Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C7/00—Purification; Separation; Use of additives
  • C07C7/12—Purification; Separation; Use of additives by adsorption, i.e. purification or separation of hydrocarbons with the aid of solids, e.g. with ion-exchangers
  • C07C7/13—Purification; Separation; Use of additives by adsorption, i.e. purification or separation of hydrocarbons with the aid of solids, e.g. with ion-exchangers by molecular-sieve technique
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
  • B01J20/06—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
  • B01J20/10—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate
  • B01J20/16—Alumino-silicates
  • B01J20/18—Synthetic zeolitic molecular sieves
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/30—Processes for preparing, regenerating, or reactivating
  • B01J20/34—Regenerating or reactivating
  • B01J20/3408—Regenerating or reactivating of aluminosilicate molecular sieves
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/30—Processes for preparing, regenerating, or reactivating
  • B01J20/34—Regenerating or reactivating
  • B01J20/3433—Regenerating or reactivating of sorbents or filter aids other than those covered by B01J20/3408 - B01J20/3425
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/30—Processes for preparing, regenerating, or reactivating
  • B01J20/34—Regenerating or reactivating
  • B01J20/3441—Regeneration or reactivation by electric current, ultrasound or irradiation, e.g. electromagnetic radiation such as X-rays, UV, light, microwaves
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B17/00—Sulfur; Compounds thereof
  • C01B17/48—Sulfur dioxide; Sulfurous acid
  • C01B17/50—Preparation of sulfur dioxide
  • C01B17/60—Isolation of sulfur dioxide from gases
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/04—Purification or separation of nitrogen
  • C01B21/0405—Purification or separation processes
  • C01B21/0411—Chemical processing only
  • C01B21/0422—Chemical processing only by reduction
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/04—Purification or separation of nitrogen
  • C01B21/0405—Purification or separation processes
  • C01B21/0433—Physical processing only
  • C01B21/045—Physical processing only by adsorption in solids

Definitions

• Adsorbents are solid materials used to selectively remove contaminants or components from fluid process streams. Activated charcoal, zinc oxide, activated alumina, and molecular sieves are typical examples of the variety of known adsorbents.
• the adsorbent may be self-supporting or may be fixed to a substrate. The process stream is caused to contact the adsorbent for the required time period for the desired removal of the contaminant or component.
• the adsorbent may also be used to effect a separation of a gas stream into two components if, after removal of one component, the flow of the process stream is stopped long enough to desorb and recover the adsorbed component.
• the adsorbed material is not- recovered for further use (e.g., it may merely be a contaminant and not a useful by-product of the separation process) , it still must be removed period ⁇ ically after it saturates the adsorbent or the adsorbent will cease its function.
• One method of regeneration is by heating the adsorbent (and substrate) to a temperature sufficient to desorb the adsorbate. Typically, this heating is accomplished with a flow of hot gas since it not only heats the adsorbent, but also purges ' the adsorbate as it is desorbed.
• Effective adsorbents create a problem in regeneration since, generally, the more effective the adsorbent, the more difficult it is to remove the adsorbate. Long regeneration times and large purge gas volumes are therefore required for a moderate temperature purge gas to desorb the adsorbate. This is due in part to the poor thermal transport inherent
• the present invention provides dielectric heating which eliminates the problems and provides benefits unobtainable with hot purge gas heating and with conventional heating, and with an energy savings.
• dielectric heating in particular, microwave heating
• U.S. Patent 3,771,234 suggests the use of microwave radiation for removing volatile polar vehicles from non-polar materials (dielectric loss factors of about 0.0001 to 0.1), specifically drying of synthetic polymers.
• Coventional heating plus a purge gas flow is also used (see U.S. Patent 4,011,306), but as a result of poor heat transfer this can-require long regener ⁇ ation times or high temperatures.
• Microwave heating and a purge gas are apparently disclosed in Japanese Kokai 76/43,394, 76/43,395 and 76/145,491 (Chemical Abstracts; Nos. 8522166187w, 8522166188x and 8702008041f) .
• heating with microwaves provides high frequency oscillatory movement of the molecules within the material by the combined interaction of the electric and magnetic fields associated with absorbed electromagnetic energy.
• the rapid temperature increase of the material is caused by this molecular friction.
• the invention is a process for the rapid, thermal regeneration of adsorbents wherein the saturated adsorbent is heated dielectrically to desorb the adsorbate, after which a small quantity of purge gas stream may flush the adsorbate from the area of the adsorbent.
• Heating dielectrically preferably with microwave radiation, effects internal heating of the adsorbent thereby minimizing the effects of poor heat transfer of the absorbent and substrate which delays the effectiveness of a conventional form of heating.
• the invention can be used to desorb materials which are physically adsorbed on the adsorbent and also to desorb chemisorbed materials which may have further undergone chemical reaction with the adsorbent.
• An example of the latter "absorption" is the reaction of S0 2 n flue gases with a modified ZnO absorbent.
• the effects of 'dielectric heating are also utilized in separating a fluid mixture into two or more concentrated component streams. Each repetition of the inventive process may result in separation into two components. Successive treatments over different adsorbents may eventually reduce a fluid mixture to many of its individual components.
• the fluid mixture is passed over an adsorbent which preferentially adsorbs at least one component thereof.
• the component is adsorbed as the mixture passes and the fluid stream remaining after adsorption is collected.
• This effluent stream is more concentrated than the input fluid mixture in components other than those removed by the adsorption.
• the fluid mixture flow over the absorbent is temporarily halted and the absorbent is heated dielectrically to a temperature at which the adsorbed component desorbs (or to a temperature at which the "adsorbent" chemical reaction reverses and the fluid mixture component reactant is desorbed) .
• a small quantity of purge gas may then be passed over the adsorbent to remove the desorbed component to a collection area. This purge gas stream is now concentrated with the desorbed component. After purging the adsorbent, the original fluid mixture may again be passed over the adsorbent and the cycle repeated.
• the adsorbed (desorbed) component is truly a waste contaminant of the original fluid mixture it can be collected for disposal. But if the component has some value, it can be more easily upgraded or used from this concentrated form than it could in prior processes.
• a purge gas is optional since the process is effective in either case. Use without a purge gas is preferred, however, since it generally increases throughput. Without a purge gas, heating causes the desorption and an increase in pressure in the adsorber chamber. This pressure increase causes most of the desorbed component to exit the chamber to be collected. The remaining desorbed component is merely readsorbed when the heating is eliminated and the fluid mixture is again allowed to flow through the adsorber. The readsorption lowers efficiency per cycle but many more cycles can be run without the purge gas since purging requires appropriate valving and time consuming sequencing with the fluid mixture flow. In total, the speed of the regeneration without purging outweighs the slight efficiency advantage enjoyed by purging. Of course, purge gas also dilutes the desorbed component stream.
• Separations that are advantageously effected by the method include air separation (O2 production) , CO2 and H2S removal from natural gas, light hydrocarbon separation (replaces distillation) , and SO2 or other contaminants from flue gas. Many other separations are possible in practicing the invention.
• microwave frequency radiation is defined as electromagnetic energy in the region of the spectrum having wavelengths of about 1 meter to 1 millimeter and frequencies of about 300 MHz to 300 GHz. However, this energy is conventionally operated in the region of 915, 2450, 5800, or 22,125 MHz in the industrial, scientific and medical (ISM) band as assigned by the Federal Communications Commission.
• the term radio frequency radiation will mean the same type of energy as microwave but in the lower range of frequencies of about 300 kHz to 300 MHz.
• the conventional ISM frequencies are 13.56, 27.120, and 40.68 MHz.
• Adsorbent shall mean a solid material which has the property of being able to physically or chemically immobilize or adsorb molecules whether or not the adsorbent further enters into a chemical reaction with the adsorbate, as in the "adsorption" of SO2 by ZnO.
• the adsorbents shall have dielectric loss factors in excess of about 0.1 at operating frequency and be capable of being heated dielectrically.
• Adsorbents which are selective in any particular separation are well known in the art. For example, see U.S. Patent 4,011,306 which discusses adsorption of oxygen from
• the best mode for carrying out the invention is demonstrated by the following examples.
• the benefits to be derived on a commercial scale are much greater since the size of adsorbers is much greater.
• the laboratory adsorber is 2.5 inches in diameter and 4 inches deep whereas commercial adsorbers can be, for example 3-12 feet in diameter and 3-20 feet deep.
• Thermal problems and delays with conductive and connective methods of regeneration increase substantially at this scale.
• the time necessary to heat (and cool) the adsorber is critical to the adsorbent inventory (or the amount of adsorbent needed) . Slow heating and cooling neces ⁇ sitates the high capital costs of higher adsorber inventory.
• a fluid mixture of C0 2 and H-S in nitrogen was investigated.
• a source of the fluid mixture analyzing 14.78% C0 2 and 6.79% H 2 S (balance nitrogen) was connected to the inlet of a 2 1/2 inch (6.35 cm) diameter cylindrical adsorber reactor chamber and a gas flow bellows meter was connected to the outlet thereof.
• the adsorber was contained within a microwave oven capable of delivering 200- 2500 watts of power at 2450 MHz.
• a nitrogen purge gas source was also connected to the inlet of the adsorber chamber with appropriate valving to admit only one source at a time through the inlet.
• Thermocouples were removably installed in the adsorber chamber at spaced locations to monitor temperature when microwaves were temporarily turned off.
• About 800 grams of molecular sieve 4A was placed in the adsorber column to a depth of about 12 inches (30.5 cm) and the power was turned on to run the column through a heating/cooling cycle to outgas the system. After outgassing the weight of the molecular sieve 4A was determined by difference to be 702 grams.
• the adsorbent was then loaded by flowing the gas mixture therethrough for 30 minutes at about 0.5 cubic feet per minute (0.24/sec). Total flow through the adsorber was determined from the bellows gas meter to be about 10.5 cubic feet (298 liters). During the loading, samples were taken at elapsed times of 5, 15, 25 and 30 minutes at the outlet of the gas meter for chemical analysis by gas chromatography. * After loading, the gas mixture source was turned off and the adsorber was heated at 1000 watts power (150 watts reflected) for 5 minutes. A sample of evolved gases was taken after 3 minutes of heating. The temperature reached 275°C within the adsorber column.
• Example 2 To quantify results found in Example 1, a second experiment was conducted to measure the degree of concentration which can be achieved in the removal of C0 2 and H 2 S from a nitrogen carrier gas.
• the apparatus was similar to Example 1 using the cylindrical reactor, 1/16 inch pellets of molecular sieve 4A as adsorbent and a source of the fluid mixture analyzing 17.2% C0 2 and 5.5% H 2 S, balance nitrogen.
• a quantity of the 4A sieve was placed in the adsorber column and outgassed. The weight thereafter was about 240 grams.
• the adsorbent was loaded by flowing the fluid mixture therethrough for 27 minutes at 2000 cc/min. Referring to Figure 1 it can be seen that break-out of C0 2 took place after about 5 minutes and break-out of H 2 S after about 15 minutes.
• the bar graph shows the percentage of the components in the effluent stream at various times.
• the C0 2 and H 2 S during this period made up more than 90% of the effluent gas.
• the C0 2 made up 36-64% of the effluent (versus 17.2% in the original fluid mixture) and H 2 S made up 27-56% of the effluent (versus 5.5% in the original fluid mixture). Maximum temperature was about 230°C.
• Figure 1 shows the percentages of the components in the effluent and the cumulative desorption over the period of desorption.
• This experiment shows that a substantial amount of the adsorbed component can be removed from the adsorber column without purge gas.
• it might be advantageous to begin desorption immediately after break-out (after 5 to 10 minutes in the example) and to end desorption and begin loading again after 80%, for example, of the components have been desorbed.
• Example 3 An experiment to separate C0 2 and H_S from methane was conducted using the equipment of Example 1.
• the 4A molecular sieve was loaded until breakthrough of H 2 S occurred as measured by gas chromatigraphic analysis. After breakthrough, feed gas was interrupted and microwave heating commenced. As the flow of desorbed gases diminished, nitrogen purge gas flow was initiated and followed by inter ⁇ mittent heating cycles to maintain the bed temperature at between about 200 and 260°C. Three load and desorption cycles were run to determine cyclic behavior.
• Heating at 300 watts for 11 minutes from this point resulted in removal of 68% of the C0 2 and 29% of the H 2 S from the adsorbent. While heating periodically for a total of 46 minutes during the next 85 minutes at 150 watts to maintain the temperature at about 250°C, a total of 95% of the C0 2 and 50% of the H 2 S were desorbed.
• the feed gas was methane containing 18.5% C0 2 , 8.6% H 2 S and 1.2% N,. Break ⁇ through of H 2 S occurred in 25 minutes and microwave heating thereafter for 11 minutes at 300 watts resulted in 74% desorption of C0 2 and 20% desorption of the H 2 S. Heating for 39 minutes of the next 80 minutes to maintain the temperature resulted in 99% of the CO- and 36% of the H 2 S being removed from the adsorbent.
• Example 4 The results of the percentage desorptions in Example 3 were compared with the energy exposure of the adsorbent (the energy exposure being the output power of the microwave generator times the exposure time) to determine the effectiveness of this heating. An experiment was then run with the same loading but with conventional resistance heating to effect the desorption. The energy exposure of the adsorbent during this type of heating was calculated and compared to the percent desorption of C0 2 , H 2 S and COS to determine its effectiveness. The results showed that the first cycle with microwave heating produced the most effective desorption over the range of 0 to 5000 watt-minutes. The total desorption increased slowly to 25% over 2000 watt-minutes, then accelerated to over 70% within the next 1000 watt-minutes, and finally slowed to a steady desorption rate, reaching almost 100% desorption at 5000 watt-minutes.
• the second and third cycles using microwave heating resulted in steady desorption up to 60% desorption after 5000 watt-minutes.
• the resistance heating was provided by a 288 watt heat tape and produced desorption which increased steadily to only 20% after 5000 watt-minutes. It might be expected that desorption would begin to increase at a much faster rate if longer times were employed, however, time is a significant factor in throughput and extended times are not desirable on a commercial scale. Further, the temperature of the adsorbent near the wall was much hotter during the resistance heating, raising the problem of damage to the adsorbent if excessive power is employed in resistance heating. Moreover, the hotter the adsorber, the longer the cooling time which would be necessary to begin another cycle, again adversely affecting throughput.
• Example 5 An experiment was conducted to show the ability to recover SO- sorbate from a sorbent.
• An effective 0 sorbent was prepared by reacting ZnO with S0 2 and H 2 0 to form ZnS0 3 • 2 1/2 H-0 and then driving off the S0 2 and H 2 0 by heating.
• the ZnO is an effective sorbent for S0 2 when H 2 0 is present, and after the above pretreatment, is much more effective in sorbing S0 2 than is ZnO without the treatment. The increase in efficiency is probably due to a surface area increase.
• Example 6 The apparatus of Example 1 was modified by 5 placing the bellows meter before the adsorption column and a wet test meter at the output side of the column. This provided more accurate loading and desorption flows from the separation of this example.
• a 13X molecular sieve was employed in the column to adsorb 0 C-, C- and C . hydrocarbons from the impure methane feed.
• the feed gas analyzed 81.6% CH., 10.5% C 2 Hg, 5.3% C 3 H- and 2.6% C ⁇ O.
• ethane was not totally adsorbed. It made up about 15% of the output with the balance being methane. Selection of a better adsorbent or a second adsorption would separate the ethane and leave essentially pure 0 methane.
• microwave heating was commenced at 300 watts for 7.5 minutes, followed by a 1 minute pause, 2 minutes of heating, a 2 minute pause and 2 more minutes of heating. During this time 5075 cc of the adsorbed ethane and propane gases were desorbed. The composition of the offgas was between 85 and 97% ethane plus propane with the balance methane. Continued periodic heating with microwaves using a nitrogen purge produced an offgas mixture comprising 30-40% propane and butane with the balance nitrogen.
• a second loading at 2450 cc/min. of the adsorbent resulted in a 5% propane breakthrough after 63 minutes. Eleven minutes of microwave heating at 300 watts followed by a 1 minute pause and 3 minutes additional heating desorbed 5800cc of the C--C. gases and resulted in a gas which was 95% C--C.. Inter ⁇ mittent heating over an additional 90 minutes removed a cumulative total of about ll,400cc of the adsorbed gases.
• Example 7 The experiment of Example 6 was continued with a third loading/desorption cycle but using resistance heating in place of dielectric heating to desorb the adsorbed gases.
• a 288 watt resistance heating tape was wrapped around the adsorber column and heating equivalent to the microwave energy input to the adsorber was used.
• Example 8 Apparatus as used in Example 6 was used to separate 0 2 and N 2 from air. A 5A molecular sieve was used to adsorb the nitrogen. The adsorbent column was first saturated with 98% 0 2 and then air was passed therethrough and the oxygen rich offgas collected until the exit stream contained only 30% 0 2 (70% nitrogen) .
• the adsorbent was heated with microwaves at 500 watts power. During the first 2.5 minutes of heating a large percentage of the nitrogen was desorbed and the offgas increased from 70% 2 to about 82% N-. Thereafter, less gas was desorbed but the nitrogen content increased to 94% after 10 minutes of heating. The final temperature of the column was about 125°C.

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• 1978
  • 1978-10-25 JP JP50008178A patent/JPS54500045A/ja active Pending
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• 1979
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