Reforming processes

A new generation of bifunctional catalysts was introduced in 1967. The catalyst containing rhenium in addition to platinum provides greater stability.In 1975, the process using a catalyst containing platinum and iridium was commercialized. These catalysts are called bimetallic catalysts. The bimettillic catalysts are typically 3 to 4 times more active than the all-platinum catalyst. A bimetallic catalyst with rhenium typically contains about 0.3% platinum and 0.3% rhenium. The reasons for the effectiveness of these bimetallic catalysts are beyond the scope of this volume and the readers should refer to the appropriate monographs or reviews.  

All reforming processes use fixed bed reactors in a series (usually three). Fig. 4.27 shows the process flow diagram of a typical reforming process. The feed mixed with recycle hydrogen is heated to the reaction temperature (about 750 K) in the first heater and passes into the first reactor. Since the major reaction occurring in the first reactor is the most endothermic of the reactions, dehydrogenation of cyclohexanes to aroma- 

Since dehydrogenation and dehydrocyclization are the most important for the octane number gain, operation conditions favoring these reactions are selected. Increasing the reaction temperature favors the thermodynamics, but accelerates the hydrocracking reactions, leading to a loss in yield. 

High pressure is harmful to the thermodynamics, but affords better selectivity. Thus a temperature of 770 — 820 K and pressure of 3000 kPa are used for the operation. The molar ratio hydrogen to the hydrocarbon ratio is another important variable. A reduction in the ratio increases the rate of coke make, but enhances dehydrogenation and inhibits hydrocracking. A ratio of 10 1 to 3 1 is employed. 

The liquid product, commonly known as reformate, consists essentially of Cs through about Cio hydrocarbons. Compared to the feedstocks, there is a substantial increase in aromatic content (60 — 70 wt%) at the expense of naphthenes. The gaseous product consists of hydrogen and Ci — C4 hydrocarbons with a hydrogen concentration of commonly 60 — 90 mole percent. 

KINPTR is an overall process model thus it simulates all important aspects of the process which affect performance. In order to lay a foundation for upcoming discussions related to KINPTR development, the important aspects of naphtha reforming—chemistry, catalysis, and reactor/hardware design—will be summarized. More extensive reviews are available in the literature (1-3). 

0 Weight of aromatic produced divided by weight of paraffin converted at 783 K. 

An important part of the model development was first defining a set of lumped chemical species from the 300 identified species and then defining 

Although the reaction classes discussed earlier are sufficient to describe the hydrocarbon conversion kinetics, an understanding of the elementary reaction sequence is needed to describe catalyst deactivation. Several of the overall reactions require formation of olefinic intermediates in their elementary reaction sequence. Ultimately, these olefinic intermediates lead to coke formation and subsequent catalyst deactivation. For example, the ring closure reaction 

a normal paraffin is converted to an isoparaffin first by dehydrogenation to a straight-chain olefin, then by rearrangement to form an isoolefin, and by hydrogenation to an isoparaffin. 

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The modern reforming process operates with continuous regeneration of the catalyst, at low pressure (2 to 5 bar) and high temperature (510-530°C). 

Some of ihe carbon monoxide and hydrogen produced in ihe steam-naphtha reforming process react to form methane ... 

Natural gas is by far the preferred source of hydrogen. It has been cheap, and its use is more energy efficient than that of other hydrocarbons. The reforming process that is used to produce hydrogen from natural gas is highly developed, environmental controls are simple, and the capital investment is lower than that for any other method. Comparisons of the total energy consumption (fuel and synthesis gas), based on advanced technologies, have been discussed elsewhere (102). 

Mixtures of CO—H2 produced from hydrocarbons, as shown in the first two of these reactions, ate called synthesis gas. Synthesis gas is a commercial intermediate from which a wide variety of chemicals are produced. A principal, and frequendy the only source of hydrogen used in refineries is a by-product of the catalytic reforming process for making octane-contributing components for gasoline (see Gasoline and OTHER MOTOR fuels), eg. 

These gases are then fed to the water gas converter as in the steam-reforming process, after which they are compressed to ca 20.3 MPa (ca 200 atm) for processing in the catalytic ammonia converter. 

Steam Reforming Processes. In the steam reforming process, light hydrocarbon feedstocks (qv), such as natural gas, Hquefied petroleum gas, and naphtha, or in some cases heavier distillate oils are purified of sulfur compounds (see Sulfurremoval and recovery). These then react with steam in the presence of a nickel-containing catalyst to produce a mixture of hydrogen, methane, and carbon oxides. Essentially total decomposition of compounds containing more than one carbon atom per molecule is obtained (see Ammonia Hydrogen Petroleum). 

Several significant reforming processes are ia use (37,38). These iaclude Powerforming (Exxon), Ultraforming (Standard Oil Co.), Rheniforruing... 

The principal chemical uses of BTX are illustrated in Figure 1 and Hsted in Table 1 (2). A very wide range of consumer products from solvents to fibers, films, and plastics are based on BTX. The consumption of BTX is approximately in the proportions of 67 5 28, respectively. However, no BTX process gives BTX in these proportions. The economic value of benzene and xylenes (especially -xylene) is normally higher than that of toluene. Because of this, processes that convert toluene to benzene by hydrodealkylation (3) and disproportionate toluene to benzene and xylenes (4) have been commercialized. In addition, reforming processes that emphasize production of either benzene or -xylene [106 2-3] have been described (5). Since these are not classified as BTX processes they are not discussed in detail here. 

The catalyst is then transferred back to the first process reactor and is reheated to the reforming process temperature at the reactor inlet using a flow of hydrogen-rich process recycle gas, thereby achieving reduction of the platinum to a catalyticaUy active state. 

Since the reforaiing of CH4 produces 1 mole of CO for each 2 moles of H2, the dominant heat effect in the reduction process is the endothermic reduction by hydrogen. However, since the reforming process is canied out with ah as the source of oxygen, the heat content of the nitrogen component is a drermal reservoir for die overall reduction process. 

Plants have now been installed by some manufacturers to produce ethylbenzene via catalytic reforming processes. The reforming process is one which converts aliphatic hydrocarbons into a mixture of aromatic hydrocarbons. This may be subsequently fractionated to give benzene, toluene and a xylene fraction from which ethylbenzene may be obtained. 

A catalytic reforming process produces similar products. The relative amounts may differ, however, depending on the catalyst selectivity and process conditions, the main product, of course, is a high octane C, -1- gasoline fraction. 

Powerforming is basically a conversion process in which catalytically promoted chemical reactions convert low octane feed components into high octane products. The key to a good reforming process is a highly selective dual-function catalyst. The dual nature of this catalyst relates to the two separate catalyst functions atomically dispersed platinum to provide... 

Powerforming is a version of the platinum reforming process. Basically there are two types of unit semi-regenerative and cyclic. The choice of unit and the exact process conditions used will depend to a large extent on the particular application. However, certain generalizations regarding each of the two types can be made. 

By 1950 a reforming process was introduced using a catalyst to improve the yield loline components while minimizing the formation of unwanted material. In catalytic as in thermal reforming, a naphtha-type material serves as the feedstock, but the reactions are carried out in the presence of... 

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