WO2011098091A1

WO2011098091A1 - Pvc composition material that contains oil shale ash and a product made from the said material

Info

Publication number: WO2011098091A1
Application number: PCT/EE2011/000002
Authority: WO
Inventors: Ivar Viira; Tiiu Kiil
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-02-15
Filing date: 2011-02-14
Publication date: 2011-08-18
Anticipated expiration: 2012-08-15
Also published as: EE05625B1; EE201000022A

Abstract

Invention is related to composite material based on polyvinylchloride (PVC), where as filler is used certain fractions of mineral industrial waste oil shale ash more specifically dust burn ash and boiling layer burn ash. Such a composite material has reduced or does not at all have HCl emission in increased temperatures. Oil shale ash added to the PVC contains a certain amount of free CaO, wherein due to its chemical reactivity it is able neutralize/bind the HCl emitting during thermal disintegration of PVC according to the formula CaO + 2HCl = CaCl₂ + H₂O. Content of the oil shale ash in the PVC composite material is 0,5-60%. The invention also includes product made from the said composite material.

Description

PVC composite material that contains oil shale ash

and a product made from the said material

Technical field

This invention belongs into the field of material industry. The invention is related to PVC (Polyvinylchloride) based composite material, where as a filler is used certain fractions of mineral industrial waste, i.e. oil shale ash. Such a composite material has reduced or absent HC1 emission at increased temperatures.

Combustion of oil shale causes large amounts of fly ash, which types are different with their physical-chemical and surface characteristics. Oil shale fly ash that is added to PVC comprises a certain amount free CaO, wherein due to its chemical reactivity it is able to neutralize/bind HC1 emitted by PVC during thermal decomposition according to the formula (I).

CaO+2HCl=CaCl₂+H₂0 (I)

Oli shale fly ash originates from the combustion of the mixture of carbonaceous, terrigenous and organic material produced through refining of oil shale. The ash from combustion is a set of particles with different dimensions, density, magnetic and electrical characteristics and chemical and mineralogical content. Thus it is a polyfractional mixture, which can be characterised and classified after several qualities [1]. As there are currently two combustion technologies in use (pulverized combustion - PF and circulating fluidized bed combustion - CFBC), which are essentially different for their combustion temperatures (correspondingly 1200-1400 °C and 750-800 °C) as well as fraction size of the fuel, we hereby provide data of both ash types basing on the source [2]. Ash will separate in several technological assemblies of boiler aggregate and has been marked as follows: BA - bottom ash, INT - intrex ash, SHA - steam heater ash, ECO - economizer ash, PHA - air preheater ash, CA - cyclonic ash, ESPA1-4 - ash from the section of electric filter with relevant number.

Ashes originating from PF and CFBC technologies (see tables 1, 2, 3 and 4) differ mainly with the absolute content of their components, but also with phase content and physical characteristics (specific surface and porosity, shape of particle surface and existence of molten phase (see figures 2 and 3). Chemical and phase content of oil shale ashes [2]

The content of general CaO in CFBC as well as PF ashes decreases along ash tract, remaining the lowest in fine-fraction electric filter ashes. At the same time, the content of insoluble residue increases along ash tract in the ashes of both types. Compared to CFBC ashes, PF ashes contain essentially more free CaO (up to 25%). Among CFBC ashes, the content of free CaO is the highest in intrex ash (up to 19%), decreasing essentially in electric filter ashes. As in case of PF technology the combustion temperature is essentially higher, carbonates will decompose almost entirely in the course of fuel combustion, and C0₂ content of the ash is low. In CFBC ashes C0₂ content is essentially higher, referring to the fact that carbonate part of oil shale has not completely decomposed. In case of CFBC technology the binding of S0₂ from flue gases takes place mainly in the combustion chamber and intrex, causing higher sulphur contents in bottom and intrex ash (correspondingly 4,5% and 7,8%). The main part of sulphur is in sulphate form in ashes, only in the beginning of ash separation tract of CFBC boilers traces can be found of sulphite and pyrite sulphur. Sulphur bound in PF ashes is distributed more evenly between different ash types and is the highest in electric filter ashes (2,7-3,7%).

The analysis of quantitative XRD confirms the results of chemical analysis. Compared to PF ashes, CFBC ashes contain more calcite (up to 34,8% in bottom ash) and less lime. Magnesium is found in ashes mainly in the form of periclase, being partially bound into carbonates (dolomite in CFBC bottom ash) and silicates (mervinite, melilite). Of silica compounds, CFBC ashes contain mainly quartz (up to 17,9%) orthoclase (up to 15,7%). However, PF ashes contain essentially more secondary silicates, such as belite (up to 20,3%) and mervinite (up to 13,2%). Relatively higher content of secondary silicates in PF ashes refers to essentially higher combustion temperature, causing reactions between lime and minerals of sand-clay part upon initiation of the molten phase. Table 1. Chemical content and physical characteristics of CFBC ashes [2]

Table 2. Chemical content and physical characteristics of PF ashes [2]

Table 3. Phase content of CFBC ashes [2]

Table 4. Phase content of PF ashes [2]

Fraction size of CFBC ashes is varying along ash separation tract in very broad scale (Figure la). Bottom ash is the coarsest (-45% of the particles have the diameter >0,63 mm), intrex ash has average coarseness (-90% of the particles have the diameter 0,4- 0,045 mm) and electric filter ashes are the finest (85-95% of the particles have the diameter <0,045 mm). PF ashes have more uniform fraction size, containing less particles with the diameter >0,63mm compared to CFBC ashes (Figure lb).

Due to above described differences it is expected differences in reaction ability. Main components, that promise to presume binding ability of ashes related to acidic gases, are free lime and portlandite, but also a lot of mixed silicates, which have knowingly secondary origin (created in burning process).

Technical level

On technical level various use of fly ash produced through the combustion of coal has been known. However, this ash differs from oil shlae fly ash with its composition, shape of particles as well as colour (grey to black), and therefore it is not suitable for the production of light profiles.

JP2009073989 discloses the use of fly ash as a filler material or reinforcing agent in a polyvinyl chloride resin, rubber resine, polyolefin resin etc, whereby the fraction of fly ash shall be <5 μηι, the amount of unburned carbon shall remain below 1% and sphericity of ash particles shall be 0,9-1 ,0.

US2002040084 (Al) discloses a composition containing fly ash, which particles have average size not exceeding 100 μηι and humidity content not exceeding 0,25%. The composition including filler material forms 1-80 mass fractions in 100 mass fractions of polymer. The composition is especially useful for the production of tubes in polyvinyl cloride compositions.

JP2001043737 (A) discloses the content of PVC cover (composite) of electric cables, including 10-100 fractions of coal fly ash per 100 fractions of PVC resin. A plasticizer has been added, and if necessary, also colouring agents, additives inhibiting combustion and facilitating processing.

JP1 1 140331 (A) discloses a composite, which would not emit HC1 gas upon incineration. For this purpose a 1-10% synthetic zeolite has been added to a resin such as polyethylene or polyvinyl chlorie, which has been obtained through alkaline processing of coal ash. CN1 1 10773 (A) discloses a tube made of plasticized fly ash, containing fly ash with granular mesh size exceeding 200-300, mixed together with the use of polyethylene or polyvinyl chloride at 160-180 °C.

Oh, S. C, Kwon, W.-T., Kim, S.-R. Dehydrochlorination characteristics of waste PVC wires by thermal decomposition. - Journal of Industrial and Engineering Chemistry, 2009, 15, 438-441. [Online] ScienceDirect (17.11.2009) has disclosed characteristics of dehydrochlorification of cable covers made of PVC at various temperatures. The effect of CaO additive was studied, in order to reduce separation of HCl upon thermal decomposition of PVC. In result of work it was found that the amount of produced gaseous products and HCl decreased essentially upon addition of CaO. Thermal decomposition of PVC basically includes two steps. In the first step (temperature up to 350 °C) the process of dehydrochlorification takes place and C=C bonds form in macromolecule:

(-CH₂-CHCl-)_n→ (-HC=CH-CH=CH-)_n + HCl

Dehydrochlorification of PVC takes place until 350 °C. Above this temperature, polymer will be already a dehydrochlorinated product and upon further decomposition linear or cyclically structured hydrocarbons will form. The amounts of separated HCl will decrease most in the ratio of additive and polymer CaO/PVC=0,5.

Tiikma, L., Johannes, I., Luik, H. Fixation of chlorine evolved in pyrolysis of PVC waste by Estonian oil shales. - Journal of Analytical and Applied Pyrolysis, 2006, 75, 205-210. According to the study published in [Online] ScienceDirect (17.1 1.2009), HCl separated in the process of pyrolysis of mixed plastic waste containing also polyvinyl chloride does not only cause corrosion of equipment, but will also produce organochlorine compounds. This paper describes the possibilities for stabilization of HCl separated during the pyrolysis of PVC by adding Estonian oil shale products to PVC. In result of the study it was found that HCl separated during the pyrolysis of PVC can be absorbed, if mixing into the PVC also kukersite, its half coke and ash. The extent of absorbing of HCl depended on the amount of additives (CaC0₃, CaO, MgO).

Summary of the invention

Objective of the invention was to develop a cheap composite material, which could be used for the production of PVC products, which use at higher temperatures would be environmentally safer due to decrease or lack of HCl emission in the course of thermal decomposition of PVC. The use of such material would enable to raise the temperature of safe use. It is known that oil shale fly ash added to PVC contains free CaO to some extent and there is some basis to assume that CaO can neutralise HC1 emitted during thermal decomposition of PVC in accordance with the following formula:

CaO + 2HC1 = CaCl₂ + H₂0

The technical level has not introduced interactions of PVC and oil shale fly ash by the presence of oxygen at moderate temperatures (up to 300-400 °C). Objective of the invention is met by a composite material, where in a preferred embodiment the amount of oil shale ash with suitable composition in PVC composite varied within the range 0,5-60 mass percent. Fluidized bed ash (CFBC) and pulverized combustion ash (PF) were used.

Description of the drawings

Figures la and lb. Fractional composition of oil shale ashes: la - CFBC-ashes and lb - PF-ashes.

Figures 2a and 2b. 2a: SEM images of CFBC ashes: BA (ground to <1 mm), ECO, ESPA1 and 2b: PF ashes: BA, CA, ESPA1 [2].

Figure 3. Distribution of pores in PF and CFBC-ashes [3].

Figure 4. Composition of balance mixture in the system CaO - HC1 - C0₂ - H₂0 depending on the temperature.

Figure 5. Dependence of the loss of mass of PVC 1 and PVC2 on temperature. The upper curve has been calculated as difference between curves PVC1 - PVC2.

Figure 6. Decomposition curves of samples in PVC1 mixture with pure calcium oxide with mass ratio 1 : 1 or 1 :2.

Figure 7. Decomposition curves of samples in PVC2 mixture with pure calcium oxide with mass ratio 1 : 1 or 1 :2.

Figure 8. Decomposition curves of pulverized combustion ash PF mixtures with material PVC2.

Detailed description of the invention

The most common filler material of powder PVC composite is chalk. Objective of the invention is to replace chalk with oil shale fly ash. In realisation of the invention the other components of the composite were left constant, changing only the amount of oil shale fly ash in the composite.

Characterisation of ash samples

Table 5. Characterisation of ash samples

Stages of production/testing of composite:

- mixing of a powder with the composition needed for the production of PVC profiles with additives in a heated drum mixer with blades, whereby the traditional chalk additive is replaced by oil shale fly ash.

- testing of physical-mechanical qualities of the resulting powder and test objects made of it.

In a preferred embodiment of the invention the amount of oil shale ash with suitable composition in PVC composite varied within the range 0,5-60 mass percent. Fluidized bed ash and pulverized combustion ash were used.

During the development of a suitable composite content, binding of HC1 belonging into the composition of PVC and separating from it on higher temperatures was tested.

Studying of high temperature interaction PVC - oil shale fly ash:

Selected samples

In this study two different PVC samples were used (PVC1 - SorVyl DB 60241 Natur and PVC2 - Polanvil S-67 HBD - PVC-S,G,1 10-60-98). The earlier PVC1 already included filler material, while PVC2 was pure PVC.

The used oil shale ashes were one pulverized combustion ash (PF ash ESPAl), with free calcium oxide content 14,9% and specific surface 1,6 m²/g, and one fluidized bed ash (CFBC ash ESPAl with free CaO content 8,2% and specific surface 6,7 m²/g) according to Table 1. Comparative tests were performed with pure calcium oxide obtained through heating of CaC0₃ at 1000 °C and not containing calcium hydroxide or non-decomposed calcium carbonate (the verified mass loss to the temperature 1000 °C was 0%).

Test methodology

Binding tests of HC1 were performed with a thermal analysis equipment MOM with the objective to determine the temperature range of decomposition of PVC and binding of HC1 and assess the extent of binding. Composition of mixtures was varied in accordance with mass ratios of PVC and the binding component (lime material) 1 : 1 and 1 :2. In case of pure CaO the mass ratio 1 : 1 also meets approximately the mole ratio CaO:HCl«l : 1.

Tests were performed in the conditions of dynamic increase of temperature with heating speed 10 °C min^-1 to the end temperature 1000 °C. Standard platinum crucibles were used. Heating was performed in oxidizing conditios, atmospheric environment, with air feed rate 25 1 h^_I. Sample mass in a crucible was 100 mg. PVC and lime material were mixed mechanically, without using any additional grinding or influencing physical qualities of the particles. In these tests the solid phase was not analysed.

In order to determine the content of chloride ions in solid products, separate test series were performed in muffle furnace with larger sample quantity (1,2...1 ,5 g). Also in these tests the mixtures were heated in the air with the speed 10 °C mkf¹, but to the end temperature 650 °C, presuming that by that temperature the reactions with participation of HC1 would be ended and PVC would be completely decomposed. After that, the products were cooled in a desiccator. The chloride ion content of heated products was determined argentometrically, using potassium chromate solution as indicator.

Test results - description and short analysis

Initial assessment of binding of HC1 was provided on the basis of thermodynamical calculation in a simplified system CaO - HC1 - C0₂ - H₂0, proceeding from stoichiometric ratio of CaO and maximum possible hydrochloride separating from PVC according to the reaction equation

CaO + 2HCl→ CaCl₂ + H₂0

Figure 4 shows that thermodynamically the produced balance mixture contains a stable CaCl₂. At higher temperatures (over 600 °C) some hydrochloride will start to appear again in the balance mixture in the system, in the range 600...800 °C also the amount of CaC0₃ increases to some extent due to the presence of C0₂ and at the temperature over 900 °C the latter will decompose, increasing the amount of free CaO in the mixture. Thus the binding of HC1 with oil shale ash facilitates thermodynamically the production of calcium chloride in a broad range of temperature.

Two obtained PVC samples were compared with thermal analysis (Figure 5). The figure shows that decomposition of pure PVC (PVC2) starts on a somewhat lower temperature, compared to the sample containing calcium carbonate PVC1. When the curve PVC2 is deducted from the curve PVC1, a curve will be obtained that will characterise temperature ranges of binding/separation of the components of the gaseous phase (upper curve on the figure). Peak in the temperature range 250-350 °C is caused by the binding of HC1 by the filler material in accordance with the reaction equation

CaC0₃ + 2HCl → CaCl₂ + H₂0 + C0₂

As in the atmospheric environment also much C0₂ appears in the gaseous phase, and also water vapour is produced during the reactions, several side reactions are possible: production and decomposition of calcium hydroxide, binding of C0₂ by lime material and decomposition of the produced calcium carbonate at higher temperature. All these reactions are related to the increase or decrease of mass, therefore it is not possible to provide a precise quantitative assessment to the extent of the binding of HC1 on the basis of these curves. A smooth peak in the upper curve in the range 600-800 °C is characteristic to the reactions of C0₂ with filler material, and the fact that the difference of mass losses of the two materials remains within 5% by the end of the test confirms that in the reactions with filler material PVC1 is binding HC1 produced upon decomposition of PVC to some extent.

Tests with the use of pure calcium oxide. The resulting decomposition curves and the curves describing binding of the components of gaseous phase calculated through deduction of curves are presented on the figures 6 and 7. The figure shows that in case of both PVC samples HC1 is bound from the gaseous phase in the temperature range 250-350 °C. As in case of use of pure CaO the CaO has excess, also intensive binding of C0₂ takes place in the gaseous phase. Binding of C0₂ starts at the temperature over 350 °C and will last until the temperature -700 °C, after which the produced calcium carbonate will decompose. This production and decomposition can be seen as a slanting peak on the figure. By the end of the test, when the entire calcium carbonate has decomposed, the calculated differences of curves (4 and 5 on the upper and 3 on the lower figure) vary from zero to 20%. This difference is characteristic to the binding of HCl from gaseous phase. It can be seen that increase of the mass ratio CaO.PVC will further increase the percentage of bound HCl - therefore rather high contents of lime filler material should be used for complete binding of HCl.

Also the thermal analysis tests with oil shale ashes were conducted with mass ratio of PVC and ash 1 : 1 or 1 :2. As PVC1 already contained filler material, here the graphic results are presented for the mixtures of pure polyvinyl chloride PVC2 and pulverized combustion ash PF (Figure 8). The results of PVC 1 mixtures both in case of pulverized combustion ash as well as fluidized bed ash were similar with these.

The used oil shale ashes do not have any significant mass loss until the temperature 600 °C. Only at the temperature over 650 °C the carbonate part contained in the ash will start to decompose significantly. Therefore the curve characterising binding, calculated from the difference of the curves describing decomposition of mixture and PVC, should also describe binding of HCl from gaseous phase qualitatively until this temperature.

The figure 8 shows that in case of the temperatures of HCl separation (250-350 °C) the peak characterising the binding has also clearly formed (curve 4). Calculated curve of a mixture with higher mass ratio matched the curve 4. Slanting peaks corresponding to the reactions of formation and decomposition of carbonates cannot be seen as clearly here as in case of pure calcium oxide, because these ashes already contain carbonates; also this graph does not enable to draw conclusions about the percentage of bound HCl, because there are more and different parallel reactions with increase and decrease of mass in this system.

For more specific assessment of the amount of HCl several tests were performed in muffle furnace with larger mixture quantities and determination of the subsequent chloride ion content in solid product. In these tests it was calculated, how much of the maximum separated amount of hydrochloride was bound into solid phase as chlorides (binding efficiency of CI, %) and how much of the free calcium oxide contained in the mixture was used (usage efficiency of free CaO, %). Also a stoichiometric standard of free calcium oxide is shown, which developed in accordance with the selected mass ratio of PVC and lime material. The results are presented in the following sorted tables 6, 7 and 8.

Analysis of results shows that in case of use of pure calcium oxide, which already in case of mass ratio 1 : 1 provides five-fold excess of free CaO in relation to HCl contained in PVC, 65-75% of the separated hydrochloride is bound in the mixture. Due to high excess the usage efficiency of calcium oxide remains low in these mixtures.

If pulverized combustion ash is used in the mixture, approximately 5% of the separated hydrochloride is bound at mass ratio 1 : 1. Increase of the mass ratio to 1 :2 will increase binding of HCl to 10%, but even in case of the extreme mass ratio of 1 :5 it is only 20% of the separated amount of HCl. 15% of the free calcium oxide contained in the ash will be used.

In case of fluidized bed ash, upon mass ratio 1 : 1 10% of the separated hydrochloride will be bound into the solid phase, increase of the mass ratio to 1 :2 will increase this parameter to 25%. Thereby 65...70% of the free calcium oxide contained in the ash will be used, and upon lower stoichiometric standard compared to PF ash. It should be noted, of course, that there are also other components in the ash, which are able to bind HCl, first and foremost calcium carbonate contained in fluidized bed ash, but also other oxides, therefore the calculation only of free calcium oxide would be somewhat formal. More precise calculations would be possible in case of much more complicated analytical measurements, but in this stage of work it was not considered practical.

Table 6. Binding of HCl with pure calcium oxide

CI CaO^v CaO^v

Mass

PVC additive binding usage eff., stoich.

ratio

eff., % % standard

PVC1 CaO 1 :2 65% 15% 5.0

PVC1 CaO 1 :4 74% 7% 10.0

Table 7. Binding of HCl in a mixture of various materials with mass ratio 1 :2

Table 8. C. Binding of HCl in various mixtures with increasing mass ratio

CI CaO^v CaO^v

Mass

PVC additive binding usage eff., stoich.

ratio

eff., % % standard

PVC2 PF 1:1 5% 14% 0.3

PVC2 PF 1:2 10% 14% 0.7

PVC1 PF 1:2 11% 15% 0.7

PVC1 PF 1:5 21% 11% 1.9

PVC2 CFBC 1:1 10% 58% 0.2

PVC2 CFBC 1:2 25% 71% 0.4

PVC1 CFBC 1:2 26% 64% 0.4

PVC1 CFBC 1:5 44% 43% 1.0 Summary

The tests proved that hydrochloride separated during decomposition of PVC can be partially bound to oil shale ash. Thermodynamically the process is favourable in a broad temperature range. The actual bound amount will depend on the properties and content of material.

Analysis of results showed that binding of HC1 will increase relatively slowly upon increase of the amount of lime materials, therefore rather high content of lime material would be necessary in relevant composites.

Of the used ashes, the fluidized bed ash was much more efficient binder of HC1 compared to pulverized combustion ash, in spite of higher content of free CaO in pulverized combustion ash. The difference of these two ashes is mainly in specific surface, therefore an oil shale ash with as large specific surface as possible would be preferred. Fluidized bed ash contains somewhat more calcium carbonate, which can also react with hydrochloride, its surface is more porous and access of hydrochloride to non-reacted oxide or carbonate is easier due to lower diffusion resistance. This leads to a conclusion that in terms of binding of HC1 the fluidized bed ash would be the most suitable among various oil shale ashes.

REFERENCES

[1] A. Ots, Polevkivi poletustehnika, Tallinn, 2004.

[2] R. Kuusik, M. Uibu, and K. Kirsimae, Characterization of oil shale ashes formed at industrial scale boilers. Oil Shale 22 (2005) 407-420.

[3] M. Uibu, M. Uus, and R. Kuusik, C02 mineral sequestration in oil shale wastes from Estonian power production. Journal of Environmental Management 90 (2009) 1253-1260.

[4] R. Kuusik, L. Tiirn, A. Trikkel, and M. Uibu, Carbon dioxide binding in the heterogeneous systems formed at combustion of oil shale. 2. Interactions of system components - thermodynamic analysis. Oil Shale 19 (2002) 143-160.

[5] R. Kuusik, M. Uibu, M. Toom, M.-L. Muulmann, T. Kaljuvee, and A. Trikkel, Sulphation and carbonization of oil shale CFBC ashes in heterogeneous systems. Oil Shale 22 (2005) 421-434.

Claims

1. OVC composite material containing oil shale ash, characterized by the fact that oil shale ash forms 0.5-60% of the composition of the composite material.

2. Composite material of claim 1, characterized by the fact that oil shale ash has been chosen from the following: fluidized bed ash, pulverized combustion ash.

3. Composite material of claim 1, characterized by the fact that oil shale ash contains up to 25% of free CaO and its specific surface is up to 10 m²/g.

4. Composite material of claim 1, characterized by the fact that fraction size of the oil shale ash is less than 0,045 mm.

5. Composite material of claim 1, characterized by the fact that free CaO contained in the oil shale ash is able to neutralise HC1 emitted during thermal decomposition of composite material according to the following reaction:

CaO + 2HC1 = CaCl₂ + H₂0.

6. Composite material of claim 1, characterized by the fact that it has been obtained through mixing of a powder with necessary composition with additives in a heated drum mixer with blades, using oil shale fly ash as an additive.

7, A product, characterized by the fact that it has been made of composite material in accordance with any of the claims 1 to 6.