Treating petroleum fractions to remove acidic and basic components thereof has been practiced for many decades. In the early days of refining acidic components such as hydrogen sulfide and even mercaptans were removed by treatment with caustic solution.
Some attempts were made to simply use solid beds of caustic to remove acidic components from refinery and petrochemical streams, but these have not been too widely used as the beds usually plug or become coated with salts, reducing their effectiveness.
U.S. Pat. No. 3,254,137, Hutto el describe use of a solid KOH caustic treater to remove HF from propane.
A bed of granular alkalies was used to treat a variety of liquid hydrocarbon streams in Sun U.S. Pat. No. 3,761,534, which is incorporated by reference.
Example 1 used 4-8 mesh granular NaOH to remove sulfuric acid from an alkylate stream of tert.-butylated ethyl-benzene containing about 0.3 N total acid, primarily sulfuric acid. Although efficient acid removal first occurred, the bed plugged before 100 volumes of alkylate could flow through the bed.
Example 4 used no NaOH, but treated an effluent from the alkylation of benzene with ethylene in the presence of HCl with soda lime and glassmaker's (G.M.) alkali to remove acid.
Example 5 used pellets of C. P. NaOH to treat crude tert. butylated ethyl-benzene containing 570 ppm H.sub.2 SO.sub.4. NaOH pellets plugged at 92 weights of alkylate per weight of alkali, while beds of soda lime and G. M. alkali did not plug.
Example 7 used G. M. alkali on a support grid to treat crude tert.butylated ethylbenzene containing about 600 ppm sulfuric acid. The organic flowed up through the support grid, through the alkali to an outlet above the bed of alkali. A white precipitate built up in the reservoir below the grid, which was periodically removed through a drain valve by a water purge. The bed of alkali was reported essentially unchanged by casual observation and there was no increase in resistance to flow through it.
The streams treated in '534 were probably saturated with water, as periodic water purges were reported in many examples, and salts seemed to collect as solid deposits in a sump under the bed of alkaline solid. Some of the results reported could be summarized as follows:
U.S. Pat. No. 3,658,694 McCreary et al disclosed use of lump caustic to treat hydrocarbons, with centrifugal separation of lump caustic from fluid hydrocarbon. PA1 U.S. Pat. No. 4,316,998 Van Pool described water washing a propane stream to remove HF, then drying the resulting stream by passage over solid caustic alkali. PA1 U.S. Pat. No. 5,330,946 discussed removing thiophene or mercaptans in an extractor feed by passing a benzene fraction over solid caustic. PA1 a. hydrotreating and distilling a naphtha fraction to produce a hydrotreated naphtha containing less than 1 wt ppm acidic halide compounds and less than 50 wt ppm water; PA1 b. catalytically reforming said hydrotreated naphtha over a halogen and Pt containing reforming catalyst at catalytic reforming conditions to produce a reformate liquid fraction containing at least 0.1 wt ppm acidic halide compounds and less than 25 wt ppm water; and PA1 c. depositing solid salt deposits on a bed of solid caustic by contacting said reformate liquid containing acidic halide compounds with solid caustic at reaction conditions sufficient to remove at least a majority of said acidic halide compounds and produce: PA1 d. regenerating, at least periodically, said solid caustic containing solid salt deposits by contacting said solid caustic with a wash liquid hydrocarbon phase containing dissolved or entrained water, and wherein the water content of said liquid hydrocarbon phase is greater than that of said reformate liquid fraction, to produce solid caustic containing no or less solid deposits. PA1 washing said solid particles with a hydrocarbon liquid phase saturated with water to produce a wash liquor containing dissolved salt and solid particles of caustic containing a reduced amount of solid salt deposits; PA1 extracting or removing salt from said wash liquor by contact with an aqueous phase to produce an aqueous phase containing dissolved salt deposits and a regenerated hydrocarbon phase saturated with water; and PA1 recycling said regenerated hydrocarbon phase to contact said solid particles of caustic. PA1 a. charging a flow vapor stream containing at least 0.1 wt ppm acidic halide and less than 100 vol ppm water through a bed of solid caustic material, and wherein the halide content of the gas and the water content of the gas are such as to form solid salt deposits on said solid caustic material in an amount sufficient to reduce the effectiveness of said solid caustic for halide removal; PA1 b. periodically removing said solid caustic from contact with said flowing vapor stream; PA1 c. periodically regenerating said solid caustic by contact with a liquid hydrocarbon stream which is saturated with water but contains less than 1 wt % entrained water and dissolving said solid deposits in said dissolved and/or entrained water from said solid caustic to produce a substantially salt free surface on said solid caustic particles; and PA1 d. returning said substantially salt free solid caustic particles to contact with said flowing gas stream.
Although some use has been made, as described above, of solid caustic to treat or sometimes dry hydrocarbon streams, this has never been very popular. There are several reasons for the limited use of this inexpensive alkaline reagent.
Solid caustic can not be used to treat aqueous streams. All the caustic would soon dissolve.
Solid caustic used as a bed of solid particles to treat relatively dry hydrocarbon streams containing acid contaminants will soon plug. Salts form and rapidly plug the bed and/or cause the bed to fuse into a solid mass. Such beds are difficult to regenerate, because if water washing is used to remove the salt much of the caustic will also dissolve.
Some attempts have been made to overcome the shortcomings of conventional solid caustic beds. Many refiners use caustic impregnated solids, such as caustic impregnated alumina, to remove acidic components from refinery streams. While such beds are mechanically stronger than neat caustic, the beds are still susceptible to plugging, and cost far more because the caustic is only 5 or 10 wt % of the alumina treater.
Alumina beds can exhibit catalytic activity. When alumina beds are used to remove chlorides from flowing vapor streams, aluminum chloride can form, and cause catalytic reactions which convert some of the hydrocarbon vapor species into a much higher molecular weight material. In some units, the gas is turned to goo, at least enough is formed that the effectiveness of the alumina bed is much impaired. This heavy viscous material must be removed to "regenerate" the alumina bed, so that it may be used to absorb additional amounts of chlorides or other acidic components from the flowing gas stream. Steam stripping will usually "regenerate" such a bed.
Disposal of solid adsorbents can be a serious waste management problem. Solid bed adsorbents must eventually be retired and frequently contains too much hydrocarbon to permit dumping in a landfill. The adsorbent bed may be steam stripped as a prelude to disposal. The resulting water/hydrocarbon product must be stripped to remove benzene from the waste water.
I have discovered a way to use a simple solid caustic bed to remove acidic components from relatively dry liquid or vapor streams in refinery and petrochemical processes and the like. My method can be used to regenerate solid caustic particles used to remove acidic contaminants such as chlorides from relatively dry streams such as reformate.
Instead of using water to wash salts from the bed (and dissolve much of the solid caustic and create an alkaline disposal problem), I use a hydrocarbon continuous phase. If this phase contains small amounts of entrained or even simply dissolved water the salt can be selectively dissolved.
Surprisingly, this approach effectively removes salt deposits from caustic beds, without removing appreciable amounts of the solid caustic. The method can even produce a salt water wash liquor which is almost neutral.