[Gasification] Fe + H2O = FeO + H2

[Peter Singfield]

At 05:14 PM 12/1/2006 -0500, you wrote:
>Dear List,
>
>Interesting information at below link:
>http://gasifiers.bioenergylists.org/?q=node/218
>
>
>Snip:
>"The above equation tells us that with steam and hot or molten iron we can
>make H2 with rust being the byproduct. This rust can be converted back to
>iron. Check out the below links for more information."
>
>
>Jeff
>

Why not just make gaoline and diesel??

1. 1. United States Patent: 5,763,716 
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   6.           ( 9 of 44 )


   7.       United States Patent 5,763,716 
   8.       Benham ,   et al. June 9, 1998 


   9. Process for the production of hydrocarbons 


  10. Abstract
  11. A process of converting a feed of hydrocarbon-containing gases into
liquid 
  12. hydrocarbon products including a first reaction of converting the
feed into one 
  13. to 2.5 parts of hydrogen to one part carbon monoxide in the presence
of carbon 
  14. dioxide and then secondly reacting the hydrogen and carbon monoxide
in a 
  15. Fischer-Tropsch synthesis reactor using a promoted iron oxide
catalyst slurry to 
  16. form liquid hydrocarbon products, wherein the carbon dioxide from the
first and 
  17. second reactions is separated from the product streams and at least a
portion of 
  18. the separated carbon dioxide is recycled into the first reaction feed
and the 
  19. hydrocarbon products are separated by distillation and a normally
gaseous 
  20. portion of the separated products are further reacted in another
Fischer-Tropsch 
  21. synthesis reactor to produce additional liquid hydrocarbon product. 

Jumping to:

106. There have only been a few instances wherein the Fischer-Tropsch
reaction has 
 107. been incorporated into a complete system, starting with a solid or
gaseous feed 
 108. stock. Germany placed several plants in operation during the 1930's
and 1940's 
 109. using coal as the feed stock, referenced in Twenty-Five Years of
Synthesis of 
 110. Gasoline by Catalytic Conversion of Carbon Monoxide and Hydrogen,
Helmut 
 111. Pichler, Advances in Catalysis, 1952, Vol. 4, pp. 272-341. In
addition to the 
 112. foregoing, South Africa has been using Fischer-Tropsch technology
based upon 
 113. this German work for the past 35 years to produce gasoline and a
variety of 
 114. other products from coal, referenced in Sasol Upgrades Synfuels with
Refining 
 115. Technology, J. S. Swart, G. J. Czajkowski, and R. E. Conser, Oil &
Gas Journal, 
 116. Aug. 31, 1991, TECHNOLOGY. There was also a Fischer-Tropsch plant
built in the 
 117. late 1940's to convert natural gas to gasoline and diesel fuel
described in 
 118. Carthage Hydrocol Project by G. Weber, Oil Gas Journal, 1949, Vol.
47, No. 47, 
 119. pp. 248-250. These early efforts confirmed that commercial
application of the 
 120. Fischer-Tropsch process for the synthesis of hydrocarbons from a 
 121. hydrocarbon-containing feed stock gas requires solving, in an
economical manner, 
 122. a set of complex problems associated with the complete system. For
example, 
 123. initially, it is important for the hydrocarbon-containing feed stock
to be 
 124. converted into a mixture consisting essentially of hydrogen and
carbon monoxide 
 125. before introduction of the mixture into the Fischer-Tropsch reactor.
Economic 
 126. operation of specific sizes of Fischer-Tropsch reactors, generally
requires the 
 127. ratio of hydrogen to carbon monoxide to be within well established
ranges. The 
 128. Hydrocol plant, referenced hereinbefore, used partial oxidation of
natural gas 
 129. to achieve a hydrogen to carbon monoxide ratio of about 2.0. An
alternative 
 130. approach to partial oxidation uses steam reforming for converting light 
 131. hydrocarbon-containing gases into a mixture of hydrogen and carbon
monoxide. In 
 132. this latter case, steam and carbon dioxide, methane and water are
employed as 
 133. feed stocks and carbon dioxide can be recycled from the output of the
reformer 
 134. back to its inlet for the purpose of reducing the resultant hydrogen
to carbon 
 135. monoxide ratio. 

 136. There are therefore, two primary methods for producing synthesis gas
from 
 137. methane: steam reforming and partial oxidation. 

 138. Steam reforming of methane takes place according to the following
reaction: 

 139. H.sub.2 O+CH.sub.4 .apprxeq.3H.sub.2 +CO (1) 

 140. Since both steam and carbon monoxide are present, the water gas shift
reaction 
 141. also takes place: 

 142. H.sub.2 O+CO.apprxeq.H.sub.2 +CO.sub.2 ( 2) 

 143. Both of these reactions are reversible, i.e., the extent to which
they proceed 
 144. as written depends upon the conditions of temperature and pressure
employed. 
 145. High temperature and low pressure favor the production of synthesis
gas. 

 146. Partial oxidation reactions utilize a limited amount of oxygen with 
 147. hydrocarbon-containing gases, such as methane, to produce hydrogen
and carbon 
 148. monoxide, as shown in equation (3), instead of water and carbon
dioxide in the 
 149. case of complete oxidation. 

 150. 1/2 O.sub.2 +CH.sub.4 .fwdarw.2H.sub.2 +CO (3) 

 151. In actuality, this reaction is difficult to carry out as written.
There will 
 152. always be some production of water and carbon dioxide; therefore the
water gas 
 153. shift reaction (2) will also take place. As in the steam reforming
case, 
 154. relatively high temperatures and relatively low pressures favor
production of 
 155. synthesis gas. 

 156. The primary advantage of partial oxidation over steam reforming is
that once the 
 157. reactants have been preheated, the reaction is self-sustaining
without the need 
 158. for the addition of heat. 

 159. Another advantage of partial oxidation is the lower ratios of
hydrogen to carbon 
 160. monoxide normally produced in the synthesis gas which ratios better
match the 
 161. desired ratio for use in the Fischer-Tropsch synthesis of hydrocarbon
liquids in 
 162. the overall process. 

 163. A still further advantage of partial oxidation resides in the
elimination of a 
 164. need for the removal of carbon dioxide and/or hydrogen from the
synthesis gas 
 165. before being fed to the synthesis reactors. 

 166. While adjustment of the hydrogen to carbon monoxide ratio can be
achieved by 
 167. removal of excess hydrogen using a membrane separator, for example.
This 
 168. approach requires additional capital equipment and can result in
lower oil or 
 169. liquid hyrdrocarbon yields due to a loss of hydrogen to the process. 

 170. In order for the overall process considerations to be used in a
manner which can 
 171. produce economical results whether employing either steam reforming
or partial 
 172. oxidation of a feed stock, the Fischer-Tropsch reactor must typically
be able to 
 173. convert at least 90% of the incoming carbon monoxide. If a 90%
conversion 
 174. efficiency is to be achieved in single pass operation and hydrogen is
not 
 175. removed before introduction of the gas stream into the reactor, the
build up of 
 176. unreacted hydrogen due to the excess of hydrogen will necessitate a
larger 
 177. reaction vessel to maintain a sufficiently long residence time in the
reaction 
 178. vessel. Recycle of unreacted hydrogen and carbon monoxide from the
outlet of the 
 179. Fischer-Tropsch reactor back to its inlet is commonly employed to
achieve the 
 180. required conversion. However, when an excess of hydrogen is employed,
an even 
 181. greater excess of unreacted hydrogen will build up under such a recycle 
 182. operation. This condition, in turn, can necessitate an even larger
reaction 
 183. vessel or alternatively the hydrogen removal described must be
employed. 

 184. Major drawbacks to the commercialization of many of the prior
processes were the 
 185. high cost of product specific catalysts, and when an inexpensive
catalyst was 
 186. utilized an unacceptable overall process conversion efficiency of the
carbon 
 187. input into the hydrocarbon products produced. 

 188. The two catalyst types attracting the most serious attention for the 
 189. Fischer-Tropsch reaction are either cobalt based or iron-based
catalysts. In 
 190. practice, a cobalt-based catalyst will favor the following reaction: 

 191. CO+2H.sub.2 .fwdarw.(--CH.sub.2 --)+H.sub.2 O (4) 

 192. While an iron catalyst will favor the following overall reaction (due
to its 
 193. high water gas shift activity): 

 194. 2CO+H.sub.2 .fwdarw.(--CH.sub.2 --)+CO.sub.2 ( 5) 

 195. Theoretically, cobalt-based catalysts can produce higher conversion
yields than 
 196. iron-based catalysts since cobalt can approach 100% carbon conversion 
 197. efficiency, whereas iron tends toward 50% carbon conversion
efficiency during 
 198. the Fischer-Tropsch synthesis reaction since the reaction (5) favors
the 
 199. production of carbon in the form of CO.sub.2. The major drawbacks
encountered 
 200. are, first, that cobalt-based catalysts are very expensive compared to 
 201. iron-based catalysts and, further, if the Fischer-Tropsch technology
was 
 202. embraced worldwide on a large scale, the higher demand for relatively
scarce 
 203. cobalt might drive the cost even higher. 

 204. The use of cobalt-based catalysts has typically included recycle of
tail 
 205. effluent back to the inlet of the Fischer-Tropsch reactor to achieve
90% 
 206. conversion primarily because cobalt favors formation of water. Too
much water 
 207. has been considered to be an inhibitor of either catalytic reaction
scheme. 
 208. Thus, as the reaction proceeds in the presence of water, not only is
the 
 209. concentration of reactants less, but the concentration of inhibiting
water vapor 
 210. is greater. In practice, generally 70% carbon monoxide conversion is
the maximum 
 211. attainable in single-pass operation using a cobalt-based catalyst.
Iron-based 
 212. catalysts, which favor carbon dioxide formation permit up to 90% of the 
 213. theoretical conversion of carbon monoxide per pass without great
difficulty, and 
 214. without the formation of additional water, thereby eliminating the
necessity for 
 215. effluent recycle back to the inlet of the Fischer-Tropsch reactor. 

 216. It has generally been considered undesirable to form CO.sub.2 in the 
 217. Fischer-Tropsch synthesis reaction as happens using iron-based
catalysts and 
 218. therefore many process schemes use cobalt-based catalysts including
the recycle 
 219. of some of the reactor effluent directly back into the
Fischer-Tropsch reactor. 
 220. In summary, therefore, iron-based catalysts, while efficient in
converting 
 221. carbon monoxide into the products shown in equation (5), have
previously been 
 222. limited in overall carbon conversion efficiency since their use
favors the 
 223. production of carbon dioxide, and therefore, they were not as
efficient in 
 224. overall carbon conversion efficiency to hydrocarbon products compared
to the 
 225. process schemes utilizing cobalt based catalysts. 

 226. The Fischer-Tropsch synthesis has commercially therefore been used in 
 227. combination with an up-stream steam reforming reactor which must then
be 
 228. followed by CO.sub.2 removal from the carbon monoxide and hydrogen
reaction 
 229. products before the CO and H.sub.2 synthesis gas produced by the
steam reforming 
 230. reaction are subjected to a Fischer-Tropsch reaction using cobalt-based 
 231. catalysts. 

 232. In selecting a suitable catalyst for use in a system which favors
reaction (5), 
 233. several considerations are important. In the Fischer-Tropsch
synthesis using 
 234. appropriately designed equipment, the hydrogen to carbon monoxide
feed ratio to 
 235. the Fischer-Tropsch reactor will optimally be in the range of from
0.6 to 2.5 
 236. parts of hydrogen for every part of carbon monoxide. This is
necessary in order 
 237. to obtain reasonably acceptable percent conversion of carbon monoxide
into 
 238. hydrocarbon per pass through the Fischer-Tropsch reactor without the
undesirable 
 239. formation of carbon in the catalyst bed. 

 240. In order to provide the H.sub.2 /CO ratio in the range of optimum
ratios 
 241. described hereinbefore for the catalyst selected, it is necessary and
typical 
 242. that an additional stage of hydrogen removal, by a membrane or the
like, is 
 243. inserted into the product stream between the steam reformer and the 
 244. Fischer-Tropsch reactor. 

 245. The present invention overcomes the foregoing difficulties, and
provides a 
 246. novel, unobvious and effective economically viable natural gas to oil
conversion 
 247. process using steam reforming or partial oxidation and a
Fischer-Tropsch 
 248. synthesis using a promoted iron-based unsupported catalyst in a
slurry reactor. 
 249. The present invention includes a solution to the problems of reducing
the 
 250. formation of excess hydrogen from the reformer or partial oxidation
unit and 
 251. increasing the overall carbon conversion efficiency for the entire
carbon input 
 252. to the system when using specifically prepared promoted iron
catalysts. As will 
 253. be shown hereinafter, the carbon dioxide produced by such iron
catalysts, 
 254. contributes to the low carbon conversion efficiencies previously
discussed, and 
 255. can be used to solve both the excess hydrogen and low overall carbon
conversion 
 256. efficiency problems. 

Again jumping to:

461. The hydrogen and carbon monoxide-containing gas stream 12 is then
introduced 
 462. into a Fischer-Tropsch reactor which employs a catalyst slurry using an 
 463. iron-based catalyst and preferably a precipitated iron catalyst and
most 
 464. preferably a precipitated iron catalyst that is promoted with
predetermined 
 465. amounts of potassium and copper depending on the preselected
probability of 
 466. linear condensation polymerization, i.e. chain growth, and product
molecular 
 467. weight distribution sought. 

 468. There are three fundamental aspects to producing a catalyst for a
particular 
 469. application: (1) composition, (2) method of preparation, and (3)
procedure for 
 470. its activation. 

 471. The preferred catalyst herein is an unsupported precipitated iron
catalyst 
 472. promoted with copper and potassium. The catalyst is made using
elemental iron 
 473. and copper as starting materials. 

 474. The first step in the cataylst preparation process is dissolution of
the 
 475. starting metals in nitric acid to form a mixture of ferrous nitrate,
ferric 
 476. nitrate and cupric nitrate in appropriate proportions. The ratio of
water to 
 477. acid is an important parameter and should be adjusted to give a
weight ratio of 
 478. about 6:1. The dissolution of the metals in nitric acid either by the
addition 
 479. of the metal to the acid or the acid to the metal produces an
evolution of 
 480. nitrogen oxides, principally nitric oxide and nitrogen dioxide.
Nitric oxide has 
 481. limited solubility in the acid, but can be readily oxidized to
nitrogen dioxide 
 482. by contact with air or oxygen. Nitrogen dioxide dissolves in water
producing 
 483. nitric acid and nitric oxide, respectively. Therefore, in order to
reduce 
 484. nitrogen oxide emissions from the reaction vessel and, at the same
time, to 
 485. reduce the consumption of nitric acid needed for dissolution of the
metals, 
 486. oxygen is bubbled through the solution while the metals are being
dissolved. The 
 487. small amount of nitrogen dioxide which escapes from the vessel is
scrubbed using 
 488. a potassium hydroxide or other basic solution such as of ammonium
hydroxide. The 
 489. mixture is stirred until the metals are totally dissolved. The
temperature of 
 490. the solution increases as the metals dissolve, but is preferably
controlled to a 
 491. maximum temperature of about 150.degree. C. 

 492. The next step in the catalyst process is precipitation of a catalyst
precursor 
 493. from the nitrate solution using ammonium hydroxide. Ammonium
hydroxide is 
 494. prepared by dissolving anhydrous ammonia in water. Ammonium hydroxide
at ambient 
 495. temperature is added to the hot nitrate solution until the pH of the
solution 
 496. reaches 7.4. At this point, all of the metals have precipitated out
as oxides. 
 497. The mixture is cooled to 80.degree. F. and the final pH is adjusted
to 7.2. 

 498. After precipitation, the catalyst precursor must be washed free of
ammonium 
 499. nitrate using high quality water which is free of chlorine. The
slurry is first 
 500. pumped from the precipitation vessel into a holding tank located
upstream of a 
 501. vacuum drum filter. The catalyst precursor is allowed to settle in
the holding 
 502. tank, and a clear layer of concentrated ammonium nitrate solution
forms above 
 503. the solids. This layer is drawn off, such as by decantation or by
centrifugation 
 504. before the slurry is washed and filtered. A vacuum drum filter fitted
with water 
 505. spray bars is used for washing the catalyst precursor and
concentrating the 
 506. slurry. The electrical conductivity of the filtrate is monitored to
ensure 
 507. complete removal of ammonium nitrate from the slurry. 

 508. After the catalyst precursor has been washed, the last ingredient of
the 
 509. catalyst, potassium carbonate, is added in an amount appropriate for
the 
 510. quantity of iron contained in the batch. The potassium carbonate is
dissolved in 
 511. a small amount of water and this solution is mixed thoroughly into
the slurry to 
 512. distribute the potassium uniformly. At this point, catalyst present
in the 
 513. slurry should preferably be between about 8 to about 12% by weight. 

 514. Heat, such as from a spray dryer, is used to remove most of the water
from the 
 515. catalyst and at the same time to produce roughly spherical catalyst
particles 
 516. having diameters in the range of about 1 to about 5 up to about 40 to
about 50 
 517. microns. 

 518. The last step in the process is annealing by heating the catalyst in
air to 
 519. about 600.degree. F. to remove residual moisture and to stabilize the
catalyst. 
 520. Chemically, the annealing step converts the hydrous iron oxide
Goethit Fe.sub.2 
 521. O.sub.3 H.sub.2 O, to Hematite, Fe.sub.2 O.sub.3. This step is
carried out in a 
 522. fluidized bed which can be electrically heated. The annealed catalyst
is then 
 523. ready for induction or activation and use. 

 524. Determining the "best" activating procedure for a catalyst is
difficult at best 
 525. even if it is known what changes in the catalyst are needed to give
the desired 
 526. activity, selectivity and stability. Many different activating
procedures for 
 527. making promoted Fischer Tropsch iron catalysts have been described in
the 
 528. literature. For example, one of the most definitive studies on
activating 
 529. Fischer Tropsch iron catalysts for use in fixed-bed reactors was
published by 
 530. Pichler and Merkel. (United States Department of Interior Bureau of
Mines, 
 531. Technical Paper 718, By H. Pickler and H. Merkel, Translated by Ruth
Brinkley 
 532. with Preface and Foreword by L. J. E. Hofer, United States Government
Printing 
 533. Office, Washington, D.C., 1949, Chemical and Thermomagnetic Studies
on Iron 
 534. Catalysts For Synthesis of Hydrocarbons). In this study, high
activity of the 
 535. catalyst was correlated with the presence of iron carbides after the
activation 
 536. procedure. The most effective procedure used carbon monoxide at
325.degree. C. 
 537. at 0.1 atm. pressure. The study also showed how the presence of
copper and 
 538. potassium in the catalyst affected activation of the catalyst. 

 539. The following equations show the stoichiometry for some of the
reactions which 
 540. can take place during activation: 

 541. Production of Cementite from Hematite using hydrogen-rich synthesis
gas: 

 542. 3Fe3.sub.2 O.sub.3 +11H.sub.2 +2CO.fwdarw.2Fe.sub.3 C+11H.sub.2 O(6) 

 543. Production of Cementite from Hematite using carbon monoxide alone: 

 544. 3Fe.sub.2 O.sub.3 +13CO.fwdarw.2Fe.sub.3 C+11CO.sub.2 (7) 

 545. In the presence of an iron-based catalyst, the following reactions
take place: 

 546. 2nH.sub.2 +nCO.fwdarw.C.sub.n H.sub.2n --+nH.sub.2 O (olefin)(8) 

 547. and ##EQU1## 

 548. Water gas shift reaction: 

 549. H.sub.2 O+CO.apprxeq.H.sub.2 +CO.sub.2 (10)