Catalytic reforming

Catalytic reforming ( remodel from Latin reformare = ) is a refinery process in which alkanes and cycloalkanes from naphtha from various sources into aromatic compounds and branched alkanes are converted, with the aim of octane increase. The main liquid product, the so-called reformate mainly consists of benzene, toluene, xylenes, C9 and C10/C11-Aromaten and branched and linear alkane compounds.

An important by-product is hydrogen, which is required among other things, in desulfurization and hydrocracking processes. By cracking gaseous hydrocarbons, methane, ethane, propane and butane are produced.

• 5.1 reformate fractionation

• 6.1 AROMAX
• 6.2 Fully - regenerative reformer

History

The first catalytic reforming process was developed in the 1930s by the company Kellog, of which from 1939 seven plants were built and operated. The method used a molybdenum-containing catalyst but low selectivities and lifetimes had.

In the 1940s Vladimir Haensel developed by Universal Oil Products (UOP ), a more stable and enable reforming catalyst based on platinum on alumina. Already in the 1940s, was the first commercial Platformer, a body established by UOP composition of platinum and reformers built. The process displaced due to the higher life of the catalyst, the Kellog method.

In the aftermath of the catalyst developed by Haensel was further developed. In particular, the use of tin (Sn), and rhenium (Re) as co-catalysts increase the service life and the activity. The focus of procedural development was in the area of ​​catalyst regeneration. The installed until the early 1970s, process type is called Semi Regenerative Catalytic Reformer called (SRR ). Here are three reactors with the respective heaters connected in series ( see Figure 1).

Today the common process variation is the so-called continuous regenerative reforming Catalyst (CCR ), in which the four moving bed reactors are connected in series. The catalyst runs through all four reactors and is then regenerated continuously.

Process

The reforming takes place at temperatures of about 500 ° C and, depending on the type of process at pressures of 30 bar in the semi- regenerative method, or 3.5 to about 8 bar in the process with continuous catalyst regeneration from. Are being introduced bifunctional catalysts such as platinum -tin and platinum - rhenium on chlorinated alumina or zeolites.

The ongoing reactions are endothermic. The reactor outlet temperature can thus drop by 100K. Therefore, several reactors with intermediate heater, usually installed in the form of gas-fired furnaces to compensate for the temperature loss and to achieve an adequate degree of conversion.

By dehydration and polymerization reactions is produced on the catalyst coke, which impairs the activity of the catalyst by physical blockage of the active sites. Burning off the coke during the semi- regerativern method at intervals of 6 to 24 months, while the catalyst remains in the reactor. Subsequently, a so-called oxychlorination reaction, wherein the acid functionality is restored. The reactor pressure of a semi- regenerative reformer is approximately 30 bar. The yields are inferior to those of a continuous regenerative reformer, since the high pressure of hydrogen to re- hydrogenation of aromatics leads.

In the process of continuous regeneration, coke formation takes place due to the lower hydrogen partial pressures much faster. To regenerate the koksbeladene catalyst is discharged at the bottom of the last reactor and transported from the type fluidized bed reactor via a gas - lift system to the head of a so-called regenerator. There, the catalyst is burned off gently until the coke in different zones and then he will oxychlorinated. Then, the backfeed is performed by a gas - lift system on the bottom of the regenerator to the top of the first reactor.

UOP the system, the four reactors are stacked (stacked ). This catalyst running alone by gravity from the top of the first reactor to the bottom of the fourth reactor, Axens uses a horizontal position, similar to the semi- regenerative processes. The catalyst is transported between the reactors by a lift system from the bottom of each reactor to the top of the next.

A lower hydrogen partial pressure increases the coke formation, but improved yield and quality of the reformate by dehydrogenation reactions increased with increased hydrogen production and higher aromatics. The quality of the hydrogen gas is also improving because it contains less cracking products such as methane or ethane. To maintain the acid function, small amounts of a chlorinated hydrocarbon are fed into use, which are hydrogenated under the prevailing process conditions immediately to HCl and the corresponding hydrocarbon. Chloride losses, caused for example by nitrogen and water entry be compensated as a result.

The typical equipment of a catalytic reformer are

• Feed pump
• Feeding in the recycle gas
• Heat exchangers (for a reactor outlet of the last reactor ), a so-called feed - effluent -Heat Exchanger.
• Furnace / reactor combination (3-4 times), then re- heat exchanger
• Product cooler
• High pressure separator (SRR ), head over Recycle and hydrogen gas Hydrogen-rich gas is fed cleaned again in the hydrogen network of the refinery
• Recycle gas is conveyed to the recycle gas compressor back to the use of
• Unstabilized reformate runs to the stabilizer ( pressure distillation at ~ 8-15 bar)

Reactions

On the metal sites of the catalyst preferably the Hydrierungs-/Dehydrierungsreaktionen run, while the acid sites catalyze isomerization and cyclization reactions. An undesired side reaction is the cracking of alkanes in niedrigkettige products, and dealkylation reactions

Typical reactions in reforming are

Reactants

The feedstock of a reformer can come from various sources. Major source is the distillation of crude oil, which provides so-called " straight-run " naphtha, an unstabilized, i.e. propane and butane containing hydrocarbon mixture having a boiling range of circa 25 to 135 /180 ° C. The final boiling point is selected depending on the process conditions for the reformer. This naphtha still contaminated with nitrogen and sulfur compounds.

Hydrotreating

Sulfur and nitrogen compounds are the catalyst poisons, which must be removed. A common procedure is therefore to be desulfurized the virgin naphtha directly through a hydrotreater or to denitrification. The hydrogen sulfide formed under the process conditions of the reformer ( H2S) would react with the metals in the reforming catalyst and thereby deactivate the catalyst. A typical reformer feed requires a sulfur content of about 0.5 ppm. In the reformers formed ammonia ( NH3) reacts with Cl -to ammonium chloride ( NH4Cl) and destroys the acidic function. Therefore, nitrogen compounds must also be largely removed.

Stabilizer

After the naphtha hydrotreater is stabilized, that is, butane, propane, ethane, methane, hydrogen sulfide, and the resulting product in the presence of water and the residual hydrogen is removed by distillation in a stabilizer. Propane and butane fall as yet H2S -containing LPG (liquefied petroleum gas, LPG ) to. The lighter components are released into the still unentschwefelte refinery gas. Water collects in a pocket of water head reflux tank. Water is a catalyst poison, since it washes out the chloride.

The final boiling point of this stabilized, desulfurized naphtha and thus the proportion of heavy Reformatkomponenten ( C9/C10/C11 ) is already defined in the distillation of crude oil, but should not exceed about 180 ° C, otherwise the final boiling point of the reformate increases significantly above 210 ° C and ensure compliance with the gasoline Siedeendespezifikation is not guaranteed. LPG and light petroleum crude oil already to hydrogenate at this point avoids the installation of additional desulphurisation plants for LPG or light petroleum.

Reformer feed prefractionation

The initial boiling point of the stabilized naphtha must be set after stabilization by redistillation, as pentanes (C5) do not contribute to hydrogen production in naphtha to aromatics and. n- pentane would indeed isomerized in large part to i -pentane, but provides only a small contribution to the octane boosting. In addition, pentanes lead to increased coke formation by cracking. For these reasons, the pentanes are removed from the reformer feed.

Hexane (C6), in particular n-hexane, methylcyclopentane and cyclohexane are converted in the reformer mainly to benzene ( benzene -called precursors). Together with the already existing in the straight-run naphtha, benzene would result in the reformate benzene content of about 8 wt - % to 12 % by weight. Refineries usually distilled therefore reach from hexanes and benzene levels of about 2% to 4 %. Refineries, which have a benzene extraction, pursue a benzene maximization strategy. Unsuitable iso -hexanes, however, also distilled off.

Heptane (C7) produce sufficient hydrogen. If not reflect glare from technical reasons ( petrol) one is dependent on C7 shares in the reformate, increasingly wants to produce xylenes and has enough reformer feed is available, then you cut the heptanes from the reformer feed.

One can thus distinguish three basic types of reformer feed:

• Pentane / i -hexane -reduced naphtha (benzene production desired boiling range: 70 - 135/180 ° C)
• C6 -reduced naphtha ( default feed, boiling range: 85 - 135/180 ° C)
• C7 -reduced naphtha ( Xylolproduktion preferred boiling range: 115 - 135/180 ° C).

The distilled desulfurized light gasoline can be used depending on the quality as the gasoline component or steam cracker feed.

Other Naphthaquellen

In addition to the straight-run naphtha, distillation of crude oil, there are other Naphthaquellen in the refinery, the non -straight- run naphtha. Including count hydrocracker heavy naphtha, which must be desulfurized optionally the coker heavy naphtha or FCC naphtha, it must be hydrogenated to remove sulfur and olefins. If necessary, the boiling point and the final boiling point is already set in the corresponding systems, hydrogenation can be carried along with the straight-run naphtha under certain circumstances.

The quality of the reformer feed is determined by the so-called analysis PIONA (paraffins, isomers, olefins, naphthenes, aromatics ). This is a gas chromatographic determination of the individual components in mass fraction ( wt - %).

Products

The products of the catalytic reformer, the following components can be distinguished

• Refinery gas ( sulfur free)
• LPG ( sulfur free)
• Reformat: depending on process control: boiling range ~ 25-155/210 ° C, ie C5 - C11 compounds of the group: n-and i -alkanes, aromatic hydrocarbons [ C6 ! ], About 0.1 % to 0.2 % of olefins, such as 1% to 2 % cycloalkanes.

In the reformer process caused by cracking and Deakylierung also groups of substances which were not originally included in the reformer feed or only to a very minor extent. Even when the feed contains only C8 compounds, the reformate a not inconsiderable proportion of n -and i- pentane, further benzene and toluene, and hexanes, and heptanes.

Reformate fractionation

The direct blending of " full-range reformate " into motor gasoline is not common in Europe, there is already a content of 2 % to 4 % benzene in the reformate quickly leads to the crossing of benzene specification. The reformate is usually worked up by distillation to remove the benzene. A sensible solution is a so-called 3 -cut splitter ( distillation column with overhead and bottom product, as well as a side draw ). Is the head, similarly to the reformer feed distillation, a section with pentane and i- Hexanverbindungen and small amounts of benzene (about 1 vol - % to 1.5 vol - % in the product ) are distilled off, so-called light reformate, used in motor gasoline or steam crackers.

In the side draw a so-called Heartcut ( heart cut ) is withdrawn containing the major amount of benzene and hexanes and lighter C7 alkanes. The heartcut is sold. The bottom product (C7 - C11) also contains very little benzene and can be used directly as a gasoline component. Some refineries prepare the bottoms to further distill and C7 ( C7 - toluene and non-aromatics ), C8 ( xylenes, very few C8 non-aromatic ) and C9/C10/C11-Verbindungen (almost exclusively aromatics ) apart. C7 and C9/C10/C11 run into motor gasoline that is sold or a xylene mixture Xyloltrennung (eg PAREX ) supplied.

Reformer special forms

AROMAX

Aromax is a special reformer to process a C6/C7-Naphthaschnittes. High conversion rates of C6 - and C7 -alkanes, high yields are achieved in the benzene and toluene, the H2 generation rate is also excellent.

Fully - regenerative reformer

Works as an SRR, it is a fourth, so-called swing reactor, the cyclic function is performed by the other when the latter is regenerated off-line. This must this so-called Powerformer (Exxon - name) every six to 24 months will be worn, but can be operated five years without stopping. However, this litigation requires a complicated system of engine valves with appropriate switching logic.

View

The reduction of aromatic content in gasoline from 2005 by the European Auto / Oil Programme (Auto Oil 2, short AOP II) of 42 vol - % to 35% by volume presented in the past, a challenge for the operation of a reformer dar. a method which produces a product having an aromatics content of about 65% does not fit into the plant 's portfolio.

On the other hand, the hydrogen production for many refineries is essential. Many producers have then taken "negative" reformer margins into account, produces more gasoline and exports the surplus to overseas (USA). With decreasing gasoline demand in Europe and the USA is this " loophole" but no longer available. Simultaneously, the hydrogen demand continues to increase, for example by reducing the sulfur content in fuel oil from 1000 to 50 ppm.

The producers responded / respond with three strategies

• Installation of expensive hydrogen production (steam reforming), stopping the reformer and throughput reduction, sale of naphtha ( steam cracker feed).

• Removal of aromatic compounds from the gasoline pool, through the sale of pure toluene or xylene,
• Production of benzene and xylenes from toluene ( transalkylation )

• Decommissioning of entire refineries, especially FCC refineries that produce a lot of fuel.