南华大学化学化工学院毕业设计
up losses of the sulfuric acid by passing a sulfuric acid make-up stream to the process.
Even though the gaseous light ends stream recovered from the vacuum distillation system contains valuable unreacted ethylene, recycle of this stream to recover and use the ethylene therein is not feasible because of the presence of sulfur dioxide in the light ends stream. It has been suggested in the prior art that the light ends stream be scrubbed to remove sulfur dioxide therefrom, and then recycled to the ethyl acrylate reaction zone. Although removal of the sulfur dioxide is possible, the difficulty and expense of accomplishing the removal makes it commercially unfeasible to do so. No economical process has heretofore been presented to recover the ethylene values contained in the light ends stream, and consequently this light ends stream has generally been disposed of and a resulting loss of the ethylene values therein.
It is thus an object of the present invention to provide and disclose a method for treating said gaseous light ends stream from said ethyl acrylate process so as to recover ethylene values contained therein. It is an additional object of the present invention to provide and disclose a method for treating said light ends stream from the ethyl acrylate process so as to recover ethylene values contained therein and recycle same to said ethyl acrylate process without recycling the sulfur dioxide contained in the light ends stream. These and additional objects will become apparent from the following description of the present invention. SUMMARY OF THE INVENTION
The foregoing and other objects are accomplished by the present invention which, in one of its aspects is an improvement in a continuous process for the production of ethyl acrylate from ethylene and acrylic acid utilizing a sulfuric acid catalyst wherein the reaction products are distilled in a vacuum distillation system at a reduced pressure less than
第 31页（共46页）
南华大学化学化工学院毕业设计
atmospheric to obtain a liquid ethyl acrylate product and also resulting in a first gaseous light ends stream from said vacuum distillation system containing sulfur dioxide and also containing ethylene and other organic light ends, and wherein losses of sulfuric acid catalyst are replenished by continuously passing to the reaction zone of said process of a liquid concentrated sulfuric acid make-up stream consisting of concentrated sulfuric acid having a water content of less than 5% by weight, which improvement comprises: continuously and intimately contacting in a gas-liquid contact zone said first gaseous light ends stream with a reactant liquid consisting essentially of said liquid concentrated sulfuric acid make-up stream and the hereafter defined liquid recycle stream, said contacting being under such conditions as to cause ethylene in said first gaseous light ends stream to react with sulfuric acid in said reactant liquid so as to form ethyl hydrogen sulfate and diethyl sulfate, the said first gaseous light ends stream being at a temperature within the range of about 25.degree. C. to 150.degree. C. when passed to said contact zone, the initial temperature of said reactant liquid being within the range of about 40.degree. C. to 150.degree. C., and the pressure in said contact zone being maintained at a superatmospheric pressure within the range of about 1.05 atmospheres absolute to 20 atmospheres absolute, said pressure being sufficient to maintain said reactant liquid in the liquid phase but insufficient to cause the gases in said first gaseous light ends stream to dissolve in said reactant liquid; continuously withdrawing as overheads from said contact zone a second gaseous light ends stream containing sulfur dioxide, ethylene and other organic light ends, the amount of ethylene in said second gaseous light ends stream being less than the amount in said first gaseous light ends stream, the amount of sulfur dioxide in said second gaseous light ends stream being substantially the same as the amount of sulfur dioxide
第 32页（共46页）
南华大学化学化工学院毕业设计
contained in said first gaseous light ends stream, the temperature of said second gaseous light ends stream being within the range of about 50.degree. C. to 150.degree. C.; continuously withdrawing as bottoms from said contact zone a liquid bottoms product consisting essentially of sulfuric acid having ethyl hydrogen sulfate and diethyl sulfate dissolved therein, said liquid bottoms product being substantially free of sulfur dioxide; and continuously recycling a major portion of said liquid bottoms product to said contact zone as a said liquid recycle stream, and continuously passing a minor portion of said liquid bottoms product to said ethyl acrylate process as a source of make-up sulfuric acid. DESCRIPTION OF THE DRAWING
The sole FIGURE is a schematic diagram of an embodiment of the invention wherein, in a tower, the gaseous light ends stream is contacted with the liquid sulfuric acid make-up stream. DETAILED DESCRIPTION OF THE INVENTION
The present invention resides in the discovery that the make-up sulfuric acid stream passed to the reaction zone of the ethyl acrylate process can be used to recover the ethylene values in the gaseous light ends stream. This gaseous light ends stream is normally disposed of with the consequent loss of the ethylene values therein. Typically the light ends stream contains sulfur dioxide and also contains ethylene and other organic light ends, such as ethyl acrylate, ethyl acetate, diethyl ether and ethanol. In most instances some nitrogen and oxygen will also be present due to air leaks in the ethyl acrylate vacuum distillation system, and carbon dioxide may also be present due to oxidation inefficiency. A typical light ends stream will contain at least 10% by weight of sulfur dioxide, usually from about 10 to 30% by weight of sulfur dioxide; and, will also usually contain at least 20% by weight of ethylene, typically from about 20 to 50% by weight of ethylene; and with the remainder of the light ends stream
第 33页（共46页）
南华大学化学化工学院毕业设计
comprising other organic light ends, nitrogen, oxygen, carbon dioxide and the like. It would be desirable to recycle the light ends stream directly to the ethyl acrylate process in order to recover ethylene values therein; however, such cannot be done mainly because of the presence of sulfur dioxide which is an undesired contaminant in the ethyl acrylate process. The presence of the gases such as nitrogen, carbon dioxide and the like also are preferably not recycled to the ethyl acrylate process. The prior art has suggested removal of the sulfur dioxide contaminant from the light ends stream and the subsequent recycling of the thus decontaminated light ends stream to the ethyl acrylate process. This suggestion has not proved practical from an economic standpoint. Unlike the prior art suggestion of removing the sulfur dioxide from the light ends stream in order that the light ends stream may be recycled, the present invention leaves the sulfur dioxide in the light ends stream and removes only the ethylene values therefrom such that these ethylene values may be recycled to the ethyl acrylate process.
In the present invention the ethylene values are recovered in the form of ethyl hydrogen sulfate and diethyl sulfate which form upon reaction of the sulfuric acid with the ethylene according to the following reactions:
H.sub.2 SO.sub.4 +C.sub.2 H.sub.4 .fwdarw.C.sub.2 H.sub.5 SO.sub.4 I C.sub.2
H.sub.5
SO.sub.4
+C.sub.2
H.sub.4
.fwdarw.(C.sub.2
H.sub.5).sub.2 SO.sub.4 II
According to Reactions I and II above, two moles of ethylene will be consumed for each one mole of sulfuric acid present; however, Reaction II is an equilibrium reaction such that the actual amount of ethylene utilized will be less than two moles per mole of sulfuric acid present. The ethyl hydrogen sulfate and diethyl sulfate, upon formation, remain in solution in the make-up sulfuric acid, along with some ethylene which
第 34页（共46页）
南华大学化学化工学院毕业设计
is in simple solution, and are passed to the reaction zone of the ethyl acrylate process along with the make-up sulfuric acid. Once in the reaction zone of the ethyl acrylate process, the ethyl hydrogen sulfate and the diethyl sulfate react directly with acrylic acid to form ethyl acrylate and sulfuric acid.
That sulfuric acid will react with ethylene to form ethyl hydrogen sulfate and diethyl sulfate is known, and it is also known that these two compounds will further react with acrylic acid to form ethyl acrylate. This in fact is the same chemistry involved in the ethyl acrylate process itself as disclosed by the prior art, such as the above referred to U.S. Pat. No. 3,894,076. It has not however been known in the prior art, nor suggested by the prior art, to apply such chemistry to the recovery of ethylene from the light ends stream according to the process of the present invention. Further, from the prior art it would have been unexpected that the reaction to form the sulfates would occur at the temperatures and pressure called for in the present invention (which are relatively low compared to those in the reaction zone of the ethyl acrylate process), and in view of the large amount of sulfur dioxide present in the light ends stream. Sulfur dioxide is generally considered to be a contaminant in the reaction zone of the ethyl acrylate process and it was unexpected that the large amounts of sulfur dioxide in the light ends stream did not prevent or severely inhibit the sulfate formation necessary to the present invention.
Reference is now made to the FIGURE for an explanation of a process conducted in accordance with the present invention. A gaseous light ends stream 10 derived from the vacuum distillation system of the above described ethyl acrylate process is passed to the base of tower 11 while a liquid make-up sulfuric acid stream is fed through line 12 to the upper end of tower 11. Also fed to the upper end of tower 11 is a liquid recycle
第 35页（共46页）