Hallo Experten
Wer kann mir (gerne auch ausführlich) den prozeß der Reformierung bzw. Konvertierung von Benzin zur Gewinnung von H2 erklären. Wer hat damit Beruflich zu tun, kennt Probleme oder Risiken. Oder weiss jemand eine gute Chemie-site die das gut erklärt. Also Ihr seht schon: Schreibt mir alles was Euch zum Thema einfällt. Das wäre Supernett.
Danke Chris
Hab zwar keine berufliche Erfahrung, aber folgendes zu bieten:
Reformieren
(von latein.: reformare = umgestalten, verbessern). Im chem. Sinne Bez. für einen Veredlungsschritt in der Petrochemie. Hierbei wandelt man therm. u./od. katalyt. bestimmte Erdöl-Produkte, insbes. Schwerbenzine u. sog. straight-run-Benzine (s. Benzin), in Aromaten u. Isoparaffine um. Zweck des R. als Raffinations-Verf. sind die Octan-Zahl-Erhöhung der Motorkraftstoffe u. die Gewinnung der BTX-Fraktion für die chem. Industrie. Während das Kracken hauptsächlich eine Spaltung größerer in kleinere Mol. bewirkt, finden beim R. an den Alkanen u. Cycloalkanen Umlagerungen, Isomerisierungen, Desalkylierungen, Cyclisationen, Dehydrierungen, Dehydrocyclisationen u. ä. Reaktionen statt. Die älteren therm. R.-Verf. (650 °C, Verweilzeiten von wenigen Zehntelsekunden) sind heute durch katalyt. Verf. verdrängt worden. Als Katalysator diente ursprünglich MoO3; heute bevorzugt man Pt-haltige sowie Bi- u. Multi-Edelmetall-Katalysatoren auf Molekularsieben bei Temp. von 490–540 °C, Drücken von 0,8–4 MPa u. unter H2-Partialdruck.
Gebräuchliche, z. T. in Einzelstichwörtern behandelte R.-Verf. sind: Platforming, Magnaforming, Rheniforming, Powerforming, Ultraforming u. IFP-Reforming. Heute weniger bedeutende od. gar nicht mehr praktizierte R.-Verf. sind: Catarolprozeß, Houdriforming, Hydroforming, Hyperforming, Isomerate, Isoplus, MHC-Prozeß, Penex, Rexforming, Sinclair-Baker-Kellogg- bzw. Udex-Verf., Unifining u. a. Über die beim R. anfallenden Nebenprodukte (Spaltgase mit Olefinen etc.) u. über die Einordnung der R.-Verf. innerhalb der Verfahrensschritte der Petrochemie s. Erdöl.
Lit.: Kirk-Othmer (4.) 4, 592–597; 5, 408 f.; 18, 448 ï Ullmann (4.) 10, 681–690; (5.) A 13, 496 f. ï Weissermel-Arpe (4.), S. 340 ff. ï Winnacker-Küchler (4.) 5, 94–104 ï s. a. Erdöl, Petrochemie.
E = F = I reforming
S reformado, reforming
Konvertierung
Im allg. Bez. für die Gleichgew.-Reaktion
CO + H2O <--> CO2 + H2,
die zur Gewinnung von Synthesegas für die NH3-Herst. (Lit. ) u. zur Entgiftung von Stadtgas ausgenutzt wird.
Lit.: 1 Winnacker-Küchler (4.) 2, 131–134.
E = F conversion
I conversione
S conversión
Quelle: Römpp Lexikon Chemie – Version 2.0, Stuttgart/New York: Georg Thieme Verlag 1999
Das folgende ist aus der "Ullmanns Encyclipedia of technical chemistry"
Dort gibt es noch ca. 10 weitere Stichworte die sich mit dem Reformieren und dem Konvertieren beschäftigen. Schau mal in eurer Bibliothek nach. Ein weiterer Vorteil des Ullmanns ist, das er eine Unmenge von Literaturangaben hat (viele Patente und Übersichtartikel!!!).
Oil, Oil Refining
3. Oil Refining Processes
3.4. Catalytic Reforming
3.4.1. Introduction
In the reforming processes, gasoline fractions (naphthas) with a low octane number are converted into a high-octane reformate, which is a major blending product for motor gasolines (® Motor Fuels - Catalytic Reformate.). Valuable byproducts are hydrogen and liquefied petroleum gas.
The naphtha feedstocks for reformers can be of straight-run or cracked origin and usually have octane numbers of only 35 – 65. Therefore these products are unsuitable for direct gasoline blending. In addition, the reformer feedstocks must be pretreated to adjust them to the required specifications (e.g., sulfur content, see Section 3.3. Hydrotreating).
With the development and introduction of noble metal catalysts at the beginning of the 1950s, the catalytic process displaced other (mainly thermal) reforming processes, because the catalytic conversion produces higher liquid yields — together with higher octane numbers — and hydrogen. Catalytic reforming is chiefly based on the catalytic conversion of normal paraffins and cycloparaffins into aromatics and isoparaffins.
The catalysts applied are either of the single metal platinum-on-alumina type, or bimetallic species where platinum is used in combination with a second metal, e.g., rhenium. The bimetallic catalysts have a better operational stability, but are more sensitive toward poisoning (e.g., by sulfur) or deficient regeneration. The catalyst metal is dispersed on the porous carrier material (alumina). The various commercial catalyst types contain 0.25 – 0.8 wt % platinum and up to 1 wt % of a halogen, usually chlorine. In these "bifunctional" catalysts the metal promotes hydrogenation and dehydrogenation reactions, while the chlorine catalyzes isomerization and cracking reactions.
The chemical reaction mechanisms of the catalytic reforming process can be characterized as follows :
Dehydrogenation of C6-Naphthenes to Aromatics. Example :
Conversion of methylcyclohexane into methylbenzene (toluene) with formation of 3 mol hydrogen per mole of converted hydrocarbon. The research octane numbers (RON) of methylcyclohexane and toluene are 75 and >100, respectively.
Dehydroisomerization of Alkyl-C5-Naphthenes to Aromatics. Example :
In the first step, methylcyclopentane is isomerized to cyclohexane (2a).
According to Equation (1), cyclohexane is then dehydrogenated in a second step to form benzene with formation of 3 mol hydrogen (2b).
The RONs of methylcyclopentane, cyclohexane, and benzene are 91, 83, and >100, respectively.
Dehydrocyclization of Paraffins to Aromatics. Example :
Normal octane is converted to 1,2-dimethylbenzene (o-xylene) under formation of 4 mol hydrogen. The RONs of these components are 0 and >100, respectively.
Hydrocracking of Paraffins and Naphthenes to Smaller Paraffin Molecules. Example :
Normal heptane is split into propane and normal butane under consumption of 1 mol hydrogen per mole of paraffin (2 mol hydrogen per mole of naphthene). This reaction does not affect the RON.
Isomerization of Normal Paraffins to Isoparaffins Example :
Conversion of normal pentane into isopentane. The respective RONs are 62 and 92.
Hydrogenation of Unsaturated Hydrocarbons. This reaction is also important because unsaturated hydrocarbons can act as coke precursors. Coke deposits would deactivate the catalyst.
The dehydrogenation reactions (Eq. 1) and (Eq. 3) are both endothermic and require appropriate heat input (i.e., 32 and 38 kJ/mol, respectively, at reforming temperature level). However, because the reaction in Equation (3) is considerably slower than that for Equation (1), higher temperatures must be applied to achieve the desired reaction rate. The isomerization reactions ( Eq. 2a) and (Eq. 5) are thermally almost neutral, whereas the hydrocracking reaction (Eq. 4) is exothermic (ca. –16 kJ/mol at reforming temperature).
Dehydrogenating cyclization of paraffins (Eq. 3) and dehydrogenation of naphthenes (Eqs. 1 and 2b) are the largest contributers to octane quality improvement. The thermodynamic equilibria of these reactions are shifted to the side of the reaction products at low hydrogen partial pressures and a reforming temperature level of ca. 500 °C. The ring-enlarging isomerization of alkyl-C5-naphthenes to C6-naphthenes (Eq. 2a) involves a decrease in the octane number, but this effect is more than compensated by the subsequent aromatization step (Eq. 2b). The theoretically attainable equilibrium compositions of the isomerization of n- to isoparaffins according to Equation (5) are not be reached at the usual reforming conditions.
Hydrocracking (Eq. 4) is favored at high temperatures and high hydrogen partial pressures. These reactions are usually undesirable in catalytic reforming, because they consume hydrogen and produce gaseous hydrocarbons from liquid ones, thereby decreasing the yield of liquid reformate. This influence is illustrated in Figure (17), where reformate yields are related to reactor pressure at various octane levels.
At a given pressure, the octane number can be increased by applying higher reactor temperatures ; this, however, results in yield loss by increased hydrocracking.
As a result, catalytic reformers should generally be operated at low pressure to achieve high liquid yields. However, the hydrogen partial pressure must be high enough to avoid the formation of unsaturated compounds which may polymerize and cause increased coke deposition on the catalyst and hence its deactivation.
Catalytic reformers are usually available in three different versions, namely the semiregenerative, the fully-regenerative, and the continuously-regenerative reformer. Common to each process type is a reactor section and a product workup section. The fully- and continuously-regenerative process versions are also equipped with a catalyst regeneration section.
Various licensed reforming processes are described in [19] and [20]. Examples are Platforming (UOP) , Magnaforming (Engelhard), Catalytic Reforming (IFP), Powerforming (Exxon), and Rheniforming (Chevron).
3.4.2. Semiregenerative Reformer
This conventional catalytic reforming process is shown in Figure (18). The plant has three or four reactors that are arranged side by side at ground level. After addition of hydrogen-rich recycle gas to the naphtha feed, the mixture is heated up in the charge – product heat exchanger (a) and brought to reaction temperature in the charge heater (b). The vaporized feed is then successively passed through the catalyst beds of the reactors (c, e, g). Between the reactors, makeup heat is provided in the intermediate heaters (d, f ) to compensate for heat losses after each (endothermic) reaction step. The effluent from the last reactor is cooled in the heat exchanger and aftercooler (i). It is then separated in the product separator (h) into hydrogen-rich gas and liquid reaction product.
The H2 gas is recompressed in the recycle gas compressor (k) and part is returned to the feed stream ; the net H2 "make gas" can be supplied to hydrogen-consuming units, such as hydrotreaters and hydrodesulfurizers.
The liquid reactor product is fractionated in a stabilizer column ( j) to separate the C4 and lighter hydrocarbons from the reformate. The LPG stream (C3 and C4) is usually split in the LPG recovery plant for propane and butane production ; (® Liquefied Petroleum Gas - 3. Production and Processing) ; the stabilized reformate can be used directly for gasoline blending or is fractionated further into light and heavy gasoline components before blending.
The catalyst is gradually deactivated during the operation period ; this can be counteracted by stepwise increase in the reactor temperatures to keep the product quality at the desired level. Once the recommended ultimate temperature is reached, the plant has to be shut down and the catalyst is regenerated. This procedure is usually performed in three successive steps, i.e., carbon burn-off, metal reduction, and metal redispersion. The plant is then restarted for its next operation period. When the operation cycles between regenerations become unacceptably short, the catalyst inventory is replaced by a new batch. The spent catalyst batch is worked up for metal recovery (platinum, rhenium).
3.4.3. Fully-Regenerative Reformer
The fully-regenerative, or cyclic, reforming processes have been devised to increase the on-stream time of the reforming plants by introducing the "swing reactor" principle. A typical example is the Power-forming process [21] . In a system of four reforming reactors, three reactors are on-stream, in the fourth the catalyst is regenerated. After completion of the regeneration, this reactor is brought on-stream, while another reactor is switched to regeneration. The cyclic process requires a complex switch system with automatically operated valves. However, with this method a continuity of operation at high reforming severities can be maintained over a long period, with catalyst lifetimes of up to five years.
3.4.4. Continuously-Regenerative Reformer
Special moving-bed techniques were developed for reforming units with continuous catalyst regeneration. The IFP catalytic reforming process which employs a conventional side-by-side arrangement of reactors uses a system of lift pots to transport the moving catalyst in portions from the bottom of a reactor to the top section of the next reactor [22] , [23] . The catalyst portions obtained from the last reactor are lifted to the regenerator, where carbon burn-off and reconditioning of the catalyst take place. The catalyst is then reinjected into the first reactor bed.
A sophisticated catalyst moving-bed system was realized in the UOP Platforming process as illustrated in Figure (19) [24] , [25] . The reactors are arranged in a "stacked" construction. The catalyst trickles through the system from the top of the first reactor to the bottom of the third reactor, where it is collected and lifted in portions to the regenerator section.
"Sluices" are incorporated in the catalyst transport system, i.e., the spent catalyst from the third reactor is depressurized, freed from hydrogen, and then lifted in an inert gas stream to the regenerator ; in turn, the regenerated and reconditioned catalyst has to be flushed free of combustion gases and pressurized with hydrogen before it is reinjected to the first reactor.
With continuous catalyst reactivation severe reforming conditions can be applied to achieve research octane numbers (RON) of well above 100 in the reformate product. Moreover, operation at low reaction pressures of 7 – 10 bar results in favorable yield structures, i.e., high reformate and hydrogen quantities at low gas production.
Gandalf
