Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Reexamination Certificate
2000-06-01
2002-06-04
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
C423S269000, C423S522000, C423S533000, C423S540000, C423SDIG002, C252S387000
Reexamination Certificate
active
06399040
ABSTRACT:
This invention relates to a process for generating recoverable sulfur containing compounds from a spent acid stream. In particular, the invention relates to a process for generating recoverable sulfur compounds from commercial processes for preparing (meth)acrylic acid esters.
Many industrial processes result in the production of spent acids. For instance, (meth)acrylic acid esters generally are prepared with a strong acid, such as sulfuric acid as a direct esterification catalyst. For example, see co-pending U.S. patent application Ser. No. 60/106947. Large amounts of sulfuric acid may be used in these processes. The majority of the sulfuric acid utilized degrades during the esterification process, thus creating a spent acid. For economic and environmental reasons, the spent sulfuric acid is generally recovered and recycled for further use.
To accomplish recycle of a spent sulfuric acid, the spent sulfuric acid is initially separated from the product ester. Once separated, the spent sulfuric acid is subjected to a regeneration process. Generally, the regeneration process includes spraying the spent sulfuric acid into a combustion furnace and generating sulfur dioxide (“SO
2
”), for instance by combusting and/or thermally decomposing the spent acid. The SO
2
is then converted to sulfur trioxide (“SO
3
”) and absorbed in 98% sulfuric acid to obtain 99+% pure sulfuric acid.
One problem associated with combusting and/or thermally decomposing spent acids is the cost of operating a large combustion furnace. The combustion furnaces used to combust and/or thermally decompose spent acids utilize natural gas to combust the spent acid. The natural gas consumption needed to provide the temperature to combust spent acids will vary depending on the spent acid droplet size.
Typically, a droplet of spent acid is large, i.e., the droplet has a Sauter mean diameter of greater than 700 micrometers. A combustion furnace typically must be operated at 1085° C. to 1120° C. to combust or thermally decompose spent acid droplets of this size. In order to reduce the operating cost of the combustion furnace utilized for the combustion or thermal decomposition of the spent acid, it is desirable and advantageous to minimize the spent acid droplet size.
Another problem associated with combusting and/or thermally decomposing spent acids is the amount and pressure of the air flow needed to atomize the spent acid in the furnace. Compressors are needed to generate the air flow. The compressors typically are electric and therefore generally create additional cost in operating the process. However, even with the increased air flow, the droplet size is not optimum. Several approaches have been attempted to overcome these and other problems in spent acid recycling processes.
External air blast nozzles have been used for spraying operations to provide an atomized spent acid stream. Such external air blast nozzles mix air with liquid after the liquid exits the nozzle. These nozzles tend to require high air flow rates, which increases the cost of operation due to energy requirements to operate air compressors.
One approach to minimizing droplet size is to provide a sonicating system which utilizes high pressure gas, i.e., pressure greater than or equal to 75 psig. Sonic Development Corporation disclosed this type of system in its product literature for Sonicore® nozzles. The literature does not specifically disclose the use of this type of system with spraying spent acids from direct esterification processes into combustion furnaces. Also, there is also no mention of reducing the amount of air flow required for the operation. Furthermore, one problem associated with the sonicating system approach to minimizing droplet size is the high cost of compressing the gas. Another problem associated with this type of system is that the spray nozzles can only handle flow rates of approximately 4 to 5 liters per minute. Commercial direct esterification processes can generate in excess of 100 liters of spent acid per minute, therefore the sonicating system may not be useful for these purposes.
U.S. Pat. No. 5,553,783 disclosed a spray nozzle for atomizing a liquid with a gas. The nozzle produces a flat fan spray pattern and greater flow rates. However, the disclosure does not specifically disclose the use of this type of nozzle with spraying spent acids from direct esterification processes into combustion furnaces.
Despite the disclosure of the references, there is a continuing need for a cost efficient process for generating recoverable sulfur compounds from a spent acid, and recovering acid from the sulfur compounds. The present inventor has now discovered a novel process wherein:
1) the spent acid droplet size is minimized, thus reducing operating costs;
2) low air/gas pressure is required to effect the spraying operation;
3) the capacity of such spraying operation is sufficient to be used in a commercial direct esterification process; and
4) the spent acid droplet size is reduced, enabling the furnace to be operated at a lower temperature, thus yielding a more efficient combustion and thermal decomposition process.
In a first aspect of the present invention, there is provided a process including: providing a spent acid stream; spraying the spent acid stream through a low pressure air assisted nozzle to form an atomized spent acid stream; and generating a sulfur dioxide stream from the atomized spent acid stream.
In a second aspect of the present invention, there is provided a process for recovering acid from a spent acid stream including: admixing magnesium sulfate with a spent acid stream; spraying the resultant spent acid stream through a low pressure air assisted nozzle to form an atomized spent acid stream; generating a sulfur dioxide stream from the atomized spent acid stream; catalytically converting the sulfur dioxide to sulfur trioxide; and absorbing the sulfur trioxide in greater than 90 percent by weight sulfuric acid to further concentrate the sulfuric acid.
As used herein, by spent acid is meant residue streams containing sulfur compounds. Also as used herein, by (meth)acrylic is meant both acrylic and methacrylic. For the purposes of this patent application, by air is meant any gaseous stream including, but not limited to air, air enriched with oxygen, pure oxygen, steam, natural gas, process gas streams, and mixtures thereof.
Throughout this specification and claims, unless otherwise indicated, references to percentages are by weight percent and all temperatures are in degree centigrade.
It is also to be understood that for purposes of this specification and claims that the range and ratio limits, recited herein, are combinable. For example, if ranges of 1-20 and 5-15 are recited for a particular parameter, it is understood that ranges of 1-15 or 5-20 are also contemplated.
As described above, acids may be used to catalyze direct esterification reactions. Although the process of the present invention is applicable to a spent acid from any source, it will be described herein in regard to a spent acid generated from a process for preparing methyl methacrylate. During the esterification process, the acids may decompose thus resulting in a spent acid. After the esterification reaction is completed, the ester is separated from impurities, which include the spent acid. The separation may occur through any means known in the art, such as distillation, gravity phase separation, et cetera. Such separation results in a product stream and a spent acid stream. The spent acid stream typically includes, but is not limited to, water, from 20% to 40% sulfuric acid, from 40% to 60% ammonium bisulfite, and possibly other impurities.
The spent acid stream is then sprayed through at least one low pressure air assisted atomizer into a combustion furnace. The low pressure air assisted atomizer may be a low pressure, air assisted spray nozzle. Suitable spray nozzles are disclosed, for instance in U.S. Pat. Nos. 5,553,783, 5,692,682, and 5,240,183 such patents being incorporated herein by reference for their disclosure of such s
Dafft Charles Anthony
White Connie René
Holler Alan
Rohm and Haas Company
Vanoy Timothy C
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