Abstrict Desiccant tablets including solid potassium formate are used to
dry gas, especially in natural gas transmission lines. The most
preferred tablets comprise 5-15% potassium formate, up to 1% of
a surfactant as a lubricant, and the balance desiccant salts, preferably
calcium chloride.
Claims 1. A deliquescent gas drying tablet comprising 0.5% to 100% solid
potassium formate and 0% to 99.5% alkali, alkaline earth metal or
ammonium formates, chlorides, bromides or mixtures thereof.
2. A deliquescent tablet of claim 1 wherein the potassium formate
comprises about 5% to about 99.5% by weight.
3. A deliquescent tablet of claim 2 comprising about 0.5% to about
95% calcium chloride.
4. A deliquescent tablet of claim 1 wherein the potassium formate
comprises 5% to 95% by weight of said tablet.
5. A deliquescent tablet of claim 1 wherein the potassium formate
comprises 5% to 15% of said tablet.
6. Method of drying gas comprising contacting gas with a bed of
tablets comprising potassium formate thereby forming an aqueous
solution of potassium formate comprising water from said gas and
potassium formate from said tablet, and separating said solution
from said bed of tablets.
7. Method of claim 6 wherein at least some of said solution is
permitted to remain in contact with said bed of tablets and to contact
said gas, whereby said solution continues to remove moisture from
said gas until said tablets are substantially dissolved.
8. Method of claim 6 wherein said tablets comprise 5% to 99.5%
potassium formate.
9. Method of claim 8 wherein said tablets comprise about 5% to
about 15% potassium formate and the balance is desiccant salts.
10. Method of claim 6 wherein said gas is natural gas.
11. Method of claim 9 wherein said balance of desiccant salts comprise
predominantly calcium chloride.
12. Method of claim 6 wherein said separating is accomplished by
draining.
13. Method of claim 7 followed by replacing said bed of tablets
with new tablets comprising solid potassium formate.
14. Method of claim 13 followed by another iteration of the method
of claim 13.
15. Method of claim 9 wherein said desiccant salts include lithium
chloride.
16. Method of claim 9 wherein said desiccant salts include cesium
chloride.
17. Method of claim 6 wherein contacting of said gas with said
bed of tablets is accomplished by flowing said gas upwardly through
said bed of tablets.
18. A desiccant tablet comprising about 5% to about 15% by weight
potassium formate, about 0.1 to 1% surfactant, and the balance at
least one desiccant salt.
19. A desiccant tablet of claim 18 made by compression, wherein
said surfactant is sodium lauryl sulfonate.
20. A desiccant tablet of claim 18 wherein said at least one desiccant
salt comprises calcium chloride.
Description RELATED APPLICATION
[0001] This application is based upon and incorporates the entire
disclosure and claims of my Provisional Application Serial No. 60/217805
filed Jul. 12 2000 and claims the full benefit of its filing date.
TECHNICAL FIELD
[0002] Tablets containing potassium formate are useful for drying
gases because of their deliquescent properties.
BACKGROUND OF THE INVENTION
[0003] In the past, desiccants have been commonly used to dry gases
such as natural gas, particularly for its transmission through pipelines.
Typically the pipelines carry natural gas over hundreds of miles,
and it is necessary and desirable to remove whatever moisture is
present in the gas and/or in the pipeline. To this end, the art
has employed common desiccant salts such as calcium chloride, made
into tablets which tend to absorb the moisture.
[0004] An early patent to Hutchinson, U.S. Pat. No. 2804940
suggests passing a partially dehydrated natural gas upwards through
a bed of solid particulate deliquescent material such as calcium,
magnesium, or lithium chloride, or mixtures of them. Certain molar
ratios of chlorides and bromides are suggested by Heath in U.S.
Pat. No. 2143008 and by Thomas in U.S. Pat. No. 5733841; see
also Thomas U.S. Pat. No. 5766309.for a good illustration of the
placement of the solid deliquescent materials in a contemporary
drying vessel; this patent (5766309) is incorporated by reference
herein in its entirety.
[0005] A solution of 40-70% potassium formate is suggested for
use as a moisture absorbent in dehumidifiers and similar devices
by Atkinson in U.S. Pat. No. 5846450.
SUMMARY OF THE INVENTION
[0006] Tablets are made of powdered or crystalline potassium formate
and used to remove moisture from gases such as natural gas. The
tablets may contain from 0.5% to 100% by weight potassium formate,
the balance being alkali or alkaline earth metal formates (preferably
sodium, calcium, cesium and/or magnesium formate), chlorides and/or
bromides (preferably calcium chloride, potassium chloride, cesium
chloride, lithium chloride, or mixtures thereof). The tablet is
preferably made under compression and, for use in gas dryers in
natural gas transmission lines, preferably weighs about 7 to 15
grams so it can conveniently form a bed in a more or less conventional
gas dryer. A pillow shape is convenient, but no particular shape
is required for this invention. Preferred tablets comprise 97.5%
calcium chloride and 2.5% potassium formate. An additional 0.5%
of a binder, which is preferably sodium lauryl sulfonate, may also
be used. The preferred tablets need not use these exact proportions,
however--they may comprise 0.5% to 100% potassium formate, an additional
0.01% by weight to 1% by weight of a surfactant used as a lubricant,
and the balance one or more alkali metal or alkaline earth metal
halides.
DETAILED DESCRIPTION OF THE INVENTION
[0007] Comparisons have been made of the tablets of the present
invention, containing potassium formate, to various tablets containing
calcium chloride. For the comparisons, tablets were made of each
of the materials indicated. Tablets of each description were placed
in a screen basket which in turn was placed in a humidifier and
permitted to remove moisture from the same air. The baskets retained
the tablets but permitted liquid to drain into a pan. The pans were
preweighed and weighed again periodically. Results are reported
in terms of weight gain (liquid) in the pans, in grams, over time.
Table I presents the data obtained.
[0008] In Table 1 and elsewhere herein, CaCl2 77% is calcium chloride
containing 23% moisture. 10% KCOOH means 77% CaCl.sub.2 having an
additional (based on the calcium chloride) 10% potassium formate.
"94%+10% KF" means, in flake form, 94% calcium chloride,
6% moisture and an additional 10% potassium formate based on the
calcium chloride and moisture.
1TABLE 1 Weight increase over time (grams) Product 3 hours 18 hours
25 hours 90 hours CaCl2 77% 0.7295 4.609 6.5831 19.5703 CaCl2 77%
0.4096 3.2685 4.5123 17.9454 +10% KCOOH 0.6026 6.0434 7.6411 19.6084
+10% KCOOH 0.781 5.8817 7.7085 22.1131 94% + 10% KF 0.002 4.5483
5.6003 16.0585 94% + 10% KF 0.0931 3.2718 4.294 16.8932
[0009]
2TABLE 2 Weight increase over time (grams) Product 16 hours 20
hours 24 hours 40 hours CaCl2 77% 8.9011 9.6635 10.0889 12.4836
94% + 2.5% KF 6.9944 8.4999 9.5212 14.1517 94% + 5.0% KF 8.245 9.0611
9.6312 12.8922 94% + 7.5% KF 7.8536 8.7734 9.9184 13.9462 94% +
10% KF 7.259 8.1575 9.1607 13.2313
[0010] In Table 2 "94%+10% KF" means 94% calcium chloride,
6% moisture and an additional 10% potassium formate based on the
calcium chloride and moisture. "2.5% KF," "5% KF,"
and "7.5% KF" mean the indicated percentages of potassium
formate in addition to the 94% calcium chloride. In Table 3 the
term NH4F means ammonium formate.
3TABLE 3 Weight Increase Over Time (grams) Hours Product 16 hrs
20 hrs 24 hrs 40 hrs 77% CaCl2 6.547 8.5854 9.5619 15.3974 94% CaCl2
+ 5% NH4F 4.964 6.3635 7.2397 12.9733 94% CaCl2 + 7.5% NH4F 8.2826
10.3386 11.3232 15.2833 94% CaCl2 + 10% NH4F 6.4756 8.0257 9.0649
13.1451
[0011]
4TABLE 4 Weight Increase Over Time 2 hours 5 hours 24 hours LiCi
0.2913 1.8077 9.8172 KCOOH 0.5877 2.2647 9.993 77% CaCl2 0.0111
0.4246 4.9159 Sm. Mesh CaCl2 0.2023 0.5881 4.9159 Prilled CaCl2
0.0991 0.7136 4.6106
[0012]
5TABLE 5 Weight Increase Over Time 7 hrs 22 hrs 29 hrs 46 hrs 53
hrs 70 hrs 77% CaCl2 2.7918 10.2764 12.082 15.7432 16.809 19.0542
+2.5% 3.9704 11.7115 13.8077 17.9961 19.2392 21.8174 KCOOH +5.0%
3.8633 11.5287 14.0292 17.9577 19.0072 21.1038 KCOOH +7.5% 4.8065
10.7662 13.1887 16.4462 17.7821 19.7666 KCOOH +10.0% 4.7849 10.0518
12.7825 15.8435 17.2899 18.937 KCOOH
[0013] For Table 5 the indicated percentages of potassium formate
were added to the standard 77% calcium chloride, which contained
23% by weight moisture at the beginning of the test.
6TABLE 6 Weight Increase Over Time 4 hrs 8 hrs 24 hrs 28 hrs 48
hrs 94% CaCl2 + 10% NaCl 0.8145 2.1562 8.3738 9.5873 15.6393 94%
CaCl2 + 20% NaCl 1.4649 2.6146 8.4068 9.303 14.9175 100% KCOOH +
20% NaCl 2.0998 3.8347 10.8299 12.3011 15.5572 100% KCOOH + 20%
NaCl 1.3877 2.6183 9.3758 11.2575 14.1278 94% CaCl2 + 20% CaBr.sub.2
0.8164 1.5235 6.7693 7.7308 13.4968
[0014] For Table 6 the indicated additions of sodium chloride
and calcium bromide were made to 94% calcium chloride in the case
of the first, second and fifth tests, and to a 100% aqueous solution
of potassium formate in the third and fourth tests.
[0015] In each case where potassium formate was present, the formation
of the drained solution was faster than with compositions not including
potassium formate. Potassium formate clearly absorbs more moisture,
more readily, than the other salts tested, and clearly enhances
these abilities for any of the solution combinations
[0016] Thus it will be seen that my invention comprises a deliquescent
gas drying tablet comprising 0.5% to 100% solid potassium formate
and 0% to 99.5% alkali, alkaline earth metal or ammonium formates,
chlorides, bromides or mixtures thereof. The composition is preferably
comprises about 5% to about 99.5% by weight potassium formate and
most preferably about 5% to about 15% potassium formate with the
balance being desiccant salts such as alkali (including cesium),
alkaline earth metal or ammonium formates, chlorides, bromides or
mixtures thereof, with calcium chloride being preferred. |