen rich plasma to stabilize PAN fibers in the early stages of the process. Does this patent teach the use of non-thermal plasma?

Due to the overwhelming interest in hydrogen fuel cells, recent research and developments in the field of plasma auxiliary fuel reforming and fuel conversion have also made significant strides. For example, US Pat. No. 6,322,757 to Cohm et al. And references cited herein disclose plasma fuel conversion, such as plasmatrons to reform hydrocarbons for producing hydrogen rich gases. US Pat. No. 6,395,197 to Detering et al. Describes a method and high temperature apparatus for thermal conversion to the end products required for light hydrocarbons (natural gas), in particular biatomic hydrogen and elemental carbon. In another patent invention, US Pat. No. 6,375,832 to Eliasson et al. Teaches a method for chemically converting hydrogen (such as methane) and carbon (such as carbon dioxide) rich gases into standard liquid fuels. This plasma assisted Fischer-Tropsch synthesis is performed by using dielectric barrier discharge under conjugation with a solid zeolite catalyst.

Another notable area of plasma processing is plasma active surface treatment of polymeric materials to increase wettability and / or surface adhesion, e.g. "Electircal Characterization by LA Rosenthal and DADavis. of a Corona Discharge for Surface Treatment ", IEEE Transaction on Industry Applications , vol. 1A-11 No. 3, pp.328-335 (May / June 1975), "Polymer Surface Modification by S. Han, Y. Lee, H. Kim, G. Kim, J. Lee, J. Yoon, G.Kim Plasma Source Ion Implantation ", Surface & Coatings Technology , vol. 93, pp. 261-264 (1997), and US Pat. 6,399,159.

Therefore, U.S. Patent No. No. 09 / 738,923 and US patent no. Filed Feb. 19, 2002. As described in 60 / 358,340, it is desirable to utilize the chemical process optimally by using NT-CDP / SDP, with each application incorporated by reference in its entirety.

Summary of the Invention

The present invention relates to a method of enhancing a chemical process, and more particularly, to a method of activating a chemical reaction using an NT-CDP / SDP unit. The NT-CDP / SDP unit according to the invention comprises a first electrode disposed between two dielectric layers, wherein the first electrode and the dielectric layer have one or more openings (eg, capillaries or slots) defined therethrough. Have One or more second electrodes (eg, pins, rings, metal wires or paper metal blades) are placed in fluid communication with combination openings. When the voltage difference between the first electrode and the second electrode is applied, the nonthermal plasma discharge is released from the opening. The chemical feedstock to be treated is then exposed to non-thermal plasma. This process is suitable for the following exemplary chemical reactions; (i) partial oxidation of hydrocarbon feedstocks to produce functional organic compounds; (ii) chemical stabilization of polycer fibers (eg, PAN fiber precursors in carbon fiber production processes); (iii) pre-reforming longer chain length petroleum hydrocarbons to generate feedstocks suitable for reforming. ); (iv) natural gas reforming in a chemically reducing atmosphere (eg, ammonia or urea) to produce carbon monoxide and hydrogen gas; Or (v) plasma enhanced water gas shifting.

This application is part of US Patent Application Serial No. 09 / 738,923, filed December 15, 2000, which is a copy of US Provisional Patent Application No. 60 / 309,530, filed August 2, 2001, and 2002. Claim the benefit of US Provisional Patent Application No. 60 / 358,340, filed February 19. All applications are hereby incorporated by reference in their entirety.

TECHNICAL FIELD The present invention relates to plasma assisted chemical processes, and in particular, to conventional discharge techniques using non-thermal capillary discharge plasma (NT-CDP) or non-thermal slot discharge (NT-SDP) (collectively referred to as "NT-CDP / SDP"). Higher yields and better energy by energizing certain species in a more uniform manner compared to arcs (e.g., arcing, gliding arc, dielectric barrier discharge (DBD) and corona) Enable efficient chemical conversion. Unlike conventional discharge technology, which is prone to spatially and temporally inhomogeneous filament discharges, NT-CDP / SDP devices minimize diffusion inefficiencies in maintaining equivalent treatment to ensure diffusion stability. Generate a plasma (diffuse stable plasma). NT-CDP / SDP devices can be specifically tuned to selectively produce specific rate crystallization chemical reactions that can easily cascade towards the desired product. By adding energy to the system in this particular way, chemical reactions which were originally possible only at high temperatures and pressures are possible under ambient conditions. Tuning is accomplished by changing the power, composition and concentration of reactants, carrier gas composition and flow rate, temperature, pressure and / or reactor geometry.

The foregoing and other features of the present invention will become more apparent from the following detailed description and drawings of embodiments of the invention which show like reference numerals to like elements throughout the several views.

1A is a side perspective view of an exemplary annular NT-CDP processing apparatus for chemical stabilization (oxidation) of PAN fibers according to the present invention.

1B is a side cross-sectional view perpendicular to the longitudinal axis of the device of FIG. 1A.

1C is an enlarged longitudinal sectional view of a single capillary ring electrode in the device of FIG. 1B.

2A is a cross-sectional view of an exemplary gas phase NT-CDP auxiliary chemical process unit in accordance with the present invention.

FIG. 2B is an enlarged view of a single capillary of the device of FIG. 2A.

3A is an exemplary graph of hydrogen detector readings versus time for forming H ₂ from NH ₃ .

3B is an exemplary graph of hydrogen gas concentration over time.

4A is a side perspective view of an exemplary annular NT-SDP processing apparatus for chemical stabilization (oxidation) of PAN fibers in accordance with the present invention.

4B is a side cross-sectional view perpendicular to the longitudinal axis of the device of FIG. 4A.

4C is an enlarged longitudinal sectional view of a single longitudinal wire electrode in the device of FIG. 4B.

The present invention relates to a method of activating (promoting) a chemical reaction. Chemical processes exposed to electrical discharges supplied in plasma volumes can improve the yield and / or energy efficiency of certain chemical changes. Gas, liquid, water phase and / or solid precursors can be treated. Some illustrated types of exemplary chemical reactions that are enhanced when exposed to NT-CDP / SDP are provided below, where each process is performed by a specific exemplary reaction.

(i) partial oxidation of hydrocarbon feedstocks to produce functional organic compounds such as alcohols, aldehydes, ketones and carboxylic acids

Example

(ii) chemical stabilization "oxidation" of PAN precursors in the carbon fiber production process pathway

Example

(iii) pre-modification (“cracking”) of longer chain length petroleum hydrocarbons to generate a feedstock suitable for reforming.

Example

(iv) natural gas reforming in a chemical reduction (ammonia or urea) atmosphere for carbon monoxide and hydrogen gas production;

Example

; And

(v) plasma enhanced water gas shift reaction

Example

In steps (i) and (ii) above, NT-CDP / CT-SDP is used to activate the non-thermal partial oxidation ("cold combustion") of the hydrocarbon feedstock. The plasma generates the following oxidizing species from the ambient air: oxygen atoms (O ( ¹ D)), hydroxyl radicals (OH), ozone (O ₃ ) and peroxide radicals (HO ₂ ) in the gas stream. These highly reactive species then selectively oxidize the hydrocarbon molecules to produce the product required for the reaction. In the case of example (i), the desired result is CH ₃ (CH ₂ ) _n CH ₂ OH.

The reaction described in (iii) above is preferably carried out in a chemical neutral plasma. The term: "chemically neutral" refers to an environment with a carrier gas that is chemically inert, such as but not limited to helium, which is the result of direct electron impact dissociation. Processes (iv) and (v) occur preferentially in chemically reducing plasmas, which are plasmas that tend to increase the number of electrons in the target chemical. (Reduction is the opposite of oxidation.) Electron rich plasma suitable for adding chemical ammonia or urea to the gas stream to chemically reduce hydrogen in methane to hydrogen gas (step (i)) and water (step (ii)). To produce.

1A-1C illustrate another aspect of an exemplary cyclic NT-CDP process that is particularly well suited for chemical stabilization (oxidation) of polymer fibers such as PAN fibers. The process unit comprises a second electrode 2 disposed at two yarns of insulating dielectric layers 8, 9 for forming the hollow tube. The second electrode 2 is selected to have the desired expansion coefficient. Although the processing unit is shown and described in the form of a cylindrical unit, alternatively, geometric forms may be considered, which are within the scope of the present invention. A high voltage bus 5, for example a wire mesh or an outer metallic sheath, is disposed around the outer dielectric layer 9.

FIG. 1B is a side cross-sectional view perpendicular to the longitudinal axis of the process unit of FIG. 1A. As clearly shown in FIG. 1B, the plurality of capillaries 4 is preferably radially outwardly through the dielectric layer 8, the second electrode 2 and the opposite dielectric layer 9. For example, a dielectric sleeve 3 made of quartz is inserted into each capillary 4, and the fin electrode 1 is insulated from each dielectric sleeve 3 so as to insulate the fin electrode 1 from the second electrode 2. I put it in). The high voltage bus 5 connects a series of pin electrodes 1 to a common high voltage source HV. In an alternative arrangement, as long as the electrode is in fluid communication by the capillary, the electrode may have other geometric shapes and need not necessarily fit within the capillary. Some alternative arrangements of capillary discharge arrangements are shown and described in US patent application Ser. No. 09 / 738,923. FIG. 1C is an enlarged view of the single capillary tube shown in FIG. 1B.

In operation, PAN fibers 6 are received through the channels of the tubes and NT-CDP is generated. In the process unit 10 the PAN fiber 6 discharges the NT-CD plasma and at the opposite end is the stabilized PAN fiber 7.

2A and 2B show two cross sections of an NT-CDP gas phase chemical process unit according to the present invention. Referring to the cross-sectional view of FIG. 2A, the series of capillary tubes 20 is limited to through the dielectric sheet 11. Dielectric sleeve 12 is inserted into each capillary 20 to form a high dielectric current limiting capillary. Inserted into each capillary 20 is a pin or needle electrode 10. Electrically connecting the array of pin or needle electrodes 10 to a typical high voltage source is a high voltage bus 13, such as a wire mesh or metallic sheath. Dielectric plate 14 made from, for example, quartz, glass or ceramic is used to insulate electrode plate 15. Each of the inlet and outlet transitions 16, 17 can be processed to pass the gas substantially across the series of capillary plasma jets by a reactor volume 21. The sealed manifold 18 may pass directly through the plasma jet via the needle electrode 10 and the capillary 20, and then discharge the gas chemistry into the process stream. Element 19 is an auxiliary gas outlet port. In a preferred embodiment, the system can easily scale the plasma power in the range of about 500 watts to about 10 KW. The process unit preferably utilizes the use of radio frequency power supply optimally. The peak-to-peak voltage required to cross the reactor gap is preferably ranged from about 5 KV to about 50 KV, depending on the carrier gas.

3A and 3B are experimental graphical results for NT-CDP auxiliary hydrogen formation from iso-octane and ammonia in nitrogen carrier gas. The discharge started after an equilibrium time of 300 seconds to insulate steady state reduction. In particular, FIG. 3A shows a graph showing the hydrogen detector reading (mA) over time during the experiment to form H ₂ from NH ₃ . This experiment was conducted at a power of 200 W, a concentration of NH ₄ OH of 15 M, and an N ₂ flow rate of 11 L / min. Figure 3b shows a graphical result of the ppm concentration of H2 gas over time. This experiment was performed at a power of 2000 W, a concentration of NH ₃ (aq) OH 15 M, and an N ₂ flow rate of 11 L / min.

When using the NT-CDP arrangement in accordance with the present invention, interference is reduced because only a minimal amount of hydrogen is formed from iso-octane reforming in the plasma (N ₂ trace) and chemically neutral plasma (iso-octane trace). Even if it exists, it shows a little experimental result. The ammonia traces show significant amounts of hydrogen formation (~ 1000 ppmV) due to ammonia procatalyst imbalance. The synergistic effect of using iso-octane in the presence of ammonia produced large amounts of hydrogen (~ 1500 ppmV). GC / MS analysis of the product stream also shows a significant amount of plasma assisted pre-modification (cracking) under this hydrogen formation and conjugation. Optimizing them can provide a cost-effective way of producing hydrogen gas from concentrated fuels.

The NT-CDP chemical process method according to the present invention is advantageous over conventional heat and / or catalyst processes which minimize the consumption of catalyst over time and significantly lower power consumption. The lower power consumption is because the bulk gas does not have to be heated to generate the conversion. NT-CDP chemical processes are also preferred over other plasma processes such as dielectric barrier discharge (DBD) and corona discharge (CD). The reason is that the relatively large volume of diffusion plasma implemented using NT-CDP allows for a substantially uniform and effective chemical process. The disclosed chemical process is merely an example for the purpose and is not intended to limit the scope of the invention to the use of other chemical processes.

4A-4C illustrate exemplary embodiments of NT-SDP gas phase chemical processes in accordance with the present invention. This embodiment is similar to that shown and described in FIGS. 2A-2C except that the unit uses a slot discharge arrangement instead of a capillary discharge arrangement. The slot discharge arrangement in FIGS. 4A-4C is particularly well suited for chemical stabilization of polymer fibers such as PAN fibers. The number of this reference component is the same as the reference component described in the unit shown in Figs. 2A-2C. It is shown in FIG. 4A by arranging the slot 4 substantially parallel to the longitudinal axis. Alternatively, the slots 4 can be arranged substantially perpendicular to the longitudinal axis of the reactor or in a helical direction. An electrode 4 is inserted into each slot. As an embodiment, the electrode 4 may be a metal wire arranged to complement the shape of the combination slot and approximate and partially insert and insert into the slot. In yet another embodiment, the slot can be a tapered blade. Another arrangement for the slot discharge arrangement is described in US patent application 60/358/340, which is hereby incorporated by reference in its entirety. This slot discharge arrangement exposes more surface area of plasma emission than the capillary discharge arrangement.

Therefore, although the basic novel features of the invention as applied to the preferred embodiments of the invention are shown, described, and pointed out, various omissions, substitutions, and changes in the details and forms of the devices described in their operation have been made. It will be appreciated that it may be performed by one of ordinary skill in the art without departing from the spirit and scope of the invention. For example, it is evident that all combinations of those elements and steps that perform the same function in substantially the same way to achieve the same result are within the scope of the present invention. The substitution of elements from one described embodiment to another is also sufficiently described and considered. While the drawings are not necessarily made to scale, it can also be seen that they are merely conceptual in nature. It is therefore intended to be limited as indicated by the scope of the claims appended hereto.

All references, publications, and patents mentioned herein are incorporated by reference in their entirety.

Claims (16)

A method of activating a chemical reaction using a nonthermal discharge unit, wherein the nonthermal discharge unit includes a first electrode disposed between two dielectric layers, wherein the first electrode and the dielectric layer have one or more openings defined therethrough, At least one second electrode is disposed in fluid communication with a combination opening, Generating a nonthermal plasma discharge from the opening by applying a voltage difference between the first electrode and the second electrode; Exposing the chemical feedstock to the non-thermal plasma released from the opening. The method of claim 1 wherein the opening is a capillary and the unit further comprises a dielectric sleeve inserted within the capillary. The method of claim 2, wherein the opening is defined radially outward through the first electrode and the dielectric layer. The method of claim 2, wherein the second electrode is a metal pin or ring. The method of claim 1 wherein the opening is a slot. 6. The method of claim 5 wherein the openings are arranged in the longitudinal direction, the helical direction, and the direction substantially perpendicular to the longitudinal axis. The method of claim 5 wherein the second electrode is a metal wire or a tapered metal blade. The method of claim 1, further comprising a voltage bus connecting the second electrode to the voltage source. The method of claim 8, wherein the voltage bus is one of a wire mesh or a metal sheath. The process of claim 1 wherein the chemical reaction is a partial oxidation of a hydrocarbon feedstock for producing a functional organic compound. The method of claim 1 wherein the chemical reaction is chemical stabilization of the polymer fiber. The method of claim 11, wherein the polymer fiber is a polyacrylonitrile precursor used in a carbon fiber process. The process of claim 1, wherein the chemical reaction is pre-reforming a petroleum hydrocarbon with a longer chain length to generate a feedstock suitable for reforming. The process of claim 1, wherein the chemical reaction is natural gas reforming under a chemical reducing atmosphere for producing carbon monoxide and hydrogen gas. The method of claim 14, wherein the chemical reducing atmosphere is ammonia or urea. The method of claim 1 wherein the chemical reaction is plasma enhanced water gas shifting.