DETAILED ACTION
Notice of Pre-AIA or AIA Status
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
Response to Amendment
The rejections of claims 1-33 are under 35 USC § 103 over Kurukchi and Sphephens are withdrawn by the examiner in view of the amendment filed on 8/27/2029.
Since a new Non-Final Office Action follows, the Applicants’ arguments will not be addressed.
Claim Rejections - 35 USC § 103
In the event the determination of the status of the application as subject to AIA 35 U.S.C. 102 and 103 (or as subject to pre-AIA 35 U.S.C. 102 and 103) is incorrect, any correction of the statutory basis (i.e., changing from AIA to pre-AIA ) for the rejection will not be considered a new ground of rejection if the prior art relied upon, and the rationale supporting the rejection, would be the same under either status.
The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
The factual inquiries for establishing a background for determining obviousness under 35 U.S.C. 103 are summarized as follows:
1. Determining the scope and contents of the prior art.
2. Ascertaining the differences between the prior art and the claims at issue.
3. Resolving the level of ordinary skill in the pertinent art.
4. Considering objective evidence present in the application indicating obviousness or nonobviousness.
This application currently names joint inventors. In considering patentability of the claims the examiner presumes that the subject matter of the various claims was commonly owned as of the effective filing date of the claimed invention(s) absent any evidence to the contrary. Applicant is advised of the obligation under 37 CFR 1.56 to point out the inventor and effective filing dates of each claim that was not commonly owned as of the effective filing date of the later invention in order for the examiner to consider the applicability of 35 U.S.C. 102(b)(2)(C) for any potential 35 U.S.C. 102(a)(2) prior art against the later invention.
Claims 1-3, 9, 11, 14-18 and 34 are rejected under 35 U.S.C. 103 as being unpatentable over Kurukchi et al. (US 6,576,132) in view of Stephens et al. (US 2022/0081623 A1) and Pfeifer (US 4,261,814).
Kurukchi teaches a steam cracking process including cooling steam cracking furnace effluent and feeding the cooled effluent to a quench water tower where the effluent is contacted with quench water, obtaining quench tower overhead vapor and liquid streams, separating the quench tower liquid into oil-containing and aqueous streams, removing coke fines and solids from aqueous streams, steam stripping treated quench water to produce stripper overhead vapor and stripped bottoms water, recycling stripper overhead vapor to the quench water tower, and generating dilution steam from stripped bottoms water (col. 8, line 16-col. 11, line 15). Kurukchi further teaches operation of the stripper at about 125-145°C and about 2-3 bar gauge and maintaining sufficient stripper pressure to recycle the stripper overhead vapor to the quench water tower (col. 10, lines 18-50).
Kurukchi, however, does not teach operating the steam cracking furnace at the claimed elevated coil outlet pressure (COP) of 200-700 kPa-gauge and recovering the olefin product using no more than three stages of compression.
Stephens teaches steam cracking an ethane-containing feed mixed with dilution steam at elevated COP, including 200-520 kPa-gauge, and expressly states that pressures greater than about 520 kPa-gauge can also be used (¶¶ [0013], [0017]). Stephens further teaches that elevated COP reduces downstream compression requirements and permits use of as few as two or three compression stages (¶¶ [0022]-[0023]).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to operate the steam cracking process of Kurukchi at the elevated COP taught by Stephens and to use no more than three compression stages in order to reduce downstream compression requirements, compressor power requirements, equipment size, and the number of compression stages, as taught by Stephens.
Kurukchi and Stephens, however, do not teach forming from the stripper overhead vapor a recycle stream having a pressure higher than the stripper overhead vapor by feeding the overhead vapor and an ejector motive stream to an ejector and/or compressing the overhead vapor, as required by claim 1.
Pfeifer teaches withdrawing a relatively low-pressure gaseous stream containing steam and hydrocarbons and passing the gaseous stream through compression means, including a steam-driven ejector, to raise the pressure of the gaseous stream sufficiently for recycle to a higher-pressure receiving zone (col. 2, line 66 through col. 3, line 17; col. 3, lines 48-65; claim 2).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to provide the stripper-overhead recycle of Kurukchi with the pressure-increasing ejector/compression means taught by Pfeifer, thereby permitting a relatively low-pressure stripper overhead vapor to be increased to a pressure sufficient for introduction into the quench tower while allowing the stripper and quench tower to operate at different pressures.
Regarding claim 2, Kurukchi does not teach the claimed radiant-effluent COP of 540-700 kPa-gauge. Stephens expressly states that pressures greater than about 520 kPa-gauge can also be used (¶ [0017]). Therefore, it would have been within the level of one of ordinary skill in the art, before the effective filing date of the claimed invention, to use any effective COP greater than about 520 kPa-gauge, including 540 kPa-gauge as presently claimed.
Regarding claim 3, Kurukchi teaches withdrawal of quench-water/liquid streams from the quench tower, including bottom liquid containing water and heavier hydrocarbons (col. 8, lines 52-67). Selection of an appropriate liquid-withdrawal location within the quench tower according to the phase and composition to be withdrawn would have been within the level of ordinary skill in the art.
Regarding claims 9 and 11, Kurukchi teaches feeding stripped bottoms water to a dilution steam generator and generating dilution steam therefrom for use in the steam cracking process (col. 10, lines 51-67; col. 11, lines 1-15).
Regarding claim 14, Kurukchi does not teach the claimed crossover temperature of 691-777°C. Stephens teaches supplying the feed/steam mixture to the radiant section at elevated crossover temperatures, including about 760-775°C (¶ [0026]), which falls within the claimed range.
Regarding claim 15, Kurukchi does not teach hydrocarbon cracking occurring in the crossover pipe. Stephens teaches preheating the hydrocarbon/steam mixture to a temperature at which thermal cracking is about to occur or is occurring to a slight extent and further teaches elevated crossover temperatures of about 760-775°C (¶¶ [0004], [0026]). It would have been obvious to operate at the elevated crossover conditions taught by Stephens, including conditions at which some hydrocarbon cracking occurs before entry into the radiant coil.
Regarding claim 16, Kurukchi does not specifically teach the claimed ethane concentration of at least 50 mol% of the hydrocarbons. Stephens teaches an ethane-containing cracking feed comprising at least 50 vol% ethane, including at least 70 vol%, at least 90 vol%, or substantially entirely ethane (¶¶ [0014], [0024]). For a gaseous hydrocarbon feed, the volume fraction corresponds to the mole fraction under common temperature and pressure conditions; therefore, Stephens teaches an ethane-rich feed satisfying the claimed concentration.
Regarding claim 17, Kurukchi does not teach three sequential compression stages having the specifically recited outlet-pressure ranges. Stephens teaches that elevated COP permits use of two or three compressor stages and that the required number of stages depends upon compressor inlet pressure and the desired downstream pressure (¶¶ [0022]-[0023], [0033]). Once three sequential stages are selected, the intermediate outlet pressures are process-design parameters dependent upon the inlet pressure, desired final pressure, and compression ratio. The claimed ranges are broad and overlapping as between successive stages. It would have been within the level of one of ordinary skill in the art to select effective successively increasing interstage pressures within the claimed ranges to achieve the desired final compression pressure.
Regarding claim 18, Kurukchi teaches the steam cracking, quench-water separation, aqueous treatment, stripping, stripper-overhead recycle, and process-water features discussed above, but does not teach the claimed COP of 540-700 kPa-gauge, no more than three compression stages, or increasing the pressure of the stripper overhead vapor before recycling it to the quench tower.
Stephens expressly states that pressures greater than about 520 kPa-gauge can also be used (¶ [0017]). Therefore, it would have been within the level of one of ordinary skill in the art, before the effective filing date of the claimed invention, to use any effective COP greater than about 520 kPa-gauge, including 540 kPa-gauge as presently claimed. Stephens further teaches that elevated COP permits operation with as few as two or three compression stages (¶¶ [0022]-[0023]). Pfeifer teaches increasing the pressure of a relatively low-pressure gaseous stream using compression means, including a steam-driven ejector, for recycle to a higher-pressure receiving zone (col. 2, line 66-col. 3, line 17; col. 3, lines 48-65; claim 2). It would have been obvious to modify Kurukchi accordingly for the reasons discussed above.
Claims 8 and 34 are rejected under 35 U.S.C. 103 as being unpatentable over Kurukchi in view of Stephens and Pfeifer as applied to claim 1 above, and further in view of Kurukchi et al. (US 9,969,944 B2).
Kurukchi, Stephens, and Pfeifer teach or render obvious the process of claim 1 as discussed above. The combination, however, does not teach operating the stripping column at an overhead pressure of 27-96 kPa-gauge as required by claim 8 or no greater than 190 kPa-gauge as required by claim 34. In particular, Kurukchi teaches about 2-3 bar gauge (200-300 kPa-gauge) (col. 10, lines 18-50).
Kurukchi ‘944 teaches a gas-cracker ethylene process employing a quench-water tower, quench-water treatment, a low-pressure water stripper, and dilution-steam generation, and teaches that stripping remaining hydrocarbons at atmospheric or slightly above atmospheric pressure is desirable. Kurukchi ‘944 further exemplifies operation of a quench-water stripper at about 0.2 bar gauge (20 kPa-gauge) (see col. 7, line 54-col. 8, line 44; col. 12, lines 1-8; col. 13, lines 7-18).
Regarding claim 34, the disclosed 20 kPa-gauge stripper pressure is no greater than the claimed 190 kPa-gauge.
Regarding claim 8, although the disclosed 20 kPa-gauge example does not itself fall within 27-96 kPa-gauge, Kurukchi ‘944 teaches operation at atmospheric or slightly above atmospheric pressure. It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to select an effective stripper pressure within the taught low-pressure, slightly-above-atmospheric operating regime, including 27-96 kPa-gauge, according to the desired stripping efficiency and process-pressure requirements. Pfeifer further teaches increasing the pressure of the resulting low-pressure overhead vapor when necessary for recycle to a higher-pressure receiving system.
Claims 4 and 10 are rejected under 35 U.S.C. 103 as being unpatentable over Kurukchi in view of Stephens and Pfeifer as applied to claim 1 above, and further in view of McCoy et al. (US 8,025,774 B2).
Kurukchi, Stephens, and Pfeifer teach or render obvious the process of claim 1 as discussed above. The combination, however, does not teach the particular use of a tar solvent with the identified quench-tower liquid/coke-rich/aqueous streams as recited in claim 4, or separating a C6-C7 aromatics-rich stream from the oil stream and using that stream as the tar solvent as recited in claim 10.
Regarding claim 4, McCoy teaches treatment of steam-cracking effluent and tar-containing streams using a light aromatic solvent, including hydrotreated steam-cracking pyrolysis gasoline, and teaches adding the aromatic solvent to tar-containing quench streams to solubilize tar and facilitate handling/separation thereof (col. 3, lines 15-67; col. 5, lines 1-45; col. 6, lines 1-67).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to employ the aromatic tar-solvent treatment taught by McCoy with the tar/coke-containing quench liquid streams of the modified Kurukchi process in order to solubilize heavy hydrocarbon/tar material and facilitate its separation and handling.
Regarding claim 10, Kurukchi additionally teaches use of aromatic-rich C6-C8 hydrogenated gasoline, BTX, and toluene in treatment of quench-water streams (col. 9, lines 23-67; col. 10, lines 1-17). In view of Kurukchi's C6-C8 aromatic-rich solvent and McCoy's teaching of using light aromatic steam-cracker-derived material as tar solvent, it would have been obvious to use the C6-C7 aromatic portion of the available aromatic-rich oil as the tar solvent.
Claims 5 and 6 are rejected under 35 U.S.C. 103 as being unpatentable over Kurukchi in view of Stephens and Pfeifer as applied to claim 1 above, and further in view of Rooney et al. (WO 2020/168062 A1).
Kurukchi, Stephens, and Pfeifer teach or render obvious the process of claim 1 as discussed above. The combination, however, does not teach removing coke from the normal cooled furnace effluent before introduction of the resulting coke-abated cooled effluent into the quench tower, as required by claim 5, or performing that separation using the separation-device arrangement recited in claim 6.
Regarding claim 5, Rooney teaches removing coke/tar from steam-cracker furnace effluent during normal processing by cooling/quenching the furnace effluent, feeding the resulting effluent to a centrifugal separator, separating a vapor product having a reduced coke/tar content from coke/tar-containing bottoms, and feeding the coke/tar-reduced vapor product to downstream equipment including a combined quench tower/primary fractionator (¶¶ [0027]-[0033], [0040]; claims 1 and 8).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to provide the cooled furnace effluent of the modified Kurukchi process with the upstream coke-separation arrangement taught by Rooney before introduction into the quench tower, in order to reduce coke/tar carryover and thereby reduce fouling, restriction, erosion, and solids-handling problems in downstream quench equipment, as taught by Rooney.
Regarding claim 6, Rooney's centrifugal separator provides an inlet receiving the cooled/quenched furnace effluent, a vapor outlet providing a coke/tar-depleted vapor product, and a lower separation/collection region from which coke/tar-containing material is obtained (¶¶ [0027]-[0033], [0040]). These teachings correspond to the claimed feed stream inlet, vapor outlet, coke-depleted vapor stream, and coke particle deposition/collection section.
Claim 19 is rejected under 35 U.S.C. 103 as being unpatentable over Kurukchi in view of Stephens and further in view of Rooney.
Kurukchi teaches the steam-cracking, furnace-effluent cooling, quench-tower, quench-water separation, and downstream recovery features discussed above (col. 8, line 16-col. 11, line 15), but does not teach operating at the claimed elevated COP with no more than three compression stages.
Stephens teaches elevated-pressure ethane steam cracking at COPs of 200-520 kPa-gauge and greater than about 520 kPa-gauge, and teaches that elevated COP reduces downstream compression requirements and permits use of as few as two or three compression stages (¶¶ [0013], [0017], [0022]-[0024]).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to operate the steam-cracking process of Kurukchi at the elevated COP taught by Stephens and employ no more than three compression stages to obtain the reduced compression and equipment requirements taught by Stephens.
Kurukchi and Stephens, however, do not teach, before introduction into the quench tower, feeding the normal cooled furnace effluent to a separation device to obtain a coke-depleted vapor stream and deposited coke as required by claim 19.
Rooney teaches removing coke/tar from normal steam-cracker furnace effluent by cooling/quenching the furnace effluent, feeding it to a centrifugal separator, separating a vapor product having reduced coke/tar from coke/tar-containing bottoms, and thereafter feeding the coke/tar-reduced vapor product to downstream equipment including a combined quench tower/primary fractionator (¶¶ [0027]-[0033], [0040]; claims 1 and 8).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to provide the cooled furnace effluent of the Kurukchi/Stephens process with Rooney's upstream coke/tar separator before introduction into the quench tower in order to reduce downstream fouling, restriction, erosion, and solids-handling problems.
Claims 21-22, 24-27, and 29-33 are rejected under 35 U.S.C. 103 as being unpatentable over Kurukchi in view of Stephens and Rooney, Pfeifer, and McCoy.
Kurukchi teaches a steam-cracking process including cooling furnace effluent, feeding the cooled effluent to a quench-water tower, contacting the effluent with quench water, obtaining overhead vapor and liquid streams, separating quench liquid into hydrocarbon/oil-containing and aqueous streams, treating the aqueous streams, steam stripping treated quench water, recycling stripper overhead vapor to the quench tower, and generating dilution steam from stripped bottoms water (col. 8, line 16-col. 11, line 15).
Kurukchi, however, does not teach operating the furnace at the claimed elevated COP and recovering the olefin product using no more than three compression stages.
Stephens teaches elevated-pressure ethane steam cracking at COPs of 200-520 kPa-gauge and greater than about 520 kPa-gauge and teaches that elevated COP reduces downstream compression requirements and permits use of as few as two or three compression stages (¶¶ [0013], [0017], [0022]-[0024]).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to operate the Kurukchi process at the elevated COP taught by Stephens and employ no more than three compression stages to obtain the reduced compression requirements and reduced equipment size taught by Stephens.
Kurukchi and Stephens, however, do not teach removing coke/tar from the normal cooled furnace effluent in an upstream separation device before introducing the coke-depleted vapor into the quench tower, as required by claim 21.
Rooney teaches cooling/quenching normal steam-cracker furnace effluent, feeding the effluent to a centrifugal separator, separating a vapor product having reduced coke/tar from coke/tar-containing bottoms, and feeding the coke/tar-reduced vapor product downstream to a combined quench tower/primary fractionator (¶¶ [0027]-[0033], [0040]; claims 1 and 8).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to provide the cooled furnace effluent of the Kurukchi/Stephens process with Rooney's upstream coke/tar separator in order to reduce coke carryover and downstream fouling, restriction, erosion, and solids-handling problems.
The combination of Kurukchi, Stephens, and Rooney, however, does not teach feeding the stripper overhead vapor together with an ejector motive stream to an ejector to obtain a recycle stream having a higher pressure than the stripper overhead vapor, as further required by claim 21.
Pfeifer teaches passing a relatively low-pressure steam/hydrocarbon-containing gaseous stream through compression means, including a steam-driven ejector, to raise the pressure of the gaseous stream sufficiently for recycle to a higher-pressure receiving zone (col. 2, line 66-col. 3, line 17; col. 3, lines 48-65; claim 2).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to provide the stripper-overhead recycle of the modified Kurukchi process with the steam-driven ejector taught by Pfeifer, thereby permitting operation of the stripper at a lower pressure while increasing the overhead-vapor pressure sufficiently for recycle to the quench tower.
The combination of Kurukchi, Stephens, Rooney, and Pfeifer, however, does not teach all of the claimed use of a C6-C7 aromatics-rich stream as a tar solvent for the identified coke/tar-containing stream.
McCoy teaches use of light aromatic solvent, including hydrotreated steam-cracking pyrolysis gasoline, to solubilize tar-containing material in steam-cracking quench streams and facilitate separation and handling of the tar (col. 3, lines 15-67; col. 5, lines 1-45; col. 6, lines 1-67). Kurukchi additionally teaches aromatic-rich C6-C8 hydrogenated gasoline, BTX, and toluene for treatment of quench-water streams (col. 9, lines 23-67; col. 10, lines 1-17).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to employ the aromatic-rich steam-cracker-derived material taught by McCoy/Kurukchi as the tar solvent in the modified process in order to solubilize tar/heavy hydrocarbons and facilitate separation and handling thereof.
Regarding claim 22, Kurukchi teaches removing suspended coke fines/solids from quench water and recycling treated water within the quench-water system (col. 8, lines 52-67; col. 9, lines 1-22).
Regarding claim 24, Kurukchi teaches feeding stripped process water to a dilution steam generator and generating dilution steam therefrom (col. 10, lines 51-67; col. 11, lines 1-15).
Regarding claims 25 and 26, Kurukchi teaches withdrawal of quench liquid from the quench-water tower, including bottom liquid containing water and heavier hydrocarbons (col. 8, lines 52-67). Selection of bottom and above-bottom withdrawal locations according to the phases/compositions being withdrawn would have been within the level of ordinary skill in the art.
Regarding claim 27, the underlying combination does not teach mixing the second quench-tower liquid effluent with a tar solvent. McCoy teaches introducing light aromatic solvent into tar-containing quench streams to solubilize tar and facilitate handling/separation thereof (col. 3, lines 15-67; col. 5, lines 1-45). It would have been obvious to apply that known tar-solvent treatment to the second quench-tower liquid stream for the same purpose.
Regarding claim 29, Kurukchi does not teach the claimed radiant-tube alloy/barrier construction. Stephens teaches coke-resistant radiant-coil surfaces employing Ni-Cr heat-resistant alloys and alumina barrier layers (¶¶ [0011]-[0012], [0021]). However, as with claim 13, Stephens does not expressly disclose every numerical constituent of the specific alloy recited in claim 29; an additional reference should be provided for the exact alloy composition if this rejection is maintained.
Regarding claim 30, Kurukchi does not teach the claimed crossover temperature. Stephens teaches crossover temperatures of about 760-775°C (¶ [0026]), which fall within the claimed 691-777°C range.
Regarding claim 31, Kurukchi does not teach cracking occurring in the crossover pipe. Stephens teaches heating the hydrocarbon/steam mixture to a temperature at which thermal cracking is about to occur or occurs to a slight extent and teaches elevated crossover temperatures of about 760-775°C (¶¶ [0004], [0026]). It would have been obvious to operate the crossover at such elevated conditions, including conditions at which some hydrocarbon cracking occurs.
Regarding claim 32, Kurukchi does not specifically teach the claimed ethane concentration. Stephens teaches ethane feeds containing at least 50 vol% ethane, including at least 70 vol%, at least 90 vol%, or substantially entirely ethane (¶¶ [0014], [0024]), thereby teaching the claimed ethane-rich gaseous feed.
Regarding claim 33, Kurukchi does not teach three sequential compressor stages having the specifically claimed outlet-pressure ranges. Stephens teaches that elevated COP permits use of two or three compressor stages and that compressor staging depends upon compressor inlet pressure and the desired downstream pressure (¶¶ [0022]-[0023], [0033]). Once three sequential stages are selected, selection of effective successively increasing intermediate outlet pressures according to inlet pressure, desired final pressure, and compression ratio would have been within the level of ordinary skill in the art. The claimed ranges are broad and permit such conventional successively increasing compressor-stage pressures.
Claim 28 is rejected under 35 U.S.C. 103 as being unpatentable over Kurukchi in view of Stephens, Rooney, Pfeifer, and McCoy as applied to claim 21 above, and further in view of Kurukchi et al. (US 9,969,944 B2).
The combination of Kurukchi, Stephens, Rooney, Pfeifer, and McCoy teaches or renders obvious the process of claim 21 as discussed above. The combination, however, does not teach operating the stripping column at the claimed overhead pressure of 27-96 kPa-gauge. Kurukchi ‘944 instead teaches operation at about 2-3 bar gauge (200-300 kPa-gauge) (col. 10, lines 18-50).
Kurukchi ‘944 teaches a low-pressure quench-water stripper in a gas-cracker ethylene process and teaches that stripping at atmospheric or slightly above atmospheric pressure is desirable, including an example operated at about 0.2 bar gauge (20 kPa-gauge) (col. 7, line 54-col. 8, line 44; col. 12, lines 1-8; col. 13, lines 7-18).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to operate the stripper of the modified process at an effective pressure within the low-pressure, slightly-above-atmospheric operating regime taught by US 9,969,944, including 27-96 kPa-gauge, according to the desired stripping efficiency and process-pressure requirements. Pfeifer's ejector permits the resulting low-pressure stripper overhead vapor subsequently to be increased in pressure for recycle to the higher-pressure quench tower.
Claim 13 is rejected under 35 U.S.C. 103 as being unpatentable over Kurukchi in view of Stephens and Pfeifer as applied to claim 1 above, and further in view of Takahashi et al. (US 2011/0318593 A1).
The combination of Kurukchi, Stephens, and Pfeifer teaches or renders obvious the process of claim 1 as discussed above. The combination, however, does not teach that the radiant tube comprises the particular cast heat-resistant alloy composition and barrier layer recited in claim 13.
Takahashi teaches heat-resistant castings particularly suitable as reactor tubes for producing ethylene and teaches a cast heat-resistant alloy comprising, in mass percent, 0.05–0.7% C, >0–2.5% Si, >0–3.0% Mn, 15–50% Cr, 18–70% Ni, 2–4% Al, 0.005–0.4% rare-earth elements, and 0.5–10% W and/or 0.1–5% Mo, with the balance Fe and inevitable impurities, and having an Al₂O₃-containing barrier layer on the surface exposed to the high-temperature atmosphere (¶¶ [0001]-[0002], [0013]). The disclosed Ni range of 18-70% encompasses the claimed range of 20-70%. Takahashi further teaches that Al improves carburization resistance and anti-coking properties and is essential for producing the Al₂O₃ barrier layer (¶ [0036]).
It would have been obvious to one having ordinary skill in the art, before the effective filing date of the claimed invention, to form the radiant tube of the modified Kurukchi process from the heat-resistant alloy and barrier-layer construction taught by Takahashi in order to provide a reactor tube suitable for high-temperature ethylene production having improved carburization resistance and anti-coking properties.
Claim 29 is rejected under 35 U.S.C. 103 as being unpatentable over Kurukchi in view of Stephens, Rooney, Pfeifer, and McCoy as applied to claim 21 above, and further in view of Takahashi et al. (US 2011/0318593 A1).
The combination does not teach the particular radiant-tube alloy composition and barrier layer recited in claim 29. Takahashi teaches the alloy composition and barrier layer discussed above (¶¶ [0001]-[0002], [0013], [0036]). It would have been obvious to form the radiant tube of the modified process from Takahashi's heat-resistant alloy and barrier-layer construction for the same reasons discussed above regarding claim 13.
Conclusion
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/TAM M NGUYEN/ Primary Examiner, Art Unit 1771
