Ammonia Plant Catalyst Chemistry

Ammonia synthesis is still hased on lite Haber-Bosch process developed 100 years ago. However, over the years, many calalyst improvemellls have led to greater efficiency and reliability. The development and enhancements of high tempera/lire shift and ammonia synthesis catalysts are dis(.'llssed within

Ihis paper.

Prasanth Kumar Clariant

Dr. Christoph Krinninger Clariant

Introduction

Over 100 years ago ammonia was first produced on an industrial scale by BASF in Germany. This process solved

the fundamental problem of securing OUf food supply by the economic production of mass quantities of fertilizers. In order to meet the rising demand of fertilizer, new plants were built but also significant improvements have been achieved by technology providers. Furthennore, catalysts have enhanced the perfonnance and reliability of ammonia plants. This paper discusses several improvements that show how the development of each catalyst led to greater efficiency and reliability.

Importance of Ammonia

The ammonia industry is looking back on a rich history of more than 100 years. Today ammonia production is one of the most important industries in the world. The first plant was based on gas ification of coke to water gas followed by a shift conversion section and the ammonia synthesis loop.

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Figure J. BASF Oppall Ammonia Plant -world's first ammonia plant. Painting by Otto Sol/hagen Courtesy of SASF Corp., Ludwigshafen, Germany

This was the first step in providing fertilizers by economic production in order to secure the food supply and laid the ground work for other important industrial processes such methanol synthesis, oxo alcohol synthesis and other high pressure processes.

The growing demand for nitrogen fertilizer brought about a rapid expansion of ammonia production in the US between 1950 and 1980.

AMMONIA TECHNICAL MANUAL

The worldwide consumption of ammonia almost doubled between 1964 and 1968. By 2014, the worldwide demand for nitrogen has increased to about 180 million MT. It is forecasted to reach 202.5 MT in 2018. 1 Today it is estimated that the annual production of ammonia is worth more than US $100 billion with some single plants producing more than 3000 MTPD of NH3.

Modern technology for the ammonia production

Modern ammonia technology is still based on the Haber-Bosch process where the ammonia synthesis occurs in a high pressure reaction where nitrogen and hydrogen react over a conventional magnetite catalyst. The most important and efficient route for the production of the needed hydrogen is the steam methane reforming of natural gas which involves the following steps: feedgas purification, steam methane reforming, shift conversion section as well as cleaning of the syngas.

I, 1 1 .. _ 1 1--._11 __ 1

~Wl , r 1,"00_ 1 lu co_ 1 Ico._ 11 11 ",,_ ... 1

Figure 2. Ammonia productionjlow sheet

Another possible route is the partial oxidation of fuel oil which is also used in many ammonia plants today. The last option, gasification is phased out in most parts of the world due to high capital costs, high energy consumption and a higher rate of pollution.

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Catalyst Developments

Girdler introduced extruded and later tabletted co-precipitated iron/chrome High Temperature Shift (HTS) catalysts to the industry during the late 1940's. These replaced the extruded iron oxide and iron carbonate HTS catalysts that were prevalent at this time. By 1950, all HTS catalysts that were used were iron/chrome in the form of tablets.

The G-3 series oftabletted HTS catalyst showed a much higher activity and allowed plants to be designed with a lower S/G ratio with improved energy efficiency. These catalysts were used in most plants by 1950 and continued to be used extensively until the early 1990's with only minor changes. During the mid-1980's, a lot of plants decided to reduce the SIC ratio in the reformer in order to reduce pressure and improve energy efficiency. However, this lead to over reduction of the HTS catalyst and hence the consequence was that Fischer Tropsch synthesis occurred. This resulted in reduced activity and a dramatic loss in physical strength of the catalyst.

This problem was recognized by United Catalysts Inc. (\JCl) by 1985, and they were ab le to provide a catalyst which eliminated or delayed the onset of Fischer-Tropsch synthesis. The first charges of G3-C (ShiftMax® 120) copper promoted HTS went on stream during the late 1980's and eliminated in most cases Fischer Tropsch synthesis. Today more than 100,000 m3 of these catalysts are on stream.

With the new Reach regulations6 governing the amount of hexavalent chrome (2017) in catalysts used in the refining and ammonia industry, Clariant, formerly SUd-Chemie, developed an essentially hexavalent chrome free HTS catalyst. By 2014, it had already been installed in a number of syngas plants. This new HTS catalyst, Clariant's ShiftMax® 120 HCF continues tbe 30 years legacy of ShiftMax

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120, the most widely used high temperature shift catalyst in the syngas industry.

RELAnYlCllUSH STR£NGTH

.. .... .... .... .... " "

0 SHftllu' l20 SllflKu' l2OIICF SNfllIu ' UOIICF (lit", BWST) (lit", 1W$1)

Figure 3. Relative Crush Strength 2

The new catalyst production process reduces the content of hexavalent chromium to non­detectable levels « 200 ppm) in the fresh catalyst. Furthermore, no special start-up procedures are required to control the exothermic reaction to trivalent chrome. Since ShiftMax 120 HCF is closely related to ShiftMax 120, the catalyst also provides the excellent resistances to breakage during plant upsets, a long service life and low operating temperatures and CO-leakages.

The first patents for Low Temperature Shift catalyst were issued during 1925. However, L TS catalysts produced under this patent were not commercially available since the producers only used them in their own plants. To improve the overall energy consumption of ammonia and hydrogen plants, CCI and Girdler started making and selling copperlzinc based low temperature shift catalyst during 1964. Initial charges were placed in plants without L TS catalyst in addition to plants that utili zed two HTS reactors with two C02 removal systems. A reduction of 0.3-0.4% in the CO concentration in the feed to the methanator in plants switching to C IS and G-66 L TS catalysts increased their production by 5-10%. After 1964, essentially all

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ammonia plants that were built utilized an L TS reactor. The CIS-HC LTS catalyst introduced by UCI during 1969 was in constant use in the ammonia industry for more than 20 years.

In plants with poisoning problems, VCI introduced the C IS-O line of L TS guard catalysts during the mid-19S0's. Inclusion of a layer of C IS-G on top of the main L TS bed resulted in much longer lives in many plants. Some plants with severe chloride poisoning saw the life of their LTS catalyst increase by as much as 50% after loading a layer of C 18-Guard catalyst1 .

In response to the need for a longer life LTS catalyst, UCI developed CIS-7 LTS catalyst during the early 1990's. This catalyst is 20-30% more active than the CIS-HC catalyst it replaced. More importantly, its stability when exposed to severe conditions is much better than other L TS catalysts. This stability and high activity have resulted in C IS-7 becoming the catalyst of choice in many applications.

As governments around the world enacted new environmental regulations on plant operators during the 1990' s, by-product make across the L TS converter became an issue. Compounds such as methanol and amines which can be made across HTS and L TS catalysts, eventually end up in the process condensate or overhead C02. Methanol in process condensate that goes to a low pressure condensate stripper usually ends up in the atmosphere with the steam exiting the stripper. Methanol is not as troublesome in plants with a high pressure stripper since the methanol in the overhead steam can be recycled back to the refonner. Methanol in the condensate knock-out overhead usually ends up with the C02 exiting the C02 removal system. This contamination reduces the value of the C02 if it is sold as a feedstock for other processes. In addition, methanol make reduces the efficiency of a synthesis gas plant. For example, in an NH3 plant, each ton of methanol that is produced reduces NH3

AMMONIA TECHNICAL MANUAL

production by 1.1 tons. This is equivalent to hundreds of thousands of dollars in lost production every year for a modem NH3 plant.

Since installation of a high pressure condensate stripper is quite expensive, the SUd-Chemie Group developed a catalyst designated C 18-HALM (high activity, low methanol) and introduced this to the industry during the mid-1990's. Whereas conventional catalysts produced about 90% of the equilibrium methanol across an LTS converter, CI8-HALM produced only 10% of the equilibrium amount. This allowed plants with low pressure condensate strippers to meet environmental regulations by simply changing their L TS catalyst. Less methanol make also improved the economics for most plants since more H2 ended up in ammonia instead of undesirable products.

The most significant catalyst development of the 2000's was the introduction of AmoMax®-IO Wustite NH] synthesis. This product is made by Clariant, formerly SUd-Chemie. Wustite is a non-stoichiometric iron oxide with properties that produce a catalyst with the following benefits:

Table I AmoMax-IO Features3-5

AmoMa'l@ is aregisteredtrademarkofCLARIANT

• Up to 42% higher activity compared to Magnetite Fe304

• Low temperature low pressure activity • Extremely good thermal stability for

long life • Easy to activate + quick reduction • High poison resistance • Very high crushing strength • Available in oxide and pre-reduced

form

The first charge of AmoMax-1 O® in a plant with 1000 MTPD capacity or higher went onstream at Liaohe Chemical Fertilizer during December 2003. This charge is currently operating at near start-of-run (SOR) conditions and has led to

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more than 85 other charges onstream since 2005. It bas been used as a drop-in replacement as well as part of a converter revamp.

Conclusion

Catalysts used in the Ammonia industry have changed a lot since the first synthesis catalyst was developed more than 100 years ago. Current generation catalysts with higher activies and stability allow producers to safely operate at lower temperatures, lower loop pressures with higher conversion rates and longer operational life. Catalyst producers are always trying to meet the ever growing demand of customer expectation and catalyst standards. Clariant is a front runner in most of the catalytic applications and with new generation catalysts produced by Clariant, Ammonia and Methanol plants can run at much lower temperatures, pressures and can sometimes avoid a necessary plant revamp. The development of hexavalent Chrome free High Temperature Shift catalyst when it was demanded is just another example of Clariant's commitment to the process industry. Last but not least, Clariant combines the creativity in performance technology and the vast knowledge on catalytic science to achieve the performance goals required by the ammonia and methanol industries.

References

[I] po. Heffer and M. Prud'homme, 82" IFA Annual Conference Sydney 26 - 28 May 2014, Fertilizer Outlook 2014 - 2018 [2] internal Research Clariant 2014 [3] Clarianl Research (EAC) [4] Kisnaduth Kesore, Norbert Ringer, Stefan Gebert & David Rice, Sud-Chemie, Nitrogen + syngas 300, July-August 2009

[5] S. Gebert, Y. Cai , and B. Kniep, SUd­Chemie, Nitrogen & Syngas 315, Jan-Feb 2012.

[6] REACH - Chromium (VI) trioxide, crO] , is classified as a CMR substance (CMR:

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carcinogenic, mutagenic or toxic to reproduction) and is identified/listed as a substance of very high concern (SVHC) because of its CMR properties. The sunset date for Cr03 is 53 months after the publication of the amended Appendix XIV of the REACH document: 21 September. 201 7 not to be used, placed on the market or imported into the EU after the sunset date unless the company is granted an authorization

(7J Clariant International Ltd.Clariant's Catalysis and Energy S U was created by the acquisition of Slid-Chemie AG in 2011. Slid­Chemie started making catalyst in Gennany during the 1960's through a N with Girdler Corporation, a Louisville, Kentucky USA based company that had started manufacturing catalyst for the syngas industry during the early 1940's. Slid-Chemie AG acquired Catalysts and Chemicals Inc. (CCI) in the 1970' s. CCI, a company fonned by former Girdler employees started producing syngas catalysts in Louisville in 1957. After gaining control of eCI, Slid­Chemie merged Girdler and CCI to fonn United Catalysts Inc.

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