RU2280022C1 - Process of producing isoprene from isobutene and formaldehyde - Google Patents

Abstract

FIELD: industrial organic synthesis.

SUBSTANCE: isoprene is produced from isobutene contained in C4-hydrocarbon fraction and formaldehyde in presence of water acid catalyst corrosive or moderately corrosive toward alloyed steel. Process is accomplished in at least two stages of liquid-phase chemical conversion to form, in the intermediates synthesis stage, isoprene precursors and withdrawing them with organic and essentially water stream followed by distillation of at least C4-hydrocarbons from organic stream and joint processing of the rest of organic stream and above-mentioned essentially water stream in intermediates decomposition stage. Decomposition of intermediates is accompanied by continuous withdrawal of vapor stream containing isoprene, isobutene, and a part of water, which stream is further subjected to separation and removal of liquid stream containing essentially water and acid and, preferably, removal of liquid organic stream containing high-boiling by-products. At least part of isobutene isolated from decomposition stage products is recycled into the beginning of this stage in such an amount that, in this stage, input streams contain summary molar amount of isobutene and tert-butanol exceeding by 1.1 times, preferably by 1.4 times, summary molar amount of formaldehyde and 4,4-dimethyl-1,3-dioxane. Organic stream obtained after condensation and stratification of vapor stream from decomposition stage is brought into contact with liquid stream from decomposition stage containing mainly water and acid and then subjected to separation involving at least rectification step, and stream containing mainly water and acid is recycled into the beginning of decomposition and/or synthesis stage.

EFFECT: simplified technology and reduced formation of high-boiling by-products.

2 cl, 2 dwg, 3 ex

Description

The invention relates to the field of production of isoprene (2-methyl-1,3-butadiene). More specifically, the invention relates to the field of production of isoprene from isobutene contained in C ₄ hydrocarbon fractions and formaldehyde.

Known and widely used in industry, the method [S.K. Ogorodnikov, G.S. Idlis. Isoprene production. L., Chemistry, 1973, p.47-64] obtaining isoprene from isobutene C ₄ fractions and formaldehyde, including the interaction of isobutene with formaldehyde in the presence of an aqueous solution of a strong acid with the formation of mainly 4,4-dimethyl-1,3-dioxane (DMD ), the separation of DMD in a concentrated state and its high-temperature (370-390 ° C) gas-phase decomposition in the presence of a solid catalyst, followed by the isolation of isoprene from the reaction mixture.

The disadvantage of this method is the complexity, low selectivity of the transformation of the starting reagents and a significant consumption of energy.

The known method [US Pat. RF №2085552, 07.27.1997] the production of isoprene from isobutene or tert-butanol and formaldehyde, which includes two zones of chemical transformation in the presence of an aqueous solution of a strong acid, the first of which, when the isobutene or tert-butanol reacts, several oxygen-containing intermediates are formed - precursors isoprene, mainly DMD, as well as 3-butane-1,3-diol and isoamylene alcohols. The resulting reaction mixture is sent without separation to the second reaction zone, where at a higher temperature (150-175 ° C), a joint liquid-phase decomposition of these products is carried out with the formation of isoprene.

The disadvantage of the method when using an isobutene-containing mixture of C ₄ hydrocarbons as a raw material is the need for preliminary extraction of isobutene from the mixture in concentrated form or in the form of tert-butanol, which requires additional costs. At the stage of decomposition of intermediates, a large number of high-boiling by-products are formed, mainly as a result of the release of formaldehyde during the decomposition of DMD and its participation in compaction reactions.

There is also known a method [US Pat. RF №2131863, 06/20/1999,] the production of isoprene from isobutene contained in the C ₄ hydrocarbon fraction and formaldehyde, comprising two stages carried out in the presence of a strongly acid catalyst and water, in the first of which the isobutene C ₄ fraction is reacted and formaldehyde with the formation of isoprene precursors, mainly DMD, followed by distillation of unreacted C ₄ hydrocarbons from the reaction mixture. The remaining mixture, preferably after additional contact with formaldehyde, is sent to the decomposition stage, where, at a higher temperature, the intermediates are converted predominantly to isoprene with continuous distillation of the resulting isoprene from the reaction zone in the composition of the vapor mixture, which also includes at least isobutene and water, followed by condensation by peeling water and separating the organic mixture (layer) by distillation. A liquid stream is also withdrawn from the reaction zone, containing mainly water, acid and high boiling point by-products, which circulate to the first stage and possibly partially to enter the reaction zone of the second stage.

The disadvantage of this method is the formation at both stages of a large number of high-boiling by-products (WFP) and their accumulation in the system, which leads to the formation of solid deposits on the equipment and its clogging. The formation of runways and solid deposits is facilitated by the release of a large amount of formaldehyde during decomposition of DMD, which tends to enter compaction reactions, and the lack of effective removal of runways from the system. The necessary technical solutions for significantly reducing runway formation and preventing solid deposits and blockages are not indicated in patent No. 2131863.

In the absence of such decisions (tricks), it is impossible to ensure long-term operation without stops for mechanical cleaning of equipment. The characteristic of the intensity of deposits in the patent of Russian Federation No. 2131863 is not given. Our experience according to patent No. 2131863 has shown that significant deposits are observed after 3-6 weeks of operation.

According to the patent of the Russian Federation No. 2131863 the yield of isoprene per 1 ton of consumed formaldehyde (the most prone to adverse reactions of the starting component) is from 1.63 to 1.71 tons; while the formation of the runway is from 0.28 to 0.51 tons

We were able to find a method for producing isoprene from isobutene C ₄ fractions and formaldehyde with a high degree and selectivity of converting isobutene and formaldehyde to isoprene without preliminary hydration of isobutene with a significant reduction in runway formation, with the exception of their accumulation in the system and a sharp decrease in their compaction and formation of solid deposits. This is achieved by applying a set of techniques (features), of which each is insufficient, but which together ensure the achievement of the indicated significant result by increasing the selectivity of the conversion of formaldehyde and isobutene to isoprene and a sharp decrease in solid deposits leading to equipment clogging. In our proposed method, chemical bonding of formaldehyde released during DMD decomposition with isobutene and tert-butanol is carried out, which leads to the formation of an additional amount of DMD, which further decomposes along with the liquid in the reaction zone to produce additional isoprene. The runway is extracted from a stream containing predominantly water and acid by extraction with an organic (mainly hydrocarbon) stream formed in the process.

We declare:

A method of producing isoprene from isobutene contained in the C ₄ -fraction of hydrocarbons and formaldehyde in the presence of water and an acid catalyst not aggressive or moderately aggressive with respect to alloy steel, at least in two stages of liquid-phase chemical conversion with the formation of isoprene precursors at the synthesis stage by removing them as part of an organic and predominantly aqueous stream, distilling at least C ₄ hydrocarbons from the organic stream, and co-processing the remainder of the organic an organic stream and said predominantly aqueous stream at the stage of decomposition of intermediates with a continuous output of a steam stream containing isoprene, isobutene and part of the water to be further separated, a liquid stream containing mainly water and acid, and preferably a liquid organic stream containing high boiling point by-products in which at least part of the isobutene released from the products of the decomposition stage is recycled to the entrance to this stage in such an amount that the total molar amount of isobutene and tert-butanol in it flows exceeds 1.1 times, preferably more than 1.4 times, the total molar amount of formaldehyde and 4,4-dimethyl-1,3-dioxane, the organic stream obtained upon condensation and delamination of the vapor stream from the decomposition stage, they are contacted with the liquid stream from the decomposition stage containing mainly water and acid, and after contacting the organic stream is separated by at least rectification, and the stream containing mainly water and acid are recycled to enter the decomposition step (s) and / or the synthesis step.

As possible clarifying options for implementing this method, we declare methods in which:

- at the synthesis stage, tert-butanol is formed in large quantities and it is supplied and possibly an additional amount of tert-butanol in the composition of the streams at the decomposition stage in a molar amount exceeding more than 1.5 times, preferably more than 2 times, the molar amount at the stage of decomposition of formaldehyde;

- for catalysis at both stages or only at the stage of decomposition, an aqueous solution is used containing phosphoric and / or boric and / or oxalic acid and corrosion inhibitors, and it is possible to use strongly acidic (e) solid catalyst (s) at the synthesis stage preferably sulfocathionite (s);

- in the reaction zone (s) at the synthesis stage, direct-flow and / or countercurrent movement and / or mixing of organic and predominantly aqueous flows are carried out, and at the decomposition stage, mainly direct-flow flows from bottom to top are carried out in the presence of distribution and / or mass transfer elements;

- at the synthesis stage, primarily isobutene is hydrated primarily, possibly at a high temperature and with a portion of formaldehyde being fed, and then isoprene precursors are synthesized predominantly with formaldehyde being fed, possibly at a lower synthesis temperature;

- less high-boiling substances than 4,4-dimethyl-1,3-dioxane are distilled off completely or partially from the remaining part of the organic stream of the synthesis stage after the C ₄ hydrocarbons are distilled off, and they are fed to the reaction zone of the decomposition stage above the boiler and / or to the separation unit products after the decomposition step;

- at the stage of decomposition using one or more vertical heated shell-and-tube reaction apparatuses and the decomposition of intermediates is carried out inside the tubes;

- at the decomposition stage, a column reaction apparatus is used, possibly containing mass transfer elements, in the lower part of which there is a boiler located or connected to it, the tubes of which communicate with the internal space of the specified column apparatus, and at least a part of the flows from the synthesis stage after distillation are fed to the specified boiler as minimum C ₄ hydrocarbons from the organic stream and recycled isobutene;

- a stream containing tert-butanol distilled from the organic stream of the synthesis step is fed to the column reaction apparatus of the decomposition step, preferably in parts, at points at different heights;

- over the entire height of the decomposition zone (s), a high temperature is maintained with a difference of not more than 30 ° C by recirculation of a sufficient amount of a heated aqueous acid stream;

- use a decomposition zone with a volume and height sufficient for the interaction of isobutene and tert-butanol with the formaldehyde released during decomposition of 4,4-dimethyl-1,3-dioxane, additional formation of 4,4-dimethyl-1,3-dioxane and its decomposition with the formation of isoprene;

- sulfocationionite is used in the synthesis stage and a water stream containing a portion of isoprene precursors is supplied to the decomposition stage from the synthesis stage, in an amount excluding excessive accumulation of water in the synthesis stage, and the stream containing mainly water and acid from the decomposition stage is recycled only to the inlet decomposition stage;

- maintain the temperature at the synthesis stage from 60 to 120 ° C and at the decomposition stage from 130 to 170 ° C;

- at the stage of synthesis, isoprene is partially obtained as part of the organic stream, after the C ₄ hydrocarbons are distilled off from the organic stream, the isoprene-containing stream is fed, which is passed bypassing the boiler to the column apparatus of the decomposition stage or to the product separation unit after the decomposition stage.

High conversion and selectivity of conversion of isobutene C ₄ fractions and formaldehyde to isoprene and practical (until a planned stop) elimination of equipment clogging are achieved due to the fact that:

- eliminates the significant influx of recycled (s) stream (s) to the stage (s) of decomposition and / or synthesis of a significant amount of high-boiling by-products capable of further compaction (polymerization, polycondensation) into solid products;

- at the decomposition stage, the interaction of incoming and / or released formaldehyde with isobutene and tert-butanol is ensured with the formation of intermediates that are converted to isoprene at the same stage;

- the isobutene released during the decomposition stage is converted into an additional amount of isoprene.

The term "predominantly water stream" is used to mean a stream containing predominantly water, and also possibly an acid with inhibitors and / or dissolved organic substances.

The use of the invention is illustrated in figures 1 and 2 and examples. The figures 1 and 2 and the examples do not exhaust all the options for using the invention, and other technological solutions are possible subject to the signs specified in paragraph 1 of the claims.

For brevity, in FIGS. 1 and 2, the recycling unit for the synthesis of intermediate precursors is depicted by one apparatus (P-1). Actually, this node may include several connected devices (zones) with direct-flow or counter-current movement of liquid flows. In this case, a distributed supply of formaldehyde is possible in different sections (zones) of the reaction unit, optionally at the entrance to the first reaction zone.

According to Fig. 1, an isobutene-containing C ₄ hydrocarbon fraction is fed through line 1, formaldehyde solution is fed through line 2, possibly an aqueous solution of acid and corrosion inhibitors along lines 30 and / or 32b, the flows are mixed, heated, and fed to line 4 through a reactor ( s) synthesis of P-1.

From the reactor (s) R-1 through line 5, a stream of reaction mass is withdrawn, which is layered in a separator-settler S-1. Perhaps delamination is carried out in the upper part of the reactor (s) R-1 and mainly water stream is discharged through line 6. An organic layer (stream) is withdrawn from C-1 through line 7, which is fed to a K-1 distillation column, and mainly a water stream is withdrawn through line 8. Stream (s) 6 and / or 8 along lines 6a and 9 (and then 9a) are fed to the decomposition stage of intermediates. It is possible that part of stream 6a via line 10 is returned to the inlet of reactor P-1, preferably after cooling. It is also possible that stream 6a, or part thereof, is fed via line 9b (and further 27) to the mixer CM.

Unreacted C ₄ hydrocarbons are removed from the K-1 column as distillate via line 11. From the bottom of the K-1 column, the rest of the stream is discharged via line 12, which is sent via line 12b to the K-2 distillation column (if used) and / or along lines 12a, 14 (hereinafter lines 15 and possibly 16) to the decomposition zone (s) intermediates.

On top of the K-2 column (if used), a relatively relatively low boiling point stream is removed via line 19, which is removed from the system via line 19a, and / or is fed via line 19b to the decomposition zone P-2 (preferably along lines 21, 21a, 21b, bypassing the boiler), and / or sent to the node separation of the products of the decomposition stage (node UR). Bottom of column K-2, stream 13 is discharged, which, possibly together with stream 12a, is fed to the decomposition step. Possibly, a stream containing mainly tert-butanol, which is fed to the decomposition zone along lines 21, 21a, 21b, is taken out from K-2 along line 20.

In the decomposition zone serves water-acid (e) stream (s) (completely or mainly from the bottom to the boiler), organic (e) stream (s) containing (e) intermediates (bottom and / or to the column part P-2), IS isobutene recycle stream (completely or predominantly from below), heavy inert solvent stream P (input via line 38) and, possibly, other substances isolated in the separation unit of SD, except for isoprene IPR and high-boiling runway by-products. In the annular space of the boiler K serves a heating agent "GA".

A steam stream containing mainly isoprene, isobutene and water, which is then condensed, is delaminated in a S-2 separator-settler and the organic stream is discharged through line 23 and the water stream is passed through line 23 from the top of the P-2 apparatus.

From the upper part of P-2, a liquid stream containing mainly water and acid is discharged through line 25, and possibly a liquid stream containing high boiling point by-products is discharged through line 26.

It is possible that the liquid (s) withdrawn (e) from P-2 is subjected to delamination in an additional separator (not shown in FIG. 1) and the corresponding streams 25 and 26 are removed from it.

Stream 25 is in contact with stream 23 and, possibly, stream 9b in the CM mixer (input via line 27) and the mixture (stream 28) is stratified in separator-settler C. Organic stream is fed from line C through line 31, which is fed to the separation unit SD. Line 29 discharges the input acid stream. It is sent to the entrance to the apparatus R-2 (along line 30a) and, possibly, partially along line 30 (hereinafter along line 4), it is fed to the entrance to the reactor R-1.

IB isobutene stream is taken out from the UR node through line 32, which is at least partially recycled to Р-2 along line 32a and, possibly, partially along line 32b - to Р-1, and IPR isoprene stream is taken out through line 33. It is possible that a tert-butanol TB stream is withdrawn through line 34, a 4,4-dimethyl-1,3-dioxane stream (recycle to P-2 and / or P-1) through line 35, and a high boiling point stream through line 36 WFP products and through line 37 - a stream of other by-products.

Preferably, in the streams 7 and 31 supplied to the separation columns (unit), the acid is neutralized by known methods (by adding alkali, contacting with calcium carbonate, calcium oxide, anion exchange resin, etc.).

According to figure 2, in contrast to figure 1 at the stage of synthesis of intermediates countercurrent movement of flows (organic and "water") is carried out in the reaction (s) zone (s), and at the stage of decomposition of intermediates use a shell-and-tube boiler K, not integrated in the reaction column zone P-2, and located separately and connected to zone P-2 by a gas-liquid line. From the boiler K, the gas-liquid stream or its gas (steam) part enters the P-2 through a distribution device. It is possible that a small aqueous acidic stream is discharged from line P-2 from line 39.

Figure 2 shows one reaction apparatus at the stage of synthesis of intermediates. It is possible to use several sequential reaction apparatuses connected by countercurrent flows (organic and "water").

The isobutene-containing stream 1 and, possibly, the isobutene stream recycled through line 32b, enter (s) into the lower part of the reaction zone through a distribution device. The water-formaldehyde stream 2 and the recycled (e) stream (s) containing (e) predominantly water are passed through line 3 to the upper part of the reaction zone. From above, a liquid, mainly organic stream 5 is removed from P-1, which is additionally separated from water in a C-1 apparatus. The aqueous layer along line 6 is returned to P-1, and the organic layer is fed to a distillation column K-1.

From below, P-1, along line 8, a mainly aqueous (possibly acid-acid stream) is withdrawn, which is completely or partially directed along line 9 to the stage of decomposition of intermediates; perhaps part of stream 8 along line 10 is recycled to the inlet to the upper part of reaction zone P-1 (possibly cooling).

The rest of the scheme of figure 2 operates similarly to figure 1 and does not require additional explanation (they are given in the description of figure 1).

In the examples, concentrations are everywhere indicated in wt.%.

EXAMPLE 1

Processing is carried out according to figure 1 (without the use of distillation column K-2).

As isobutene-containing feed F is fed through line 1 (and further 3 and 4) in an amount of 25.33 kg / h of a mixture of hydrocarbons With ₄ containing 45% isobutene, as well as mainly isobutane and 2% n-butenes.

15.57 kg / h of a solution of formaldehyde in water containing 38% formaldehyde and 2% methanol is fed through line 2 (and further 3 and 4).

17.70 kg / h of an aqueous solution of phosphoric acid (7.4%) with corrosion inhibitors and a small amount (less than 3.5% in total) of tert-butanol, methanol, methyldihydropyran and other impurities are also fed into the reaction unit P-1.

In the reaction unit of the synthesis stage, the temperature is maintained at 80-100 ° C. The conversion of isobutene is 93%, the conversion of formaldehyde is 86%. Isoprene precursors - 4,4-dimethyl-1,3-dioxane (DMD), 3-methylbutane-1,3-diol (MBD) and unsaturated C ₅ alcohols are formed in the ratio of 8.5: 1: 0.5.

The molar amount of the resulting tert-butanol is almost equal to the sum of the molar amounts of the resulting DMD and unconverted formaldehyde.

An organic stream containing hydrocarbons C ₄ , DMD (29.2%), tert-butanol (12.6%), and unsaturated alcohols C ₅ (0, 9%), partially methyl tert-butyl ether, MTBE (1.1%), high-boiling by-products, runway (3.2%) and other impurities. On line 9, a stream containing mainly water (78.4%), phosphoric acid with inhibitors (4.2%), MBD (4.5%), tert-butanol (5.9 %), partially formaldehyde (2.6%), high boiling point by-products (3.2%) and impurities.

Organic stream 7 is fed to a distillation column K-1. From K-1, a distillate containing predominantly C ₄ hydrocarbons (including 5.1% isobutene) and an admixture of methanol (0.1-0.2%) is withdrawn in an amount of 14.66 kg / h. From the bottom, from K-1, a stream containing 62.1% DMD, 26.8% tert-butanol, 1.9% C ₅ unsaturated alcohols and runway impurities (4.6%) is withdrawn via line 12 in the amount of 13.04 kg / hr. ), methyl tert-butyl ether, etc.

Streams 9 and 12 are fed to the reaction unit (R-2) of the stage of decomposition of intermediates, which are also fed (to a boiler) recycled isobutene in an amount of 7.0 kg / h and an inert hydrocarbon solvent (T _boil ~ 150-160 ° C) in an amount 1.0 kg / hour. The molar ratio of the sum of tert-butanol and isobutene to the sum of formaldehyde and 4,4-dimethyl-1.3-dioxane in the streams entering the decomposition stage is 1.95: 1; the molar ratio of tert-butanol to formaldehyde is 2.6: 1.

In R-2 maintain a temperature of 160-165 ° C. On top of P-2, a steam stream containing 35.3% of isoprene, 22.7% of isobutene, 38.1% of water, and also impurities is removed via line 22 in an amount of 30.86 kg / hr. The stream is condensed, layered in a separator, and an aqueous layer is discharged through line 24 in an amount of 11.85 kg / h, and an organic layer containing 57.3% isoprene, 36.8% isobutene and line 23 in an amount of 19.01 kg / h and impurities.

Two liquid streams are discharged from the upper part of P-2: a water-acid stream containing 6.9% phosphoric acid (FC) with corrosion inhibitors, 6.9% of the runway and impurities, and 2 in an amount of 2 9 kg / h, a stream containing 51.8% of an inert solvent, 37.9% of hydrocarbon-soluble runways, 10.3% of methyldihydropyran, MDHP, and methylenetetrahydropyran, MTHP is removed.

Streams 23 and 25 are mixed in a diaphragm mixer (SM) and then layered in separator C. At the same time, most of the runway (~ 80%) from the aqueous-acid stream passes into the organic stream. A water-acid stream containing 7.4% FC (with corrosion inhibitors) and 0.6% of the runway is withdrawn through line 29. Most of it is recycled to the entrance to R-2, and the other part in the amount of 17.85 kg / h is fed through line 8d to the stage of synthesis of intermediates. The organic layer through line 31 in an amount of 19.96 kg / h is fed to the separation unit of the SD, from which, in particular, a stream of 7.0 kg / h of isobutene is removed, which is recycled to the inlet of P-2, and a stream of 10.9 kg / isoprene hour.

During the 5-month run of the pilot plant, there were no signs of solid product deposition and equipment clogging. For 1 kg of used formaldehyde, the yield of isoprene was 1.84 kg, the formation of a runway-0.22 kg (versus 1.63-1.71 kg of isoprene and 0.28-0.51 kg of runway according to RF Pat. No. 2111863, respectively). Consumption per 1 kg of isoprene obtained: 0.54 kg of formaldehyde and 0.894 kg of isobutene (from a C ₄ fraction).

EXAMPLE 2

Processing is carried out according to figure 1 using, in contrast to example 1, also a distillation column K-2. The composition and amount of feed is similar to example 1.

In the reaction unit of the R-1 synthesis stage, Amberlist-36 sulfocationionite (particle size 0.3-1.3 mm, static exchange capacity 5.1 mEq / H ⁺ / g of catalyst) is used as a catalyst and the process is conducted in direct-flow mode . In the reaction unit of the decomposition step, an aqueous solution of phosphoric acid (7.5%) with corrosion inhibitors is used as a catalyst.

The water stream from the synthesis stage (line 6a) is partially recycled to the inlet of P-1, and the other part is in the amount of 29.60 kg / h (containing 4.7% MBD, 6.1% tert-butanol, 2.7% formaldehyde and impurities) are fed to the stage of decomposition of intermediates.

In R-1 maintain a temperature of 65-85 ° C. In contrast to Example 1, partial isoprene formation occurs at the stage of intermediate synthesis. The organic stream fed through line 7 to the distillation column K-1 contains 2.9% of isoprene. The rest of the composition (proportions of components) of the organic stream is almost similar to example 1.

14.60 kg / h of distillate, which contains mainly C ₄ hydrocarbons, including 4.5% isobutene, as well as 0.2% methanol, are withdrawn from the K-1 column. The bottoms stream from K-1 is fed to the K-2 column. On top of K-2, a stream containing 67.7% of isoprene, 1.5% of C ₄ hydrocarbons, 30.1% methyl tert-butyl ether and impurities, which is fed to the separation unit stage decomposition of intermediates (site UR).

The organic stream 13 from the K-2 cube and mainly the water stream 9 from the stage of synthesis of intermediates are sent to the reaction zone of the decomposition stage; there is recycled isobutene stream from the separation unit SD in the amount of 4.5 kg / h.

The molar ratio of the sum of isobutene and tert-butanol to the sum of DMD and formaldehyde in the streams fed to P-2 is 1.5: 1; the molar ratio of tert-butanol and formaldehyde is 2.5: 1.

In R-2 maintain a temperature of from 155 to 167 ° C. The output of the streams 23, 24, 25, 26 and the contacting of the streams 23 and 25 are carried out similarly as described in example 1. From the aqueous-acid stream, 85% of the runway contained in it is extracted. After delamination in separator C, the water-acid stream with a content of 0.4% of the runway is completely recycled to the inlet of the boiler R-2.

Obtain 11.0 kg / h of isoprene.

Solid deposits and blockages of equipment during long-term operation (4 months) were not observed. For 1 kg of spent formaldehyde, the yield of isoprene was 1.86 kg, runway formation 0.20 kg. Consumption per 1 kg of isoprene produced: ~ 0.54 kg of formaldehyde and 0.892 kg of isobutene (from a C ₄ fraction).

EXAMPLE 3

Processing is carried out according to figure 2. The amount of hydrocarbon feed, the concentration of isobutene in it and the concentration of formaldehyde in the initial aqueous solution are similar to examples 1 and 2.

In contrast to Examples 1 and 2, the C ₄ fraction of gasoline pyrolysis after extraction of butadiene and acetylene hydrocarbons, including 45% of isobutene, 41.5% of n-butenes, 13% of butanes and ~ 0.5-1.3, serves as an isobutene-containing feedstock. % butadiene.

In contrast to examples 1 and 2, in the reaction unit for the synthesis of intermediates, the process is carried out in countercurrent mode. The reaction unit P-1 includes two successive reactors (not shown separately in FIG. 2). The initial C ₄ fraction (line 1) is fed from below to the first reactor from the bottom, and an aqueous acidic solution (with a part of formaldehyde) from the second reactor is fed from above. The organic mixture discharged from the top of the first reactor is fed down to the second reactor, and the aqueous-acid mixture discharged from the bottom of the second reactor (with additional formaldehyde inlet) is fed to the top of the first reactor. A mainly aqueous acid solution is discharged from the bottom of the first reactor (line 8), a predominantly organic stream is discharged from the top of the second reactor (line 5), which is settled in a separator-settler С-1, and the organic stream from С-1 is then fed to distillation line column K-1.

In both stages, an aqueous solution of phosphoric acid (FC) with the addition of boric acid (0.5 rel.%) And corrosion inhibitors is used as a catalyst.

In the first reactor of the synthesis stage, a temperature of 100-120 ° C is maintained, in the second reactor of this stage, a temperature of 80-90 ° C is maintained. In the reaction zones of the second stage maintain a temperature of 150-165 ° C.

The conversion of isobutene at the stage of the synthesis of intermediates is 95%, the conversion of formaldehyde is 85%. DMD, MBD, and C ₅ unsaturated alcohols (total) are formed in a ratio of 5.33: 1: 0.33. In streams from the first stage, the molar ratio of tert-butanol to formaldehyde in the streams entering the decomposition stage is 3: 1.

The water-acid stream from the first stage (in it 4.9% MBD and 6.4% tert-butanol) is fed through lines 8, 9 and 9a in an amount of 32.0 kg / h directly to the decomposition stage.

During rectification of the organic stream from the synthesis step, K-1 is discharged from above to K-1 in an amount of 14.54 kg / h C ₄ hydrocarbon stream containing 3.9% isobutene and an admixture of 0.3% methanol. From below, K-1 stream 12 (hereinafter 12b) is fed to the K-2 column.

On top of K-2, an amount of 4.09 kg / h is removed from the stream, including tert-butanol (85.4%), MTBE (7.2%), MDGD and MTGD, which are fed to R-2 along two lines in cross-section, located at different heights. Bottom K-2 stream 13 is fed into the boiler K, connected to the P-2. It also serves a recycled stream of isobutene from the separation unit SD in the amount of 8.0 kg / h. In the streams entering the decomposition zone (s), the molar ratio of the sum of isobutene and tert-butanol to the sum of formaldehyde and DMD is 2.1: 1.

The output of the streams from P-2, the condensation and delamination of the stream 22 and then the contacting of the organic stream 23 and the input-acid stream 25 (followed by delamination) are carried out analogously to examples 1 and 2.

From stream 25, 90% of the runway contained is recovered by organic stream. The water-acid stream 29 from the separator With the majority (3/4) is fed into the boiler K decomposition stage. A smaller portion (1/4) of stream 29 is fed to the intermediate synthesis step.

When separating the organic stream 31 in the site of UR receive 11.2 kg / h of isoprene.

In the system, with a long run (4.5 months were spent), the formation of solid deposits and equipment clogging were not noted. For 1 kg of spent formaldehyde, the yield of isoprene was 1.89 kg, runway formation 0.18 kg. Consumption per 1 kg of isoprene produced: 0.53 kg of formaldehyde and 0.886 kg of isobutene (from a C ₄ fraction).

Claims (14)

1. A method of producing isoprene from isobutene contained in the C ₄ -fraction of hydrocarbons and formaldehyde in the presence of water and an acid catalyst that is not aggressive or moderately aggressive with respect to alloy steel, at least in two stages of liquid-phase chemical transformation with the formation of intermediates at the synthesis stage - precursors of isoprene, their removal in the composition of organic and predominantly aqueous streams, distillation of at least C ₄ hydrocarbons from the organic stream and joint processing of the remaining an organic stream and said predominantly water stream at the stage of decomposition of intermediates with a continuous output of a steam stream containing isoprene, isobutene and a portion of the water subjected to further separation, a liquid stream containing mainly water and acid, and preferably a liquid organic stream containing high boiling point by-products in which at least a portion of the isobutene released from the products of the decomposition stage is recycled to the entrance to this stage in such an amount that in their flows in it, the total molar amount of isobutene and tert-butanol exceeds by more than 1.1 times, preferably more than 1.4 times, the total molar amount of formaldehyde and 4,4-dimethyl-1,3-dioxane, an organic stream, obtained by condensation and delamination of the steam stream from the decomposition stage, is contacted with the liquid stream from the decomposition stage containing mainly water and acid, and after contacting the organic stream is separated by at least distillation, and the stream containing mainly but water and acid are recycled to enter the decomposition step (s) and / or the synthesis step. 2. The method according to claim 1, wherein at the synthesis stage, tert-butanol is formed in a large amount and fed and possibly additional tert-butanol in the composition of the streams to the decomposition stage in a molar amount exceeding more than 1.5 times, preferably more than 2 times the molar amount of formaldehyde entering the decomposition stage. 3. The method according to claim 1, in which for catalysis at both stages or only at the stage of decomposition, an aqueous solution is used containing phosphoric and / or boric and / or oxalic acid and corrosion inhibitors, and strongly acidic (e ) solid (e) catalyst (s), preferably sulphocationite (s). 4. The method according to claim 1, in which in the reaction (s) zone (s) at the synthesis stage, direct-flow and / or counter-current movement and / or mixing of organic and predominantly aqueous flows are carried out, and at the decomposition stage, mainly direct-flow movement of flows is performed from the bottom up in the presence of distribution and / or mass transfer elements. 5. The method according to claim 1, in which at the stage of synthesis primarily isobutene is hydrated, possibly at a high temperature and with a portion of formaldehyde being fed, and then isoprene precursors are synthesized predominantly with formaldehyde being fed, possibly at a lower synthesis temperature. 6. The method according to claim 1, in which less than high boiling substances than 4,4-dimethyl-1,3-dioxane are distilled off completely or partially from the remaining part of the organic stream of the synthesis stage after the C ₄ hydrocarbons are distilled off, and they are fed to the reaction zone of the stage decomposition above the boiler and / or to the product separation unit after the decomposition step. 7. The method according to claim 1, in which at the stage of decomposition using one or more vertical heated shell-and-tube reaction apparatuses and the decomposition of intermediates is carried out inside the tubes. 8. The method according to claim 1, in which at the stage of decomposition using a column reaction apparatus, possibly containing mass transfer elements, in the lower part of which is located or connected to it a boiler, the tubes of which communicate with the interior of the specified column apparatus, and are fed into the specified boiler as at least a portion of the streams from the synthesis stage after distillation of at least C ₄ hydrocarbons from the organic stream and recycled isobutene. 9. The method according to claim 1, wherein the stream containing tert-butanol distilled from the organic stream of the synthesis step is fed to the column reaction apparatus of the decomposition step, preferably in parts, at points at different heights. 10. The method according to claim 1, in which over the entire height of the decomposition zone (s), a high temperature is maintained with a difference of not more than 30 ° C by recirculating a sufficient amount of the heated aqueous acidic stream. 11. The method according to claim 1, wherein a decomposition zone is used with a volume and height sufficient for the interaction of isobutene and tert-butanol with the formaldehyde emitted during decomposition, additional formation of 4,4-dimethyl -1,3-dioxane and its decomposition with the formation of isoprene. 12. The method according to claim 1, in which sulfonation is used in the synthesis step, and a water stream comprising a portion of isoprene precursors is supplied to the decomposition step from the synthesis step, in an amount excluding excessive accumulation of water in the synthesis step, and a stream containing predominantly water and acid , from the decomposition stage recycle only at the entrance to the decomposition stage. 13. The method according to claim 1, wherein the temperature is maintained at the synthesis stage from 60 to 120 ° C and at the decomposition stage from 130 to 170 ° C. 14. The method according to claim 1, in which at the stage of the synthesis part of the organic stream is partially obtained isoprene, from the organic stream after distillation of C ₄ hydrocarbons, the stream containing isoprene is distilled off, which is fed bypassing the boiler to the column apparatus of the decomposition stage or to the separation unit products after the decomposition stage.

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