FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patent Rules, 2003
Provisional Specification
(See section 10 and rule 13)
Method of scavenging hydrogen sulphide from liquids
Dorf Ketal Chemicals (I) Pvt. Ltd
Dorf Ketal Tower, D'monte Street, Orlem, Malad (W), Mumbai, 400064
Maharashtra State, India
An Indian company registered under the Companies Act, 1956

The following specification describes the invention:


METHOD OF SCAVENGING HYDROGEN SULPHIDE FROM LIQUIDS
Field of the invention
This invention generally relates to scavenging hydrogen sulphide from liquids to reduce or remove the levels of hydrogen sulphide therein, and particularly relates to scavenging of hydrogen sulphide from liquid hydrocarbon.
Background of the invention
The toxicity of hydrogen sulfide in hydrocarbon streams is well known in the industry and considerable expense and efforts are expended annually to reduce its content to a safe level. Many regulations require pipeline gas to contain no more than 4 ppm hydrogen sulfide.
In large production facilities, it is generally more economical to install a regenerative system for treating hydrogen sulphide streams. These systems typically employ a compound used in an absorption tower to contact the produced fluids and selectively absorb the hydrogen sulfide and possibly other toxic materials such as carbon dioxide and mercaptans. The absorption compound is then regenerated and reused in the system. Typical hydrogen sulfide absorption materials include alkanolamines, PEG, hindered amines, and the like.
However, during a development stage of a field or in small producing fields where regenerative systems are not economical, it is necessary to treat the sour hydrocarbon production with nonregenerative scavengers.
Based on an article appearing in the Oil & Gas Journal, Jan. 30, 1989, nonregenerative scavengers for small plant hydrogen sulfide removal fall into four groups: aldehyde based, metallic oxide based, caustic based, and other processes. In the removal of hydrogen sulfide by nonregenerative compounds, the scavenger reacts with the hydrogen sulfide to form a nontoxic compound or a compound which can be removed from the hydrocarbon. For example, in the formaldehyde


type reaction, the reaction produces a chemical complex known as formthionals (e.g., trithiane).
Description of Invention
The method of the present invention may be used in the treatment of sour gas and oil production streams, as well as in petroleum (e.g. crude oil, asphalts, and refined products) contained in storage tanks, vessels, pipelines, etc.
As mentioned above, the scavenging composition useful in the method of the present invention is a combination of aldehyde and polyethylene glycols. The preferred aldehyde is glyoxylic acid (Cas No 298-12-4) and the polyethylene glycols (PEG) are of various molecular weights. The range of ratios of the compounds used in the combinations are between 99 parts of aldehyde to 1 part of PEG and 1 part of aldehyde to 99 parts of PEG.
In carrying out the method of the present invention, the scavenging composition is added to the hydrocarbon oil or gas stream in a concentration sufficient to substantially reduce the levels of H2S and/or mercaptans therein.
In treating hydrocarbon streams, the scavenging compound contained in a solvent, such as a mutual solvent or water, may be injected by conventional means such as a chemical injection pump or any other mechanical means for dispersing chemicals in the stream. The injection may be in the flow lines or the gas may be passed through an absorption tower containing a solution of the combination of glycoxalic acid and PEG.
The H2S scavenging ability of the hexahydro-triazine is believed to be due to its reaction with hydrogen sulfide to produce sulfur containing organic compounds such as dithiazines.


The compounds used in making the combination can be added indidually or as a mixture thereof.
Examples
Experiments were carried out to demonstrate the effectiveness of the scavenger compound of the present invention, that is, combination of glyoxylic acid and PEG vis - a - vis other scavengers.
The Table I and Table II data reveal the combination of glyoxylic acid and PEG to be the most effective scavenger tested.
Hydrogen sulfide scavenging tests were conducted by partially saturating kerosene with H2S gas at room temperature. The H2S in each sample was the same. The selected scavenger sample was added in to the sample bottles. The bottles, each containing a scavenger sample, was shaken for 2 minutes and the concentration of H2S in the vapor phase of each bottle was measured with elapsed time (at room temperature) using dragger tubes. The data are presented in TABLE I and II.
The Table I and Table II data reveal the combination of glyoxylic acid and PEG to be the most effective scavenger tested.
One test (blank test) was conducted without adding any additive combination.
Table I- H2S Scavenger Data
Reading after 20 hrs
Blank = 1000 ppm
Product Dosage ppm % Efficiency
Glyoxylic Acid 50% 1000 82
Glyoxylic Acid 50% 500 60
Glyoxylic Acid/PEG 200 (95/5) 500 92
Glyoxylic Acid/PEG 200 (90/10) 500 90

Table II - H2S Scavenger Data
Reading after 20 hrs Blank = 600 ppm

Product Dosage ppm % Efficiency
Glyoxylic Acid 50% 500 42
Glyoxylic Acid/PEG 200 (95/5) 500 95
Glyoxylic Acid/PEG 400 (95/5) 500 93

It can be seen from the results presented in Table I and Table II that the synergy occurring due to combination additive made by addition of PEG to glyoxylic acid is clearly established.

(Mr. Tase, Sharatchandra Dattatraya)
Patent agent for the applicant Patent Agent registration Number IN/PA 879
To,
The Controller of Patents,
Patents Office Branch, Mumbai