(a) Field of the Invention
The present invention relates to a method for the production of alkylates by sulfuric acid alkylation of isoparaffins with olefins. This method is particularly well adapted for use in the petroleum refining industry, using isobutane as isoparaffin, and butylenes as olefin.
The invention also relates to a device for mixing and reacting at least two and preferably three liquid components. This device is particularly well adapted for carrying out the above method even though it can be used for carrying out many other methods.
(b) Brief Description of the Prior Art
Alkylates are main components of high-octane motor fuels. They are produced by alkylation of isoparaffins (mainly isobutane) by olefins (such as propylene, butylenes or amylenes) in the presence of sulfuric or hydrofluoric acid that serves as a process catalyst. The most widely known method for the production of alkylates in the petroleum refining industry consists of carrying out a sulfuric acid alkylation of isobutane by olefin.
Numerous methods for carrying out sulfuric acid alkylation of isobutane by olefins are known. The method according to the invention distinguishes over most of these known method in that the reaction is carried out in a compact reactor which does not contain moving parts and in which jet mixing of the reagents is achieved.
U.S. Pat. No. 3,544,652 issued on Dec. 1st, 1970 discloses a method for the alkylation of isoparaffin by olefins in the presence of sulfuric acid, where the olefin is reacted with an alkylating hydrocarbon-in-acid emulsion formed by thoroughly mixing isoparaffin with sulfuric acid before contact with the olefin. In this patent, the isoparaffin-to-olefin volume ratio is disclosed as being equal to about 12:1. The acid-to-hydrocarbons volume ratio is disclosed as being within the range of 2.5:1 to 15:1 but it is mainly maintained at about 6:1. The reaction is carried out adiabatically, mainly in a continuous manner, in a reactor called “alkylation contactor”, which is provided with a mixer that is devised for forming the isoparaffin-in-sulfuric acid emulsion and for thoroughly and homogeneously mixing the so-formed emulsion with the olefin at the points of delivery of the latter into the reactor.
As the liquid flows through the reactor, the temperature of the alkylating mixture rises continuously by 5 to 15° C., thereby reducing viscosity of the mixture and increasing its turbulence. The method is carried out at a temperature of 5 to 60° C. under a pressure sufficient for keeping the reagents in a liquid state (from 2 to 10 ATMs). Prior to being mixed with the isoparaffin, sulfuric acid at a concentration of 88 to 99% is cooled down to a temperature of about 4° C.
The emulsion preparation and the olefin injection and distribution inside the reaction area are not disclosed in detail in this U.S. patent.
The method disclosed in U.S. Pat. No. 3,544,652 is efficient but it requires a substantial amount of power for circulating the acid due to the very high acid-to-hydrocarbons ratio. It also requires a settling equipment of a very large size. Moreover, the method disclosed in this patent cannot guarantee a low consumption of sulfuric acid and a reasonably high quality of the final product.
Russian patent No. 2,131,861 granted on Jul. 25, 1994 (corresponding to U.S. Pat. Nos. 5,443,799 and 5,777,189) discloses a method for sulfuric acid alkylation of isoparaffins by olefins and a device for carrying out this method. At the initial stage of the method disclosed in this patent, a thin isoparaffin-in-sulfuric acid emulsion is made by injecting isoparaffin into an acid medium through a set of nozzles. Then the emulsion is delivered into a reaction area where olefin is fed, through a number of points normal to the emulsion flow. In this method, the alkylation is carried out under isobaric and isothermal conditions.
Russian patent No. 2,131,861 also discloses that the emulsion should preferably flow in the emulsion area at a rate of 0.2 to 2 m/s—and within the reaction area at a rate of 0.04 to 0.27 m/s. Depending on the selected flow rate, the contact between the reagents may last from a few to 60 seconds, thereby reducing to a minimum the possibility of not-wanted side reactions such as oligomerization of olefins and autoalkylation of isoparaffins. Tests have shown that this method permits to prepare a thin unstable emulsion. Separation of the reaction mixture into a hydrocarbon phase and an acid phase takes 5 to 8 seconds, thereby allowing reduction in the setting time.
Since the method described in Russian patent No. 2,131,861 does not require rotary mixers, the equipment required for carrying it out is rather cheap and of easy control and maintenance.
Russian patent No. 2,131,861 further discloses a device for carrying out the above method. This device comprises a tank for preparing the emulsion. A special appliance is provided for isoparaffin injection within the tank. Such an appliance essentially consists of a set of axially arranged nozzles. An appliance is also provided for sulfuric acid injection within the tank. The device also comprises a mixing chamber that is part of the tank, with an outlet throat, and a cylindrical reactor which is connected in line to the throat of the emulsion preparation tank. To provide olefin injection, the device comprises a perforated branch pipe extending along the axis of the reactor.
The method and device described in the above Russian patent No. 2,131,861 and its foreign counterparts have rather acceptable technical and economic parameters of operations, as proved by industrial tests. However, those parameters could be improved if use is made of a higher level of flow turbulence in the reaction zone. In practice, such a higher level of flow turbulence could be obtained if the flow rate is increased in the reaction zone and the mixing conditions of olefin and emulsion flows are improved by using a more efficient olefin feed unit instead of using a perforated branch pipe extending along the axis of the reactor.
Russian patent No. 2,092,475 granted on Dec. 6, 1995 is the closest prior art known to the Applicant. It discloses a method for the production of alkylates in a tubular reactor, which comprises mixing sulfuric acid with isobutane previously cooled down to a temperature of not over −2° C.; mixing the obtained emulsion with olefins also previously cooled to a temperature of not over −2° C., in a plurality of stages; separating the sulfuric acid from the obtained reaction mass; and recycling it. This method requests that the sulfuric acid be mixed with the isobutane and the obtained emulsion be mixed with the olefin in an injector-type mixer, with an isobutane-to-sulfuric acid injection ratio of 3.3 to 5.2 and an isobutane-to-olefin volume ratio of 3000-5000:1. In this method, sulfuric acid is separated from the reaction mass in a hydrocyclone.
Russian patent No. 2,092,475 also discloses a device for carrying out the above method, which consists of a reactor provided with three concatenated injection mixers. Each mixer is provided with an olefin injection appliance that distributes the feed in a helical fashion along the length of a device.
With the method and device disclosed in Russian patent No. 2,092,475, one may carry out sulfuric acid alkylation of isoparaffins by olefins in a compact reactor that has no moving parts. One may also obtain a high quality alkylate, as proved by industrial tests. However, in practice, an isobutane-to-olefin ratio of 3,000-5,000:1 can be obtained in the reaction area only with very high power consumption. Alkylate quality and specific sulfuric acid consumption could actually be improved by using a more efficient olefin feed unit than the perforated tube with helical openings as described in this patent. Besides, alkylate quality and specific sulfuric acid consumption could be improved by optimization of the alkylation process conditions, by proper selection of different size ratios of the reactor elements and by an improved process of separation of the reaction mixture and a device to carry out this process.