GB391786A - Improvements in the separation of weak acids from gaseous mixtures - Google Patents

Abstract

<PICT:0391786/III/1> A process for the separation of carbon dioxide, alone or together with other weak vaporized acids but in the absence of sulphur and its compounds, from gases comprises absorbing the weak vaporized acids by means of aqueous solutions containing alkalis in chemical combination with sulphonic or carboxylic organic 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 temperatures, continuously withdrawing part of the solution from contact with the gases and finally expelling the weak vaporized acids at an elevated temperature from this part of the solution which is then returned to the washing process. Gases which may be purified include those containing hydrogen which have been obtained by catalytic conversion of purified water gas with steam, or cracking gases which have been catalytically converted with steam, or illuminating gas, or gas obtained by gasifying coal with oxygen, freeing the gas from oxygen and reacting the gas catalytically with steam. The organic acids referred to are amino-sulphonic 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 and imino acids such as imino di-propionic acid. The hydroxides and oxides of sodium, potassium, lithium, or the salts of these metals, such as the carbonates, which in the warm loose their acid constituent by the action of the organic acids 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. Precipitation of insoluble salts may be hindered by keeping the absorbing solutions in constant movement. The absorption step may take place at elevated temperatures not exceeding 90 DEG C. The expulsion of the carbon dioxide &c. may be effected by bringing the absorbing solution into indirect heat-exchange relation with a hot liquid or into direct contact with steam. 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 The liquid is withdrawn by a pump 8 and passed through a heat exchanger 3 into an expelling vessel 9, the greater part of the acidic gases being expelled through a pipe 10.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 expelling 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. The liquid is pumped thence into the second washing tower. After passage through this tower, part of the liquid flows back to the storage vessel and a 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 addition of a small amount of divalent sulphur compounds, e.g. hydrogen sulphide, ammonium sulphide or polysulphide, &c., to the washing liquid whilst avoiding the presence of chlorine in any form. Examples are given. The first Provisional Specification describes also the employment of the following as the organic acids; p-nitrophenol, 4-nitroresorcinol, trichlorphenol, benzene sulphonic and naphthalene sulphonic acids, amino benzene sulphonic and amino naphthalene sulphonic acids, anthranilic acid and its derivatives such as acetyl-anthranilic acid, nitro- and chlorobenzoic acids, phthalic acid and its derivatives and aspartic acid, and also describes the use of the hydroxides, oxides, carbonates and formates of barium, strontium, magnesium and beryllium, and the formates of sodium, potassium and lithium as the bases. Further, it describes the process as applicable for the removal of hydrogen sulphide or 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. It also describes the prevention of corrosion of the apparatus by the addition of divalent sulphur compounds to the gases.