Desulfurization and Sweetening THOMAS TAIT
Downloaded by UNIV OF CINCINNATI on November 10, 2014 | http://pubs.acs.org Publication Date: January 1, 1951 | doi: 10.1021/ba-1951-0005.ch014
Research Station, Anglo-Iranian Oil Co., Ltd., Sunbury-on-Thames, Middlesex, England
The paper presents a general picture both on a geographical and on a product basis of the distribution of sulfur in petroleum. Early processes for desulfurization and sweetening are briefly reviewed and process developments are discussed on the basis of a simple division of petroleum products into gases, light distillates, and middle distillates and fuel oils. Future needs of the industry are discussed, and the ways in which research is likely to be applied.
o u l f u r is present i n one form or another i n every crude oil which contributes significantly to total world production. A simple picture of its distribution on a geographical basis is given i n Table I . Distinction between so-called sulfurous and nonsulfurous crudes is indefinite, but if an arbitrary value of 1% by weight of sulfur content is selected the production figures shown i n Table I I are obtained. Of the N o r t h American total, about 1,100,000 barrels per day came from Texas, 420,000 from California, 170,000 from Mexico, and the remainder largely from Arkansas, Mississippi, and N e w Mexico. The sulfurous Venezuelan crudes come from the Lake Maracaibo area and these, like the Mexican crudes, give relatively low yields of naphtha and middle distillates, thus differing from the M i d d l e East crudes. Only small amounts of crude o i l with sulfur contents greater than 1% b y weight exist i n U . S . S . R . , Europe, and the F a r East. Although sulfur compounds i n crude oil have always created problems for the refiner, the information available today is meager on the form i n which the sulfur is actually present i n crude oil. One reason is because refining treatments are generally a last step in a sequence of processing operations and because the sulfur contents of individual distillate fractions bear little relation to those of the crudes from which they are prepared. Tables I I I and I V illustrate this. They refer to products from conventional refinery distillation which neglect hydrogen sulfide liberated during distillation. The problems created b y sulfur have changed as the industry progressed; just over twenty-five years ago the main problems were to make straight-run gasoline and kerosene without offensive odor and of suitably low sulfur content. Since then the complexities Table I.
World Crude Oil Production—1949 (14, 20) Approximate Production, M Bbl./Day
Area North America, including U . S., Mexico, and Canada South America including Trinidad Near and Middle East, including Persia, Saudi Arabia, Kuwait, Iraq, Bahrein, and Egypt U.S.S.R. and Eastern Europe Far East, India, Pakistan, and Burma Western Europe Total
Average Sulfur Content % Wt.
U, 16, 19, 22, 28,
84, 86, 88, 89, 40)
5270 1570
1.0 1.8
1430 810 200 30 9310
1.6 Less than 0.4 Less than 0.2 Less than 1.0
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In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.
152
ADVANCES IN CHEMISTRY SERIES
Table II.
Production of Crude Oils Containing More Than 1.0% by Weight of Sulfur
Downloaded by UNIV OF CINCINNATI on November 10, 2014 | http://pubs.acs.org Publication Date: January 1, 1951 | doi: 10.1021/ba-1951-0005.ch014
North America South America Middle East
M Bbl./Day
Range of Sulfur Content, Wt. %
% of Total Production in Area
1800 1100 1400
1-5.5 1-2.5 1-2.6
34 70 98
have increased largely through the introduction of more complicated processes. T h e consumers of petroleum products have naturally exercised a n influence toward the manufacture of sweet smelling and lower sulfur content products but developments have occurred largely through the desire of refiners for more efficient refining procedures for established finished products. I n certain cases the refiner has been assisted b y the fact that desulfurization leads to recovery of commercially valuable sulfur or sulfur compounds, but on the whole this has not been a driving force.
Processes and Products I n this part of the paper, development of processes is summarized on the following simple classification of products: Gases Light distillates Middle distillates and fuel oils Gases (2 5, 18). T h e sulfur present i n natural gas or i n refinery cracked gases is predominantly hydrogen sulfide, though quantities of organic sulfur compounds m a y occur. T h e hydrogen sulfide content m a y range from v i r t u a l l y zero t o about 15 volume % b u t the content of organic sulfur compounds is always s m a l l ; thus, desulfurization of petroleum gases is largely a question of hydrogen sulfide removal. F o r the principal use of natural gas as a domestic and industrial fuel, the total sulfur content is frequently regulated b y law to a maximum of 15 grains per hundred cubic feet. Sometimes i t is specified that the hydrogen sulfide content shall be substantially zero. Similar requirements with respect to total sulfur and hydrogen sulfide apply to liquefied petroleum gas. I n other uses of natural gas—for example, carbon black manufacture— the limitations about sulfur content are less severe but a relatively low hydrogen sulfide content is preferred. Probably the most stringent requirement is i n gas for conversion to synthesis gas; here hydrogen sulfide must be absent and the total sulfur content is limited to 2 p.p.m. with 0.2 p.p.m. preferred. I n the polymerization of refinery cracked gases, i t is rare that the allowable sulfur content—mainly hydrogen sulfide—is limited b y the sulfur tolerance of the catalyst used; the desired quality of the finished polymer is more usually the controlling factor. The early processes tended to be of a chemical nature and examples of these are the Seaboard (21) process using sodium carbonate solution as absorbent; the T h y l o x (15) process using sodium thioarsenate; and the early iron oxide process, which is still i n common use for removal of traces of hydrogen sulfide. Although there have been i m provements i n processes of the above type, for example the recovery of hydrogen sulfide by the vacuum carbonate (29 > 32) process, the main trend i n hydrogen sulfide removal has been toward the use of liquid absorbents which can be regenerated with recovery of hydrogen sulfide for sulfur or sulfuric acid manufacture. These processes can usually be applied equally to natural and refinery gases. I n recent years the Girbotol (10) process has been widely used with a n ethanolamine absorbent, usually monoethanolamine, b u t triethanolamine is used i n particular cases. Another development is the glycol-amine (12) process which accomplishes dehydration of natural gas at the same time as desulfurization. Other hydrogen sulfide removing processes of this type are the phosphate (27) process employing tripotassium phosphate and the alkacid (5) process using the potassium or sodium salt of an amino acid. I n these developments an important feature has been the recovery of sulfur i n one form or another for further use. Usually this recovery has been associated with the }
In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.
153
Downloaded by UNIV OF CINCINNATI on November 10, 2014 | http://pubs.acs.org Publication Date: January 1, 1951 | doi: 10.1021/ba-1951-0005.ch014
TAIT—DESULFURIZATION AND SWEETENING
sweetening of gas for sale as fuel or refinery processing, but i n some circumstances the recovery of sulfur has become an economic proposition even where the gases are flared. I n such cases, a less complete removal of hydrogen sulfide can be tolerated. Light Distillates (6). T h e main products i n this category are gasolines and kerosenes. A s far as sulfur is concerned i n these products, i n most countries there is now a fair agreement with regard to quality requirements. B o t h products are expected to have no objectionable smell, to pass a corrosion test, and to have sulfur content below 0.25% by weight. Types of sulfur compounds fall into two main classes, the acidic compounds such as hydrogen sulfide and mercaptans, and the neutral compounds which include sulfides both a l k y l and cyclic, thiophenes, and disulfides. The acidic bodies are objectionable because of their smell and corrosive nature and are responsible for a crude oil or a distillate being given the term "sour." Their conversion by refining is normally termed sweetening. Refiners were chiefly concerned with sweetening, before many of the less desirable properties now known to characterize sulfurous distillates were appreciated. Table III. T.B.P. Boiling Range, • F. Sulfur
Crude Oil Total
Far East East Texas East Venezuela Iranian West Texas West Venezuela Kuwait
0.15 0.36 0.55 1.4 2.0 2.2 2.45
Sulfur Contents of Products of Distillation
Gasoline and Naphtha Boiling below 300 Mercaptan Total < 0.003 < 0.003 < 0.003 0.063 0.14 < 0.003 0.010
0.003 0.012 0.011 0.087 0.17 0.023 0.015
(% wt.) Kerosene 300-450 Total Mercaptan < 0.003 0.003
