SYN GAS

NOMULA DEVADEEKSHITH B130943CH

OMPRAKASH HADA B130980CH

POLUPARTHI JAGADISH B130322CH

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DEFINITION

Synthesis gas is generally considered to be a variable mixture of CO and H2 for the synthesis of organic compounds.

There are cases where CO is not needed and these specific cases are so labelled :

Ammonia synthesis gas ( 3H2 + 1N2 )

Hydrogenation of coal ( H2 only)

NOTE that all synthesis gases contain hydrogen.

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CONTENTS

RAW MATERIALS CHEMICAL REACTIONS PROPERTIES FLOW DIAGRAM PROCESS DESCRIPTION ENGINEERING PROBLEMS USES OF SYN GAS

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RAW MATERIALS

• REFINERY NAPHTHA OR OFF-GASES

• AIR (OPTIONAL)

• STEAM

• SMALL MAKE UP QUANTITIES OF NICKEL AND PROMOTED IRON OXIDE CATALYST, ETHANOLAMINES, AND AMMONICAL CUPROUS FORMATE

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REACTIONS Reforming reactions

(a) CnH2n+2 + nH2O nCO + (2n+1)H2

Ho = 52 Kcal for n=1

= 238 Kcal for n=6

(b) CO + 3H2 CH4 + H2O

Ho = -52 Kcal

Water gas shift reaction

(c) CO + 3H2 CO2 + H2 Ho = -9.806 Kcal

Synthesis Gas(various mixtures of CO/H2)

Some ( about 16%) made from coal, but most from natural gas and oil in the presence of steam.

-CH2- + 0.5 O2 CO + H2 ∆H = -22 kcal/mol

-CH2- + H2O CO + 2H2 ∆H = + 36 kcal/mol

CO/H2 ratio adjusted by varying the amount of O2 and H2O

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PROPERTIES

Physical State: Gas

Appearance: Transparent colourless

pH: Not currently available.

Solubility in Water (by weight): Not determined.

Odour: Odourless

Boiling Point (760 mmHg): Not determined.

Freezing Point: Not determined.

Specific Gravity (H2O = 1): Not determined.

Vapour Pressure at 20°C: Not determined.

Vapour Density (air = 1): 0.45 - 0.57

Melting Point: Not applicable.

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WATER-GAS SHIFT

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PROCESS DESCRIPTION

The hydrocarbon feed is mixed with steam and fed to the reforming furnace. The nickel catalyst is packed in vertical tubes of 3-4 inches in diameter and about 20-25 feet long. Heat for the endothermic reaction is supplied by combustion gas. The reaction temperature must be maintained in the range of 700-1000oC . The process takes three alternates depending on the end products.

For CO-H2 Synthesis Gas

The effluent reformer gas is cooled to 35oC and pumped to a hot potassium carbonate scrubbing system to remove CO2

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For H2 gas

A water gas shift converter is used to remove CO and form more hydrogen. Reformer gas is quenched with steam to give 350oC input gas to a catalytic converter using iron oxide catalyst promoted with chromium oxide. A space velocity 100-200/hr is maintained. After scrubbing CO2, the traces of Co are removed by methanation reaction. For high purity hydrogen, one or two additional stages of the shift converter, CO2 absorber combination are added with either ammonical cuprous formate or molecular sieves used to remove residual CO and CO2 down to 10 ppm or less.

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For NH3 synthesis gas

The correct amount of nitrogen for NH3 synthesis is added via air and the oxygen is burned out by hydrogen in a nickel catalysed combustion chamber inserted immediately following the reformer. Gases are cooled to 350oC by a water quench tower and then passed to shift the converter. Except for the additional N2 which passes through, the remainder of the process is the same as for hydrogen preparation. 14

MAJOR ENGINEERING PROBLEMS Sulphur contamination of reforming catalyst. Naphtha must be purified by catalytic hydrogen treatment to remove sulphur to yield a vapour feed of less then 5 ppm sulphur. Design of an efficient reformer furnace to economically supply endothermic heat of reaction. Avoid carbon formation on catalyst by use of highly specific catalyst ( ICI patents ).Removal of CO and CO2 . The bulk of CO2 is absorbed by either potassium carbonate or monoethanolamine ( MEA ). The latter requires more heat, but has higher driving force for absorption giving smaller towers. 15

SYN GAS - USES

• Chemical feedstock - source of CO and H2

• Production of methanol• Synthesis of aldehydes/alcohols from olefins via hydroformylation• Manufacture of hydrocarbons

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