Patent GB-391780-A (GB)
Title: Improvements in the separation of weak acids from gaseous mixtures
IPC: C01B17/16
Filed: 1931-10-30
Abstract: <PICT:0391780/III/1> A process for the separation of hydrogen sulphide alone or together with other weak vaporized acids from gases comprises absorbing the weak vaporized acids by means of aqueous solutions containing strong inorganic bases in chemical combination with organic sulphonic or carboxylic acids which have an electrolytic dissociation at ordinary temperature about the same as or less than that of the vaporized acids and which are capable of expelling the vaporized acids at elevated temperature.  A part of the aqueous solution may be continuously withdrawn from the gases, being returned to the washing step after the expulsion of the absorbed hydrogen sulphide, if desired at elevated temperature.  The washing treatment may be carried out at elevated pressure.  The gases which may be purified include producer gas, coke oven gas, waste gases from destructive hydrogenation, blast furnace gases and gases from the destructive distillation of brown coal.  The organic acids referred to are aminosulphonic acids such as taurine, amino acids such as glycocoll, alanine, asparagine and mixtures of amino acids obtained by the degradation of albumens, weak aliphatic mono-and di-carboxylic acids or imino acids such as imino-di-propionic acid.  The hydroxides or oxides of sodium, potassium, lithium, barium, calcium, strontium, magnesium and beryllium or salts of these metals such as the carbonates which in the warm lose their acid constituent by the action of the aforementioned organic acids, may serve as the bases. Mixtures of several of the organic acids may be employed. The organic acids and alkalis are preferably maintained in a nearly equivalent ratio.  The absorption step may take place at elevated temperature not exceeding 90 DEG  C.  The expulsion of the hydrogen sulphide &c. may be effected by bringing the absorbing solution into indirect heat exchange relation with a hot liquid or into direct contact with steam.  If hydrogen sulphide and carbon dioxide are present in the gas, the carbon dioxide may be first washed out alone at elevated temperature, the hydrogen sulphide and other weak vaporized acids being removed by a subsequent washing treatment at ordinary temperature.  Alternatively, the hydrogen sulphide may be removed first in a washing device by passing the treated gas at great speed through relatively small amounts of washing liquid, the carbon dioxide being subsequently removed at an elevated temperature in a second washing step. Hydrogen sulphide is evolved more quickly than carbon dioxide when the washing liquid is heated.  This may be made a basis for their separation if they are washed out of the gases together.  In carrying out the process with the apparatus shown in Fig. 1, the gases are washed in a tower 1, the washing liquid being introduced by a spraying device 6.  The liquid is withdrawn by a pump 8 and passed through a heat exchanger 3 into an expelling vessel 9, the greater part of the acidic gases being expelled through a pipe 10. The liquid then passes down a tower 12 in countercurrent with steam, the remainder of the acidic gases being expelled.  The regenerated liquid is pumped from the bottom of the tower 12 by a pump 18 through the heat-exchanger 3 and a cooler 19 from whence it is circulated to the tower 1.  The acidic gases and steam from the vessel 9 and tower 12 are combined and freed from steam by treatment with cold water in a cooling tower 15.  According to a modification, two washing towers are employed, the washing liquid being introduced into the first tower and then collecting in an overflow vessel from which it passes to a storage vessel.  From thence the liquid is pumped into a second washing tower.  After passing through this tower, part of the liquid flows back to the storage vessel and part is pumped away for regeneration.  The apparatus may be made of lead, chromium-nickel steel, aluminium or iron.  The stability of these metals is increased by the presence of the hydrogen sulphide but the presence of chlorine in any form should be avoided.  Examples are given.  The first Provisional Specification describes also the employment of the following as the organic acids: p-nitrophenol, 4 - nitroresorcin, trichlorophenol, benzene sulphonic and naphthalene sulphonic acids, amino benzene sulphonic and amino naphthalene sulphonic acids, anthranilic acid and its derivatives such as acetylanthranilic acid, nitro- and chlorobenzoic acids, phthalic acid and its derivatives and aspartic acid and also describes the use of formates of the alkali or alkaline earths as bases.  It also refers to the employment of the process for removing hydrocyanic acid from gases.  The second Provisional Specification describes the employment of phenol and its alkylated derivatives such as cresol or ethyl, propyl, butyl and hexyl phenols or cresols as the organic acids.