Hydrogen Requirements in Shale Oil and Synthetic Crude from Coal

14 Hydrogen Requirements in Shale Oil and Synthetic Crude from Coal J. L. SKINNER

ARCO Oil and Gas Company, Division of Atlantic Richfield Company,

Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: March 26, 1980 | doi: 10.1021/bk-1980-0116.ch014

P.O. Box 2819, Dallas, TX 75221

The development of a significant synthetic fuels industry in the United States will probably occur first in the liquids area.

This is because the near-term outlook for increased

natural gas supplies is much more favorable than for increased supplies of petroleum liquids. All indications are that a world-wide, chronic shortage of petroleum liquids is imminent. The delay in putting an alternate liquids industry on stream is because the economic incentives, to date, have not been sufficient to warrant heavy front -end investments in ventures of high technological risk. A very substantial cost element in the production of shale oil and coal liquids is the cost of hydrogen necessary to produce needed liquids, such as gasoline, jet fuel, diesel oil, and clean fuel oils. This paper addresses

the question of the hydrogen requirements for producing useful liquids from shale oil and coal.

Shale Oil

The hydrogen requirements for the upgrading of raw shale oil are governed by one primary factor--its extraordinarily high nitrogen content. An examination of Table I, which shows a representative range of ultimate analyses for petroleum crudes and for shale oils, shows that the carbon, hydrogen, sulfur, and oxygen levels for raw shale oil are all within the range typical for petroleum crudes. The nitrogen content of shale oil, however, is twice that for high nitrogen crudes.

Shale oil is not a uniquely hydrogen deficient feedstock

vis-a-vis petroleum tive data presented ratio is within the atomic H/C ratio is

crudes. As can be seen from the representain Table II, its atomic hydrogen to carbon range of some mid-continent crude oils. Its that of a naphthenic base petroleum crude.

In order to produce acceptable liquid fuels from raw shale oil most processing schemes incorporate either hydrotreating of 0-8412-0522-l/80/47-116-279$05.00 © 1980 American Chemical Society In Hydrogen: Production and Marketing; Smith, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

280

HYDROGEN: PRODUCTION AND MARKETING TABLE I.

ULTIMATE ANALYSES OF CRUDE AND SHALE OILS


Molecule

Formula

% in Crude Oil

% in Shale Oil

Carbon

C

84-87

84.5-85.2

Hydrogen

H

11-14

11.2-11.3

Sulfur

S

0-3

0.64-0.76

Nitrogen

N

0-1

2.0-2.2

Oxygen

0

0-2

1.3-1.5

TABLE II.

ATOMIC H/C RATIO OF REPRESENTATIVE CRUDE OILS AND SHALE OIL

Oil Type

Atomic H/C Ratio

Pennsylvania Crude

1-98

Healdton, Oklahoma Crude

1.81

Humbolt, Kansas Crude

1.73

Coalinga, California Crude

1.61

Beaumont, Texas Crude

1.53

SHALE OIL

1-58

In Hydrogen: Production and Marketing; Smith, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


14. skinner

Hydrogen Requirements in Shale Oil

281

the whole oil followed by subsequent processing, or fractionation of the whole oil followed by hydrotreating of the naphtha and gas oil fractions. Regardless of the processing scheme, hydrotreating for the removal of heteroatoms is required for transportation fuels and may be required for fuel oils. Although highly selective hydrodesulfurization can sometimes be achieved, selective hydrodenitrogenation is much more difficult. The order of hydrotreating severity required for hydrogénation reactions is presented in Table III. As shown in this table, if sufficient hydrotreating severity is employed to remove most of the nitrogen, then hydrodesulfurization and hydrodeoxygenation should be nearly complete. In addition, the olefins will have been saturated. (Olefins are not normally present in raw petroleum crudes, but they are present in raw shale oil from a retort.) If sufficient hydrotreating severity is employed to remove all, or nearly all, of the nitrogen, then substantial saturation of aromatics (including non-nitrogen containing rings) will also occur. There will also be some hydrocracking, although the hydrogen uptake for hydrocracking will be substantially less than for aromatic saturation. Because hydrodenitrogenation is not highly selective one can view Table III as a series of overlapping bell curves with regard to hydrogen consumption. By the time one type of reaction is nearly complete the next type of reaction is in substantial progress. It is often useful to use a "model compound" approach when attempting to analyze hydrogen consumption during hydrotreating operations. Dineen, et al (1), report that the predominant nitrogen compound types in shale oil are pyridines and pyrroles. These heterocyclics are very stable and refractory to hydrogénation. Hence, severe hydrotreating conditions are required to reduce nitrogen to acceptable levels. Rollmann (2) has reported that with nitrogen and oxygen species, saturation of any aromatic ring attached to the heteroatom is required prior to C-N or C-O bond scission. Thus, the hydrogen requirement for denitrogenation of pyridines and

pyrroles is much higher than the hydrogen content of the ammonia

product from a hydrotreater . Figures 1 and 2 show the hydrogen requirement for the hydrodenitrogenation of pyrrole and pyridine, respectively. It can be seen that four hydrogen molecules are required for the formation of one ammonia molecule from pyrrole, and that five hydrogen molecules are required for the denitrogenation of a pyridine molecule. In an analogous manner one can show that thiophenes will consume four molecules of hydrogen for each molecule of hydrogen sulfide produced, and thioethers

will consume only two molecules of hydrogen per hydrogen sulfide molecule. Rollmann has reported that saturation of aromatic rings attached to sulfur species is not required prior to C-S bond scission. However, at the high severities required for

hydrodenitrogenation, it seems reasonable to assume saturation of the thiophenic rings .


282

HYDROGEN: PRODUCTION AND MARKETING


H

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C — H

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PYRROLE

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THUS, 4 H2 ARE REQUIRED FOR THE PRODUCTION OF ONE NH3 Figure 1. Hydrodenitrogenation of pyrrole


+

NH3

14. skinner


H


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H

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283

H

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PIPERIDINE H

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C

/

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y

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n-PENTANE + AMMONIA

PIPERIDINE

THUS, 5H2 ARE REQUIRED FOR THE PRODUCTION OF ONE NH3. Figure 2. Hydrodenitrogenation of pyridine


+

NH3


284


In order to make an a priori estimate of the hydrogen requirement for heteroatom removal from raw shale oil the following assumptions were made: (1) Nitrogen is present in pyrroles and pyridines, with the nitrogen divided evenly between the two compound types. (This implies a hydrogen requirement of 4.5 moles per mole of ammonia produced.) (2) Sulfur is present predominantly as thiophene, with the remainder as thioethers. The assumption of 75 percent in thiophenes and 25 percent as thioethers implies a hydrogen requirement of 3.5 moles per mole of hydrogen sulfide produced. (3) Oxygen is predominantly present as phenols. An assumed hydrogen requirement of 2.5 moles per mole of water produced is reasonable. Consider a raw whole shale oil with the following properties: API Gravity Carbon, Wt %

20.3 84.71

Hydrogen, Wt % Nitrogen, Wt % Oxygen, Wt %

11.32 2.14 1.35

Sulfur, Wt %

Molecular Weight

0.68

297

Using the assumptions outlined above, an estimate of hydrogen requirements for heteroatom removal can be made. This estimate is shown in Table IV. This particular shale oil is, in fact, the Paraho shale oil (direct heated mode) which was hydrotreated for the U.S. Navy by The Standard Oil Company (Ohio) . Results from hydrotreating tests on this oil were reported by Robinson (3) . The hydro treat er was said to add

about 1,600 SCF per barrel of shale oil feed (12.05 kmol/m3) .

However, complete heteroatom removal was not achieved during hydrotreating. The composition of the hydrotreated whole shale oil was reported as: Carbon, Wt %

85.93

Hydrogen, Wt % Nitrogen, Wt %

12.96 0.30

Sulfur, Wt %

< 0.002

Oxygen, Wt %

0.53

Using the previously discussed assumptions it can be estimated

that another 220 SCF/bbl (1.66 kmol/m3) of hydrogen would be consumed in achieving complete heteroatom removal. Thus, the

results of the SOHIO study coupled with the above "model compound" estimation process, indicates a hydrogen consumption

of about 1,820 SCF/bbl (13.70 kmol/m3) for complete heteroatom removal (neglecting the hydrogen uptake for non-hetero aromatic


14. skinner


285

TABLE III.

ORDER OF HYDROTREATING SEVERITY REQUIRED FOR HYDROGENATION REACTIONS


Increasing Severity

*N0TE:

1.

Saturation of Olefins

2.

Desulfurization and Deoxygenation

3.

Denitrogenation*

4.

Saturation of Remaining Aromatics

5.

Hydrocracking

Nitrogen containing aromatic compounds must be saturated before the nitrogen can be removed. TABLE IV#

ESTIMATED HYDROGEN REQUIREMENTS FOR HETEROATOM REMOVAL FROM PARAHO SHALE OIL (DIRECT HEATED MODE)

SCF/bbl

kmol/m3

Denitrogenation

850

6.40

Desulfurization

90

0.68

260

1 . 96

1,200

9.04

Deoxygenation

Subtotal, Heteroatom Removal


286


saturation and hydrocracking associated with the removal of the remaining heteroatoms) . A similar approach can be followed when looking at the results of hydrotreating studies carried out by Chevron Research Company for the Department of Energy. These studies, which were carried out on a Paraho shale oil (indirect heated mode), were

reported by Sullivan, et al (£) . Using Chevron's results and

"model compound" analysis one can estimate hydrogen consumptions

of 1,874 SCF/bbl (14.11 kmol/m3) and 1,925 SCF/bbl (14.49 kmol/


m3) for the two hydrotreating conditions reported. The somewhat higher consumption figure reported by Chevron may be due to the fact that they were processing a slightly different oil (average molecular weight of 326, as opposed to the average molecular weight of 297 of the oil processed by SOHIO) .

What both the Chevron study and the SOHIO study indicate is

that complete heteroatom removal from whole shale oil will require between 1,800 and 2,000 SCF of hydrogen per barrel of

feedstock (13.55 kmol/m3 to 15.06 kmol/m3). What model compound

analysis indicates is that hydrotreating of raw shale oil is rather selective, in that only about one-third of the hydrogen consumed is for olefin saturation, saturation of non-hetero aromatics, and hydrocracking. A simplified processing scheme for fractionation of the whole oil followed by hydrodenitrogenation of the naphtha and gas oil cuts is shown in Figure 3. This approach minimizes potential problems with hydrotreating at the expense of overall liquid yield. There are two sources of hydrogen in this scheme— the retort gas stream and the bottoms. The bottoms can be fed to a coker in order to make more liquids and a coke product, or they can be fed to a partial oxidation unit to produce syngas. The final selection of a processing scheme will involve not only bringing the shale oil plant into energy and hydrogen balance,

but also will involve economic optimization with regard to coke and pipeline gas.

A simplified process diagram for hydrotreating of whole

shale oil followed by fractionation and subsequent processing is shown in Figure 4. This approach maximizes the possible yield of usable liquids at the expense of "overhydrotreating" of some of the light and middle distillate cuts. What is common, however, with the scheme discussed previously is that the potential hydrogen sources are in the gas and the bottoms. Those liquids streams in the middle are far too valuable to be con-

sidered as hydrogen sources. Again, market considerations and

economic optimization will determine the method of hydrogen production and the split of gas and bottoms between hydrogen

production and plant fuel. In all cases, the market factors will be influenced by geographic locations, and environmental considerations will impact on the selection of processing schemes.


14. skinner


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Hydrogen Requirements in Shale Oil and Synthetic Crude from Coal

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