RU42185U1 - INSTALLATION FOR ONE-STAGE LIQUID PHASE SYNTHESIS OF ISOPRENE - Google Patents

Abstract

The proposed utility model relates to devices for producing monomers for the production of synthetic rubber, in particular, isoprene by a single-stage method in the liquid phase from isobutylene and formaldehyde (or their constituent substances) in the presence of an aqueous solution of an acid catalyst. A utility model is an installation including a vertically mounted hollow apparatus, a shell-and-tube heat exchanger, an external pipe for circulating the reaction mass, and distribution devices for supplying raw materials inside the hollow apparatus. A shell-and-tube heat exchanger is integrated inside the hollow apparatus, dividing its volume into upper and lower parts with a ratio of 2 to 2.5, respectively, while the diameter of the heat exchanger tubes is at least 5 times smaller than the diameter of the circulation pipe connecting the upper and lower parts hollow apparatus, and the circulation of the reaction mass through the tubes of the shell-and-tube heat exchanger is ensured either by force or due to the difference in the densities of the liquid and gas. The upper and lower parts of the hollow apparatus are connected by one or two remote pipes. The proposed installation model allows to reduce the metal consumption of the reactor block, use the reactor shell as a shell of the heat exchanger, which simplifies the design of the installation, as well as minimize equipment corrosion and loss of isoprene continuously removed from the reaction volume .

Description

This utility model relates to devices used in the production of monomers for synthetic rubber, in particular, to the design of an apparatus for the synthesis of isoprene by a one-stage method in the liquid phase from isobutylene and formaldehyde or substances that are sources of isobutylene and formaldehyde, for example, trimethylcarbinol (TMK) or dimethyldioxane (DMD), in the presence of an aqueous solution of an acid catalyst.

There are several design options for reactors designed for one-stage synthesis of isoprene in two stages. Thus, a reactor block for one-stage synthesis of isoprene is known, consisting of two series-connected similar shell-and-tube apparatuses, each having 7 tubes, with internal circulation of the aqueous phase in both apparatuses. In both devices, under the lower tube sheet, special design valves are installed that have six holes along the perimeter opposite each of the 6 tubes. Opposite the 7th tube, located in the center, there is no hole, which creates an internal circulation of the water layer. At the top of the second reactor there is a separation zone in which gaseous and liquid reaction products are separated and removed from the system [Auth. testimonial. USSR No. 1216940, BI ,, No. 8, 1983]. The main disadvantage of this design is the irrational use of the reactor volume, since the flow rises along part of the pipes, and falls partly, and the annulus is practically not used, which leads to a large metal consumption of the structure. In addition, the design of the second reactor does not provide an effective removal of isoprene from the reaction zone, as evidenced by

high yield of products of its polymerization, amounting to approximately 30% per 1 kg of monomer.

Also known is a unit for one-stage synthesis of isoprene, including one or more hollow apparatuses installed in series or in parallel (I reaction zone) and a plate column with a remote boiler (II reaction zone). Instead of hollow apparatuses, shell-and-tube apparatuses or apparatuses with integrated structures (plates, grids, tubes, nozzles) can be used in reaction zone I, and other apparatuses with a highly developed heat exchange surface, for example, a tubular apparatus or its combination with columned or capacitance [US Pat. RF №2085552, publ. BI, No. 21, 1997]. The disadvantage of this design is the large metal consumption, low productivity of the contact equipment and the inefficiency of the removal of isoprene from the reaction zone.

Also known apparatus for the liquid-phase synthesis of isoprene, including two series-connected apparatus - airlift and shell-and-tube columns with switchgears located at the bottom of each column. The airlift column (isoprene precursor synthesis unit) contains a lifting section in the form of a tube bundle, the annular space of which acts as a lowering section. The shell-and-tube column (isoprene production unit) is equipped with an external circulation loop connecting the upper separation and lower reaction zones [Pat. RF №2061538, publ. BI, No. 6, 1989]. However, this design has a common disadvantage of all tubular apparatuses used as devices for carrying out reactions with the formation of gases. In the second reactor, due to the transition of isobutylene and isoprene to the gas phase, the ratio of gas to liquid phases sharply changes from the minimum at the inlet to the pipe to the maximum at the outlet. And since the chemical reaction

occurs exclusively in the liquid phase, the efficiency of the use of the reaction space decreases as the reaction mixture rises along the height of the tube.

Also known is the design of the reactor block, which includes two series-connected devices — an airlift column and a shell-and-tube column with an external circulation loop connecting the upper separation and lower reaction zones, with distribution devices located in the lower part of the columns, and equipped with identical height ring constrictions designed to increase the actual residence time of the reactants in the reaction volume [US Pat. RF 2096076, publ. BI, No. 32, 1994]. This design partially eliminates the common drawback of tubular reactors - a sharp change in the ratio of gas and liquid phases along the height of the tube. The achieved effect is based on the fact that in the pipe sections located above the narrowing, the density of the moving mixture slightly increases. However, the installation of ring constrictions cannot eliminate other disadvantages of this design, such as significant metal consumption, the complexity of process control, the inevitable loss of isoprene due to inefficiency of its withdrawal from the reaction medium, etc.

The closest in technical essence to the proposed design is the design of a unit for liquid-phase synthesis of isoprene in one step, consisting of a vertically mounted hollow reactor connected in a single block with a shell-and-tube heat exchanger parallel or coaxially mounted below, designed to heat the reaction mass and process part of the raw material. Steam is supplied into the annular space of the heat exchanger, and the reaction mass circulates through the pipes. At the bottom of the cylindrical part of the reactor on the same axis with the axis of the pipe connecting the reactor with the upper part of the heat exchanger,

a switchgear is installed for inputting the main part of the raw material. A similar design switchgear is installed in the lower part of the heat exchanger (under the tube sheet) on the same axis with the axis of the pipe connecting this apparatus to the reactor (above the top tube sheet). From the lowest point of the spherical part of the reactor, a second pipe leaves, connecting the reactor with the lower zone of the heat exchanger located below the tube sheet, and from the highest point of the reactor leaves the pipe, designed to divert contact gas to the separator [US Pat. RF №32706, publ. 09/27/2003 - prototype]. This design ensures good mixing of the reaction mass and, no less important, the effective removal of isoprene in the isobutylene stream from the reaction zone, however, its main drawback is the presence of an external heat exchanger in its composition, which leads to an increase in the metal consumption of the installation (the cost of manufacturing heavy flanges and a shell and tube housing heat exchanger), and most importantly, is associated with inevitable heat loss. Due to the presence of the latter, it is necessary to preheat the raw material to the reaction temperature or to overheat it 5-7 ° C above this temperature. Since the feed enters the reactor together with an aqueous solution of an acid catalyst, this operation inevitably leads to loss of feed for the formation of additional quantities of by-products and creates conditions for gum formation.

The problem to which the proposed model is aimed is to develop a simplified design of a liquid-phase synthesis plant for isoprene from isobutylene and formaldehyde, which allows synthesis in one reaction zone (in one step), and provides a combination of intensive heat supply, efficient mixing of the reaction mass and vigorous removal from the reaction zone of its products with the minimum required contact time of the reactants and subject to a sufficiently high productivity of the reactor device TWA and reducing the metal consumption of the installation. Specified task

was solved by using the proposed installation for the synthesis of isoprene in one step, consisting of a vertically mounted hollow reactor 1, in which a shell-and-tube heat exchanger 2 is installed, designed to supply heat necessary for the reaction, and one or two circulation pipes 3 connecting the upper and lower parts of the reactor (Fig. 1), the diameter of which is at least five times the diameter of the tubes of the heat exchanger 2. The body of the hollow reactor 1 is at the same time the shell of the heat exchanger 2. The volume ratio is top it and the lower parts of the hollow reactor 1, separated by a built-in heat exchanger 2, is a value of not less than 2-2.5. The reaction mass is circulated in the tubes of the heat exchanger due to the difference in the densities of gas and liquid. For intensification of mixing can be used forced circulation using a pump 4. Both parts of the reactor contain switchgear 5, designed for the supply of raw materials.

Switchgears 5 are a system of tubes with holes with a diameter of 2-5 mm parallel to the central (feed) pipe. The area of switchgears, calculated by their overall dimensions, is no more than 25% of the cross section of the vessels in which they are installed.

The installation for liquid-phase synthesis of isoprene from isobutylene and formaldehyde in one step (Fig. 1) works as follows. The feedstock is mixed with an aqueous solution of an acid catalyst and at 70-90 ° C in the form of a homogeneous mixture through a distributor 5 is fed into a hollow reactor 1, heated to the reaction temperature using high-temperature steam supplied to the annular space of the heat exchanger 2. In the reactor 1 and in the heat exchanger 2 maintain a pressure sufficient for the reagents to remain in the liquid phase, but below the pressure of saturated water vapor at the reaction temperature, thereby preventing boiling of water. Under reaction conditions at a temperature of 150-200 ° C and pressure

6-17 atm TMC dehydration and the formation of isoprene in a homogeneous medium proceed at high speed and gas flows of isobutylene and isoprene effectively mix the reaction mass in reactor 1 and remove organic products and part of water (in the form of liquid) from upper part 1 through the upper nozzle to the separator . Even better mixing is achieved by forced circulation of the reaction mass using a pump installed on the supply line of the mixture through an external pipe into the reactor 1.

The advantages of the proposed installation are as follows. Since the movement of the reaction mass occurs from the bottom up, the tubes of the heat exchanger 2 are constantly under the inlet, which largely prevents corrosion of the walls of the tubes and eliminates the contact of reaction products with a heated metal surface. Due to the significant difference in the density of water and hydrocarbons in the gas phase, the rise of the reaction mass inside the tubes is significantly accelerated and, accordingly, the frequency of its circulation increases. Since the reaction medium is constantly in the liquid phase, losses of isoprene continuously removed from the reaction volume in the isobutylene stream are minimized. Due to the intensive circulation of the aqueous catalyst solution, an almost constant temperature is maintained at all points of the reactor. The temperature difference between the upper and lower parts of the reactor does not exceed 1 ° C.

Reducing the metal consumption of the reactor unit, compared with the installation of the prototype, is achieved in the proposed installation due to the simplification of the design - elimination of flange connections and the use of the reactor vessel as a shell of the heat exchanger.

Claims (2)

1. Installation for one-stage liquid-phase synthesis of isoprene from isobutylene and formaldehyde or the substances that are their sources, for example, trimethylcarbinol or dimethyldioxane in the presence of an aqueous solution of an acid catalyst, including a vertically mounted hollow apparatus, a shell-and-tube heat exchanger, a remote pipe for circulation of the reaction mixture, and distribution devices for raw material supply inside the hollow apparatus, characterized in that the shell-and-tube heat exchanger is integrated inside the hollow apparatus, dividing it about the removal to the upper and lower parts with a ratio of 2 to 2.5, respectively, while the diameter of the tubes of the shell-and-tube heat exchanger is not less than five times smaller than the diameter of the circulation pipe connecting the upper and lower parts of the hollow apparatus, and the circulation of the reaction mass through the tubes of the shell-and-tube heat exchanger carried out either by force, or due to the difference in density of liquid and gas. 2. Installation according to claim 1, characterized in that it contains two remote pipes connecting the upper and lower parts of the hollow apparatus.