Chapter 1: Hydrogen Generation Flashcards

Question

Selective Methanation

Answer 1

- Manage heat of reaction - Designing a catalyst that maintains its activity after prolonged exposure to high T (1) CO + 3H2 <==> CH4 + H2O Catalyst: Co, Fe, Ru; highly exothermic; Δ H= 206.1KJ/mol Reduce CO and H2 yield (2) CO2 + 4H2 <===> CH4 + 2H2O ΔH= 165.2KJ/mol CO is not reduced; it consumes even more H2 Need a catalyst that to promote (1) while suppressing (2)

Answer 2

A catalyst selectively promotes a reaction that removes CO over another that consumes H2 CO + 0.5 O2 <==> CO2 H2 + 0.5 O2 <==> H2O The change in Δ G (Gibbs free energy) for the CO reaction is increasingly more negative at lower T CO reaction is favourite at lower T (ie a higher of CO adsorbs onto the catalytic surface) Series of consecutive selective oxidation catalyst beds that operate at increasingly lower T

Answer 3

Shale gas is methane (natural gas) which is trapped in impermeable shale rock deep underground The gas cannot flow through the shale, so simply drilling a well, as you would for conventional natural gas, is not enough The shale rock must be cracked to free the gas, so large quantities of water, sand, and a range of chemicals are pumped in under high pressure (fracking = hydraulic fracturing) Tens or hundreds as many wells are needed to produce as much gas as in a conventional gas field

Answer 4

stage 1: Drill down to shale level stage 2: Water sand and chemicals pumped to a pressure of approx 1500 lb/inch^2, forcing the rock apart releasing the gas in the pores stage 3: Liquid pumped out of well, sand keeps the rock separated allowing gas to seep out of the broken shale layer to be piped to the surface.

Answer 5

- Energy security - Job creation - Lower emission than liquefied natural gas - Natural gas is cleaner than coal and oil (clean oil is very expensive) - Horizontal drilling - Cheaper (???)

Answer 6

* Environmental pollution (aquifer, soil, water, air, chemicals): Barnett shale: heavy metals release, Se, Sr, As . * Use of huge quantity of water (but compared to what?) * Earthquakes * Impact on habitat, landscape? (Assessment and Impact studies are still very limited, REGULATIONS????)

Answer 7

Methane trapped in the crystal structure of water ( (CH4) 5.75(H2O) ) Present in seabeds and permafrost 1m^3 of methan clathrate = 168 m^3 CH4 Reservoir (sediments) = 2- 10 times conventional natural gas Estimates = 1 × 10^15 and 5 × 10^15 m³ (500 2500 Gt C) Widely distributed, but low total volume and low concentration at the sites, so is it economically viable?

Answer 8

Physical separation process that removes CO2, CO but also other species except H2 H2 = 99,99% Beds composed by zeolites, silica, and carbons Adsorption based on molecular weight at high P

Answer 9

Palladium membrane hydrogen purifiers operate via pressure driven diffusion across palladium membranes H2 molecules in contact with the Pd membrane surface dissociates into monatomic hydrogen and passes through the membrane On the side of the Pd membrane, the monatomic hydrogen is recombined into molecular hydrogen Only hydrogen can diffuse through the palladium membrane Pd is very expensive (less expensive than Pt)

Answer 10

Biomass is a biological derived from living or recently living organisms Biomass is composed of a mixture of organic molecules containing hydrogen usually including atoms of oxygen, nitrogen and also small quantities of other species, such as alkali, alkaline earth and heavy metals

Answer 11

Energy produced from biomass including woody biomass, agricultural biomass, and other biological materials

Answer 12

For plants, The carbon is absorbed from the atmosphere as CO2 by plant life, using energy from the sun Microbial degradation: CO2, CH4 Burning: CO2 "Carbon Cycle"

Answer 13

Coal,oil, gas It derives too from biological materials (i e CO2 adsorbed millions of years ago fossil fuels => burning => CO2 + energy (and heat) Difference of timescale from biomass

Answer 14

Biomass: While it is growing C is taken out from atmosphere and returns to it when it is burned (in relatively shorter times) - sustainable Fossil: Oil, gas, coal: produced from C sequestered millions of years ago. CO2 generated released quickly. - not sustainable

Answer 15

Huge resources of residues, by products and waste are potentially become available, in quantity, at relatively low, or even negative costs where there is currently a requirement to pay for disposal. 1. Virgin wood: from forestry, arboricultural and from wood processing activities 2. Energy crops high yield crops grown specifically for energy applications 3.Agricultural residues residues from agriculture harvesting or processing 4.Food waste from food and drink manufacture, preparation and processing, and post consumer waste 5.Industrial waste and by products from manufacturing and industrial processes

Answer 16

- Renewable - Widely available - Significant reduction in net carbon emissions when compared with fossil fuels - Sustainable It is a “carbon lean, so it produces a fraction of carbon emissions of fossil fuels Sourced locally Local business opportunity and support rural economy If not used they would generally rot. This will generate CO2 in any case, and may also produce methane (CH4 ), a greenhouse gas 21 times more potent that CO2

Answer 17

Pre processing may be required to change the physical form or to reduce the moisture content. Physical pre processing consists of: Cutting to uniform length Chipping Grinding or shredding Reducing moisture content

Answer 18

-Suitable for a range of energy applications - It can be burned for heat and/or power at a range of scales - Virgin wood is untreated and clean - It may range in moisture content from oven dry to 60% or higher as freshly harvested, green wood

Answer 19

Energy crops are grown specifically for use as fuel and offer high output per hectare with low inputs. Short rotation energy crops Grasses and non woody energy crops (miscanthus, oilseed rape,......) Agricultural energy crops (sugar, starch, and oil crops) Aquatics (hydroponics)

Answer 20

Dry: Straw Corn Stover Poultry Litter Wet: Grass silage Animal slurry and farmyard manure

Answer 21

Dry & Wet About a third of all food grown for human consumption in the UK is thrown away

Answer 22

“Woody” Materials and “Non Woody” Materials Combustion: Basic process of oxidation Gasification: It is a partial oxidation process whereby a carbon source such as coal, natural gas or biomass, is broken down into CO, H2 CO2 and possibly hydrocarbon such as CH4 Pyrolysis: It is the precursor to gasification, and takes place as part of both gasification and combustion. It consists of thermal decomposition in the absence of O2 . Ex.: charcoal burning.

Answer 23

Gasification is a thermochemical process in which biomass at high heat is turned directly from a solid into a gaseous fuel called syngas (a mixture of CO, H 2 and some CH4)

Answer 24

Pyrolysis is the thermal degradation of organic components in biomass in the absence of O 2 . Major products are oil, gas, and char.

Answer 25

1. Thermochemical 2. Biological

Answer 26

This is a high T two step process involving: (i) thermal conversion of CH4 ( CH4 ==> C + 2H2) (ii) Methanol Synthesis ( CO2 + 3H2 ==> CH3OH + H2O ) (iii) Overall (2CO2 + 3CH4 ==> 2CH3OH + 2H2O + 3C) Near zero CO2 emission results from removal of CO 2 from the coal burning plant and emission of equivalent amount of CO2 when methanol is burnt as a fuel

Answer 27

This process produces H2 and CH3OH from biomass with reduced CO2 emissions. Phase 1: (1a) C + CH2 ==> CH4 (1b) C + 2H2O ==> CO + H2 (1c) CO2 + H2 ==> CO + H2O Phase 2: (2a) CH4 + H2O ==> CO2 + 3H2 (2b) CO2 + H2 ==> CO + H2O Phase 3: (3a) CO + 2H2 ==> CH3 + OH (3b) CO2 + 3H2 ==> CH3Oh + H2O

Answer 28

*Since H2 content in Biomass is low, the yield of H2 is low (ca 6% vs 25% of CH4) *Energy content of biomass is also low due to 40% O2 content *Low energy content of biomass is an inherent limitation of the process since over half of H2 from biomass comes from splitting of water in steam reforming *The production of H2 from biomass is not presently economically competitive with natural gas SR without the advantage of high value co products, very low cost biomass and potential environmental incentives

Answer 29

Aerobic digestion is a process in which bacteria use O2 to convert organic material into CO2. Products include nutrient rich fertilizers (N, P derivatives) and composts

Answer 30

Anaerobic Digestion is the decomposition of biomass by bacteria in the absence of O2. Biogas, or CH4 is the primary product produced.

Answer 31

Fermentation is a biological process in which enzymes produced by microorganisms cause chemical reactions to occur. Products include EtOH, commercial levels of therapeutic and research enzymes, antibiotics, and specialty chemicals.

Answer 32

- Diesel - Jet fuel - Kerosene - Gasoline

Answer 33

Pros: Low CO, CO2 , HC emission Cons: NOx , sulfur, particulate matter (PM) General: -Heavier than gasoline (C 14 H 30 ) vs (C 9 H 20 -Easier to refine compared to gasoline -Cheaper -Higher energy density (147K BTU vs 132K)