Process for the treatment of liquefied hydrocarbon gas using 3-(amino) propane-1,2-diol compounds

Abstract

A method for treating liquefied hydrocarbons including acid gases to remove said acid gases while minimizing loss of amine species, said method comprising the steps of contacting the liquefied hydrocarbons with an absorbent aqueous solution of a first amine compound, the first amine compound having the structure: ##STR00001##
wherein R.sub.1 is propane-2,3-diol; R.sub.2 is hydrogen, methyl ethyl, 2-hydroxyethyl, or propane-2,3-diol; and R.sub.3 is hydrogen, methyl, ethyl, 2-hydroxyethyl or propane-2,3-diol.

Claims

1. A method for treating liquefied hydrocarbons comprising acid gases to remove said acid gases while minimizing loss of amine species, said method comprising the step of contacting said liquefied hydrocarbons with an absorbent aqueous solution of a first amine compound, said first amine compound having the structure: ##STR00008## wherein R.sub.1 is propane-2,3-diol; R.sub.2 is hydrogen, methyl, ethyl, 2-hydroxyethyl, or propane-2,3-diol; and R.sub.3 is hydrogen, methyl, ethyl, 2-hydroxyethyl or propane-2,3-diol.

2. The method of claim 1, wherein said absorbent aqueous solution comprises from about 0.1 wt. % to 90 wt. % of said first amine compound and additionally comprising from about 1 wt. % to 90 wt. % of a second amine compound.

3. The method of claim 1, wherein said absorbent aqueous solution comprises from about 0.1 wt. % to 50 wt. % of said first amine compound and additionally comprising from about 5 wt. % to 50 wt. % of a second amine compound.

4. The method of claim 1, wherein R.sub.1 is propane-2,3-diol; R.sub.2 is 2-hydroxyethyl and R.sub.3 is methyl.

5. The method of claim 1, wherein R.sub.1 and R.sub.2 are propane-2,3-diol and R.sub.3 is methyl.

6. The method of claim 1, wherein said acid gases comprise one or more gas selected from the group consisting of CO.sub.2, H.sub.2S, a mercaptan compound, COS, CS.sub.2, and mixtures thereof.

7. The method of claim 1, wherein said aqueous solution comprises a second amine compound comprising a piperazine compound selected from the group consisting of piperazine, 2-methylpiperazine, 1-hydroxyethylpiperazine, 3-(piperazin-1-yl)propane-1,2-diol, 3,3′-(piperazin-1,4-diyl)bis(propane-1,2-diol) and mixtures thereof.

8. The method of claim 1, wherein said absorbent aqueous solution comprises a second amine compound selected from the group consisting of triethanolamine, diethanolamine, methyldiethanloamine, diisopropanolamine, 2-amino-2-(hydroxymethyl)propane-1,3-diol, 2-methylamino-2(hydroxymethyl) propane-1,3-diol, 2-dimethylalmino-2-(hydroxymethyl)propane-1,3-diol and mixtures thereof.

9. The method of claim 1, wherein said absorbent aqueous solution additionally comprises an acid, said acid selected from the group consisting of boric acid, hydrochloric acid, sulfuric acid, phosphoric acid and mixtures thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a graphical illustration of the relative solubility of the tested amines compared to MDEA plotted against their pKa values.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(2) Generally, the invention is a method for treating liquefied hydrocarbons comprising the removal of acid gases while minimizing loss of amine species. The method comprises the step of contacting the liquefied hydrocarbons with an absorbent aqueous solution of a first amine compound, the first amine compound having the structure:

(3) ##STR00004##
wherein R.sub.1 is propane-2,3-diol; R.sub.2 is hydrogen, methyl, ethyl, 2-hydroxyethyl, or propane-2,3-diol; and R.sub.3 is hydrogen, methyl, ethyl, 2-hydroxyethyl or propane-2,3-diol.

(4) A principal disadvantage of the amines commonly used in the prior art is their relativity high solubility in LPG. The invention addresses that problem by providing an amine compound with a lower LPG solubility.

(5) Most refineries operate at a total amine concentration of no more than about 35 weight % of the amine-containing aqueous treatment composition. Operation at about 40 weight %, preferably even about 50 weight % total amine(s) or more is desirable since high strength solutions provide additional acid gas removal capacity at low cost. Also, it is likely that the concentration of sulfur in crude oil will rise in the future.

(6) Accordingly, in order to maintain or increase production, the refinery must, on the average, process/remove more sulfur. Nevertheless, because of the increased loss of amines at the higher concentrations, it has not been economically feasible to operate above about the 35% level in most cases. One advantage of the invention is that it allows the refinery to operate economically at higher total amine strengths without the high amine replacement costs they would otherwise incur.

(7) Generally, the compounds used in the process of the invention will have a structure:

(8) ##STR00005##
wherein R.sub.1 is propane-2,3-diol; R.sub.2 is hydrogen, methyl, ethyl, 2-hydroxyethyl, or propane-2,3-diol; and R.sub.3 is hydrogen, methyl, ethyl, 2-hydroxyethyl or propane-2,3-diol. Useful amine aminopropanediol compounds include but are not limited to:

(9) ##STR00006##

(10) Compounds such as these, as listed above, may be used individually or in mixture to comprise the first amine to sweeten or otherwise remove acidic gases from the untreated LPG. Generally, the first amine compound may be synthesized through any number of means known to those of skill in the art. Moreover, most of these structures can be synthesized by the simple reaction between glycidol epoxide or 3-chloro-1, 2-propanediol with ammonia, methylamine dimethylamine or 2-(methylamino)ethanol as seen below.

(11) ##STR00007##

(12) In addition to the first amine compound used in the process of the invention, the aqueous solution used to sweeten LPG may comprise a second amine compound. Amine compounds useful as the second amine compound include trisamine compounds such as 2-amino-2-(hydroxymethyl) propane-1,3diol, 2-methyl amino-2-(hydroxymethyl) propane-1,3-diol, dimethylamino-2-(hydroxymethyl)propane-1,3-diol, or mixtures thereof; piperazine compounds such as 3-(piperazin-1-yl)propane-1,2-diol, 3,3′-(piperazin-1,4-diyl)bis(propane-1,2-diol), or mixtures thereof; alkyl amines such as mono ethane amine, diethanolamine, methyldiethanolamine, diisopropananolamine, triethanolamine and mixtures thereof; and mixtures of compounds within each of these species heretofore listed above.

Method of Treatment

(13) The process of this invention may be readily implemented by contacting LPG with the 3-aminopropane-1,2-diol compound mixtures in ordinary liquid-liquid contacting equipment, and under operating conditions within the ordinary limitations of such equipment. While some optimization of conditions, within the skill of the art, should preferably be done, it is to be expected that a reduction in amine solubility losses will be experienced even at existing operating conditions. A further advantage of the invention, therefore, is that it does not require significant substitutions or modifications in equipment, packing, operating conditions, and the like. Accordingly, the invention is particularly beneficial to refineries which need more acid gas removal capacity, but are reluctant to pay for extensive capital upgrades.

(14) It is another advantage of this invention that operating parameters are not narrowly critical. As a general guideline, it may be said that the higher the concentration in the system, the higher will be the amine losses. Representative concentrations are found in the Table below. While there is not known specific upper limit on concentration, it is suggested that the concentration be held to no more than about 95 weight % of the amine mixture, the remaining being water, in order to avoid operational problems, such as inadequate removal of H.sub.2S. A useful approach to determining the maximum usable concentration of in a given system is to gradually increase the content until problems are detected, then back off on the concentration until such problems disappear.

(15) Similarly, there is no necessary minimum concentration, this concentration may be a matter of routine experimentation. It is suggested, however, as a starting point that the concentration be at least about 5 weight %. It is believed that, in the majority of cases, the useful range of concentrations will be about 10 to about 90 weight %, preferably about 25 to about 75 weight %, and more preferably about 35 to about 65 weight % of the amine mixture, the remaining being water.

(16) Additionally, the aqueous absorbent composition may also comprise an acid such as boric acid, sulfuric acid, hydrochloric acid, phosphoric acid, and mixtures thereof. The concentration of acid may vary in an amount effective from 0.1 to 25 weight % and most preferably from 0.1 to 12 weight %. The acid source is effective in recovering the amine compound once the acid gas has been stripped from the system.

(17) The operating temperature for the contacting of the LPG with the containing amine mixture is not narrowly critical, but will usually be in the range of about 50° F. to about 190° F., preferably about 70° F. to about 160° F., and more preferably about 80° F. to about 140° F.

(18) In general terms, the lower temperatures are preferred in order to minimize solubility losses. Since most refineries do not have much flexibility in this regard, it is an advantage of this invention that significant reduction in amine loss will be effected at any given operating temperature.

WORKING EXAMPLES

(19) The following examples provide a non-limiting illustration of the features of the invention.

(20) A solution of heptane (10 g), toluene (0.1 g) and the tested amine (2.5 g) are mixed at 20° C. for 1 hours. The mixture is decanted for 15 minutes and the neat heptane phase is analyzed by gas chromatography using toluene as internal standard. The injection is repeated three times and peak areas of tested amine are averaged. Results are presented below:

(21) TABLE-US-00001 Amine MDEA TEA DIPA HEMAPD APD MAPD area 9210 40 2082 290 0 176 counts

(22) The pKa of the tested amines was recorded using an automated Mettler Toledo titration system using 50 weight % aqueous amine solutions and 0.5 N hydrochloric acid. Results are presented below:

(23) TABLE-US-00002 Amine MDEA TEA HEMAPD APD MAPD pKa 8.7 7.9 8.5 9.3 9.7

(24) Although the present invention has been described by reference to its preferred embodiment as is disclosed in the specification and drawings above, many more embodiments of the present invention are possible without departing from the invention. Thus, the scope of the invention should be limited only by the appended claims.