Integrated process for producing iso-butene and alkyl tert-butyl ethers.

Integrated process for the production of iso-butene and alkyl tert-butyl ethers

Full description

Background of the invention:

This invention relates to an integrated process for the production of iso-butene and alkyl tert-butyl ethers such as methyl tert-butyl ether (MTBE ether), ethyl tert-butyl ether (ETBE), etc. Alkyl tert-butyl ethers are used as high-altane additives for gasoline, and are produced by reacting isobutane with corresponding alcohols (methanol in the case of MTBE, ethanol in the case of ETBE, etc.). ) in a liquid medium over a suitable catalyst at a pressure of 15-40 atmospheres and a temperature between 60 and 100 C (see patent 1012690 - IT).

The current trend in the production of increasingly large quantities, especially of MTBE in gasoline technology, and the almost complete use of refining streams containing isobutene has led to the development of complex compounds for the production of iso-butene by dehydrogenation of iso-butane.

The raw material is usually a mixture of field butane, and Figure 1 shows a block diagram of an MTBE plant.

The feedstock 1, consisting of regular isobutane and isobutane, is fed into the distillation column 2, from which the isobutane 3 exits mainly at its top, and the stream 4 containing

On n-C4 and the upper hydrocarbon at its bottom. Section 5 of the bottom stream is isomerized in reactor 6 and then recycled through 7 in column 2. Hydrogen is separated from isobutane 3 in the plant 8, which supplies the MTBE construction reactor 11 with a light gas stream 9 and 10 containing isobutane and isobutene, which reacts with methanol 12 to produce MTBE 13.

In addition to MTBE, plant 11 also supplies dehydrogenation reactor 8 with a stream 14 containing isobutane, which is recycled until it reaches the maximum stream point in the reactor.

It should be noted that the origin of dehydrogenation techniques was not related to the production of MTBE. However, it is expected that the majority of MTBE plants will use isobutene produced from isobutane dehydrogenation and similarly the majority of isobutane dehydrogenation plants will supply isobutene to MTBE plants.

Thus, the integration of these two types of factories becomes important as it leads to saving investment and/or operating costs.

The isobutane dehydrogenation unit, which is shown graphically in Figure 2, relies on a process similar to the processes generally used in the commercial field, which are the processes of gas preparation, compression, and purification. Specifically, isobutane 21 is fed into the dehydrogenation reaction 22, followed by a compression stage 23 and a purification stage 24.

Purification involves separating hydrogen, nitrogen, and light hydrocarbons 25 from the C4 hydrocarbon component of the reaction product 26. The most important problem is the recovery of C4 hydrocarbons from the light gas stream remaining in a non-condensable state after compression.

This restoration is carried out in the usual factories by justification methods. It can also be accomplished by absorption in a suitable solvent, then depletion of C4 and recovery of the solvent. For example, the solvent in isobutane dehydrogenation plants is a mixture of...

Hydrocarbons C6-C10.

Figure 3 shows a typical diagram of the Snamprogetti-Yarsintez process for isobutane dehydrogenation with cryogenic recovery (see Actan Week, October 8, 1990, pp. 7-8).

Isobutane 31 is preheated in heat exchangers 22, 33 before being fed into the dehydrogenation reactor 34, which is connected to the dehydrogenation catalyst extraction reactor 35 in lines 36 and 37.

The gas stream 38 leaves the top of the reactor 34 and is then fed into the separation device 39 after cooling it in 33, then it is filtered in 40, compressed in 41 and partially condensed in 42. Two streams are obtained from the separation device 39, one 43 containing mainly C4 hydrocarbons and the other 44 containing mainly hydrogen and C3 hydrocarbons.

The current 43 in the depropane device 45 is fed from the bottom with the current 46, which mainly includes the drawn ISO-C4.

The stream 44 is fed into a low-temperature recovery device 47 to recover the isobutane and isobutane 48 mixed with it, to be added to the stream 43. The stream 49 coming out of 47, which contains mainly hydrogen and C1-C3 hydrocarbons, combines with the stream 50 coming out of the top of the depropane device 45.

The air 51 is fed into the extraction column 39 after being compressed in 52 and heated in 53.

The gas stream 4 5 exits from the top of the column 39 and is then cooled 53 and filtered through 55 before being used as fuel gas 56 .

Figure 4 shows a typical diagram of the process of dehydrogenation of isobutane with recovery by absorption and respiration.

Since the rest of the process is similar to what is shown in Figure 3, the description of purification is only given in

Figure 3.

The stream 38 leaving the reactor 34 is cooled in 33, then compressed in 41 and partially condensed in the condenser 42 before being fed into the separation device 39 to separate the heavy hydrocarbons 43 from the light hydrocarbons 44, and the latter are fed into the absorption device 60. Light gases and hydrocarbons 61 exit from the top The aforementioned absorption device, while the rest is absorbed into the nutrient solvent through line 62, then withdrawn from the bottom 63. The stream 63 containing the spent solvent and C4 hydrocarbons is fed into the distillation column 64, where it obtains the recovered solvent from its bottom 5 6 and from its top a stream containing mainly C4 hydrocarbons 66. These are fed into the depropanization column 67 after adding them to the stream 43. A stream consisting mainly of iso-C4 is drawn from the bottom 68 of column 67, and a stream containing mainly C3 hydrocarbons is drawn from the top 69.

These extraction methods are very expensive and complex. In particular, the refrigeration current suffers from high investment and operating expenses because the refrigeration cycle operates at very low temperatures, which requires expensive machines (such as turbine propellers). One of the disadvantages of absorption and recovery extraction is that the solvent is introduced deep into the production unit, which then requires its careful recovery, which increases the burden of costs and increases hydrocarbons.

Heavy, rich in C4 section, and the consumption of complex equipment must be taken into account in separating C4 hydrocarbons from the solvent.

General description of the invention

Surprisingly, it was found that it was possible to recover C4 hydrocarbons from the vapors generated from the first condensation by absorption in alkyl-butyl-tert ether and/or in the corresponding alcohol used, without a decrease in yield compared to the previously mentioned methods, despite the high vapor pressure of the materials used in the process conditions. Which encouraged its use.

In comparison with absorption of heavy hydrocarbons, as used in the process shown in Figure 4, the most important advantage of using these solvents is that the compounds exist in the form of reagents (methanol, ethanol, etc.) or in the form of products (ETBE, MTBE, etc.). ) The streams containing C4 hydrocarbons and recovered solvents can be fed directly into the process units already provided in the alkyl-butyl-tert ether production plant. Without any additional processing. Regarding the cooling schedule used globally, it also appears that the system that operates at very low temperatures is more complex than the absorption column that operates at temperatures of 40-60°C.

It includes the integrated process for producing isobutene and alkyl-butyl-tert ether according to the present invention. Mainly the following stages:

A) Dehydrogenation in a stream containing isobutane, then partially compressing and condensing the gases to obtain, after separation, a gaseous stream containing hydrogen, nitrogen, and C1-C4 hydrocarbons, and a liquid stream containing mainly C4 hydrocarbons.

b) Feeding the gaseous stream into an absorption column using a solvent to obtain from the top

A gaseous mixture containing mainly hydrogen, nitrogen, and C1-C3 hydrocarbons and, at the bottom, a liquid mixture containing mainly C4 hydrocarbons and the spent solvent;

C) Feeding the liquid stream containing mainly C4 hydrocarbons into a distillation column to obtain from the top a gaseous mixture containing mainly C3 hydrocarbons and from the bottom a liquid mixture containing mainly isobutane and isobutane.

d) Feeding the liquid mixture containing isobutane and isobutene from stage (c) into a reactor, or into a first reactor when two or more reactors are used, with the corresponding alcohol to obtain alkyl-butyl-tert ether.

e) Feeding the product from the reactor into a distillation column to obtain a stream containing mainly unreacted gases from the top and a liquid containing mainly alkyl tetrabutyl ether from the bottom.

f) Feeding a stream containing mainly unreacted gases from phase (e) directly into a washing column if only one reactor is used, or into the second reactor if more than one reactor is used, then feeding the output from the aforementioned second reactor into a distillation column to obtain A liquid mixture containing alkyl-butyl-tert ether from the bottom, which is recycled in the distillation column in stage (e) or in a third reactor when several reactors are used, and a mixture containing unreacted gases from the top, where this stream is fed into the washing column,

g) Separation in the washing column to obtain from the top mainly unreacted C4 hydrocarbons and from the bottom a liquid mixture containing mainly the water and alcohol used, then the water is separated from the alcohol in a distillation column, and the process is characterized

The solvent used in the absorption column in stage (b) is part of the liquid containing mainly alkyl butyl-tert ether in stage (e) and/or part of the corresponding alcohol used in that process.

The full impression of the invention and many of its advantages will become clear if it is properly understood, and becomes best understood, by referring to the detailed description when the accompanying drawings are taken into consideration.

Brief explanation of the drawings

Figure 1: Shows a typical diagram of an MTBE plant.

Figure 2: Shows a diagram of the isobutane dehydrogenation unit.

Figure 3: shows a typical diagram of the process of dehydrogenation of isobutane in a manner

Figure 4: shows the process of using absorption in heavy hydrocarbons.

Figure 5: shows a diagram of an integrated process for producing MTBE.

Figure 6: Shows a diagram of an integrated process for producing MTBE using MTBE as an absorbent 0

Figure 7: A diagram of an integrated process for producing MTBE using methanol as an adsorbent.

Detailed description

The liquid mixture containing primarily C4 hydrocarbons and alkyl butyl-tert ether as a spent solvent emerging from the bottom of the absorption column in stage (b), may be fed into one or more of the following items of equipment either partially or completely - into the distillation column in stage (c);

- In the distillation column in stage (e);

- In the reactor of stage (D);

It should be noted that it is not necessary to recover alkyl butyl-tert ether since the aforementioned liquid mixture does not have to be fed into the distillation column in stage (c). When the corresponding alcohol is used in the process as a solvent in the absorption column in stage (b), the liquid mixture emerging from the column is fed into the reactor in stage (d). The separated alcohol can be recycled in the distillation column at the bottom of the washing column in stage (g) in the reactor of stage (d), and/or in the reactor of stage (f) if two or more reactors are used, and/or in the absorption column in stage (b).

The unreacted C4 hydrocarbons separated in the washing column in stage (g) can be easily mixed with the stream containing isobutane in stage (a) so that they can be dehydrogenated together. The previously described process can be performed using a vertical reactor in which the reactor is coupled with the distillation column in one piece of equipment. In this case, a portion of the liquid containing mainly alkyl-butyl-tert ether leaving the vertical reactor is recycled directly into the upstream absorption column

( B ).

It is preferable that the amount of solvent used in the absorption column in stage (b) range between the following values:

- When alkyl-butyl-tert ether is the only solvent, the values are 0.5-2 mol/mol C4 content in the absorption column, most preferably between 1 and 1.5;

- When the conforming alcohol is the only solvent, the values are 1-3 mol/mol of C4 hydrocarbon content in the absorption column, and the most preferable is between 1.5 and 2. In the case of a mixed solvent, the amounts of alkyl-butyl-tert ether and the conforming alcohol can be reduced to Without the previously specified proportions.

When alkyl butyl-tert ether is used alone as a solvent, the percentage of the liquid fraction containing the nutrient in the absorption column is preferably between 15% and 50% by volume, and most preferably between 30 and 45%, of the total liquid leaving the stage (e) distillation column. . The invention will be better illustrated by the attached figures, which show some preferred examples, but not limited to them.

Figure 5 shows a diagram of an integrated process for producing MTBE, using MTBE as an absorbent. The feedstock 101, containing normal butane and isobutane, is preheated in heat exchangers 102 and 103, before being fed into the dehydrogenation reactor 104 which communicates with the dehydrogenation catalyst activator 105 at lines 106 and 107. The gas stream leaves

108 The top of the reactor 104 is then fed into the separation device 109 after cooling in 103, then it is filtered through 110, compressed in 111, then partially condensed in 112, to separate the heavy hydrocarbons 113 from the light hydrocarbons 114 that are fed into the absorption device 115 in which MTBE is used as a solvent. The light gases 117 leaving the top of the absorber 115 are cooled in 118 and then separated in 119 from the gases 121, MTBE 120, which are recycled in the absorber.

The liquid stream 113 is fed into the distillation column 122 to obtain C3 hydrocarbons from the top 123 and isobutane and isobutene from the bottom 124.

C4 iso-hydrocarbons 124 are destroyed in the first reactor 125 in the company of methanol 126 to obtain a stream containing MTBE 127, which is fed into the distillation column 128 to obtain the required MTBE 129 from the bottom and the unreacted gases (methanol, isobutane, and isobutane) 130 from the top.

The gaseous stream 130 is fed into the second reactor 131 with methanol to obtain an additional stream containing MTBE 132 (it contains less MTBE than the stream 127), where it is fed into the distillation column 132, from the bottom of which it obtains a stream 134 that contains mainly MTBE, which is recycled into Column 128, from its top also receives a stream 135 containing methanol, isobutane, and isobutane, which is fed into the washing column 136 into which water is fed 137.

Isobutane 138 leaves the top of column 36 1 where it is recycled by addition to stream 101, and methanol and water 139 leave the bottom where they are separated in column 140. A portion of the stream 129, containing primarily MTBE 141 as a solvent, is recycled into the absorption column 115. The liquid stream 142 containing hydrocarbons C4 and MTBE is fed into the distillation column 128. It may be fed completely or partially via 143 into the reactor 125. Air 144 is fed into the activation column 105 after being compressed in 145 and heated in 146. The gaseous stream 147 leaves the top of the column 105 and is then cooled in 146 and filtered in 148 before being used as fuel gas 149.

Figure 6 shows a diagram of a possible integrated process for producing MTBE using MTBE as an absorbent, as in the diagram of Figure 5, but with the difference that the bottom stream is fed from the absorption device 142 along with the liquid 113 from the separation device 109 and the distillation column 122.

In this method, C3 hydrocarbons that were partially absorbed in the solvent are also removed.

The reference numbers in the chart of Figure 6 are similar to those in Figure 5, in terms of meaning

It symbolizes it.

Figure 7 shows a diagram of a possible integrated process for producing MTBE using methanol as an adsorbent. This diagram differs from the diagram of Figure 5 in that a portion of the methanol is fed into the absorption column 115 instead of a portion of the MTBE, where the numbers symbolize the same meaning as they symbolize in Figure 5.

Below are two examples to illustrate the invention: 0

Example 1

100 kilomol/hour of isobutane is fed into a dehydrogenation reactor operating in the mortal state at a temperature of 580°C and atmospheric pressure, with the Cr-Al catalyst. The current leaving the reactor includes the following:

52.0 kmol/h of isobutane.

43.9 kmol/h of isobutene.

49.0 kmol/h of hydrogen.

3.8 kilomol/hour of methane.

2.3 kmol/h of C3 hydrocarbons.

1.5 kilomol/hour of C5 hydrocarbons and higher.

The reactor stream is compressed to 20 atmospheres and cooled to 40°C to separate it into a liquid stream and a gaseous stream. The liquid stream consists mainly of C3, C4 and higher hydrocarbons.

The gas stream still contains about 25% of C4 hydrocarbons and consists of the following:

12.2 kmol/h of isobutane. 9.4 kmol/hour of isobutene.

47.7 kilomol/hour of hydrogen.

3.4 kilomol/hour of methane.

1,0 kmol/h of C3 hydrocarbons.

This stream is fed to the bottom of the absorption column, at the top of which it feeds liquid MTBE at 35 m in an amount such that the partial ratio between MTBE and C4 hydrocarbons is 1:1. The column temperature stabilizes between 35 and 0.6°C.

In this method, 99.6% of the isobutane and isobutane contained in the feed stock is recovered with a loss of 0.5% of the solvent in the steam stream passing overhead. The liquid bottom stream consists of the following:

12.15 kmol/h of isobutane. 9.36 kmol/hour of isobutene.

0.65 kilomol/hour of hydrogen.

0.20 kilomol/hour of methane. 0.62 kilomol/hour of C3 hydrocarbons. 21.49 kmol/h of MTBE.

Mix this stream with the liquid stream from the condensate at 40°C, to obtain the following stream:

51.95 kmol/hour of isobutane. 43.86 kmol/h of isobutene. 1.95 kilomol/hour of hydrogen.

0.60 kilomol/hour of methane.

1.92 kmol/h of C3 hydrocarbons.

1.50 kilomol/hour of C5 hydrocarbons and higher hydrocarbons.

21.49 kmol/h of MTBE.

This mixture is fed into a distillation column from which a residual precipitate containing MTBE, C4 hydrocarbons, and a small amount of propane and propylene is recovered. This residual residue is mixed with methanol in an amount in which the ratio between methanol and isobutene is 1:1, and is fed at LHSV 5 into the primary reactor in the MTBE construction process, where it reacts over the amberlyst 15 resin at a temperature of 60 °C and a pressure of 15 atmospheres. The following current leaves the reactor:

51.95 kmol/hour of isobutane.

5.48 kmol/hour of isobutene.

5.48 kmol/hour of methanol.

42.0 kmol/h of C3 hydrocarbons

0 1.50 kmol/h of C5 hydrocarbons and higher hydrocarbons.

59.87 kmol/h of MTBE.

This stream is fed into the fractionation column to obtain MTBE with a purity of 98% from the bottom and onto the liquid dropper from the top, which is fed into the second reactor after adding methanol until the molecular ratio of methanol/isobutene becomes 1.3:1. By running again over the Amberlyst 15 resin at 60°C and at LHSV at 5, a stream consisting of the following is obtained:

51.95 kmol/h of isobutane.

0.60 kmol/hour of isobutene.

2.24 kmol/hour of methanol.

0.42 kilomol/hour of C3 hydrocarbons.

4.88 kmol/h of MTBE.

Thus, a yield of 98.4% of the fed isobutane is obtained, despite the fact that MTBE is fed into the first reactor.

Example 2

This example is similar to the first example regarding the absorption column. In this case, methanol is used as a solvent in a ratio of 1.5:1 to C4 hydrocarbons. 98% of the isobutane and 99.5% of the isobutene can be recovered with a loss of 0.1% of the solvent. The liquid stream leaving the bottom of the absorption column consists of the following:

12.02 kmol/hour of isobutane.

9.35 kmol/hour of isobutene.

32.37 kmol/h of methanol.

0.25 kmol/h of hydrogen.

0.35 kilomol/hour of methane.

0.65 kilomol/hour of C3 hydrocarbons.

This stream is mixed with the residue left over from the separation of light hydrocarbons on the fractionation column fed by the condensed liquid stream at 40 m after compression. After degassing it and mixing it with methanol at a molecular ratio between methanol and isobutene of 1:1, it is fed into a construction reactor.

The first MTBE that operates under the conditions of Example 1.

In this case, without feeding the product into the MTBE plant, a total yield of 99% of the isobutene feed stock is obtained.