Process for the recovery of pure aromatics from reforming gasoline and apparatus for carrying out this process

The invention relates to a process for the production of pure aromatics from reformed gasoline. The invention further relates to a device for performing the method. - In reformate is an aromatics fuel, which is produced by reforming, particularly catalytic reforming of crude oil fractions. When reforming take place on the contained in the crude oil or crude oil alkanes and cycloalkanes isomerizations, rearrangements, cyclizations, dehydrogenation and similar reactions. In catalytic reforming produced aromatics reformate is an important starting material for the production of aromatics is. Aromatics, especially benzene, toluene, xylenes and ethylbenzene, are important starting materials for the chemical industry, mainly for the production of plastics and synthetic fibers. Moreover aromatics are used as octane booster in gasoline fuel. Due to the increasing needs of the chemical industry of aromatics, are aligned, the reaction conditions and the catalyst used to a high aromatics in catalytic reforming of crude oil fractions. However, this falls at the same time also a higher proportion of unsaturated non-aromatics, especially olefins, to. The chemical industry, however, requires first and foremost pure aromatics, ie aromatics that have the least possible contamination of unsaturated non-aromatics. These impurities having unsaturated non-aromatics can hitherto only consuming separated by physical and chemical separation processes of the aromatics and is generally not possible to complete removal of the non-aromatics. As a measure of the purity of the aromatics, especially for pure benzene, and thus a measure of the contamination with unsaturated non-aromatics of the bromine index and the acid color index are (Acid Wash Color). According to the requirements of the chemical industry, the bromine index of pure benzene should not exceed the limit of 20 and is the acid color index does not exceed the limit of Figure 1.

In the method known from practice for the separation of aromatics, the aromatic-containing mixtures of an extractive distillation or a liquid-liquid extraction are first subjected. In order to achieve the above-mentioned purity limits, the aromatic fractions obtained during the extraction, however, must be post-consuming. In general, a chemical after-treatment is carried out, is washed by using either concentrated sulfuric acid or the fraction is treated with bleaching earth. Both chemical treatment processes are complex and expensive. The obtained in the sulfuric acid wash sludge must be disposed of only consuming and costly. The reaction with bleaching earth takes place at higher temperatures and leads to the formation of polymers that adhere to the bleaching earth. At the same time formed oligomers of unsaturated olefinic non-aromatics, which require a relatively high acid color number. Following the clay treatment, therefore, a complicated separation by distillation of pure aromatics from non-aromatics is the required verusacht high costs.

In contrast, the invention, the technical problem of specifying a method of the type mentioned, can be obtained with the aromatic high purity, which in relation to the required by the industry purity requirements, particularly bromine index and acid color index, meet all the requirements and the method distinguishes besides reliability and simplicity and low cost. The invention is also the technical problem of specifying an apparatus for carrying out this process.

To solve this technical problem, the invention provides a process for production of pure aromatics from reformed gasoline, wherein the reformed gasoline is selectively hydrogenated in a first process step, while the hydrogenation conditions are set so as to be hydrogenated substantially non-aromatics, especially olefins, diolefins and triolefins. and wherein subsequently the selectively hydrogenated and aromatics products from the first process stage by extractive distillation and / or liquid-liquid extraction in aromatics and non-aromatics can be separated in a second process stage.

Reformed means within the scope of the invention also reformatbenzinhaltige mixtures or Reformatschnitte or distillation cuts from reformed.

The invention is based on the finding that highly by combining the selective hydrogenation of unsaturated non-aromatics in the reformate, especially olefins, diolefins and triolefins one hand and the Extraktivdesillation and / or liquid-liquid extraction of the product of the hydrogenation on the other hand, aromatics high purity can be obtained. The invention is also based on the recognition that in the initially described, known from practice extraction process for obtaining pure aromatics, the high acid color number of the extraction product is particularly caused by the olefins, and already at very low diolefin high acid color index is effected. In particular, it was found that especially C₆-Cyclodiene And C₆Dienes and C₆Trienes require a high acid color number. This is especially true for those of the olefins mentioned, whose boiling point is near the boiling point of benzene and are therefore difficult to separate from benzene. According to the invention, in particular, these olefins are selectively hydrogenated upstream hydrogenation in the extraction stage. The inventive combination of selective and downstream extractive distillation and / or liquid-liquid extraction aromatics are obtained in which the bromine index is below 20 and the acid color index is below. 1 In this respect the pure aromatics obtained by the inventive process are sufficient with respect to the bromine acceptance and the acid color index all the requirements of the chemical industry. The method is both inexpensive and cost-effective. Therefore, considerable advantages are achieved over the methods known from practice.

According to a preferred embodiment of the method according to the invention, which in the context of the invention of particular importance, a Reformatschnitt is used as reformed gasoline which contains, as the aromatic portion substantially benzene. To produce this Reformatschnittes or distillation section, the reformate is prior to the selective hydrogenation first subjected to a fractional distillation so that the Reformatschnitt thus obtained contains substantially only the aromatics benzene. This embodiment of the method according to the invention is distinguished by the advantage that on the one hand a Entbenzolung of Reformatbenzins is achieved and on the other hand at the same time pure benzene can be recovered, which is the chemical industry of considerable importance. The Entbenzolung of Reformatbenzinen, which are further processed into fuels, is important for health reasons and to minimize the benzene content in gasoline is demanded increasingly. - According to a further preferred embodiment of the invention is as a reformed Reformatschnitt with aromatics of a selected carbon number C_x or with aromatics more selected carbon numbers C_x, C_y ... Used. Such Reformatschnitt or distillation cut is obtained by fractional distillation from reformate, wherein aromatics other carbon numbers are separated by distillation substantially. According to a preferred embodiment of the Reformatschnitt contains only aromatic carbon number, for example, C₆- Or C_8thAromatics. According to another preferred embodiment of the method of Reformatschnitt contains aromatics with two or three carbon numbers, wherein the boiling points of these aromatics are preferably in the boiling range of benzene, toluene or xylenes. The embodiments of the method according to claims 2 and 3 characterized by the advantage that particularly pure aromatics are recoverable in respect of the bromine index and acid color number. Has proven particularly useful embodiment of the method according to the invention, in which is hydrogenated in the first step with nickel or palladium on a support material as hydrogenation. Preferably nickel or palladium are used as the hydrogenation catalyst on an alumina support. Within the scope of the invention but can also hydrogenation of different composition are used. The hydrogenation conditions for the selective hydrogenation can be adjusted depending on the desired hydrogenation reaction and depending on the desired hydrogenation conversion. It is within the skill of a professional, these conditions, such as pressure, temperature, catalyst composition, hydrogen / hydrocarbon ratio and throughput and bed volume in the hydrogenation reactor adjust accordingly. Preferably, the selective hydrogenation is carried out, that in particular the diolefins and triolefins are fully hydrogenated. According to a preferred embodiment of the invention the hydrogenation conditions are adjusted such that conjugated diolefins and triolefins are fully hydrogenated. Preferably, in the context of selective hydrogenation C₆Dienes and C₆-trienes, And C₆-Triolefine Whose boiling point is close to the boiling point of benzene and are therefore difficult to separate from benzene, preferably fully hydrogenated.

After the hydrogenation, gaseous components are discharged from the hydrogenation reactor and the liquid, the selectively hydrogenated and aromatic hydrocarbons are fed with still dissolved residual gases of the extractive distillation and / or liquid-liquid extraction. In the extractive distillation and liquid-liquid extraction is usually carried out with a selective solvent as the extraction agent, to be separated with the insulating material of the other substances. As part of the process of the invention, the aromatics are dissolved in the solvent used selectively and, with this, the extract, while the non-aromatics are deducted from the raffinate. Has proven particularly useful embodiment of the method according to the invention, wherein the extractive distillation and / or liquid-liquid extraction with a selective solvent of the group N-formyl, N-methylpyrrolidone, sulfolane, ethylene glycol or ethylene glycol derivative is carried out. According to a preferred embodiment of the invention an N-substituted morpholine with 1 to 8 carbon atoms in the substituent is used as selective solvent. According to another preferred embodiment of the method according to the invention alkanediols having 2 to 5 carbon atoms and / or their monoalkyl and / or dialkyl ether are used as selective solvent. It is also within the scope of the invention to use mixtures of the solvents mentioned as a selective solvent. Incidentally, other solvents can be used which are suitable as a selective solvent for the separation of aromatics under the extractions. In addition, solvent / water mixtures may be used.

It is within the scope of the invention, that mixtures of the selectively hydrogenated Reformatbentzin and other hydrogenated aromatic-containing raw products and / or mixtures of these distillation cuts crude products are used in the second process stage, in which the extraction is carried out.

Expediently be separated after the extractive distillation and / or liquid-liquid extraction, the pure aromatics by distillation from the selective solvent.

The invention is explained in more detail, reference being made embodiment drawing depicting. Show it<dl id="dl0001" compact="compact"><dt>Fig. 1</dt><dd>a device for performing the method according to the invention, </dd><dt>FIG. 2</dt><dd>a diagram of the further discussed below in Embodiments 1 and 2. FIG.</dd></dl>

In the following, the inventive method is illustrated by the apparatus for carrying out the method illustrated in FIG. 1. Fig. 1 shows the device for performing the method according to the invention with a hydrogenation reactor 1 and a downstream extraction means 2. The hydrogenation reactor 1 has a first feed line 3 for supplying reformed gasoline to. In the exemplary embodiment is a supplied by fractional distillation from reformate obtained Reformatschnitt through the feed line 3 the hydrogenation reactor. 1 The hydrogenation reactor 1 has a second supply line 4 for the supply of hydrogen. Supply of hydrogen in the invention comprises also the supply of a hydrogen-rich gas. The hydrogenation reactor 1 further includes a fixed bed of a hydrogenation catalyst. Preferably, and in the exemplary embodiment made of nickel or palladium catalysts are used on an alumina carrier. The hydrogenation conditions for the selective hydrogenation, such as temperature, pressure, hydrogen / hydrocarbon ratio and throughput and bed volume in the hydrogenation reactor 1 are set depending on the desired hydrogenation reaction and depending on the desired hydrogenation conversion. Gaseous components leaving the hydrogenation reactor 1 via the discharge conduit 10. The liquid selectively hydrogenated and aromatics products from the selective hydrogenation leaving the hydrogenation reactor 1 along with still dissolved residual gases via the connecting line. 5

The extraction device 2 is connected via the connecting line 5 for the liquid selectively hydrogenated and aromatics products from the selective hydrogenation to the hydrogenation reactor, the first In the embodiment of Fig. 1, the extractor 2 is an extractive distillation column. As can be seen in Fig. 1, the product of the hydrogenation via the connection line 5 in the middle part of the extractive distillation column is fed. In the extractive separation of aromatics from non-aromatics takes place. For this purpose, the extraction means 2 a feed 6 for a selective solvent. Referring to FIG. 1, the selective solvent is fed by the feeding means 6 in the upper part of the extractive distillation column. The selective solvent causes the separation by distillation from non and the dissolved in the selective solvent aromatics (extract). The extraction device 2 has for this purpose a first withdrawal conduit 7 for the extract of selective solvent and aromatics. The extraction device 2 has henceforth to a second discharge line 8 for the raffinate with the non-aromatics.

According to a preferred embodiment of the invention and the embodiment of FIG. 1 is a distillation apparatus 9 is connected to the separation by distillation of selective solvents and pure aromatics to the first withdrawal conduit 7 for the extract. In the embodiment of Fig. 1, in the distillation device 9 remote distillation selective solvent is recycled via the feed device 6 in the extractive distillation column. The in the distiller 9 removed by distillation clean machines are dissipated via the Reinaromatenleitung 11 and supplied for further use.

In the following the invention will be explained in more detail with reference to embodiments. In these embodiments, the bromine index according to ASTM D-1492, the acid color index (Acid Wash Color, AWC) is continuously indicated by ASTM D-848 and the Hazen color number according to ASTM D-1209th

First, a benzene-rich Reformatschnitt from a catalytic reforming of an extractive distillation was subjected according to the prior art and the aforementioned known from practice. This feedstock for the extractive distillation had a relatively high olefin, which increased with the catalyst life of the reforming catalyst (see Table 1). After extractive distillation benzene the product had a non-aromatics content of &lt;1000 ppm, a bromine index of &lt;20 and an acid color index, which was always greater than 1. It has been found that the high acid color number of the benzene product is already caused by traces of olefins, in particular the group C₆-Cyclodiene (Especially methyl-1,3-cyclopentadiene bp: 73 ° C and 1,3-cyclohexadiene b.p. 81.5 ° C) or C₆Diolefins and C₆-Triolefine (Especially methyl-1,3-pentadienes bp: 80 ° C ~76 ° C or 1,3,5-hexatriene bp: 77.6 ° C or 2,6-hexadiene Kp) belong. These olefins have a boiling point which is close to the boiling point of benzene, and are therefore difficult to separate from benzene. It has been found that in particular methyl-1,3-cyclopentadiene (MCPDEN) has been responsible for a high acid color number of the benzene product in trace amounts. For example, &lt;1 5 ppm MCPDEN became a pure benzene with acid color index added and this increases the acid color number to 2. In the following Table 1 and MCPDEN benzene content are given with respect to the extractive distillation as a function of catalyst life of the reforming catalyst. The weight ratio of the selective solvent / hydrocarbon was in the extractive distillation 2.4. In the following said application product that the extractive distillation supplied product and benzene product to the product of the extractive distillation.<tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="5" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left"><b>Catalyst runtime</b></entry><entry namest="col2" nameend="col2" align="center"><b>H</b></entry><entry namest="col3" nameend="col3" align="center"><b>100</b></entry><entry namest="col4" nameend="col4" align="center"><b>1000</b></entry><entry namest="col5" nameend="col5" align="center"><b>1500</b></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene in the feed</entry><entry namest="col2" nameend="col2" align="left">Wt .-%</entry><entry namest="col3" nameend="col3" align="right">60</entry><entry namest="col4" nameend="col4" align="right">58</entry><entry namest="col5" nameend="col5" align="right">61</entry></row><row><entry namest="col1" nameend="col1" align="left">MCPDEN in feedstock</entry><entry namest="col2" nameend="col2" align="left">ppm</entry><entry namest="col3" nameend="col3" align="right">35</entry><entry namest="col4" nameend="col4" align="right">83</entry><entry namest="col5" nameend="col5" align="right">900</entry></row><row><entry namest="col1" nameend="col1" align="left">MCPDEN in benzene product</entry><entry namest="col2" nameend="col2" align="left">ppm</entry><entry namest="col3" nameend="col3" align="right">15</entry><entry namest="col4" nameend="col4" align="right">25</entry><entry namest="col5" nameend="col5" align="right">139</entry></row></tbody></tgroup></table></tables>

From Table 1 it appears that a relatively high MCPDEN content is also present in the benzene product of the extractive distillation, which makes up the high acid color number. - Next, the benzene product was cleaned of bleaching earth at temperatures between 160 ° C and 200 ° C. The product of this clay treatment showed a bromine index of 120, an acid color index of&gt; 14 and a Hazen color number of 380. MCPDEN and other C₆Dienes were fully implemented. Subsequently, a distillation of the product of the bleaching earth treatment was required. The pure benzene from the distillation showed a bromine index of 4, an acid color number &lt;1 and a Hazen color number &lt;3. However, these latter cleaning measures are very complex and expensive.

In the following four embodiments of the extractive distillation was connected upstream in accordance with the method according to claim 1 of the invention a selective hydrogenation to hydrogenate olefins and selectively as possible not to implement aromatics to saturated hydrocarbons.

Embodiment 1 (Table 2)

In this embodiment a Reformatschnitt with maximum benzene content from a catalytic reforming was used which had 65 ppm toluene, a bromine index of 3000 and a MCPDEN content of 120 ppm. In Table 2, test conditions and measurement results are listed to the example 1a, was carried out at the selective hydrogenation and only without extractive distillation. In examples 1b to 1d, the selective hydrogenation was combined with the extractive distillation according to the inventive method. As the catalyst of the selective hydrogenation nickel was used on aluminum oxide as support material in all three examples. The selective hydrogenation was conducted as in 1b to 1d that only 0.96% of the set benzene was hydrogenated to cyclohexane. The extractive distillation (ED) was to 1d carried out in all Examples 1a with N-formyl as a solvent and having a theoretical number of ED column of 50. The solvent shown in the table under the conditions of extractive / KW-use ratio means the weight ratio of selective solvent for the hydrocarbon used in the extractive distillation. Heat demand of the distillation column refers to the heating requirements of the extractive downstream distillation device or distillation column 9 for separating pure benzene from the selective solvent. The heat demand is here and indicated in Tables 3 and 4 in kJ / kg of produced benzene.<tables id="tabl0002" num="0002"><table frame="all"><title>Table 2</title><tgroup cols="5" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left"><b>Example:</b></entry><entry namest="col2" nameend="col2" align="center"><b>1a</b></entry><entry namest="col3" nameend="col3" align="center"><b>1b</b></entry><entry namest="col4" nameend="col4" align="right"><b>1c</b></entry><entry namest="col5" nameend="col5" align="right"><b>1d</b></entry></row><row><entry namest="col1" nameend="col1" align="left">selective</entry><entry namest="col2" nameend="col2" rowsep="0" align="center">No</entry><entry namest="col3" nameend="col3" rowsep="0" align="center">Yes</entry><entry namest="col4" nameend="col4" rowsep="0" align="right">Yes</entry><entry namest="col5" nameend="col5" rowsep="0" align="right">Yes</entry></row><row><entry namest="col1" nameend="col1" align="left">Conditions of the extractive distillation (ED):</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /><entry namest="col5" nameend="col5" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Solvent / KW-use ratio kg / kg</entry><entry namest="col2" nameend="col2" align="right">2.3</entry><entry namest="col3" nameend="col3" align="right">2.7</entry><entry namest="col4" nameend="col4" align="right">2.3</entry><entry namest="col5" nameend="col5" align="right">2.0</entry></row><row><entry namest="col1" nameend="col1" align="left">Heat demand of ED column kJ / kg</entry><entry namest="col2" nameend="col2" align="right">712</entry><entry namest="col3" nameend="col3" align="right">833</entry><entry namest="col4" nameend="col4" align="right">708</entry><entry namest="col5" nameend="col5" align="right">649</entry></row><row><entry namest="col1" nameend="col1" align="left">Heat demand of the distillation column kJ / kg</entry><entry namest="col2" nameend="col2" align="right">996</entry><entry namest="col3" nameend="col3" align="right">984</entry><entry namest="col4" nameend="col4" align="right">988</entry><entry namest="col5" nameend="col5" align="right">963</entry></row></tbody></tgroup><tgroup cols="5" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">Feedstock for ED:</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /><entry namest="col5" nameend="col5" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene content wt .-%</entry><entry namest="col2" nameend="col2" align="right">66.5</entry><entry namest="col3" nameend="col3" align="right">66.1</entry><entry namest="col4" nameend="col4" align="right">66.1</entry><entry namest="col5" nameend="col5" align="right">66.1</entry></row><row><entry namest="col1" nameend="col1" align="left">Toluene content ppm</entry><entry namest="col2" nameend="col2" align="right">65</entry><entry namest="col3" nameend="col3" align="right">65</entry><entry namest="col4" nameend="col4" align="right">65</entry><entry namest="col5" nameend="col5" align="right">65</entry></row><row><entry namest="col1" nameend="col1" align="left">MCPDEN content ppm</entry><entry namest="col2" nameend="col2" align="right">120</entry><entry namest="col3" nameend="col3" align="right">&lt;1</entry><entry namest="col4" nameend="col4" align="right">&lt;1</entry><entry namest="col5" nameend="col5" align="right">&lt;1</entry></row><row><entry namest="col1" nameend="col1" align="left">Bromine mg Br₂/100 g</entry><entry namest="col2" nameend="col2" align="right">3000</entry><entry namest="col3" nameend="col3" align="right">330</entry><entry namest="col4" nameend="col4" align="right">330</entry><entry namest="col5" nameend="col5" align="right">330</entry></row></tbody></tgroup><tgroup cols="5" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene product of ED:</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /><entry namest="col5" nameend="col5" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene content wt .-%</entry><entry namest="col2" nameend="col5" align="center">-&gt; 99.96 each -</entry></row><row><entry namest="col1" nameend="col1" align="left">Toluene content ppm</entry><entry namest="col2" nameend="col2" align="right">140</entry><entry namest="col3" nameend="col3" align="right">130</entry><entry namest="col4" nameend="col4" align="right">125</entry><entry namest="col5" nameend="col5" align="right">112</entry></row><row><entry namest="col1" nameend="col1" align="left">MCPDEN content ppm</entry><entry namest="col2" nameend="col2" align="right">41</entry><entry namest="col3" nameend="col3" align="right">&lt;1</entry><entry namest="col4" nameend="col4" align="right">&lt;1</entry><entry namest="col5" nameend="col5" align="right">&lt;1</entry></row><row><entry namest="col1" nameend="col1" align="left">Bromine mg Br₂/ 100</entry><entry namest="col2" nameend="col2" align="right">32</entry><entry namest="col3" nameend="col3" align="right">1</entry><entry namest="col4" nameend="col4" align="right">3</entry><entry namest="col5" nameend="col5" align="right">6</entry></row><row><entry namest="col1" nameend="col1" align="left">Acid Wash Color</entry><entry namest="col2" nameend="col2" align="right">7</entry><entry namest="col3" nameend="col3" align="right">&lt;1</entry><entry namest="col4" nameend="col4" align="right">&lt;1</entry><entry namest="col5" nameend="col5" align="right">&lt;1</entry></row><row><entry namest="col1" nameend="col1" align="left">Hazen color number</entry><entry namest="col2" nameend="col2" align="right">&lt;3</entry><entry namest="col3" nameend="col3" align="right">&lt;3</entry><entry namest="col4" nameend="col4" align="right">&lt;3</entry><entry namest="col5" nameend="col5" align="right">&lt;3</entry></row></tbody></tgroup></table></tables>

The values ​​in Table 2 show that was reduced in the selective hydrogenation of the bromine index of the Reformatschnittes to 330th Moreover, were the selective hydrogenation C₆Diolefins away at concentrations below detection limit. As an example, the MCPDEN content is indicated in the table, which was reduced to &lt;1 ppm. show the values ​​for benzene product from the extractive distillation that in Example 1a without selective an unfavorably high bromine index and an unfavorably high acid color index is measured while in Examples 1b to 1d with selective hydrogenation of the bromine index &lt;10 remains and the acid color index is &lt;1 and so pure benzene obtained thus satisfies all requirements. A comparison of Examples 1b to 1d shows that even in a solvent / KW-use ratio of 2.0 even pure benzene is obtained with the required values. A low value of this feed ratio means higher throughput in the same column dimensions and a lower specific heat demand in extractive distillation and distillation column.

Embodiment 2 (Table 3):

In the context of this embodiment, the embodiment 1 corresponding Reformatschnitt was used. As the catalyst of the selective here Palladium was used on aluminum oxide as support material. The selective hydrogenation was carried out here milder than in Embodiment 1, so that only about 0.29% of the benzene was hydrogenated to cyclohexane. The hydrogenated feedstock for extractive distillation showed a bromine index of 1.730 and a MCPDEN content of 4 ppm. Extractive distillation was carried out in all of the examples 2a to 2d with N-formylmorpholine as the selective solvent, and having a theoretical number of plates of the extractive distillation of 50th<tables id="tabl0003" num="0003"><table frame="all"><title>Table 3</title><tgroup cols="5" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left"><b>Example:</b></entry><entry namest="col2" nameend="col2" align="right"><b>2a</b></entry><entry namest="col3" nameend="col3" align="right"><b>2 B</b></entry><entry namest="col4" nameend="col4" align="right"><b>2c</b></entry><entry namest="col5" nameend="col5" align="right"><b>2d</b></entry></row><row><entry namest="col1" nameend="col1" align="left">selective:</entry><entry namest="col2" nameend="col2" rowsep="0" align="right">No</entry><entry namest="col3" nameend="col3" rowsep="0" align="right">Yes</entry><entry namest="col4" nameend="col4" rowsep="0" align="right">Yes</entry><entry namest="col5" nameend="col5" rowsep="0" align="right">Yes</entry></row><row><entry namest="col1" nameend="col1" align="left">Conditions of the extractive distillation (ED):</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /><entry namest="col5" nameend="col5" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Solvent / KW-use ratio kg / kg</entry><entry namest="col2" nameend="col2" align="right">2.7</entry><entry namest="col3" nameend="col3" align="right">2.7</entry><entry namest="col4" nameend="col4" align="right">2.4</entry><entry namest="col5" nameend="col5" align="right">2.0</entry></row><row><entry namest="col1" nameend="col1" align="left">Heat demand of ED column kJ / kg</entry><entry namest="col2" nameend="col2" align="right">735</entry><entry namest="col3" nameend="col3" align="right">729</entry><entry namest="col4" nameend="col4" align="right">657</entry><entry namest="col5" nameend="col5" align="right">544</entry></row><row><entry namest="col1" nameend="col1" align="left">Heat demand of the distillation column kJ / kg</entry><entry namest="col2" nameend="col2" align="right">1177</entry><entry namest="col3" nameend="col3" align="right">1181</entry><entry namest="col4" nameend="col4" align="right">1168</entry><entry namest="col5" nameend="col5" align="right">1093</entry></row></tbody></tgroup><tgroup cols="5" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">Use product for ED:</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /><entry namest="col5" nameend="col5" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene content wt .-%</entry><entry namest="col2" nameend="col2" align="right">70.3</entry><entry namest="col3" nameend="col3" align="right">70.1</entry><entry namest="col4" nameend="col4" align="right">70.1</entry><entry namest="col5" nameend="col5" align="right">70.1</entry></row><row><entry namest="col1" nameend="col1" align="left">Toluene content ppm</entry><entry namest="col2" nameend="col2" align="right">101</entry><entry namest="col3" nameend="col3" align="right">93</entry><entry namest="col4" nameend="col4" align="right">93</entry><entry namest="col5" nameend="col5" align="right">93</entry></row><row><entry namest="col1" nameend="col1" align="left">MCPDEN content ppm</entry><entry namest="col2" nameend="col2" align="right">135</entry><entry namest="col3" nameend="col3" align="right">4</entry><entry namest="col4" nameend="col4" align="right">4</entry><entry namest="col5" nameend="col5" align="right">4</entry></row><row><entry namest="col1" nameend="col1" align="left">Bromine mg Br₂/100 g</entry><entry namest="col2" nameend="col2" align="right">3260</entry><entry namest="col3" nameend="col3" align="right">1730</entry><entry namest="col4" nameend="col4" align="right">1730</entry><entry namest="col5" nameend="col5" align="right">1730</entry></row></tbody></tgroup><tgroup cols="5" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene product of ED:</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /><entry namest="col5" nameend="col5" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene content wt .-%</entry><entry namest="col2" nameend="col2" align="right">&gt; 99.96</entry><entry namest="col3" nameend="col3" align="right">&gt; 99.96</entry><entry namest="col4" nameend="col4" align="right">&gt; 99.96</entry><entry namest="col5" nameend="col5" align="right">&gt; 99.96</entry></row><row><entry namest="col1" nameend="col1" align="left">Toluene content ppm</entry><entry namest="col2" nameend="col2" align="right">98</entry><entry namest="col3" nameend="col3" align="right">103</entry><entry namest="col4" nameend="col4" align="right">98</entry><entry namest="col5" nameend="col5" align="right">110</entry></row><row><entry namest="col1" nameend="col1" align="left">MCPDEN content ppm</entry><entry namest="col2" nameend="col2" align="right">56</entry><entry namest="col3" nameend="col3" align="right">2</entry><entry namest="col4" nameend="col4" align="right">3</entry><entry namest="col5" nameend="col5" align="right">2</entry></row><row><entry namest="col1" nameend="col1" align="left">Bromine mg Br₂/100 g</entry><entry namest="col2" nameend="col2" align="right">43</entry><entry namest="col3" nameend="col3" align="right">8th</entry><entry namest="col4" nameend="col4" align="right">18</entry><entry namest="col5" nameend="col5" align="right">56</entry></row><row><entry namest="col1" nameend="col1" align="left">Acid Wash Color</entry><entry namest="col2" nameend="col2" align="right">6</entry><entry namest="col3" nameend="col3" align="right">&lt;1</entry><entry namest="col4" nameend="col4" align="right">&lt;1</entry><entry namest="col5" nameend="col5" align="right">2</entry></row><row><entry namest="col1" nameend="col1" align="left">Hazen color number</entry><entry namest="col2" nameend="col2" align="right">&lt;3</entry><entry namest="col3" nameend="col3" align="right">&lt;3</entry><entry namest="col4" nameend="col4" align="right">&lt;3</entry><entry namest="col5" nameend="col5" align="right">&lt;3</entry></row></tbody></tgroup></table></tables>

A comparison of Examples 2b to 2d shown in Table 3 that are obtained due to the lower or milder hydrogenation compared to the embodiment 1 with low solvent / KW-use ratio of 2.0, satisfactory values ​​of the bromine index and the acid color index. A comparison of Examples 1 and 2, in particular with respect to the examples 1b and 2b shows, however, that, is possible by adjusting the hydrogenation conditions or the solvent / KW-use ratio to optimize the process, depending on the desired proportions.

In FIG. 2, the bromine index of the pure benzene is represented as a function of the solvent / HF feed ratio to the extractive distillation. The measurement point 1a gives the corresponding values ​​from Example 1a in Table 2 again, has worked at the without selective. The solid curve gives the corresponding values ​​of examples 1b to 1d of the table 2 again, in which the selective hydrogenation was carried out so that approximately 0.96% of the benzene was hydrogenated to cyclohexane used. The measuring point 2a is the appropriately named example in Table 3 without selective hydrogenation. The dash-dotted curve represents the Examples 2B to 2D in Table 3, in which the selective hydrogenation was carried out so that only about 0.29% of the benzene was hydrogenated to cyclohexane used. The dashed line in Fig. 2 indicates the limit value 20 for the bromine index again. From Fig. 2 can be taken that the process depending on the desired result, ie, depending on nehmendem in buying benzene loss recorded and depending on the desired bromine index on the other hand, varied by changing the hydrogenation conditions or Hydriertiefe and by changing the solvent / KW-use ratio can be.

Embodiment 3 (Table 4):

In the context of this embodiment the Entbenzolung of reformed gasoline was conducted under the recovery of pure benzene, as claimed in claim 2nd A reformed gasoline with a distillation end point of 165 ° C was first subjected to fractional distillation. The top product of the distillation contained 98% of the benzene used. Table 4 shows the example 3a, was carried out at the not selective hydrogenation as well as the examples were 3b and 3c, in which selectively hydrogenated with a nickel catalyst supported on alumina. The selective hydrogenation was so out, moreover, that the benzene loss was about 0.89%. With extractive 3a worked to 3c with N-formyl as selective solvent and having a theoretical plate number of the extractive distillation column 48 in all three examples.<tables id="tabl0004" num="0004"><table frame="all"><title>Table 4</title><tgroup cols="4" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left"><b>Example:</b></entry><entry namest="col2" nameend="col2" align="right"><b>3a</b></entry><entry namest="col3" nameend="col3" align="right"><b>3b</b></entry><entry namest="col4" nameend="col4" align="right"><b>3c</b></entry></row><row><entry namest="col1" nameend="col1" align="left">selective:</entry><entry namest="col2" nameend="col2" rowsep="0" align="right">No</entry><entry namest="col3" nameend="col3" rowsep="0" align="right">Yes</entry><entry namest="col4" nameend="col4" rowsep="0" align="right">Yes</entry></row><row><entry namest="col1" nameend="col1" align="left">Conditions of the extractive distillation (ED):</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Solvent / KW-use ratio kg / kg</entry><entry namest="col2" nameend="col2" align="right">2.3</entry><entry namest="col3" nameend="col3" align="right">2.3</entry><entry namest="col4" nameend="col4" align="right">1.5</entry></row><row><entry namest="col1" nameend="col1" align="left">Heat demand of ED column kJ / kg</entry><entry namest="col2" nameend="col2" align="right">4985</entry><entry namest="col3" nameend="col3" align="right">5006</entry><entry namest="col4" nameend="col4" align="right">3089</entry></row><row><entry namest="col1" nameend="col1" align="left">Heat demand of the distillation column kJ / kg</entry><entry namest="col2" nameend="col2" align="right">1473</entry><entry namest="col3" nameend="col3" align="right">1498</entry><entry namest="col4" nameend="col4" align="right">926</entry></row></tbody></tgroup><tgroup cols="4" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene feedstock for ED:</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene content wt .-%</entry><entry namest="col2" nameend="col2" align="right">17.3</entry><entry namest="col3" nameend="col3" align="right">17.1</entry><entry namest="col4" nameend="col4" align="right">17.1</entry></row><row><entry namest="col1" nameend="col1" align="left">Toluene content ppm</entry><entry namest="col2" nameend="col2" align="right">350</entry><entry namest="col3" nameend="col3" align="right">304</entry><entry namest="col4" nameend="col4" align="right">304</entry></row><row><entry namest="col1" nameend="col1" align="left">MCPDEN content ppm</entry><entry namest="col2" nameend="col2" align="right">44</entry><entry namest="col3" nameend="col3" align="right">&lt;1</entry><entry namest="col4" nameend="col4" align="right">&lt;1</entry></row><row><entry namest="col1" nameend="col1" align="left">Bromine mg Br₂/100 g</entry><entry namest="col2" nameend="col2" align="right">5060</entry><entry namest="col3" nameend="col3" align="right">650</entry><entry namest="col4" nameend="col4" align="right">650</entry></row></tbody></tgroup><tgroup cols="4" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene product of ED:</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene content wt .-%</entry><entry namest="col2" nameend="col2" align="right">&gt; 99.7</entry><entry namest="col3" nameend="col3" align="right">&gt; 99.7</entry><entry namest="col4" nameend="col4" align="right">&gt; 99.7</entry></row><row><entry namest="col1" nameend="col1" align="left">Toluene content wt .-%</entry><entry namest="col2" nameend="col2" align="right">0,195</entry><entry namest="col3" nameend="col3" align="right">0,183</entry><entry namest="col4" nameend="col4" align="right">0.176</entry></row><row><entry namest="col1" nameend="col1" align="left">MCPDEN content ppm</entry><entry namest="col2" nameend="col2" align="right">20</entry><entry namest="col3" nameend="col3" align="right">&lt;1</entry><entry namest="col4" nameend="col4" align="right">&lt;1</entry></row><row><entry namest="col1" nameend="col1" align="left">Bromine mg Br₂/100 g</entry><entry namest="col2" nameend="col2" align="right">25</entry><entry namest="col3" nameend="col3" align="right">&lt;5</entry><entry namest="col4" nameend="col4" align="right">&lt;16</entry></row><row><entry namest="col1" nameend="col1" align="left">Acid Wash Color</entry><entry namest="col2" nameend="col2" align="right">5</entry><entry namest="col3" nameend="col3" align="right">&lt;1</entry><entry namest="col4" nameend="col4" align="right">&lt;1</entry></row><row><entry namest="col1" nameend="col1" align="left">Hazen color number</entry><entry namest="col2" nameend="col2" align="right">&lt;3</entry><entry namest="col3" nameend="col3" align="right">&lt;3</entry><entry namest="col4" nameend="col4" align="right">&lt;3</entry></row></tbody></tgroup></table></tables>

The example of Figure 3a shows that unsatisfactory values ​​of the bromine index and the acid color index was achieved in the benzene product without selective here. A comparison of Examples 3b and 3c shows that (0.89% benzene loss) can also be achieved with a solvent / KW-use ratio of 1.5 still satisfactory values ​​of the bromine index and the acid color index at the hydrogenation conditions selected here. Consequently this embodiment is an example of the respect to the FIG. 2 mentioned optimization of the method. Benzene loss 3c In the example at very low solvent / KW-use ratio and thus low energy consumption on the one hand and relatively low on the other hand, nevertheless a satisfactory result with respect to the bromine index and reached the acid color index.

Embodiment 4, Table 5

Here a Reformatschnitt was used with the aromatics benzene, toluene, ethylbenzene and xylenes, and was carried out with this Reformatschnitt a liquid-liquid extraction. To this was added a mixture of N-formyl used as a selective solvent / water (95/5) in all three examples 4a to 4c and the number of theoretical plates of the liquid-liquid extractor in each case was 50. The catalyst of the selective hydrogenation was 4b and 4c in the examples nickel on alumina, and used the selective hydrogenation was carried out here so that the benzene to cyclohexane by hydrogenation loss was 1%. The specific heat consumption is given in Table 5 in kJ / kg of aromatics.<tables id="tabl0005" num="0005"><table frame="all"><title>Table 5</title><tgroup cols="4" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left"><b>Example:</b></entry><entry namest="col2" nameend="col2" align="right"><b>4a</b></entry><entry namest="col3" nameend="col3" align="right"><b>4b</b></entry><entry namest="col4" nameend="col4" align="right"><b>4c</b></entry></row><row><entry namest="col1" nameend="col1" align="left">selective</entry><entry namest="col2" nameend="col2" rowsep="0" align="right">No</entry><entry namest="col3" nameend="col3" rowsep="0" align="right">Yes</entry><entry namest="col4" nameend="col4" rowsep="0" align="right">Yes</entry></row><row><entry namest="col1" nameend="col1" align="left">Conditions of the liquid / liquid extraction (FFE):</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Solution center / KW-use ratio kg / kg</entry><entry namest="col2" nameend="col2" align="right">3.0</entry><entry namest="col3" nameend="col3" align="right">3.0</entry><entry namest="col4" nameend="col4" align="right">3.0</entry></row><row><entry namest="col1" nameend="col1" align="left">Specific heat consumption kJ / kg</entry><entry namest="col2" nameend="col2" align="right">1873</entry><entry namest="col3" nameend="col3" align="right">1690</entry><entry namest="col4" nameend="col4" align="right">1868</entry></row></tbody></tgroup><tgroup cols="4" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">BTX feedstock for FFE:</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene content wt .-%</entry><entry namest="col2" nameend="col2" align="right">7.0</entry><entry namest="col3" nameend="col3" align="right">7.0</entry><entry namest="col4" nameend="col4" align="right">7.0</entry></row><row><entry namest="col1" nameend="col1" align="left">Toluene wt .-%</entry><entry namest="col2" nameend="col2" align="right">19.3</entry><entry namest="col3" nameend="col3" align="right">19.2</entry><entry namest="col4" nameend="col4" align="right">19.2</entry></row><row><entry namest="col1" nameend="col1" align="left">Ethylbenzene / xylene content wt .-%</entry><entry namest="col2" nameend="col2" align="right">20.5</entry><entry namest="col3" nameend="col3" align="right">20.4</entry><entry namest="col4" nameend="col4" align="right">20.4</entry></row><row><entry namest="col1" nameend="col1" align="left">MCPDEN content ppm</entry><entry namest="col2" nameend="col2" align="right">38</entry><entry namest="col3" nameend="col3" align="right">&lt;1</entry><entry namest="col4" nameend="col4" align="right">&lt;1</entry></row><row><entry namest="col1" nameend="col1" align="left">Bromine mg Br₂/100 g</entry><entry namest="col2" nameend="col2" align="right">5280</entry><entry namest="col3" nameend="col3" align="right">510</entry><entry namest="col4" nameend="col4" align="right">510</entry></row></tbody></tgroup><tgroup cols="4" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene product of FFE:</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Benzene content wt .-%&gt;</entry><entry namest="col2" nameend="col2" align="right">99.96&gt;</entry><entry namest="col3" nameend="col3" align="right">99.96</entry><entry namest="col4" nameend="col4" align="right">&gt; 99.96</entry></row><row><entry namest="col1" nameend="col1" align="left">Toluene content ppm</entry><entry namest="col2" nameend="col2" align="right">145</entry><entry namest="col3" nameend="col3" align="right">152</entry><entry namest="col4" nameend="col4" align="right">143</entry></row><row><entry namest="col1" nameend="col1" align="left">Ethylbenzene / xylene content ppm</entry><entry namest="col2" nameend="col2" align="right">nn</entry><entry namest="col3" nameend="col3" align="right">nn</entry><entry namest="col4" nameend="col4" align="right">nn</entry></row><row><entry namest="col1" nameend="col1" align="left">MCPDEN content ppm</entry><entry namest="col2" nameend="col2" align="right">125</entry><entry namest="col3" nameend="col3" align="right">&lt;1</entry><entry namest="col4" nameend="col4" align="right">&lt;1</entry></row><row><entry namest="col1" nameend="col1" align="left">Bromine mg Br₂/100 g</entry><entry namest="col2" nameend="col2" align="right">47</entry><entry namest="col3" nameend="col3" align="right">6</entry><entry namest="col4" nameend="col4" align="right">2</entry></row><row><entry namest="col1" nameend="col1" align="left">Acid Wash Color</entry><entry namest="col2" nameend="col2" align="right">&gt; 14</entry><entry namest="col3" nameend="col3" align="right">&lt;1</entry><entry namest="col4" nameend="col4" align="right">&lt;1</entry></row><row><entry namest="col1" nameend="col1" align="left">Hazen color number</entry><entry namest="col2" nameend="col2" align="right">&lt;3</entry><entry namest="col3" nameend="col3" align="right">&lt;3</entry><entry namest="col4" nameend="col4" align="right">&lt;3</entry></row></tbody></tgroup></table></tables>

As part of the liquid-liquid extraction, the aromatics benzene, toluene, ethylbenzene and xylenes were removed with the selective solvent. Because of this aromatics extraction then pure benzene was distilled off. Example 4A shows that without the selective hydrogenation of pure benzene ungüngstig having high levels of bromine index and acid color number. By contrast with an upstream selective hydrogenation are optimum values ​​achievable.