Method for producing high concentration carbon dioxide product

Abstract: A method for producing carbon dioxide in a high concentration suitable for direct usage or more facile further purification wherein microbial growth and fermentation of one or more carbonaceous materials are carried out with the use of defined oxygen-enriched fluid.

Description: This invention relates generally to the production of carbon dioxide. Background Art Carbon dioxide has a large number of uses. For example, carbon dioxide is used to carbonate beverages, to chill, freeze and package seafood, meat, poultry, baked goods, fruits and vegetables, and to extend the shelf-life of dairy products. It is an important environmental component in industrial waste and process water treatment as a replacement for sulfuric acid to control pH levels. Other uses included drinking water treatment, an environmentally-friendly pesticide and an atmosphere additive in greenhouses to improve the growth of vegetables. Generally carbon dioxide is produced by purifying a waste or other stream which is a by-product of an organic or inorganic chemical process. The waste stream comprising the carbon dioxide may be condensed and then processed in a distillation column to produce the product grade carbon dioxide. The higher is the concentration of carbon dioxide in the waste stream, the easier and less expensive is the final purification to produce commercially useable carbon dioxide and thus it is desirable to have the feed stream to a final product carbon dioxide facility to have as high a carbon dioxide concentration as possible. Indeed, it would be very desirable if the byproduct carbon dioxide containing fluid from the chemical process had a sufficiently high carbon dioxide concentration so that no further purification were necessary to produce commercially useable carbon dioxide. Accordingly, it is an object of this invention to provide a method for producing carbon dioxide from a biological process wherein the concentration of the carbon dioxide produced is sufficiently high so as to reduce the level of, or eliminate the need for, further processing of the carbon dioxide product from the process in order to produce commercially useable carbon dioxide. Summary Of The Invention The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention which is: A method for producing carbon dioxide comprising: (A) providing to a fermentation broth comprising one or more carbonaceous species an oxygen-enriched fluid; (B) employing oxygen from the oxygen-enriched fluid to promote microbial growth within the fermentation broth, carrying out fermentation within the fermentation broth, and producing carbon dioxide within the fermentation broth in a fermentation vessel; (C) passing a fermentation broth stream out from the fermentation vessel, through a heat exchanger, and then back into the fermentation vessel in a recirculation loop; (D) bubbling carbon dioxide out from the fermentation broth to form a gas mixture having a carbon dioxide concentration of at least 97.5 mole percent; and (E) recovering said gas mixture as product carbon dioxide. As used herein the term "fermentation broth" means a liquid medium containing microbes and one or more carbonaceous species which could be metabolized and/or fermented by the microorganisms. As used herein the term "oxygen-enriched fluid" means a gas having an oxygen concentration of at least 40 mole percent. As used herein the term "fermentation" means a biochemical process carried out by microorganisms wherein carbon dioxide is produced. Brief Description Of The Drawings Figure 1 is a simplified schematic representation of one preferred embodiment of the microbial growth and carbon dioxide production method of this invention. Figure 2 is a simplified schematic representation of another preferred embodiment of the invention wherein the oxygen-enriched fluid is provided to the fermentation broth within a recirculation loop. Detailed Description The invention will be described in detail with reference to the Drawings. Referring now to Figure 1, fermentation vessel 1 contains fermentation broth 20. Typically fermentation broth 20 comprises an aqueous mixture of carbohydrates such as sugars and microorganisms such as yeast for fermentation to produce ethanol. However this invention is not limited to ethanol fermentation. Any fermentation or microbial process wherein oxygen is used to sustain the growth of a microorganism and/or microbial or biochemical activity and wherein carbon dioxide is produced as a byproduct may be carried out in the practice of this invention. Oxygen-enriched fluid 21 is provided to the fermentation broth through piping 5. The oxygen-enriched fluid has an oxygen concentration of at least 40 mole percent, preferably at least 80 mole percent, most preferably at least 90 mole percent. The oxygen-enriched fluid may, if desired, be commercially pure oxygen having an oxygen concentration of 99.5 mole percent or more. In the embodiment illustrated in Figure 1, the oxygen-enriched fluid is provided to the fermentation broth while the fermentation broth is housed within vessel 1. The oxygen-enriched fluid passes from piping 5 through one or more fine bubble diffusers 4 and, as small bubbles, out into fermentation broth 20. Oxygen from the oxygen-enriched fluid is used by the microorganisms or other oxygen consuming entity within broth 20 to carry out microbial growth and fermentation of various carbonaceous materials, e.g. carbohydrates, within broth 20 to produce carbon dioxide and, for example, ethanol. In the embodiment illustrated in Figure 1 the oxygen-enriched fluid distribution is facilitated by stirring or mixing broth 20 by means of agitator 3 driven by motor 2. The carbon dioxide and other gases within broth 20 bubble out of broth 20 and form a gas mixture 22 having a carbon dioxide concentration of at least 97.5 mole percent. Depending upon the process conditions, the carbon dioxide concentration of gas mixture 22 could exceed 98.5 mole percent and even exceed 99.5 mole percent. Indeed, the carbon dioxide concentration of gas mixture 22 could be up to about 99.9 mole percent. Gas mixture 22 is withdrawn from vessel 1 in piping 6 and recovered as product carbon dioxide which may be used commercially as is or may undergo one or more further purification steps such as low temperature distillation or solvent absorption. The fermentation of the carbonaceous materials is exothermic. The exothermic nature of fermentation can lead to such a heat buildup within the fermentation broth that the microbial growth rate and fermentation rate within the fermentation broth may decline. In order to avoid this decline in production, a fermentation broth cooling recirculation loop is employed. Referring back now to Figure 1, fermentation broth is withdrawn from vessel 1 in stream 23, passed through valve 24 and as stream 25 to recirculation pump 7. Resulting pumped stream 26 is passed through heat exchanger 8 wherein it is cooled by indirect heat exchange with cooling fluid 30 such as water. Resulting cooled fermentation broth 9 is returned back into fermentation vessel 1 through main recirculation stream 27 and/or bypass recirculation stream 28 and bypass valve 29. Figure 2 illustrates another embodiment of the invention wherein the oxygen-enriched fluid is provided to the fermentation broth as it is passing through the recirculation loop. The numerals in Figure 2 are the same as those for Figure 1 for the common elements and these common elements will not be described again in detail. Referring now to Figure 2, cooled recirculation stream 27 is passed into receptacle 31 which houses fine bubble generation device 10. Device 10 could, for example, be a sintered metal fine bubble sparger/diffuser, a ceramic fine bubble diffuser, a membrane type bubble diffuser, a sonic-nozzle, a gas/liquid mixing nozzle, a venturi-type gas liquid mixing nozzle, an orifice plate or a gas/liquid flow restriction device. Oxygen-enriched fluid is passed in stream 32 into device 10 and is bubbled out into the fermentation broth within receptacle 31. The resulting oxygen-containing fermentation broth is withdrawn from receptacle 31 in stream 33. If desired, some or all of stream 33 may pass through gas/liquid contact loop 11 which serves to increase gas/liquid contact time and thus enhance the dissolution of the oxygen-enriched fluid into the fermentation broth. The remainder of stream 33, if any, is passed through valve 34 and then is mixed with the fluid, if any, from loop 11 to form stream 35 which is provided to diffuser 12 and out from diffuser 12 into the fermentation broth housed in vessel 1 where the bulk of the microbial growth and fermentation take place in the same manner as was previously described. Diffuser 12 can be any effective gas/liquid dispersing nozzle such as, for example, a liquid circulation eductor. The high concentration of oxygen within the oxygen-enriched fluid in the practice of this invention serves to reduce the amount of inerts and residual oxygen passed into the fermentation vessel which will ultimately find their way into the carbon dioxide gas mixture product, thus serving to attain and maintain the carbon dioxide concentration at a beneficially high level. In addition, this high oxygen concentration serves to reduce the energy required to operate the fermentation plant, and, in addition, will reduce odor emissions from certain types of fermentation plants. Although the invention has been described in detail with reference to certain preferred embodiments, those skilled in the art will recognize that there are other embodiments of the invention within the spirit and the scope of the claims.

Claims: A method for producing carbon dioxide comprising: (A) providing to a fermentation broth comprising one or more carbonaceous species an oxygen-enriched fluid; (B) employing oxygen from the oxygen-enriched fluid to promote microbial growth within the fermentation broth, carrying out fermentation within the fermentation broth, and producing carbon dioxide within the fermentation broth in a fermentation vessel; (C) passing a fermentation broth stream out from the fermentation vessel, through a heat exchanger, and then back into the fermentation vessel in a recirculation loop; (D) bubbling carbon dioxide out from the fermentation broth to form a gas mixture having a carbon dioxide concentration of at least 97.5 mole percent; and (E) recovering said gas mixture as product carbon dioxide. The method of claim 1 wherein the oxygen-enriched fluid is provided to the fermentation broth while the broth is in the fermentation vessel. The method of claim 1 wherein the oxygen-enriched fluid is provided to the fermentation broth. while the broth is in the recirculation loop. The method of claim 3 wherein the oxygen-enriched fluid is provided to the fermentation broth downstream of the heat exchanger. The method of claim 4 wherein the fermentation broth is provided to a receptacle, and the oxygen-enriched fluid is provided to the receptacle and diffused into the fermentation broth within the receptacle. The method of claim 4 wherein at least some of the oxygen-containing fermentation broth is passed through a contact loop prior to being passed back into the fermentation vessel. The method of claim 1 wherein the fermentation comprises the fermentation of one or more carbohydrates by microorganisms to produce ethanol. The method of claim 1 wherein the product carbon dioxide undergoes at least one further purification step. The method of claim 8 wherein the said at least one further purification step comprises distillation. The method of claim 8 wherein the said at least one further purification step comprises solvent absorption.

Inventors: GRUNWALD DAN, HO CHRIS KA KEE, GRUNWALD, DAN, HO, CHRIS KA KEE
Applicants: PRAXAIR TECHNOLOGY INC, PRAXAIR TECHNOLOGY, INC.
Application year: 2001
Main classification: C01B31
IPC codes: F25J3, C01B31, C12F3, B01D53