Mercaptans, removal

Caustic Treatment. Amine treatment may be followed by a caustic treatment step in which the LPG is brought into contact with 10—20 wt % caustic solution to remove any residual H2S and to remove mercaptans. The mercaptans may be stream-stripped from the caustic solution, after which the stripped caustic is recycled to the LPG caustic contactor. Caustics that contain H2S must be discarded. Various promoters maybe added to the caustic to improve the efficiency of the mercaptan removal. 

Washing light hydrocarbons with water is a common refinery practice. It finds application on the feed to catalytic polymerization plants. It is used to remove any entrained caustic from the mercaptan removal facilities as well as any other impurities such as amines which tend to poison the polymerization catalyst. Another use for water wash is in alkylation plants to remove salts from streams, where heating would tend to deposit them out and plug up heat exchanger surfaces. Water washing can be carried out in a mixer- settler, or in a tower if more intimate contacting is necessary. 

In selecting acceptable combinations, the bed height should be at least 10 ft for H2S removal and 20 ft for mercaptan removal. This height will produce sufficient pressure drop to assure proper flow distribution over the entire cross-section. Thus, the correct vessel size will be one that has a bed height of at least 10 ft (20 ft if mercaptans must be removed) and a vessel diameter between df in and... 

Sulfuric acid was used extensively several decades ago to reduce fuel mercaptans, olefins, and to some extent, aromatics. Today, sulfuric acid processing has been almost entirely replaced by more effective and safer processes. Mercaptan removal was accomplished by converting mercaptans to disulfides through the following reaction ... 

Ferrocyanide process a regenerative chemical treatment for mercaptan removal using caustic-sodium ferrocyanide reagent. 

An objective of this paper it to describe the results of our further investigation of the competition for adsorption sites between water and dimethyl disulfide molecules during methyl mercaptan adsorption on activated carbons. Moreover, we attempt to indicate the apparent borderlines between the conditions of adsorption processes leading to different adsorption/oxidation paths. Those working conditions have a significant effect on the feasibility of methyl mercaptan removal. 

X 30 mesh 38 28.5 and liquid hydrocarbon and natural gas sweetening (H2S and mercaptan removal). 

In this paper we report that without alkali medium a very good mercaptan removal was achieved using bifunctional catalyst prepared by an improved one-step preparation method. 

The catalytic effectiveness of the well-crystallized catalysts (DS3 to DSe) was evaluated by a simple laboratory test (screenings). Mercaptan removals of 70 to 83 % are obtained. This important catalytic activity is attributed to a) the meaningful contamination by C03 anions in the interlayer domain, which induces the pursued basic character as described by Constantino et al. [27,28] for the decomposition of MBOH to acetone and acetylene by MgAlC03 hydrotalcite at 353 K, and b) to the dispersion of the cobalt phtalocyanine complex in the interlayer space, since an aggregation of the cobalt phtalocyanine complexes decreases the thiol oxidation effectiveness [22]. 

In conclusion, we have shown that without alkali medium a very good mercaptan removal using a bifimctional catalyst was obtained confirmii that the adequate tuning of basic and oxidant properties lead to a promising catalyst. This catalyst consists of cobalt phtalocyanine parallel-intercalated MgAl hydrotalcite obtained by a direct synthesis method. Moreover it exhibited a good mechanical resistance and did not need fijrther post treatment to improve physical properties. 

New light on the importance of the specific surface features on the feasibil% of removal of methyl mercaptan on activation carbon was thrown after study of nitrogen-enriched carbons as media for methyl mercaptan removal [138,140], The capacity on carbons modified with urea was much higher than tliat on the as received adsorbents (Table 6) and even ten times enhancement can be obtained using this route of surface modification. The enhanced performance is attributed to the effect of basic nitrogen incorporated within the carbon matrix. 

For C5 alkylation, or for TAME production, removal of petandiene is required as it increases the acid consumption in alkylation and fouling in the TAME unit. The simple hydrogenation catalyst is quite sensitive to the presence of mercaptans present in this stream from cat crackers and cokers, and mercaptan removal also becomes necessary for effective hydrogenation. However, the technology of CR L for pentadiene removal achieves both goals hydrogenation of pentadiene and removal of mercaptans in the same unit. The mercaptans react with olefins in the... 

Type 13X (ten angstroms). Type 13X is a modified form of the sodium zeolite with a pore diameter of ten angstroms. Molecules of chloroform, carbon tetrachloride and benzene can be adsorbed on type 13X molecular sieves. Type 13X is used commercially for general gas drying, air plant feed purification (i.e., simultaneous removal of H O and CO ) and liquid hydrocarbon and natural gas sweetening (i.e., H S and mercaptan removal). All molecules which can be adsorbed on molecular sieves 3A, 4A and 5A can be adsorbed on type 13X. In addition, type 13X can adsorb molecules of larger critical diameters, such as aromatics and branched-chain hydrocarbons. 

A mixture of 17j -acetoxy-2a-bromo-5a-androstan-3-one refluxed 14 hrs. with excess n-propyl mercaptan in chloroform under Ng, solvent and excess mercaptan removed in vacuo, the residue stirred and refluxed 4 hrs. in aq.-methanolic HCl, the resulting n-propyl mercaptan and disulfide removed hy co-distillation with water in vacuo, the crude product mixture reacetylated hy heating 1 hr. with acetic anhydride and pyridine, finally the 3-ketone removed as its bisulfite addition product after treatment of the mixture with aq. Na-metabisulfite in boiling methanol 17j -acetoxy-5-a-androstan-2-one. Overall Y 41.5%.—Reduction of the intermediate 2,3-bis-(n-propylthio)-5a-androst-2-en-17/ -ol acetate by n-propyl mercaptan occurs only under strongly acidic conditions and in a random manner to produce the 2- and 3-n-propylthio derivatives in essentially equal quantities. The 3-ketone forms a bisulfite addition product under conditions where the 2-ketone does not react at all. Hydrolysis of the addition product affords a 49% yield of the 3-ketone, which can be used again. R. L. Clarke, J. Org. Chem. 28, 2626 (1963). 

CO2. They also lemoved about 90% of the COS and a small fraction of the mercaptans present in the feed gas. Data on the organic sulfur removal in one of these plants are given in Table 2-26. The absorbers operate at unusually high temperatures (e.g., lean amine temperatures as high as 150°F). It is possible that this high temperature favors COS removal (by increasing the rate of the hydrolysis reaction) and inhibits mercaptan removal (by reducing equiiibiium solubility). 

Hvbison and Dingman (1972) describe a small DGA plant that was reported to remove about 98% of the mercaptans from a natural gas stream. This unit operated with a very low rich solution acid gas loading (0.27 mole acid gas per mole amine), a moderate contactor bottom temperature (rich solution 156°F), a tall absorber (25 peiforated trays), and a concentrated amine solution (50% DGA), all of which would be expected to enhance mercaptan removal efficiency. It should be noted, however, that the 98% efficiency value is based on the absorber inlet and outlet gas analyses. If the mercaptan removal efficiency is based on the amount of mercaptan in the feed gas to the absorber and the amount found in the acid gas stream, a removal efficiency of only about 45% is calculated. Kenney et al. (1994) claim that DGA solutions can achieve mercaptan removal levels as high as 90%. 

Harbison, J. L. and Dingman, J. C., 1972, Mercaptan Removal Experiences in DGA Sweetening of Low Pressure Gas, Proceedings of the 1972 Gas Conditioning Corference, University of Oklahoma, Norman, OK. 

In the practical application of the process for the purification of large volume gas streams, it is very important that H2S and CO2 concentrations be reduced to very low levels before the gas enters the mercaptan absorber. Both of these impurities are stronger acids than mercap-tans and consume caustic by forming nonregenerable salts. When the gas stream is processed in a conventional amine plant ahead of the mercaptan removal unit, the H2S concentration is normally reduced to less than 0.2S grain/100 scf (about 4 ppmv) to meet product specifications but the carbon dioxide content is often over 100 ppm. As a result modifications to the amine plant may be necessary to provide more complete carbon dioxide removal and make the removal of mercaptans with caustic economical. Alematively, the mercaptan removal unit should have an upstream caustic wash to remove trace amounts of CO2 and H2S. 

Figure 5"49. Flow sheet for mercaptan removal process with thermal regeneration. (Wanams, 1964t...

The efficiency of mercaptan removal is highest for light mercaptans (i.e R is a light hydrocarbon radical) and concentrated caustic solutions. The circulating caustic solution contains a dispersed Merox catalyst udiich promotes the conversion of mercaptans to disulfides at a relatively low tenoperatuie without ptmooting otho reactions and does not affect the formation of mercaptides. 

Figure 5-52. Block diagram of Merichem mercaptan removal process. Wizig, 1983i...

A high liquid hold-up, sparged absorber is used to improve mercaptan removal. To minimize the presence of free mercaptans in the filtercake, buffering agent makeup is used to maintain the lean solution pH at about 7. Mercaptan removal under these conditions is greater than 90%. However, if the sulfur were melted, the release of mercaptan-based compounds could create operating problems. 

Design and Operating Data for Large Mercaptan Removal Plant... 

More recently it has been learned that the use of more concentrated solutions of caustic and solutizer, which causes two phases of trealang solution to appear, may result in much more complete mercaptan removal. 

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