CS205045B2 - Process for selective production of isobutylene from mixture of hydrocarbons - Google Patents

Description

The invention relates to a process for the immediate recovery of isobutylene. By the process according to the invention, isobutylene can be separated by the selective action of methanol on the one hand from gas mixtures containing isobutylene with a high butadiene content and on the other hand from gas mixtures containing only butenes and butane. The methyl tert-butyl ether formed in the process can be easily separated from the C 1 -carbons.

The largest part of the isobutylene consumed worldwide is derived from hydrocarbon pyrosis fractionation, in particular from cracking gases of various origins and from gases produced by butane dehydrogenation. However, this process does not produce pure isobutylene, but the product also contains saturated hydrocarbons and some olefins and diolefins. Pure isobutylene can only be obtained in expensive installations in a complicated manner. The C1-fraction isolated during the pyrolysis of hydrocarbons and various gas mixtures resulting from different dehydrogenation processes have not been considered as immediate sources of isobutylene because of their high butadiene content. In the known processes, butadiene is first separated and isobutylene is isolated after butadiene extraction, generally by absorption in sulfuric acid. (G. D. Hobson, Modern Petroleum Technician, p. 460). Upon absorption, t-butanol is formed which is purified and then converted to pure isobutylene by dehydration.

Isobutylene can be converted in the presence of acidic. by treating the methyl tert-butyl ether with methanol. He can be po'dle brit. U.S. Pat. No. 1,165,479 decompose into methanol and pure isobutylene in the presence of eg. A further advantage of the methanol treatment is that the methyl tert-butyl ether thus formed can be used excellently as a component for high octane motor gasolines.

The tendency in increasingly stringent environmental regulations necessarily leads to a reduction in the lead content of fuels, thus making the cheap acquisition of high octane gasoline components an increasingly difficult problem. Thus, the production of methyl tert-butyl ether from gas mixtures containing isobutylene is a significant advance in this field.

The reaction of isobutylene with methanol in the presence of acid catalysts has already been described by T. W. Evans Ind. Eng. Chem. 28

No. 10, 1186. The most efficient catalyst is sulfuric acid. Also in another procedure of US Pat. No. 2,721,222, Esso Res. Eng.

What. is treated with sulfuric acid as a catalyzer lysator. The reaction is carried out in a heterogeneous phase and after the reaction is completed, the reaction mixture is diluted with a large amount of methanol to suppress decomposition during distillation. According to another method, US Pat. No. 2,720,547, Standart Oíl Co. however, the reaction is also carried out in a heterogeneous phase, but a reduction in decomposition in the distillation is achieved with a less active catalyst, namely 80% sulfuric acid or alkylsulfonic acid. However, catalyst separation and recirculation have not yet been solved satisfactorily. Therefore, more recent processes generally work with solid heterogeneous catalysts. In most processes, styrene-divinylbenzene-based sulfonic ion exchangers are used. Such procedures are described in some patents, e.g. belg. U.S. Pat. No. 612,338, Bayer AG., U.S. Patent No. 3,170,000, Sinclair Res. Inc., brit. U.S. Pat. C.

176 620 Shell. However, the catalysts used are considerably less active and, moreover, they are very sensitive to the least contamination of the raw materials. Said processes are generally only suitable for processing pure isobutylene, since in this case the low degree of reaction by butene recirculation can be increased and harmful impurities such as butadiene are present only in minor amounts. The treatment of the mixtures containing isobutylene and nbutylene is only limited by the narrow limits of the reaction. According to the latest findings, only a part of isobutylene is reacted and the remaining mixture, still containing isobutylene, is recovered in other ways (see German Pat.

246 00-4) .-

A prerequisite for the economical production of methyl tert-butyl ether from isobutylene is that almost all of the isobutylene in the mixture is immediately recovered. One of the most suitable raw materials for this purpose is the C 1 fraction of gasoline pyrolysis. Isobutylene - from this C-i-hydrocarbon mixture, containing about 40% butadiene, cannot be obtained in a cost-effective manner, i.e. immediately, because the butadiene readily polymerizes in the presence of strong acids and, moreover, reacts with methanol. This is also evident from the process of US Pat. No. 2,922,822, Essoi Res. Eng. Co., according to which -. butadiene-containing gases and methanol produce unsaturated ethers under conditions similar to the isobutylene reaction.

These disadvantages are overcome by the selective method; recovering isobutylene from a hydrocarbon mixture containing, in addition thereto, in particular C4-hydrocarbons such as n-butylenes, n-butane and butadiene and optionally C1-C8 hydrocarbons, in the form of methyl tert-butyl ether, by treatment with methanol in the presence of sulfuric acid; that isobutylene in the hydrocarbon mixture is treated in the presence of less than 20% sulfuric acid as catalyst, calculated on the reaction mixture, at a temperature of 50 to 120 ° C, preferably at 80 to 100 ° C, in a homogeneous liquid phase of 0.1 to 4.0, with a molar excess of methanol per 1 ml of isobutylene, the resulting mixture is cooled to -25 to +40 ° C after the reaction, and the methanol-free reaction mixture and / or the isobutylene-free mixture is returned to it. wherein after the formation of two liquid phases, the bottom phase rich in sulfuric acid is returned to the original reaction and methanol is removed from the top phase after washing with water, which is also used to the original reaction, and methyl tert-butyl ether is distilled off from the residue.

Since the concentration of the sulfuric acid catalyst and the molar excess of methanol are dependent on the amount of isobutylene in the original mixture, the isobutylene recovery is carried out so that the methanoo: isobutylene molar ratio of 1 is maintained in the homogeneous phase reaction, 5 to 5.0: 1, preferably 2.0 to 4.0: 1, and 0.5 to 6.0 wt.%, Preferably 1.0 to 5 wt. to a reaction mixture of 1 to 80%, preferably 10 to 40% by weight of an isobutylene-depleted CHrack, and / or a methanol-depleted reaction mixture.

Similarly, in the recovery of isobutylene from a mixture of C6-hydrocarbons. containing more than 80% isobutylene, the reaction is carried out by maintaining a methanol: isobutylene molar ratio of 1.1 to 2.0: 1, preferably 1.2 to 1.4: 1, using 0.7 to 13% by weight. % by weight preferably 0.5 to 7.0 wt.% sulfuric acid based on the reaction mixture.

Under these conditions, the polymerization of butadiene is absolutely negligible. Also, the rate of addition of methanol to isobutylene is more than 100 times higher than the rate at which the butadiene reacts under the stated conditions. Therefore, in the case where the feedstocks contain 40-60% by weight of butadiene, isobutylene can be completely isolated by methanol.

Increasingly stringent environmental regulations also require the reduction of waste sulfuric acid, which can be accomplished by efficient catalyst recirculation in the process of the present invention. By extensively investigating the ability of differently composed reaction mixtures to dissolve sulfuric acid, it has been discovered that there are certain conditions under which, after carrying out the reaction at 50 to 120 ° C in a homogeneous liquid phase, a major portion of catalyst together with excess methanol forms of the mixture cooled to room temperature. The precipitated bottom phase contains 10-50% by weight of sulfuric acid, which can be reused as a catalyst in the synthesis. The precipitation of the catalyst phase after the reaction is influenced by the ratio of methanol to isobutylene and the sulfuric acid content. Figure 1 shows the maximum sulfuric acid concentration values by weight at 90 ° C and 30 ° C for various methanol contents. The data refer to a raw material containing 95% by weight of isobutylene. At the same methanol content, the amount of sulfuric acid passing into the solution decreases as the isobutylene content decreases, while the amount increases as the proportion of methanol increases. The deviation between the curves, sensed at different temperatures, indicates a better elimination of catalysts on cooling. Methanol enters the sulfuric acid phase without reducing the molar ratio of methanol to isobutylene, thereby increasing the amount of sulfuric acid excreted in the sulfuric acid-methanol phase.

The precipitation of the catalyst in the sulfuric acid-methanol phase can be further increased if, after the reaction, the reaction mixture, which does not contain methanol or from the reaction resulting in a reaction containing no more isobutylene, is returned to the cooling process. Surprising effect. This curve is shown in FIG. 2. The curve illustrates the amount of phase separation from each other as a function of the amount of hydrocarbons recovered. The amount of recycled hydrocarbons is given as a percentage of the initial hydrocarbon content of the reaction mixture. The solid parameters of the curve are as follows: isobutylene content of the starting mixture of 27% by weight, methanol: isobutylene molar ratio of 3.0: 1, catalyst content of 4.29% by weight, conversion of isobutylene. 90%. As can be seen from the figure, the amount of phase separation is strongly influenced by the return of a small amount of the resulting mixture. However, the recirculation of larger amounts does not, as is also apparent, have any particular effect on the amount of phase exclusion. Both the effects of lowering the temperature and lowering the methanol content may be. both together and separately used to easily separate a large portion of the catalyst. The separating phase, which has a high sulfuric acid content, is preferably used immediately as a catalyst. The methanol content of the catalyst phase also reduces the cost of recovering the excess methanol.

On the basis of the above, the process elaborated will be further elucidated according to the schematic representation of the process in FIG. The fresh catalyst, prepared from sulfuric acid, enters the reactor 4 via line 3 and the catalyst solution separated from the reaction mixture via line 9. The reaction proceeds under a homogeneous liquid phase. The reaction mixture exiting the reactor 4 via line 5 is cooled in a condenser 6. During cooling, part of the hydrocarbon fraction leaving the process containing no more isobutylene is removed via line 7 and a portion of the methanol-free reaction mixture is returned via lines 7 and 14. Cooling and return conduction disintegrates the homogeneous reaction mixture in 2 phases. The phases are separated in separator 8 from each other. The bottom phase, rich in sulfuric acid, is fed from the separator 8 via line 9 to the reactor, while the upper phase, containing little catalyst, flows through line 10 to the water scrubber 11. Washing water is supplied via line 12 and also contains some caustic to remove catalyst traces. The washing water exiting from the scrubber 11 via line 13 contains an excess of methanol reacted, which is separated in a known manner by distillation and recycled. Through line 15, the methanol-free reaction mixture exits, part of which is passed through line 14 and 7 back to the phase separation process containing the catalyst. The remainder is passed through line 15 to a distillation column 16 where unreacted hydrocarbons are separated from the methyl tert-butyl ether. · From the column head ··. · Is passed through line · 18 hydrocarbon · isobutylene-free mixture from which it is recycled through line · 7 part of the separated phase · catalyst-containing phase. From column bottom 17 through conduit MTBE arising from · isobutylene contained in a crude mixture which · can be directly or optionally after further purification after use as ^components: honných substances or decomposed into methanol and isobutylen.Způsob of the present invention is suitable for a wide range of concentrations and even in the case of starting materials containing many butadiene · to convert isobutylene into a mixture of hydrocarbons · to methyl tert-butyl ether. Another advantage of this process is that it is possible to use as a catalyst a catalytically highly efficient yet inexpensive sulfuric acid, and that a large part of this can be:. After the reaction, the catalyst is separated and recirculated.

The process according to the invention will be explained in more detail by the following examples.

Example,

In a 0.5 liter autoclave lined with polypropylene inside, 259.8 ml · 94% (w / w) liquid isobutylene, 140.2 ml methanol · and 9.5 · g 98% sulfuric acid · are introduced at -20 degrees Celsius · at 910 ° ^C a reaction takes place, the mixture became homogeneous and in 20 minutes, 87% is converted to isobutylene · MTBE. Upon cooling of the reaction mixture, a heavy bottom phase containing more than 80% of the sulfuric acid loaded is separated.

The catalyst phase may be reused in a further reaction corresponding to its methanol and sulfuric acid content. There is no difference between the reaction and the precipitation of the catalyst.

Example 1 a d 2

To a reactor operating at a pressure of 0.2

MPa and 90 ° C, introduced continuously over an hour of 5 L of liquid CMraction (25% isobutylene and 41% butadiene), derived from the pyrolysis of gasoline, followed by 1.22 L of methanol, 15 ml

98% sulfuric acid and 0.75 L catalyst solution containing sulfuric acid. From the reaction mixture present in the reactor, 93.8% of the initial isobutylene content was converted to methyl tert-butyl ether. The mixture exiting the reactor is cooled and at the same time 1 L of C4 isobutylene-free reaction is added over 1 hour. The heavy catalyst solution is separated from the reaction mixture containing 26.9 wt.% Sulfuric acid and fed back to the reactor. . The upper phase leads to the removal of excess methanol into a water scrubber operating at 0.5 MPa. The wash water contains 2 wt% NaOH to remove traces of catalyst. The methanol-free reaction mixture is decomposed into methyl tert-butyl ether and C4-hydrocarbons in a continuously operating tumbler at about 400 psig. Some of these hydrocarbons are recycled to the catalyst phase separation. 3.6 liters of 4-iodine per 1 hour are obtained which contain 2% by weight of isobutylene and 52% by weight of butadiene.

Example 3

5 l of liquid C4-fraction passing from the catalytic cracking and containing 20% by weight of isobutylene, 1 l of methanol, 10 ml of 98% sulfuric acid and 0.65 l of catalyst solution are fed continuously into the apparatus described in Example 2 over 1 hour. . 1.2 L of the methanol-free reaction mixture was recycled to the reaction mixture leaving the reactor and cooled to room temperature. The separating catalyst phase contains 25.4 wt% sulfuric acid. Methanol was removed from the reaction mixture without catalyst by washing with water. A portion of the reaction mixture containing methyl tert-butyl ether and C4-hydrocarbons is recycled to the catalyst-phase separation stage and the remaining portion is separated into a methyl tert-butyl ether and C4-hydrocarbons by distillation. It was converted from the raised isobutylene

94.7%. The effluent C + fraction contained more than 98% of the raised n-butylene.

Claims (3)

CLAIMS 1. A process for the selective recovery of isobutylene from hydrocarbon mixtures, comprising in particular C1-hydrocarbons, such as n-butylene, n-butane and butadiene, and optionally C1-C6-hydrocarbons, in the form of methyl tert-butylene, by treatment. methanol in the presence of sulfuric acid, characterized in that isobutylene in the hydrocarbon mixture is treated in the presence of less than 20% sulfuric acid as catalyst, calculated on the reaction mixture, at a temperature of 50 to 120 ° C, preferably at 80 to 100 ° C in a homogeneous liquid phase with a 0.1 to 4.0 molar excess of m-ethanol per mole of isobutylene; the resulting mixture is cooled to -25 ° to +40 ° C after the reaction, and the methanol-free reaction mixture is returned to it; isobutylene-free mixture, after the formation of the two liquid phases, the lower - sulfuric acid-rich phase - is returned to the original reaction, and - methanol is removed from the upper phase after washing with water, which is also used in the original reaction, and methyl t-butyl ether was distilled off. 2. The process according to claim 1, for obtaining isobutylene mainly from C + fractions containing 10 to 40% isobutylene, characterized in that the reaction in the homogeneous phase maintains a molar ratio of metarno: isobutylene of 1.5 to 5.0. %, Preferably 2.0 to 4.0: 1, and 9.5 to 8% by weight, preferably 1.0 to 5% by weight, of sulfuric acid are added and, upon cooling, are added to the reaction mixture of 1 to 80% by weight. % isobutylene-free C4-fraction and / or methanol-free reaction mixture, preferably 10-40% by weight. 3. The process according to claim 1, wherein isobutylene is obtained from a mixture of C4-hydrocarbons containing more than 80% isobutylene, characterized in that the reaction is carried out with a molar ratio of methanol: isobutylene of 1.1 to 2.0 -: 1, preferably 1.2 to 1.4: 1 to use 0.7 to 13% by weight, preferably 0.5 to 7.0% by weight, of sulfuric acid, based on the reaction mixture.