ADSORBENT AND PROCESS FOR METHANOL AND OXYGENATES SEPARATION
20220056362 · 2022-02-24
Assignee
Inventors
Cpc classification
B01D53/02
PERFORMING OPERATIONS; TRANSPORTING
C10L2290/12
CHEMISTRY; METALLURGY
C10L2290/542
CHEMISTRY; METALLURGY
B01D2257/70
PERFORMING OPERATIONS; TRANSPORTING
B01D2253/1085
PERFORMING OPERATIONS; TRANSPORTING
B01D2257/704
PERFORMING OPERATIONS; TRANSPORTING
B01D53/0462
PERFORMING OPERATIONS; TRANSPORTING
B01J20/18
PERFORMING OPERATIONS; TRANSPORTING
International classification
C10L3/10
CHEMISTRY; METALLURGY
Abstract
An adsorbent separates methanol and other alcohols from gas and liquid oxygenates and hydrocarbon streams with a low silica faujasite (LSX) in a mono-, bi, or tri-cation alkali and/or alkaline-earth metal forms. The LSX has silicon to aluminum ratio from about 0.9 to about 1.15 and an ion exchange degree for each alkali or alkaline-earth metal in the range of about 10 to about 99.9% equiv. The gas streams for treatment include natural gas, individual hydrocarbons, or vaporized alkyl esters of carboxylic acids, or methyl tert-alkyl ethers and their mixtures with hydrocarbons. The liquid streams include liquefied natural gas (LNG), liquefied petroleum gas (LPG), natural gas liquid (NGL), individual hydrocarbons C.sub.3-C.sub.5, and monomers, alkyl esters of carboxylic acids including methyl acetate, methyl, ethyl, butyl acrylates and methacrylate, methyl tert-alkyl ethers including methyl tert-butyl ether (MTBE) and methyl tert-amyl ether (TAME). The adsorbent is especially suited for temperature swing or pressure swing adsorption processes.
Claims
1.-18. (canceled)
19. An adsorbent for methanol and oxygenates separation from gas and liquid streams, said adsorbent comprising mono-, bi- or tri-cation alkali or alkaline-earth metal forms of low-silica faujasite (LSX) having a silicon to aluminum ratio from about 0.9 to about 1.15.
20. The adsorbent of claim 19, wherein the ion exchange degree for each said alkali or alkaline-earth metals varies from 10 to about 99.8% equivalent.
21. The adsorbent of claim 19, wherein said alkali and alkaline-earth metals are selected from the group consisting of sodium, potassium, calcium and magnesium.
22. The adsorbent of claim 19, wherein said low-silica faujasite contains cations of at least two alkali and/or alkaline-earth metals and the degree of exchange for each of said metal cations varies in the range of 30-70% (equiv.).
23. The adsorbent of claim 22, wherein said low-silica faujasite consists essentially of potassium and sodium and the degree of ion exchange is in the range of 40-75%.
24. The adsorbent of claim 22, wherein the bications consist essentially of sodium-potassium or sodium-calcium and the sodium ion exchange degree comprises 55-80% while the potassium and calcium ion exchange degree does not exceed 45% (equiv.).
25. The adsorbent of claim 22, wherein the cations comprise Ca and Mg cations and the content of Mg/Ca ions is 60-80% equiv.
26. The adsorbent of claim 19 consisting essentially of a mono-cation form that is ion exchanged with an alkali or alkaline-earth metal.
27. The adsorbent of claim 26 wherein the mono-cation is Na or K with an ion exchange degree higher 99.2%.
28. The adsorbent of claim 26 wherein the adsorbent consists essentially of a NaLSX, KLSX, or CaLSX with an ion exchange degree not less than 99% and residual content of other alkali and alkaline-earth metals of not greater than 0.9% (equiv.).
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0026]
DETAILED DESCRIPTION OF THE INVENTION
[0027] The present invention provides an efficient and reliable adsorbent for methanol and oxygenates separations from liquid and gas streams featuring a temperature swing adsorption (TSA), concentration swing adsorption (CSA), as well as pressure swing adsorption (PSA) processes. The adsorbent of the invention is useful in a broad range of methanol concentration and partial pressures from 20 ppmv up to 2-5% v. The other feature that distinguishes the adsorbent of the invention consists of its superior performance at separation of gas and liquid streams that significantly contaminate a large amount of high polarity substances, such as water, esters, ethers, carboxylic acids, etc. and limits their use in large scale operations.
[0028] In accordance with that previously described discovery, the adsorbent, according to the invention, constitutes a low-silica faujasite (LSX) having a silicon to aluminum ratio from about 0.9 to about 1.15 and having in its composition one, two or three cations of alkali or alkaline-earth metals, preferably selected from the group of sodium, potassium, calcium or magnesium. The ion exchange degree for each said alkali or alkaline-earth metals varies from 10 to about 99.8% equivalent.
[0029] Bi-cation sodium-potassium forms of low-silica faujasite may be obtained by direct synthesis from the corresponding silicates, aluminates and hydroxides, as described for example in Kühl “Crystallization of Low-Silica Faujasite”, Zeolites, vol. 7, p. 451, 1987. Mono- and tri-cation forms of low-silica faujasite, which are useful in the preferred embodiment of the invention, can be obtained by conventional ion exchange procedure with corresponding alkali or alkaline-earth metal salts such as chlorides, nitrates, sulfates, acetates, etc. For instance, mono-cation NaLSX and KLSX forms of the adsorbent can be prepared by ion exchange of the original bi-cation NaKLSX form with sodium and potassium chlorides respectively; treating original molecular LSX sieve by calcium chloride or calcium nitrate solutions will form bi-cation sodium-calcium form NaCaLSX; and treating molecular LSX sieve with magnesium salts solutions and so forth will form MgNaLSX or MgKLSX.
[0030] It is well known that for standard faujasite X with a silicon to aluminum ratio 1.20-1.60, a replacement of original sodium cations in faujasite framework causes a decrease of its adsorption capacity for methanol.
[0031]
[0032] Similar results were obtained for all other alkali and alkaline-earth cation exchanged forms of LSX, including Ca and Mg, i.e. bi-cation NaK—, NaCa—, KCa, CaMg— and so forth. In such a manner, the bi-cation forms of molecular sieve LSX are preferential for methanol adsorption in the high adsorbate concentration range >750 ppm, while the corresponding mono-cation forms, such as NaLSX, KLSX, CaLSX, MgLSX much more applicable for methanol recovery in low concentration range of 10-500 ppm. It was also found that the same holds true for adsorption of higher molecular weight methanol homologs such as ethanol, iso-propanol and butanol, particularly at the conditions of competitive adsorption of strong polar substances, such as water, carboxylic acids and their derivatives.
[0033] The discovered principles of methanol and oxygenates adsorption over cation exchanged zeolite LSX allow formulating the scope and use of the present invention. The various adsorbents within the scope of this invention prove suitable for such processes as TSA process for natural and associated gas dehydration and purification. The TSA process will include adsorption and regeneration steps in the following description of representative steps.
[0034] In the adsorption stage, a natural gas stream saturated with water vapors, which contains methanol in the amount of 750 ppm or above, passed through a single or several adsorption vessels loaded with a bi- or tri-cation form of low-silica faujasite. Adsorption pressure may vary from about 1 to about 80 bars, temperature from about −15 to about +65 C and gas flow linear velocity from about 0.03 to about 0.35 m/sec. The adsorbent selectively picks up moisture and methanol vapors whereas other components pass through the adsorbent bed without changing natural gas composition.
[0035] Meanwhile, a mass transfer zone (MTZ) for each adsorbate is formed as natural gas feed first contacts a newly regenerated adsorbent bed. As the natural gas stream passes through the bed an MTZ (I) for methanol moves toward the outlet of the adsorbent bed in front of an MTZ (II) for the moisture adsorption. When MTZ (I) reaches the end of the adsorbent bed, a concentration of methanol in the purifying flow begins rising. Then the adsorbent bed loaded by water and methanol vapors switches to a regeneration step and the process directs the natural gas feed to newly regenerated adsorbent bed. The adsorption step typically continues until moisture breakthrough, so that the dynamic methanol capacity of the adsorbent defines methanol losses as its concentration in the dehydrated gas flow while its concentration in the regeneration liquid in turn determines the economics of the methanol reclaiming and recycle into the process.
[0036] In the regeneration stage purified natural gas or any other gas devoid of methanol, for example hydrocarbons, nitrogen, hydrogen or carbon dioxide passes as single gas or a combination of gases at an elevated temperature through the adsorbent bed now loaded with methanol and water vapors from a preceding adsorption step. The ratio of regeneration gas volume to the volume of purified gas usually varies from about 1:4 to about 1:20. Thus the invention has the advantage of giving essentially complete with very low amounts of regeneration gas. Regeneration temperature usually ranges from about 120 to about 280° C., and pressure from about 0.05 to about 80 bars. High temperatures of the adsorbent bed and regeneration gas purity carry out the desorption of methanol and moisture from adsorbent. Preferably each regeneration cycle restores the adsorbent bed to original adsorbate capacity. Each regeneration cycle also saturates the regeneration gas with the desorbed impurities that exit the adsorption vessel along with the regeneration gas.
[0037] The regeneration effluent is chilled, methanol and moisture are condensed, separated from gas flow, and subsequently transferred to a distillation column for methanol reclaiming. The regenerated adsorbent bed is cooled to the adsorption temperature, whereupon it is ready for the next purification process cycle.
[0038] In another preferred embodiment of the invention, a PSA process is applied to methanol recovery and separations of vaporized moisturized methanol and other mixtures that can include alcohols, esters and/or ethers with or without hydrocarbons and carboxylic acids. The following steps typify the operation of the preferred PSA process for methanol and oxygenates separation.
[0039] During the adsorption step, the feed enters an adsorber containing a mono-cation potassium exchanged form of LSX faujasite with a potassium exchange degree of about 92% equiv. or above and a content of other alkali or alkaline-earth metals not exceeding 8% equiv. Methanol and other impurity vapors are adsorbed at temperatures from about 25 to about 100° C., pressure from about 1.3 to about 120 bars, and feed flow linear velocity from about 0.06 to about 0.35 m/sec. Adsorption of impurities yields purified product comprising pure ether and/or ester products that exit the adsorber with a residual methanol content of less than 0.01% v. and a moisture content below 10 ppmv. The purified product can be directed to an efficient distillation or for further synthesis. Adsorption times can vary from about 5 min to about 90 min after which the adsorber undergoes depressurization.
[0040] Depressurization of the adsorption vessel pressure decreased to its lowest pressure by releasing retained gas counter-currently to gas flow direction during adsorption. In most cases the depressurized adsorbent bed is partially regenerated by full release of methanol, ethers or esters that remained in the adsorbent bed after adsorption step completion. This flow can be directed to a supplemental adsorption vessel to decrease the product losses.
[0041] Usually a purge step follows depressurization to completely or essentially completely remove remaining impurities from the adsorbent bed by using a minor part of the purified product that passes through the adsorbent bed.
[0042] A minor part of the purified product is used for re-pressurizing the adsorbent bed to the pressure level of the adsorption step thereby readying the adsorption bed for the next purification cycle.
[0043] The main advantage of the process according to the present invention consists of enhanced purity of the process products that in turn allows avoiding additional separation steps and cutting down the capital and operational costs for the separations.
[0044] Various embodiments of the invention are further illustrated by the following specific examples. It is understood that these examples are illustrative and not intended to provide any limitations on the invention.
[0045] The term about when used herein means a variation of 5% from the given value. EXAMPLES 1 to 4 (Sample preparation According to the Invention).
[0046] Beaded sodium-potassium LSX molecular sieve having Si/Al ratio of 1, a Na.sup.+ ion exchange degree of 76% and a K.sup.+ ion exchange degree of 23% equiv. was used as an Example 1 sample and as an initial material for additional sample preparation.
[0047] To increase Na content up to 85% equiv., in Example 2, 300 g of the initial material was treated at ambient temperature by contacting the material with 3 liters of 1.5 N solution of sodium chloride over 4 hours. The material was washed with deionized water (DIW) to remove excess of chloride ions, dried at 110° and calcined at 250° C.
[0048] In Example 3, 200 g of the NaKLSX adsorbent of the sample of Example 2 received treatment with 1 L of 2.5 N NaCl solution to raise its ion exchange degree to 97%.
[0049] In Example 4, 100 g of the material of Example 3 was treated at 80° C. with 1 L of 3.5 N solution of sodium chloride and then dried and calcined to obtain a mono-cation NaLSX sample.
[0050] Following the washing, drying and calcining the obtained samples were analyzed with the use of Atomic Absorption Spectroscopy (AAS) resulting in the following cation compositions of the samples:
[0051] Example 1: Na.sup.+—76%, K.sup.+—23%, Ca.sup.2+—1% (equiv.);
[0052] Example 2: Na.sup.+—84%, K.sup.+—15%, Ca.sup.2+—1% (equiv.);
[0053] Example 3: Na.sup.+—97%, K.sup.+—3%, Ca.sup.2+—0% (equiv.); and,
[0054] Example 4: Na.sup.+—99.7%, K.sup.+—0.3%.
Examples 5 to 8 (Preparation of Samples According to the Invention.)
[0055] In Example 5 a sample with increased K.sup.+ cation content was prepared from the Sample of Example 1 by its treatment with a 1 N solution of KCl at ambient temperature followed by repetition of the sample washing, drying and calcining procedures of Example 2.
[0056] Examples 6 to 8 produced samples having an elevated potassium cation content obtained by treatment of the sample of Example 5 with a 2N KCl solution at 70° C. (Example 6), a 3N KCl solution at 85° C. (Example 7) and a 4.5 N KCl solution at 90° C. (Example 8).
[0057] AAS analysis of the samples showed the following cation presence in the adsorbent compositions:
[0058] Example 5: K.sup.+—60.5%, Na.sup.+—39.0%, Ca.sup.2+— 0.5% (equiv.);
[0059] Example 6: K.sup.+—90.8%, Na.sup.+—9.0%, Ca.sup.2+—0.2% (equiv.);
[0060] Example 7: K.sup.+—98.2%, Na.sup.+—1.8%, Ca.sup.2+—0% (equiv.); and,
[0061] Example 8: K.sup.+—99.2%, Na.sup.+— 0.8%.
Examples 9 to 13 (Samples Preparation According to the Invention.)
[0062] A tri-cation CaNaKLSX sample was obtained for Example 9 by ion exchanging the original NaKLSX adsorbent of Example 1 with 1N solution of calcium chloride.
[0063] In Examples 10 and 11 bi-cation CaNaLSX samples were prepared by treatment of NaKLSX adsorbent of Example 3 with 1 and 2.2 N solutions of CaCl.sub.2) respectively.
[0064] The bi-cation CaKLSX sample of Example 12 was prepared by ion exchange of the KLSX adsorbent of Example 7 with a 1N solution of calcium chloride.
[0065] The mono-cation CaLSF sample of Example 13 was obtained by consecutive treatments of the adsorbent of Example 3 with four treatments. The first three treatments were with 1.0, 2.2, 3.0 N solutions of CaCl.sub.2) at ambient temperature followed by treatment with a 5.6 N solution at 90° C.
[0066] According to the analysis, the samples have the following cation composition:
[0067] Example 9: Ca.sup.2+—63.4%, Na.sup.+—24.9%, K.sup.+— 11.7% (equiv.);
[0068] Example 10: Ca.sup.2+—32.6%, Na.sup.+—67.2%, K.sup.+— 0.2% (equiv.);
[0069] Example 11: Ca.sup.2+—80.3%, Na.sup.+—19.6%, K.sup.+— 0.1% (equiv.);
[0070] Example 12: Ca.sup.2+—78%.0, K.sup.+—26.7%, Na.sup.+— 0.3% (equiv.); and,
[0071] Example 13: Ca.sup.2+—98.6%, Na.sup.+—1.4%, K.sup.+— 0.0% (equiv.).
Examples 14 and 15 (Samples Preparation According to the Invention)
[0072] A magnesium-containing form MgNaLSX was prepared for Example 14 using the NaKLSX sample of Example 3 and an MgCaLSX was prepared for Example 15 using the CaNaLSX sample of Example 11 by treatment of the corresponding samples with a 1N solution of magnesium chloride.
[0073] The adsorbents had the following cation content:
[0074] Example 14: Mg.sup.+—50.5%, Na.sup.+—48.8%, K.sup.+—0.7% (equiv.); and,
[0075] Example 15: Mg.sup.+—60.2%, Ca.sup.2+—38.0′%, Na.sup.+—1.8% (equiv.)
Example 16 (Equilibrium Methanol Adsorption Test)
[0076] Methanol adsorption was measured using the following methodology. A portion of the adsorbent was placed in a glass container with 100-250 ml of the stock solution. Stock solutions of methanol in n-pentane with concentration in the range of 100-1000 ppm were prepared employing Hamilton micro syringes and a measuring flask dilution method. The volume ratio solution/portion was taken up every time so that the difference between initial and equilibrium methanol concentration in the solution would not exceed 20% of the initial value. The mixture was maintained at ambient temperature for 2-3 days with intermittent shaking until the concentration of the contaminant in the solution reached the constant value.
[0077] Analysis of the stock and research solutions were carried out by means of gas chromatograph with a flame ionization detector and 30 m capillary column with a DB-WAX stationary phase. The results for measuring the adsorption capacities of the mono-, bi- and tri-cation LSX samples of the Examples 1 to 15 alongside conventional methanol adsorbents, i.e. molecular sieves 4A, 5A, 13X and silica gel are presented in Table 1.
[0078] It is clear from Table 1 data that alkali and alkaline-earth mono-, bi- and tri-cation exchanged LSX forms according to the present invention appreciably outdo all known methanol adsorbents including molecular sieves 4A, 5A, 13X and silica gel over the full range of methanol concentrations. Table 1 reveals an unusual peculiarity of adsorbent composition of this invention by the completely different behavior of mono-, bi- and tri-cation exchanged forms of the adsorbents at low, medium and high methanol concentrations in solution. The mono-cation NaLSX, KLSX and CaLSX forms of Examples 4, 8 and 13 exceed bi- and tri-cation LSX forms for methanol adsorption from low concentrated solutions below 300-350 ppm, while bi- and tri-cation exchanged LSX adsorbents of Examples 1, 2, 5, 9, 10, 14 and 15 manifest undisputable improved performance in medium and high methanol concentration range. This effect is obviously demonstrated by
[0079] Accordingly, a preferential application of mono-cation adsorbents of the present invention is in deep purification processes, when high purity of the products below 2 ppm is required, while bi- and tri-cation LSX forms are highly suitable for bulk methanol separations from complex mixtures. It is also seen that the content of other cations in mono-cation exchanged adsorbents according to the present invention should not exceed 1,5%, and preferably will not exceed 0.8% equiv. At the same time, the degree of ion exchange of any alkali or alkaline-earth cations in the bi- and tri-cation adsorbents shouldn't fall below 60% equiv.
TABLE-US-00001 TABLE 1 Adsorption Capacity, % w. Methanol Concentration, ppm Adsorbent 50 100 200 300 400 500 750 1000 NaKLSX-76 (Example 1) 4.11 4.70 6.44 8.17 11.71 15.95 18.10 19.60 KNaLSX-60 (Example 5) 4.08 5.25 6.80 8.60 11.73 14.89 17.64 19.43 CaNaLSF-80 (Example 11) 4.04 5.07 6.95 — 12.01 16.05 18.33 19.70 CaNaKLSX-63 (Example 9) 4.18 5.39 — 8.18 12.10 15.70 17.68 18.96 MgNaLSX-48 (Example 14) 3.98 4.96 6.35 — 11.75 15.90 — 19.15 NaLSX-97 (Example 3) 4.98 6.05 7.42 9.05 12.16 16.05 16.72 18.35 NaLSX-99.7 (Example 4) 5.14 6.18 7.70 8.85 11.02 13.98 15.88 17.20 KLSX-91 (Example 6) 4.85 5.96 7.21 — 11.94 13.22 15.99 16.53 KLSX-98 (Example 7) 4.97 6.04 7.27 8.77 — 12.69 15.12 16.07 CaLSX-99 (Example 13) 4.76 5.47 6.98 — 11.10 13.60 15.08 15.90 4A (Dryamax 4A) — 2.78 4.35 5.19 7.15 8.11 — — 5A (Dryamax 5A) 1.60 2.15 3.85 5.35 7.48 8.46 — 10.31 13X (Dryamax 13X) 2.19 4.11 5.22 6.51 8.57 10.28 12.82 14.13 Silica Gel (Dryamax HC-5) — 4.63 5.80 7.10 10.02 12.00 14.06 15.98
Example 17. (Natural Gas Dehydration and Purification Test)
[0080] The adsorbents of Examples 1, 5, 8 and 9 that represent the present invention were tested against the adsorbents of the prior art in a process for the simultaneous dehydration and methanol removal from natural gas using a pilot plant having an adsorbent vessel of 1 L volume and operating with gas temperature of 25° C., a pressure of 40 bar, a linear velocity of 0.15 m/sec, a relative humidity of 100%, and a methanol concentration that varied from 250 ppm up to 2.2% w. The dynamic capacity of the adsorbents for methanol was determined before moisture breakthrough dew point of −70° C. and before a methanol breakthrough of 20 ppm.
[0081] Table 2 presents the test results and clearly illustrates the advantages of the adsorbents of the present invention.
TABLE-US-00002 TABLE 2 Dynamic Capacity for Methanol, % w. To CH.sub.3OH break- To Moisture Dew Point through of 20 ppm of −70° C. CH.sub.3OH Content Methanol Initial Concentration, % w. In Regeneration Adsorbent 0.0375 2.20 0.0375 2.20 Liquid, % w. Example 1 4.15 14.20 3.12 11.90 42 (NaKLSX-76) Example 5 4.08 13.50 2.98 12.06 40 KNaLSX-60 Example 8 5.12 10.25 2.35 10.7 28 (KLSX-99) Example 9 4.00 14.34 3.17 12.00 43 (CaNaKLSX-63) 5A 3.36 10.80 1.80 4.64 13 13X 3.82 11.70 1.68 5.20 12 Silica Gel 1.21 9.46 0.86 3.90 8
[0082] Table 2 shows that although dynamic characteristics of all tested adsorbents are comparable when the gas dehydration process is interrupted after methanol breakthrough. These adsorption techniques, as verified by the experimental data, fail in commercial practicality due to the very low effectiveness of the adsorbents capacity for use in moisture removal, i.e. the adsorbents loading by water vapors decreases by 2-3 times. At the same time, the tests results demonstrate a completely reverse behavior of the prior art adsorbents and the adsorbents of the present invention at real conditions of natural gas dehydration processes that is typically conducted to reach the product gas dew point of −70 to −80° C. In such cases, methanol take-off from gas flow by the adsorbents of Examples 1, 5 and 9 is surprisingly and advantageously increased by 1.5-2 times. Therefore, the higher inlet methanol content of most natural gas makes the adsorbents of this invention significantly advantageous over the traditional ones.
[0083] The high methanol retention by the adsorbents of the present invention at conditions for displacing adsorption of water vapors clearly establishes a sharp reduction of the methanol losses. The concentration of methanol in the product gas, even at high initial contents such as 2.2% v., does not exceed 120 ppm through to the end of the gas dehydration cycle and provides a 10-fold decrease relative to the usage of the best-known 5A and 13X. Consequently, this leads to the significant 2-3 times increase of methanol content in the regeneration liquid and in turn to the substantial lowering of capital and operational expenses in the important step of reagent reclaiming.
[0084] The test results also show an essential advantage of bi- and tri-cation exchanged alkali and alkaline-earth metal LSX adsorbents of Examples 1, 5 and 9 over the mono-cation adsorbent of Example 8 in the process of simultaneous dehydration and methanol recovery. For such operations, the total content of one of the applied alkali or alkaline-earth metals has to range from about 40 to about 70% equiv.
Example 18. (Methanol and Oxygenates Separations from Liquid Streams Test)
[0085] Performance of the adsorbents of the present invention of Examples 1 and 4 in the process of methanol recovery from hydrocarbon and oxygenate liquid streams was compared with the 13X molecular sieves of WO Patent No. 029,366 to Outlaw and the silica gel of U.S. Pat. No. 4,748,281 to Whisenhunt. These adsorbents were tested for methanol separation from its mixture with n-pentane, methyl acetate (MeAc) and methyl methacrylate (MMA) employing a tube adsorber. The bed volume was 80 cm.sup.3, temperature −25° C., liquid stream flow rate −1 L/min or LHSV=12.5 h.sup.−1. The effluent samples at the adsorber discharge end were taken every 5-10 min and analyzed by means of a chromatograph as described in Example 16. Table 3 contains the data for the resulted stream purity and methanol dynamic capacity found for the various adsorbents.
[0086] The data shows that the bi-cation NaKLSX adsorbent of Example 1 does not reveal any advantages over the prior art adsorbents and is inferior to silica gel at the conditions of high methanol content in the feed and the essential absence of other polar substances. These are reasonable results because silica gel has at least 2 times higher meso- and macro-porosity than molecular sieves usually do. It is well known that meso- and micropores volume play a decisive role in liquid phase physical adsorption at a high concentration of adsorbates.
[0087] What was surprisingly discovered is the superiority of the mono-cation adsorbent of Example 4 over bi-cation forms of LSX and prior art adsorbents. The adsorbent of example 4 demonstrates much greater effectiveness in methanol recovery and obtaining high purity of the products that is unattainable by any other known adsorbents. This is particularly indicative at carboxylic esters separation, when a polar solvent partially or completely displaces methanol from a sorption volume.
[0088] Thus, the mono-cation exchanged LSX adsorbents can provide 99.99% purity of individual hydrocarbons and carboxylic acid esters and at the same time demonstrate 4.5-7.5 greater adsorption capacity for methanol removal. Accordingly, the adsorbents of the present invention require substantially lower bed volume and lower capital investments for the process commercialization. The adsorbent for fine purification of individual hydrocarbons and carboxylic acid esters should have an alkali or alkaline metal ion exchange degree greater than 99% and content of other cations lower than 0.9% equiv.
TABLE-US-00003 TABLE 3 Adsorbents Present Invention WO US Performance Exam- Exam- 029,366 4,748281 Characteristics ple 1 ple 4 13X Silica Gel n-Pentane Methanol Content: Inlet, % v. 0.63 0.63 0.63 0.63 Outlet, ppm 100 2.0 100 100 Dynamic capacity, %, w. 25.9 20.5 25.4 36.1 Methyl Acetate Methanol Content: Inlet, % v. 0.90 0.90 0.90 0.90 Outlet, ppm 100 5.0 280 850 Dynamic capacity, %, w. 19.38 17.35 4.30 2.57 Methyl Methacrylate Methanol Content: Inlet, % v. 0.55 0.55 0.55 0.55 Outlet, ppm 100 6.0 370 505 Dynamic capacity, %, w. 12.03 10.20 9.30 3.28
Example 19. (Vaporized Methyl Acetate and Ethyl Acrylate Purification and Dehydration Test.)
[0089] The adsorption unit and operating procedure of Example 17 were applied for alcohols and water recovery from vaporized methyl acetate and ethyl acrylate streams at process conditions that are representative of a PSA process. Alcohols and water vapor dosing into a vaporized ester stream were carried out by saturation of nitrogen flow in the separate bubblers filled with alcohols and water respectively. The trial series had the following compositions feed:
a) MeAc—82.2; MeOH—2.2; H.sub.2O—0.5; N.sub.2—15.1% v.
b) EtAcr—85.8; EtOH—2.2; H.sub.2O—0.6; N.sub.2—11.4% v.
[0090] The adsorbents of Examples 1, 10 and 14 were tested alongside molecular sieves 4A, 5A, 13X and silica gel of the prior art at an adsorption temperature of 55° C., a pressure of 1.3 bar, and a feed flow linear velocity of 0.1 m/sec. To provide a 99.99% product purity, alcohols concentration in the outlet stream was 100 ppm or below for all trials. The test results are given in Table 4.
TABLE-US-00004 TABLE 4 Dynamic Adsorption Capacity, % w. Adsorbent MeOH EtOH H.sub.2O Example 1 12.60 11.48 1.62 (NaKLSX-77) Example 10 11.90 12.19 1.54 (NaCaLSX-67) Example 14 10.03 8.76 1.50 (NaMgLSX-50) 4A 7.24 — — 5A 9.35 — 1.43 13X 9.83 8.66 1.56 Silica Gel 1.25 2.20 0.98
[0091] The test results in Table 4 confirm the superiority of the present invention's adsorbents over the prior art adsorbents. Dynamic capacity of the bi-cation LSX adsorbent bed for alcohols is .sup.˜30% higher than the best that the adsorbents of the prior art can achieve in processes for methyl acetate and ethyl acrylate separation. Although water capacity before alcohols breakthrough was practically on the same level for all tested adsorbents, the present invention provides an approximately 40% increase of the dynamic capacity of the adsorbent bed of this invention in processes for carboxylic acid esters simultaneous dehydration and separation.
[0092] Thus, the most effective adsorbents of the present invention for the separation of alcohols and corresponding esters from carboxylic acids are bi-cation sodium-potassium and sodium-calcium LSX zeolite, wherein sodium ion exchange degree comprises 55-80% while potassium and calcium ion exchange degree does not exceed 45% (equiv.). At the same time, performance comparison of the Example 1 adsorbent with those of Examples 10 and 14 shows that sodium cation content in the adsorbent should not be lower 50% (equiv.).
Example 20. (Liquid Phase Methyl Acetate and MTBE Dehydration and Separation Test.)
[0093] The adsorbents of the present invention were tested against the prior art adsorbents in methyl acetate and methyl tert-butyl ether (MTBE) dehydration and separation by use of the static methodology of Example 16. The liquid feed compositions were:
a) MeOH—0.5; MeAc—99; H.SUB.2.O—0.5% w.
b) MeOH—0.7; MTBE—98.8; H.SUB.2.O—0.5% w.
[0094] Liquid volume/adsorbent volume ratio was 40:1. Water content in the dried liquid samples was determined by reactive gas chromatography method through the steps of injecting the sample into a calcium carbide cartridge in a front of GC column to provide the following determination of resulting acetylene. The obtained adsorption capacity values for methanol and water are recorded in Table 5.
TABLE-US-00005 TABLE 5 MeOH Content in Regeneration Adsorption Capacity, % w. Liquid, Adsorbent MeOH H.sub.2O % w. Methyl Acetate Separation Example 2 (NaKLSX-84) 5.90 19.06 22 Example 5 (KNaLSX-60) 6.85 21.20 26 Example 10 (NaCaLSX-67) 5.10 18.07 22 13X 1.12 23.45 4.5 Silica Gel 1.71 28.17 5.9 Methyl Tert-Butyl Ether Separation Example 1 (NaKLSX-77) 4.17 20.50 18 Example 9 (CaNaKLSX-63) 5.72 17.95 24 Example 12 (CaKLSX-78) 3.78 17.23 18 Example 15 (MgCaLSX-60) 5.14 16.90 25 13X 0.98 22.00 4.3 Silica Gel 1.34 29.70 5.0
[0095] The results of Table 5 demonstrate the significant advantages of the present invention over the prior art. Comparison of the data of Tables 3 and 5 shows that the addition of water to methyl acetate and methanol mixture causes a significant decrease of the adsorbent capacity for methanol. However, the adsorbents of the present invention preserve methanol adsorption capacity on a quite impressive level and the prior art requires the use of 4-5 times greater amount of the adsorbent to reach the same methanol recovery from moisturized methanol acetate.
[0096] The data for methanol/water capacity ratios can provide another advantage of the adsorbents of this invention over those of the prior art. The adsorbent regeneration step releases methanol and water from the adsorbent bed and saturates the regeneration gas. The latter is chilled at the adsorber outlet; methanol and water vapors are condensed and separated from gas flow; and liquid condensate can be directed to a methanol reclaiming distillation unit. Thus, the ratio of methanol and water adsorption capacities defines the concentration of methanol in regeneration liquid. The data of Table 5 show that the adsorbents of the present invention provide a 4-5 time increase of methanol concentration in the regeneration liquid in the separation of methanol from methyl acetate and MTBE and a corresponding energy saving for methanol recycling into the process.
[0097] These results confirm that bi-cation sodium-potassium and sodium-calcium LSX exchanged forms are preferable for methyl acetate mixtures separations, while bi-cation alkaline-earth CaMgLSX and tri-cation sodium-potassium-calcium exchanged forms are the best adsorbents for methyl tert-butyl ether separation. In these applications, alkaline-earth metal content should not be less than 60% equiv.
Example 21. (Methanol, Carboxylic Acids and Esters Separation Test)
[0098] The experimental procedure of Example 18 was repeated to compare adsorbent performance for the separation of methanol in the processes of methyl acetate and methyl methacrylate where the separation takes place in the presence of acetic and methacrylic acids. The liquid stream compositions were:
a) MeOH—0.5; MeCOOH—0.2; H.SUB.2.O—0.5; MeAc—98.8% w.
[0099] b) MeOH—0.7; MeC.sub.2H.sub.2COOH—0.5; H.sub.2O—0.5; MeMAcr—98.3% w.
[0100] Table 6 shows the impurities content in the purified streams at the moment of methanol breakthrough along with the adsorption capacities values that can be achieved by the applied prior art and the present invention adsorbents.
[0101] As demonstrated by Example 21, the present invention provides much higher purity of the methyl acetate and methyl methacrylate products than the prior art adsorbents. Although carboxylic acids and water significantly decrease the adsorption capacity values for methanol, the present invention's adsorbents have adsorption capacity approximately 2 times higher than the prior art adsorbents.
TABLE-US-00006 TABLE 6 Dynamic Capacity Outlet Concentrations, ppm for MeOH, Adsorbent MeOH RCOOH H.sub.2O % w. Methyl Acetate Example 1 (NaKLSX-77) 100 <100 <15 3.92 Example 3 (NaKLSX-97) 55 29 37 2.44 13X 420 120 80 1.65 Methyl Methacrylate Example 1 (NaKLSX-77) 115 <100 <15 2.78 Example 10 (NaCaLSX-67) 128 105 <15 2.46 13X 490 210 110 0.95
[0102] Accordingly, the invention provides highly efficient, reliable, and energy conserving adsorbents and adsorption technology for methanol recovery and separations from varied gas and liquid streams. The invention finds use in various adsorptive separation process, such as TSA, PSA and CSA, or displacement-purge adsorption (DPA). Thus, the invention has application to existing and new techniques in adsorbent compositions and adsorptive processes. Furthermore, utilizing the mono-, bi- or tri-cation alkali or alkaline-earth metal forms of low silica faujasite as methanol adsorbents in the present invention provides many advantages over the prior art adsorbents for methanol and oxygenate separation from gas and liquid streams.
[0103] This description of invention in specific embodiment and examples do not serve to limit the invention to the details disclosed herein. Many other variations are possible. For example, other alkali and alkaline-earth cations including lithium, barium, strontium and their combinations might be applied in the mono-, bi- and tri-cation exchanged forms LSX. The adsorbent of this invention can also be used in processes that employ fixed, moving, fluidized, simulative counter-current moving bed and so forth. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the specific embodiments and examples given.