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~ ~ET~OD ~ND ~PPARA~U8 FO~ ~hY8I8 OF ~ACRO~OL~CVLAR ~AT~R~a~ ~Y
2 P~RO~YS~8 4 !~AC~GROUND OF Tl~E: INVENT10~7 6 The present invention rQlates to the field of analysis o~ materials 7 such as polymars, coal, kerogen, asphalt~nes and other macro-8 molecules by pyrolysis.
The invention has principal usefulness in the analysis of source 11 rock and reservoir rock for petroleum exploration and production and will be disclosed primarily in such ~ield, although it is ~3 useful in any instance where it is desired to study a macro-l~ molecule degradation process. For in~tance, any polymeric material lS may be analyzed. Specific examplec o~ materials which might be ~6 analyzed are paints and plastics.
~7 18 The petroleum industry utilizes sophisticated technology to explore ~9 for oil and gas. In frontier areas, geological s'cudies are performed to evaluate the conditions most favorable for abundant 21 hydrocarbon accumuIations. The regionaI geolo~y is assessed by 22 methods which accurately define the ar~al dis~ribution~ of 23 reservoirs, traps, seals, and sourc~ rocks. Source rock3 which 2~ contain oil-pron~ organic matter are respon3ible for sourcing ~5 commercial hydrocarbon accumulations. T~e source rocks are 26 evaluated by pQtrolau~ geochemical methods d~signed to identify the 27 stratigraphy of the subterranean formation in which they are found~
2~ The source rock evaluation is needed to plan ~h& immediate 2~ exploration stratagy in a frontier area. ~ Favorabla source ro~k results will anhance t~e area's hydrooarbon potential;and influence 3~ laase acquisition decisions. Frequently, th2 ~ource rock geochem-32 istry will be used with geophysical informa~ion to sel~ct the most 33 ~avorable area for tha next drill:ing location. ~ ;
~4 3S In recent years, pyrolysis GC has become. a widely uæed tool in ~: .
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1 petrolPum exploration research. It can provide use~ul composition-2 al and structural information about kerogen. The in~ormation can 3 be used to evaluate and characterize (i~ source rock guality, (ii) 4 maturity, and (iii) reservoired hydrocarbons. However, an inherent deficiency with the pyrolysis GC technique is that it only provides 6 information regarding the final or endpoin~ products of pyrolysis.
7 While this endpoint information is useful, further information 8 abou~ how each produc~ evolves during pyrolysis as a ~unction of ~ time and temperature is desirable. This information can be used to calculate kinetic parameters for each compound, such a~ activation ~ energy and frequency factor. Compound specific product volution 12 informa~ion can ~e used to further classify kerogens. Two 13 different kerogens can have similar pyrolysis end products, yet 1~ differsnt activation energies and therefore product evolution. In short, detailed information about produ¢t evolution will provide a ~6 further distinction between kerogens beyond the information 17 provided by common pyrolysis GC technigue.
a 19 One company, Ruska Laboratories, Inc. ("Ruska'l) of Houston, Texas has developed a method and apparatus to att~p~ ~o obtain detail~d 21 pyrolysis product evolution information. Ruska manufactures the apparatus which is commercially available under the name "Pyran 23 System"- which is a registered trademark o~ Ruska. The Pyran 24 System attempts to obtain detailed information on th~ pyroly~i~
23 products via a quick cooling method. Typically, samples are 26 pyrolyzed in this syste~ with a linear temperature ramp and the 27 pyrolysis products are captured in a mole sieve (or cold) trap. At 28 each o~ saveral predetermined te~peratures, the temp~rature ramp is 2~ interrupted and the sa~ple is quickly cooled to halt pyrolysi~ (the ~0 temperature is normally dropped to about 200C). The products 3~ trapped so far are then released in~o a gas chromatograph (GC) to 32 obtain compound specific in~ormation. upon co~pletion o~ the GC
33 run, the temperature ramp is resumed with the same heating r~te 3~ starting from about 200C. This approach ha~ two drawbacks: 1) .: .,, -, : .
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f~ t~j 1 pyrolysis products are generat~d before the temperature has reached 2 the previous quick cooling temperature point giving inaccurate 3 results, and 2) the method is tedious, time consuming, and gives a ~ poor time/temperature relationship. Thus, the results obtained with this method are not suitable for the kinetic study of 6 pyrolysis products.
8 In his patent number GB ~,161,2~9 Martin discloses a method and 9 apparatus which takes all of the hydrocarbon that can be thermally I0 evolved from a sample and determines the ga~ range content and the 11 oil range content of such hydrocarbon by the use o~ two cold traps.
~2 Martin describes first completely pyrolyzing the sample, then 13 analyzing the end products or end pyrolyzatec Martin discusses how 1~ the point of the gas/oil split may be varied by controlling the temperatures of the two traps. Martin further allows that by use 16 of several traps in saries having different trapping temperatures, ~7 it may be possible to isolate the evolved hydrocarbon into several ~8 different "cuts" depending on the dewpoint o~ any given ~9 hydrocarbon. It should be emphasized that these cu~s are cuts o~
the endpoint products for the completely evolved sample. Martin 21 also discusses the possibili~y of determining the amount of 22 hydrocarbon evolved for a specific temperature range and nQt just 23 the endpoint, but does not describe how this miqht be done.
2~ Further, the apparatus described by Martin would limit such an 2S application to only one temperature range ~or a particular sa~ple.
26 Alternately, if th~ sam2 sample wer~ reused, it might be analyzed 27 for more than one temperature range, such as is done in the Pyran 28 Systeml described above. Thi~, however, would not provide product 29 evolution in~ormation as discuss¢d, since such in~ormation must come ~rom continuous uninterrupted pyrolysis of a single sample.
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32 Prior art as for example U.S. Patent~ number~ 4,842,825 and 33 4,784,833 disclos~ apparatus for carrying ou~ pyrolysis of a 34 substance containing organic compounds, but do not disclose nor -- - . .:: , . ~
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1 claim a method for determining the time/temperature relationship of 2 products evolved from such pyrolysis.
4 Prior art means for heating pyrolysis traps has used either radiant S heating of the trap or direct contact of the trap with a heating 6 element. The present invention uses a novel means for heating the 7 trap by fabricating the trap from metal and using the trap itsel 8 as th metallic resistance heating elemen~. Prior art (~or example 9 U.S. Patent number 4,8~2,825) has taught away from using metal traps due to a concern over reactions between the pyrolyzate and 1~ the metal. The present inventors have detsrmined that for kerogen 12 samples thi~ is not a problem.
8~h~RY OF TR~ ~NV~IO~
17 The purpose of the Multiple Cold Trap Pyrolysis (MCTP) apparatus is 18 to generate a time resolved pyrolysis GC for a co~pound being 19 studied. The sample is heated at a linear temperature ramp without any interruptions. As the pyroly~is productq evolve, they are ~1 segmented into fractions on the basis of predeterminad te~perature 22 ranges and trapped sequentially in parallel multiple cold traps.
23 After pyrolysis is complete, the pyrolyzate in each trap iR
2~ analyzed separately by GC. Each chromatogram rapre~ents a fingerprint of the pyrolysis produc~s generated in a given ~6 temperature interval. By keeping the respon~ ~actor the same Por 27 each GC run or using an external s~andard ~Qthod, the product 29 ~volution curve i~ generat~d by taking the particular product ~9 concentration fro~ each ga~ chromatogram and plottin~ it a~ a function of the end temperature of ~ach pyrolysis fraction. These 31 points can then be connected by curve Pittin~ and a product 3~ evolution curve o~tained.
34 A novel apparatus ~or ~rapping pyrolysis product~ i~ also 3S disclosed. Th~ t~ap 18 ~ thin wall-d small diam~er ~tainless : :. ' ~ , . , .
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1 steel tube pack~d with quartz beads which act as the surface onto 2 which the pyrolysis products condense. The trap is kept cold by 3 immersion in a coolant until the time for releasing the trapped ~ products. The trap is heated by using the trap itself as a S electrically ~esistive heater element. One electrode of the 6 heating circuit having a first potential is attached to the 7 resistive midpoint of the trap. Two other electrodes having a 8 second potential are connected to each of the two ends of the trap 9 (the inlet and outlet ends). The trap is thus segmented into two parallel resistors in the heating circuit. When current is passed 11 through the heatinq circuit the resistance causes th~ two segments ~2 to heat, driving off th~ condensed pyrolysis products.
~3 1~ A novel appara~us for keeping an instrumentation valvs at an elevated temperature is also disclosed. The valve and the inl~t 16 and outlet tubing to and rom the valve is encased in a metallic 17 block. The block i5 maintained at an elevated temperature by 18 inserting heaters into holes bored into the metal block. ~or ease ~9 of fabrication, the block is assembled from seYeral segments which are stacked together. Tubing leads are disposed in passageways 21 between the segments. In this way the valv~ can be rem~ved from 22 the block by merely separating the segments and tha need ~or 23 disconnecting the tubing leads is eliminated. The apparatu~ also ~ allows one cold trap to be removed for service without disassembly 2S of the whole apparatus. The invention ha~ particular application where ~he valve i8 a ~ultiposition valve and produc~ flowing ~7 through the vælve must be maintained at an elevated temperature to 28 prevent solidifica~ion or condensation.
~9 3~ OH~T8 O~ T~ IN~E~TION
3~ It is therefore an object of the pre~ent invention to provi~e a 34 method and apparatu~ for generating product evolution data and graphical plots for macromolecular matQrials.
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- c -1 Another object of the present inventio~ is to provide a novel 2 apparatus for trapping and releasing pyrolyzate.
~ A further object of the present invention is to provide a novel apparatus for heating transfer lines and valves in a pyrolysis 6 apparatus.
8 Various other objects, adva~tages and features of the present 9 invention will become readily apparent from the sllowing detailed 1~ description.
~2 ~3 ~RIBF D~CRIP~IO~ 0~ T~ D~A~
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In order to facilitate the understanding of this invention, 16 reference will now be made to the appended drawings of the 17 pre~erred embodiments o~ the pres~nt invention, in which:
~9 FIG. 1 is a schematic drawing of the apparatus showing the various portions.
22 FIG. 2 is a schematic drawing of the apparatus ~howing details of ~3 the various portions.
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~5 FIG. 3 is a sectional elevation view of the trap portion o~ the 26 prererred embodiment of the apparatus.
~7 28 FIG. ~ i~ a sectional eleva~ion view o~ the trap portion of an ~9 alternate embodim~nt of the apparatus~
3~ FIG. 5 is a schematic of the electrical circuit for ~h~ switrhing 32 section of the control portion of the apparatu~.
34 FIG. 6 is an example of a product evolution c~rve generated from 3S data ob~ained from operation of the apparatus o~ the claimed :
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3 FIG. 7 is an example of a product rate of generation curve 4 generated from data obtained from operation o~ the appara~us of the claimed invention.
8 D~AIL~D D~8CRIPTION O~ T~B PR~F~R~BD E~BODI~T~
For purposes o~ this application, ~cold trap" or "trap" will mean 11 a tube which can be cooled below the dewpoint o~ a substance 12 passing through the tube, th~ tube further containing a porous 13 material providing a sufficient surface area for such substance to condense onto when cooled. The tube and packinq materi~l are fabricatad from materials essentially inert to the ~ubstance. For 16 substances comprised primarily of hydrocarbons, prior art has shown 1~ that preferred materials for the tube and packing material are 18 quartz and fused quartz sand, respec~ively. The pr~sent inventors 19 have deter~inad that stainless steel is also an acceptable tube material, and offers novel advantages which will be descri~ed herein.
~2 ~3 "Pyrolyzate" as usad h~rein will m~an the pxoducts evolved fro~ a 2~ sample which are capable of being carri~d away fro~ th~ sample by 2S a carrier gas strea~ ~uch as heliu~. When in thQ gas state, 26 ~pyrolyzate" will include such carrier gas.
a T~o app~satu~s ~9 Referring now to the figures, in FIG. 1 th~ multiple cold trap 3~ tMCT) apparatus 10 is comprised o~ an o~en portion IS ("the ovenl') 32 capable of holding and pyrolyzing a workpiece sa~ple 17, ~he 33 multiple cold trap portion 20 (~th~ ~rap portion"), a multiposi~ion 3~ valva ~S and v~lve positioner ~0, a control portion 65 comprisinq a logic section 6~ and a switching section 67, an analy~is portion . . . . .................. . .
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1 comprising a m~ans known in the art for analyzing compositions of 2 su~stances in the gaseous s ate 50 and accompanying analysis 3 controller S5, and all appropriate electrical, fluid and signal ~ connections between the above recited elemen~s. In the preferred embodiment a gas chromatograph is used as the analysis means.
6 Additional components such as a compu~er for recording and 7 manipulating data may be added to the MCT apparatus.
g With reference to FIG. 2, the oven portion 15 in which the sample 17 is to be pyrolyzed is known in the art and is described for 11 example in U.S. Patent number 4,842,825 which is herein 12 incorporated by reference. Attendant components to the oven are:
13 the sample chamber 16 ~or holding the sample; ~he heater l~ for 1~ heating the sample to a temperature suffioien~ to pyrolyze the sample; tha carrier gas inlet 19, said carrier gas for carrying the 16 pyrolyzate from the oven portion to ~he trap portion of the 17 apparatus; the pyrolyzate gas outlet 21; temperature sensing means 18 such as a thermocoupla 22 for determining the temperature within 19 the oven; and insulating means 23 to reduce heat flux out of the oven portion. The above recited elements are described in the 21 above referenced patent.
23 The trap portion.20 is comprised of a plurali~y of cold trap~
24 ("traps") 25 dispo ed within separated cooling chambers 30. In the example shown, 10 traps were used, although only 2 are shown for clarity. One embodiment of a single ~rap i~ de cribed in U.S.
2~ Patent numbsr 4,842,825. The trap portion further comprlses a 2~ means ~or individually heating any one trap to release ~he conken~s 29 o~ the trap wh~lR ~aintaining any or all of the re~aining traps below the dewpoint o~ their con~en~. The trap heating means is 3~ typically an electrical reaistance hea~er, although other heating 32 means such as a radiant quartz heater can be employed. For the 33 purposes of this application, any ~uch mean~ o~ heating which u~es 3~ electricity will be raferred to as the ~hea~ing circui~". In the 3S preferred embodiment the trap is fabricated fro~ metal and an .
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_ 9 _ 1 electrical current is passed through the trap to generate hea~ by 2 electrical resistance. The metallic trap material should be 3 selected so that it has a sufficiently low conductivity that a 4 large current will not be needed to generate the required heat.
Additionally, the material should be corrosion resistant.
6 Stainless steel is a preferred material since it is ~hermally a 7 poor conductor, electrically a sufficient conductor to achieve the 8 desired ~empera~ures with a relatively low vol~age and amperage, 9 and is corrosion resistant to a wide range of anticipated pyrolyzate. In one example, a nominal 1/8" diameter 316 stainless l~ steel tubing with 0.006" tubing wall thickness wa~ used to generat~
12 temperatures of up to 300C using a direct current of 17 amps at 4 13 volts. By using thicker or thinner tube wall thic~nesses, ~ore or 14 les~ current will be required respectively to achieve the sa~e temperature. To heat the trap in this manner, the ~rap is 16 connected into an electrical circuit such that ~he trap becomes two ~7 parallel paths in th~ circuit. A single electrode 110 is connected 18 to the distal midpoint of the trap and two electrodes 1~1 are ~9 connected to the points where the traps connect to the heater block. The single electrode is preferably connec~ed to a point 21 such that each leg of ~he constructive circuit has equal electrical 22 resistivity, i.e., the resistive midpoint. ~ypically the distal ~3 midpoint is also the resistive midpoint, sinc~ the linear 2~ resistivity o~ ~he tubing is essentially constan~. The advantag~
2S of the three-electrode enbodiment is that the trap can be isolated 26 as a separate circui~. This allows the metallic trap to be 27 connected to other ~etallic element~ without those other elements 28 becoming part of the circuit and short circuiting the trap heating 2D circuit. Other mean~ known in the art ~or heating the trap~ are by radiant heating as ~r example in U.S. Patent numbe~ 4,~42,825 or 3~ by contacting the trap itself with a heating ele~ent. In one 32 sxample each trap was wrapped with 28 ga. lloy heating wire with 33 a rssistance of 8.1 ohms/ft. The ~rap can also be fabricated from 3~ a non-metallic material. The preférred non-~talli~ trap material ... . ...
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l is fused quartz. Each trap is fitted with a temperature sensing 2 means such as thermocouples 26. The signal from the temperaturé
3 sensing means is preferably transferred to the control portion ~ (discussed below) and used as a control signal to control the temperature of the trap. The traps hava an inlet end 27, which 6 allows ingress of pyrolyzate into the trap, and an outlet end 28 7 which allows egress of detrapped pyrolyzat~ from the trap.
8 Pyrolyzate is swept from ~he traps when they are heated by a sweep 9 gas. The sweep gas is introduced through the multiposition valve.
The same type of gas as is used for the carrier gas carrying 1~ pyrolyzate fro~ the oven to the traps is preferably used as the ~2 sweep gas. However, the sweep gas is routed ~o the traps directly 13 from the gas source rather than through the oven to avoid carrying 14 any residual pyrolyzate from the oven ~o the traps. The sa~e ~S source can be used ~or bo~h gasses by using a splitter ~7 and 16 valves 88 and ~9 as shown in FIG. 2. In one example, ~elium was 17 the carrier and sweep gas.
~9 Although separate cooling chambers 30 are shown for each cold trap, a single cooling chamber common to all of the traps could also be 21 employed. In the embodiment where a single cooling chamber is used 22 each trap is individually covered with insulation to reduce heat 23 loss from the trap when the trap is heated. However, the 2~ insulation should not be so thick that long cooling time~ are 2S required to cool the trap. In the example shown wherein resistive 26 heating metal traps are ~sed, ~raided fiberglass sleeving is used.
27 In an embodiment wherein contact heating o~ a fused glas~ quartz 2a trap is used, braided fiberglass sleeving wa~ also used. In ~he ~9 pre~erred embodiment separate cooling chambers are used. The ~ollowing diseussion assu~es an apparatus in accordance with the 3~ preferred embodiment. The traps are dispo~ed within the cooling 32 chambers so that each trap may be cooled. The pre~erred embodi~ent 33 for the cooling cha~ber i~ a Dewar flask to minimize heat ~lux 3~ primarily into the trap. If a Dewar ~lask i~ not used the inter~or of the oooling cha~ber should be coated with a reflective surface ...
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-~ 11 --1 to minimize heat Plux. Each cooling chamber should be insulated to 2 further reduce heat flux into the trap. Each cooling chamber ha~
3 a trap inlet opening 3~ throughwhich the inlet end of the trap d protrudes, a trap outlet opening 32 throughwhich the outlet end of the trap protrudes, and a coolant inlet/outlet opening 33 ("coolant 6 opening") which admits coolant into the cooling chamber and also 7 allows coolant to be drained from ~he cooling chamberO In the 8 preferred embodiment the coolant is a liquified gas such as liquid 9 nitrogen (LN2). If a liquified gas is used as a coolant, a coolant vapor outlet opening needs to be provided in the cooling chamber to 1~ allow vaporizing gas ~o escape to avoid overpressurin~ of the 12 cooling chamber. In the example shown, the trap inlet or outlet 1 opening can b~ oversized to allow vapor to escape. The coolant 14 vapo~ outlet opening should be sized so as to minimize evaporation lS of the coolant yet avoid overpressuring of the cooling chamber. In 16 the example shown, the trap inlet and outlet openin~ were 17 oversized by 0.03". Regardless o~ whether or not the trap inlet 18 and ou~let openings are used as the ooolant vapor outlet, these 19 openings should be oversized so that there is no contact between the trap tubing and the cooling chamber. The reason this contact ~1 is to be avoided is that i~ the trap~ are in contact with the 2~ cooling chamber the cooling chamber will act as a heat sink when 23 the traps are heated during detrappinq, slowing the heating ti~e 2~ unaccep~ably. Alternately, the top of the cooling chamber can ~e 2S fabricated from an insulating material ~o that heat is not 26 tran~ferred from the ~rap in the event the trap contacts the 27 cooling chamber. Tha coolant vapor outlet opening can be plumbed 28 with a conduit ~not shown) to remove coolant vapor~ to an area 2~ remota from the work area. The a~ount of th~ coolant in each cooling chamber is controlled by thermocoupla~ 2~ which send a 31 signal to the control portion (discu~sed below). If the 32 temperature has risen abova the control point, the control portion 33 sends a signal to an auto~a~ic coolan~ fill valve 3S w~ich opens, 3~ allowing coolant from the coolant source ~3C to flow into the , ., ~ ,, , , , - , .
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~ J ~ f l cooling chamber. Pump 37 can b2 used if necessary to move coolant2 into the cooling chambers. Once sufficient coolant has entered the 3 cooling chamb~r to lower the ~emperature b~low the setpoint the 4 thermocouple siqnal to the control portion changes and the control 5 portion s~nds a signal to close the coolant fill valve. In the 6 preferred embodiment the thermocouple is a K or T-type thermocouple 7 which has been found to be resilient und~r the extreme temperature 8 changes. Each cooling chamber is fitted wi~h a separate coolant 9 fill valve 35 and a separate automatic coola~t drain valve 36 which are both connected to a common "T" fitting 3~ which is in turn 11 connected to the coolant opening 33. The coolant drain valve 36 ~2 opens upon receipt of a signal fro~ the control portion, allowinq 13 coolant to drain fro~ the cooling chamber at th~ appropriate time ~ in the sequence, as discussed below. Durin~ the time that th~
lS coolant drain valve is open, either the coolant ~ill valve is 16 disabled, remaining in the closed position, or thQ trap temperature ~7 control system is disabled, so that coolant does no~ flow into the 18 chamber while it is being emptied.
Between the oven portion pyrolyzate gas outlet 2~ and the trap 21 portion 20 is a first gas directing means for directing the 22 pyrolyzate to individual traps. B~tween the trap outlet ends 28 23 and the analysis ~eans 50 is a second gas directing means for individually directing the detrapped content.~ of each trap to the 2S analysis means. rn th~ preferred embodiment the fir~t and second 26 gas directing means are a single multiposition valve ~5 having a~
27 many station~ or po~itions as there are traps. Each station of the 28 ~ultipoRition valve has a station inlet opening 46 ("~tation ag inlet") and a station ou~le~ opening 47 ("station outlet"~. The multiposition valve haq a single main inlet ~ in communication 31 separately with each s~ation outlet. Th~ multipo~ition valve al~o 32 ha~ a single main outlet ~9 in communication ~eparately with each 33 station inlet. Each s~ation of the multiposition valv~ corresponds 3~ to a particular trap. The station outlet a~ each station of the 3S multiposi~ion valve i~ in communication with th~ trap inlet of the ' .
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1 trap corresponding to that statlon of the multiposition valve. The 2 station inlet at each station of the multiposition valve is in 3 communication with the trap outlet o~ the trap corresponding to 4 that station of the multiposition valve. The main inlet of the multiposition valve is in communication with ~he pyrolyzate outlet 6 of the oven portion. The main outlet of the multiposition valve is 7 in communication with the sample inlet o~ the analysis means. The a position of the multiposition valve i~ controlled by a valve 9 positioner/actuator ÇO ~'the positioner") which will put any given ~0 station outlet in communication with the main inlet or will put any 1~ given station inlet in communication wi~h the main outlet.
12 Preferably, when any given station inlet or outlet is in ~3 communication with t~e main outlet or inlet, respectively, no other 14 station opening is in communication with any other connection. "In ~S communication" as used herein mean~ "in fluid communication" unless 16 otherwise specified. Preferably the positioner i~ actuated ~7 automatically by the controller, preferably by electrical signal, 18 although other signal means can be used such as infrared signal or 19 pneumatic signal. In the example di~cussed, the multiposition valve was a V~CI VALCO Instrument Company E6STlOT 10 position high 21 temperature valve with an electric actuator. The valve actuator in 22 this example was actua~ed by electrical contac~ closure and 115 VAC
23 power.
2S The analysis portion i8 comprised of the analysi~ mean~ 50 and 26 analysis controller SS. In the pre~erred embodiment th~ analysis 2~ means is a gas chromatograph (hereinafter "GC"3 and the analysis 28 controller means i~ a GC controller. In the example de~cribed the ~9 analysis means wa~ a Chemical Data Systems ~odel CDS 820~S gas chromatograph.- Other analysis means known in the art include but 31 are not limited to a flame ionization detector ("FID") or a mass 32 spectrometer. Additionally, one analysis means can be used in 33 conjunction with or alternately with other analysi3 mean~. The 3~ analysis means ii~ compriied of the sample processing unit Sl having 3S a sample inlet S2, a sample outlet ~3, and an outpu~ signal means ~, '',' ' i'.'. ..
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1 56. In the example wh~rein the analysis means is a GC, the sample 2 proc~ssing unit is the GC column. The GC also has a cryofocuser 3 (not shown) which precedes the GC column itself. Cryofocusers are 4 well known in the art and are used to collect samples befor~
S rereleasing them to the GC. This assures that the GC column 6 receives the sample at a rate consistent with the design of the GC.
7 The output signal from the sample processing uni~ is typically an 8 anaIog signal. This signal can be directed to a signal recording 9 means known in the art as for example a strip chart recorder.
Alternately, the analog ~ignal can be stored electronically and/or ~1 conver~ed to a digital signal and stored in a data storage device 12 such as a computer or displayed as a numerical value. Once stored ~3 in a digital compu~er, the data may be manipulated and used in a ~4 variety of ways.
16 Th~ above recited components, the oven portion, the trap portion, ~7 and the analysis portion, are in ~luid communication as described 18 above. It is important to keep all of the fluid com~unication 19 passages including the multiposition valve heated so that pyrolyzate does not condense before the trap or the analysis means.
2~ The critical portions to heat during ~rapping are those passages 22 before the rotary valve and the rotary valve itself. There is no~
23 an equivalent concern with keQpin~ the lea~s b~tween the rot~ry 2~ valve and the packed portion o~ th2 trap hot during trapping, as long as that portion of tubing can b~ heated durinq detrapping.
26 The reason it is not critical to heat that portion during trapping 27 is any pyrolyzate which condenses in ~ha~ por~ion o~ ~ubing will be 28 released when the tubing is heated during detrapping. Heating of 29 the critical portions during trapping can be achieved by 3~ electrically heating th2 passag~ and the rotary valve with an ~1 electrical resistance contact heater and covering the h~ating 3~ element with insulation. While this is e~ctive, it consu~e~ a 33 large volume of space, and maintaining a constant and uniform 3~ temperature within any one passage is di~icul~. An inven~ive feature of the present invention is a novel method of maintaining .
3) 1 the passages and valve at a constant, uni~orm temperatur~. The 2 best mode of the present invention contemplates lO cold traps 3 radially disposed about the rotary multiposition valve, as shown in 4 FIG. 3. Rather than heating individual lines to and from the rotary valve, the rotary valve 45 is disposed within a metallic 6 heater block 70. The cooling chambers 30 in which are disposed the 7 cold traps 25 are radially disposed about the heater block. For 8 purposes o~ simplification only two of the ten ~raps are shown in 9 the sectional view of FIÇ. 3. In one variation the transf~r lines 107 and 108 between the traps and the rotary valve are entirely 11 within the heater block. In a second variation tha transfer lines 12 are mostly outside of ~he heater block. The second variation is 13 the preferred variation since it is easier to fabricate the heater ~ block and asse~ble ~he overall trap por~ion, re~ults in a more compact unit, and uses le~s energy to heat the heater block. As i6 discussed above, it is not neoessary to heat the transfer lines 17 between the rotary valve and the trap during trapping, as long a~
18 a means for heating trans~er lines during detrapping is provided.
19 The means for heating the traps during detrappinq is preferably also used to heat the trans~er lines between the traps and the ~1 rotary valve during detrapping.
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23 Referring now to FIG. 2~, a plan view of the trap portion shown in 2~ FIG. 2 shovs the 10 traps 25 in the cooling chambers 30 radially 2S disposed about the rotary valve q5.
~6 ~7 Whils the above paragraph discusses two sections of transfer lines ~8 between thQ rotary valv~ and the trap, and the trap itsel~ as 29 distinct sections, in the preferred e~bodiment the two section~ of transfer line and ~he trap are alI one continuous piec~ of tubing 31 a~ shown in FI~. 3. This ~ini~ize~ connection~ which ~ay leak 3~ under thermal cycling and ~akes for ~impler fabrication.
3~ FIG. 3 showc the preferred variation o~ the trapping portion 3S wherein a portion o~ the ~ransrer lines between t~e rot~ry valve - . . . . . - .
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1 and the traps are not disposed within the heater block. Distending 2 radially fro~ the rotary valve 45 to the edge of the heater bloc~
70 are the trap inlet lines 108 and trap outlet lines 107. The ~ trap inlet and outlet lines are disposed between the two sections 121 and' 122 of the heater block. The section~ 121 and 122 are 6 joined by fasteners such as screws or bolts and can be separated so 7 that the trap inlet and outlet line can be access~d for service 8 without having to remove the rotary valve. Further, section 121 9 can be fabricated from several l'pie" shaped pieces in the plan view so that individual trap lines can be accessed. The traps 25 are 11 disposed within the cooling chambers 30 which are mounted with 12 respect to the heater block such that minimal heat transfer between 13 the heater block and the cooling chambers occurs. Thi~ can be done 14 by suspending the cooling chambers fro~ the heater block by non-thermally conductive materials 112 or by moun~ing th~ cooling 16 chambers free from the heater block. The heater block is 17 preferably insulated with insulation 7~ such as rork wool or other 18 heavy duty, high temperature insulating material. More pre~erably 19 the insulated rotary valvQ is enclosed within a housing ~3 along with the cooling chambers and cooIant plumbing ~or personnel 21 protection against heated and cooled surfaces as well as for other ~2 obvious practical purposas. ~he heater block is maintained ak all 23 times throughout the operation of the apparatu~ at a constant 24 temperature above the dewpoint of the pyrolyzate by heating means.
2S In the example discu~ed, ~he temperatura was 300C. In the example 26 discussed, four 300W elec.trical heater cores ~30 were used as the 27 heating means by in~erting the cores into hole~ bored into the 2a heater block. Alternate heating mean~ such a~ electrical heat ~9 trac~ing can al~o be used to heat th~ heater block. Heater cores are commercially availa~le and are el~ctrically operated and have 31 temperature control circuitc which can be controlled by the control 32 portion (discussed below) u~ing thermocouple~ 77 ~ount~d on the 33 heater block for the control input signal. In the exa~ple 34 discussed the heater block was made ~rom alumlnu~. AIuminum is a .
.. . . ........... . . . .
. : :
:
P~ r`f,~
- ~7 -l preferred material for the heater block since it is a good th~rmal 2 conductor, i5 light weight, and is easy to machine for fabrication;
3 However, any good thermally conductive material could also be used 4 for the heater block. Since the traps ar~ maintained at their S cooled temperature from between the time pyrolyzate is "trapped" in 6 them until the detrapping sequence ~or that particular trap occ~rs, 7 there is a large temperature differential in the zone 81 bPtween 8 the heater block and the cooled trap. This temperature 9 differential needs to be constrained to as short of a distance as possible so that heat is not transfexred into the trap, possibly 11 releasing trapped pyrolyzate. Maintaining this sharp temperature 12 differPntial to contain volatile compounds is known as 13 "cryofocusing~'. Additionally, heat transfer into the trap will 14 cause cool points in the heater blocX~ possibly condensing pyrolyzate in undesirable areas. In one example, where the traps 16 were cooled to -195C, the temperature differential was 495C over ~7 0.10". Thus the trap ~aterial should be a poor thermal conductor ~8 to mini~ize heat transfer into the traps. Stainless steel and 19 fused quartz both meet this criteria, are essentially chemically inert, and can withstand large temperature differentials and ar~
21 therefore preferred materials for the traps. The tran~fer lines ~2 between the traps and the rotary valve may be insulated primarily 23 for safety and also to d~crease ~hermal los~.
2S In the preferred variation wh~rain the tubing of the metallic traps 26 i~ used as the trap heating element and the heater bloc~ described 27 in th~ above paragraph is u~ed, the valve heater block material i~
2a preferably a good electrical conductor. This will allow the heater 29 block to bs used a~-the electrode3 at the end~ of the trap~, i.e., the inlet ends and outlet ends, thus eli~inating th~ need for 3~ wiring to these point~. In this variation a single electrical wire 32 is attached to the heater bloc~. The heater bloc~ i~ in electri~al 33 contact with all cold ~rap inlet and outlet end~. When a potential 3~ i5 applied to the single electrode, it is thu~ appliQd to all ;. , :
: `
L~ J ;, 1 traps. In this variation aluminum is a preferred material for the 2 heater block.
~ FIG. 4 shows the les~ preferred variation of the trapping portion wherein the entirety of the transfer lines between the rotary valve 6 ~5 and the traps 25 are disposed within the heater block. Between 7 the heater block 70 and the cooling chambers 30 is an insulation 8 material 71 to reduce heat flux from the heater block to the 9 cooling chamber. The inlet end 27 and outlet end 2~ of the cold traps are disposed within ~he heater block and connect to the 1~ multiposition valve. In this emhodiment the coolant vapor outlet 12 opening is the vent 72 rather than oversizing the trap inlet or ~3 outlet opening, as described above. One me~hod of disposing the 14 multiposition valve and trap inlet and outlet ends within the ~5 heater block is to fabricate the block in the sections shown a3 73, 16 74, and 75. In all other aspects the heater block is essentially 17 as described in the preferred variation, above. In FIG. 4 the 18 traps and cooling chambers are shown as being radially disposed 19 about the bottom of the heater block. A variation wherein the traps and cooling chambers are radially disposed about the outer 21 perimeter 78 of the heater block would simplify fabrication and 22 asse~bly, but would give a substantially larger apparatus.
~3 The transfer lines 82 and 83 fro~ the oven portion to the ~ultiposition valve and fro~ the ~ultiposition valve to the 26 analysis portion, respectively, should be maintained ~t the same ~7 temperature as tha heater block. This can be achieved by wrapping 28 them in electrical resistance contact heaters 8~ and insulation ~6.
~9 A temperature sen~ing mean~ such as ~hermocouple 87 can be used ~o monitor the temperature of the lines an~ genera~e a signal which 3~ can be used to control the temperature of the heatin~ Means.
33 The oven portion, the trap portion, a~d the analy~i~ portion are in 3~ electrical and electronic com~unication with one another. The 3S electrical and electronic com~unicatio~ between these por~ions is , ~:
~:
, . .
, ~ 19 ~
1 centrally controlled by the control portion, which is comprised of 2 the logic section and the switching section. The pri~ary function~
3 performed by the control portion include controlling the rate of ~ increase of temperature in the oven portion, the selection of the trap to direct pyrolyzate to, the heating and cooling of the traps, 6 the selection of the trap to detrap pyrolyza~e from, and the 7 operation of the analysis portion. 'tTrap selection" ~s used in the 8 previous ~entence includes actuation of the rotary valve 9 positioner. While these functions could be handled by individual control units, in ~he preferred embodiment they are all handled by 1~ a single unit, resulting in a simpler, more ef~icient unit. The 12 loqic section contains timing components which determine the time ~3 at which events within the apparatus are to occur as well as the 14 duration of those events, for example, the rate of temperature lS increase in the oven, the dura~ion of time to direct pyrolyzate to 16 any given ~rap, ~he time at which de~rapping is to occur, the 17 length of time for detrapping, and any other time/sequ~nce event a which occurs in the apparatus. The logic section can al~o be used ~9 to control events based on conditions other than time, such as temperature by reading a signal from a temperature sensor and 21 comparing it to a setpoint. The logic section also pref~rably 22 contains th~ means for recording and/or displaying temperatures 23 monitored throughout the apparatus, although separate temperature 2~ monitors/recorders could be used. Th~ logic section can either be manual timers, or more preferably a programmablQ ~ulti~channel 26 timer, or most pref~rably a co~puter. In one exampl~ th~ logic 27 section was a Chemical Data Systems CDS 430 programmable timer 28 whic~ is strictly a timer and is incapable of altering its sequence 29 based on th~ state of the syste~. In another example the logic section was a ~ewlett Pac~ard HP9836 personal computer runninq a 31 control progra~ writt~ in Ba~ic. The logic por~ion sends control 32 signals to the switching sec~ion. FIG. S show3 one exa~ple of a ~3 switching section for the control portion. With r~erence To FIG.
3~ S, the switching section con~ain~ ~he electrical contact switche~
201 through 20~ for opening and clo~ing heating circuit~ 2~1 . ~ .
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~ 20 -~
1 through 2q4, switches 221 and 222 for opening and closing 2 electrically controlled valves 35 and 36, and contacts 225 for 3 sending signals to the multiposition valve actuator ~o. The 4 switching section can also contain the terminals 227 for temperature sensing devices (e g., thermocouples 26, 7~, ~7, 230, 6 231, and 232) as well as output display~ 240 and 2~1 showing the 7 status of the apparatus at any given point (e.g., current trap 8 ~eing used, temperature of oven, etc). The switGhing portion can 9 also contain power transformers and ac/dc power converters. The electrical and electronic components a~ well as the program logio ~ necessary to implem~nt the control scheme described belor~ under 12 "Operation of the Apparatus", are all well known in khe art.
14 Oper~tion of th~ App~r~tu~:
lS
16 Before running any experiment, the operator needs to determine the ~7 temperature intervals at which samples are desired, and the rate of 18 temperature increase in the oven. Thes2 parameters are th~n lg programmed into the logic section of the control portion. For example, the operator may desire to know what products are evolved 21 between 300C and 600C, with particular empha~is on the products 22 evolved during the 400C to 5aooc interval. Thus, for a heating 23 rate of 5C per minute ~tartin~ at 300C, a program might be entered 2~ as follows:
Temperature Range Send to Trapping Timer 26(C) Trap No. Time (min.) Interval (mins.) .
2~300 - 350 1 10 0 10 2~35~ - 400 2 10 ~0 - 20 3~430 - 445 5 3 ~6 - ~9 ' . . :. ' : . , ~ ~ . . .
, :
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7 This example is for demonstration purposes only, and it should be 8 observed tha~ any variety of temperature or time "slices~' can be 9 taken, limited only by the number of available traps and maximum temperature range of the oven. Addi~ionally, no~ all available ~1 traps need to be used. The program in this example is en~ered in 12 time units. Since the rate o~ heating i9 known, a particular time 13 can be closaly correlated to a particular temperature, so we can 14 talk interchangeably about ~the programmed time" or "the progra~med lS temperaturel~. Alternately, by sensing the temperature in the oven 16 and writing the program to switch traps only when particular 17 temperatures have been reached, a true "temperature pregra~" can be 18 entered. The former sys~em of programming in time intervals is 19 preferred since less equipment is needed and the program iR no less accurate since heating rates can be very closely controlled with 21 current technology.
23 The transfer lines are initially brought up to their operating 2~ temperature, which is the temperature at which no p~rolyzate is expected to condense. For the example described, thi~ includes ~6 bringing the heater block up to the transfer line operating 27 temperature as well. In the example, to preven~ condensation of ~a the heaviest pyrolyzate anticipated, a C~ hydrocarbon, the line 2~ operating temperature was 350C. The cooling ~hamber3 are filied with coolant and maintained at th~ trap coId te~perature. In the 31 example, the coola~t was liquid nitrogen and the trap cold 32 tempera~ure, i.e., the trapping temperatur~, wa~ appr~ximately ... ,.......... - ,, ; :
.
- ,. . .
. . .
1 -195C. The oven is brought up to the initial temperature at which 2 sample pyrolysis information is desired.
4 The trapping segu~n~e: During the trapping sequence, ths S pyrolyzate for each time/temperature interval is trapped in C sequential traps.
8 Once the steady state temperature o~ the syste~ has been reached, 9 the sample to be pyrolyzed is deposited in the sample holder and the sample holder inserted into the oven. The carrier gas is ll passed through the oven to carry pyrolyzate to the trap portion.
12 The carrier gas should have a boiling point below that of the trap 13 cold temperature so that no carrier gas is retained in the traps.
l~ In the example, the carrier gas i~ helium. A~ the temperature in lS the oven increases from the initial temper~ture to the second 16 programmed time/temperature, the pyrolyzate ts directed to th~
17 first trap, any hydrocarbons are condensed out in the trap and the 18 carrier gas exhausts through the analysis unit. After the time 19 interval for the first temperature range has passed (i.Q., once the second temperature has been reached), a signal is sent by the logis 2~ section to the switching section which in turn sends a signal to 22 the multiposition valve ~o redirect the ~low of pyrolyzate to the 23 next trap in the seguence. The heating in the oven continues and 2~ pyrolyzate is trapped in ~hat next trap, The proces~ of redirecting the ~low of pyrolyzate ~o sequen~ial trap~ and 26 continuing the heating continues until the ~inal temperature (time) 2~ is reached. At that point, the heating o~ the oven stop~, the flow 28 of carrier ga~ i3 stopped, and the detrapping sequence starts.
2g Th- d-trappi~q ~oquanc~: During detrapping, the "trapped" contents 3~ of each trap are ~equentially direc~ed to the analysi~ portion for 32 analysis.
3~ Th~ flow of sweep qas to the trap~ is initiated a~ter the trapping - , , .
,, , :
.- ~ . ~ .. . .
~ .. . . . .
2~7~
1 sequence has stopped and continues throughout the detrapping 2 sequence. The coolant to the first trap is drained from the 3 accompanying cooling chamber by opening the coolant drain valve ~or ~ that chamber. The coolant drain valve remains open a predetermined time, such time being slightly longer than the time required for 6 the coolant to gravity drain from ~he cooling chamber. At that 7 time the coolant drain valve is closed. Immediately a~ter the 8 coolant has drained from the trap, the trap is rapidly heated to a g temperature necessary to vaporize the pyrolyzate. In the example, a detrapping temperature of 300C wa~ used, and the trap was heated 11 from the cold temperature to the detrapping temperature (i.e., from 12 -195C to 300C) in approximately 2 minutes. The sweep gas carries 13 the pyrolyzate from the curren~ trap being detrapped to the ~ analysis portion where i~ is analyzed for composition and such lS other characteristics as may be desired. During ~he detrapping and 16 analysis of the first trap, the other traps remain at their cold 17 tèmperatures to retain their contents. A~ter the contents of the 18 first trap are analyzed the analysis unit sends a signal to the 19 control portion w~ich initiates the detrapping of the next trap.
Alternately the detrapping can be regulated by a timer, the time 21 intervals baing suf~iciently long to allow de~rapping and analysis 2~ of any given trap. Typically a time interval of 3 to 5 minute~ is 23 sufficient to detrap all of the pyrolyzate in a single trap.
2~ However, the analyqi3 time may vary ba~ed on the mean~ for analysis employed, and thus the length of time before the next sequential 26 trap can be heated may exceed the 3 to 5 minute detrapping time.
2~ The detrapping proceed~ a~ described abova for the ~irst trap, and 28 this sequence continues until all traps have been detrapped and 29 analyzed. Although in the preferred e~bodiment the traps are detrapped in the same sequence as product is trapped in them, there 3~ is no requirement that this order necessarily be followed.
32 Additionally, in the preferred embodiment the heating of a 33 particular trap stop~ once all of the pyxolyzate i~ that trap has 3~ been detrapped.
, ~ ~ .
~ .
2 ~
l Ge~erati~g th~ Pro~uot ~volu~io~ ourves:
2 once the analysis output has been recorded, processing of the 3 outpu~ can proceed. In the example and the preferred embodiment, ~ the GC output is stored on a digital computer. The data is then used to create the pyrolysis product evolution curves. A computer 6 program integra~es the GC peaks and provides a running total across 7 several GC runs. The current total is plotted against pyrolysis 8 temperature of the interval to provide the product evolution curve.
~ once the points have been plotted, any of a number of curve Pitting programs known in the art can be u~ed to ~it a curvs to these 1~ points and determine the ~irs~ derivative to said curv~. The 12 temperature of the maximum in the derivative curve can be further 13 used to determine the kinetic parameters oP the material of ~hQ
1~ original sample.
~6 In combining the separa~e GC analysis results, it is i~portant that 17 all chromatograms have the same response factor or that an external 18 standard is used and the results of each chroma~ogram are 19 normalized. GC results are qualitative and only meaninqful in relation to a reference standard. A test can be per~ormed on ~he 21 GC to determine if it has a constant r~sponse ~actor. If it does 22 not, each anàlysis for each detrapped pyrolyzate must be corrected 23 to relate to a single reference s~an~ard~ Thi~ can be accomplished 2~ by injecting a known reference into the GC colu~n with each 2S separate analysis. The results of each analysis can then be 2C normalized be~or~ combining. Alternately, the reference standard ~7 can be in~ectsd with the carrier ga~ ~o th~ traps, ~o that th~
28 standard i~ trapped along with the pyrolyzate. If th~ outputs for 29 thQ various analyses consistently show little or no variation and no normali2ation is require~, the referenc~ s~andard may be deleted 31 altogether.
33 One method of combining the GC analysis results i shown in FIG. ~
3~ which shows the cumulative fractio~ or conc2ntra~ion o~ one 3S particular compound as a function o~ temperature. With reference ~, .
, : .
, ~ :
- ~5 ~
1 to FIG. 6, ten "t~mperature slices~3 of a pyrolyzing sample were 2 taken between 280c and 6sooc. In thiæ exa~ple, the temperatur~
3 slices were not equal. The total Cl8 alkane in the sample must 4 first be determined so that fractions can be calculated. This is done by isolating the Cl8 alkane concentrations in the ten GC
6 analyses and calculating ~heir numerical su~. The Praction of C~8 7 contributed by each temperature slice is ~hen calculat~d by 8 dividinq each temperature slice~s Cla concentration by the total C~8 9 concentration. The cumulative fractions are then plotted against temperature, and a curve plotted through the points. A close ~1 approximation of the equation representing the curve plotted 12 through the points can be determined by any of several means well 13 known in the art. The resulting conversion v~ temperatur~ curve 1~ shows that ~or example approximately 24% of the Cl~ al~ane is ~5 generated between about 415C and 433C. It should be noted that 16 since each "tempera~ure slice~ of C~ alkane trapped covers a 17 temperature range, y~t the analysi~ only give~ on~ concentration 18 number for that range, a decision has to be ~ade what temperature 19 in the range to assign the concentration ~rom the analy~is to. In this example, the endpoint temperature of the range (or "slic~") 21 was used. The conversion units ~ay be expre~sed in mole fraction, ~2 total (cumulative) mass, or cumulative ma~s of produc~ as a 23 fraction of total sample weigh~. The conversion curva will be ~ called the "C vs T" curve in the following discussion.
26 Another method of displaying the data is to plot the derivative of ~7 the C vs T curve to obtain a rate of gen¢ration curve, d(C)/d(T~ vs 28 ~, where T i~ temperature. That is, the derivative of thQ curve of 29 FIG. 6 is taken to ob~ain a curv~ o~ th~ ~ype shown in FIG. 7.
Specifically, the steps are:
32 1) Plot the data points as de~cribed above for FIG. ~r 34 2) Plot a curve through the data point~, using co~puter ~ .
h 1 algorithm~ known in the art to obtain a mathematical 2 formula which closely approximates the curve when 3 plotted;
53) Use a computer algorithm known in the art to obtain the 6first derivative of the formula obtained in step 2; and 8 4) Plot the first derivative o~ the curve o~ step 2.
11 From the above description it is evident that the present invention 12 provides a method and apparatus for generating the pyrolysis 13 product temperature evolution curve for an organia compound, 1~ Although only specific embodiments o~ the present invention have ~5 been descri~-ed in de~ail, the invention is not limited thereto but 16 is meant to include all embodiments coming within the scope o~ the 1~ appended claims.