Table 4.

Relative Proportion (% area) and Retention Times (RT) of the pyrolysis compounds in lignin obtained by different extraction methods.

Peak	RT (min)	Chemical Name	Origin	MW	Conventional Alkaline Extracted Lignina	PLPW Extracted Ligninb	Flax Shives (FS)
1	1.51	Acetic acid	C	60	-	-	13.2
2	1.67	Tetrahydrofuran	C	72	-	-	-
3	1.85	Benzene	B	78	-	0.68	-
4	2.11	2,5-dimethylfuran	C	78	-	-	-
5	2.74	Toluene	C	92	0.38	1.41	0.85
6	3.04	3-Methylene-heptane	C	112	0.16	-	-
7	3.41	3-Furaldehyde	C	96	-	-	0.29
8	3.8	Furfural	C	96	-	-	2.65
9	4.4	3-Furanmethanol	C	98	-	-	0.79
10	6.26	2-Furanone	C	84	-	-	-
11	6.83	1,2-Cyclopentanedione	C	98	-	-	1.93
12	10.9	Phenol	H	94	0.50	1.91	-
13	13.3	Maple lactone	C	112	-	-	0.61
14	15.3	o-Cresol	H	108	0.30	1.05	0.59
15	16.4	p-Cresol	H	108	0.51	1.98	1.06
16	16.8	Guaiacol	G	124	1.29	8.61	1.85
17	19.8	2,4-Xylenol	H	122	-	0.38	-
18	20.9	m-Methylguaiacol	G	138	-	0.48	-
19	21.5	4-Methyl guaiacol	G	138	0.91	4.74	1.34
20	22.0	Catechol	L/Pp	110	1.22	5.15	2.89
21	22.8	Coumaran	C	120	-	0.56	-
22	23.0	5-Hydrxoymethylfurfural	C	126	-	-	1.26
23	24.1	3-Methoxy catechol	L/Pp	140	-	1.19	0.70
24	24.3	3-Methyl catechol	L/Pp	124	-	1.35	0.77
25	24.9	4-Ethyl guaiacol	G	152	0.29	1.64	-
26	25.4	Homocatechol	L/Pp	124	0.78	3.05	3.46
27	26.1	4-Vinyl guaiacol	G	150	1.49	8.24	2.53
28	27.4	Syringol	S	154	0.43	2.69	0.44
29	27.6	Eugenol	G	164	0.44	1.72	0.88
30	28.6	4-Ethylcatechol	L/Pp	138	-	1.18	-
31	28.9	Vanillin	G	152	0.95	2.82	2.61
32	29.3	trans-Isoeugenol	G	164	1.15	1.05	0.52
33	30.6	cis-Isoeugenol	G	164	-	6.69	2.70
34	30.8	4-Propylguaiacol	G	166	-	-	0.89
35	31.5	Levoglucosan	C	180	39.54	2.45	0.53
36	31.7	Acetovanillone	G	166	-	2.52	1.38
37	35.2	4-Allylsyringol	S	194	-	0.44	-
38	36.7	Syringaldehyde	S	182	-	0.42	0.54
39	37.2	cis-Coniferyl alcohol	G	180	1.31	0.84	0.63
40	38.0	Methoxy eugenol	G	194	-	1.39	0.54
41	38.7	4-Hydroxy-2 methoxycinnamaldehyde	H	178	-	0.92	2.13
42	38.8	trans-Coniferyl alcohol	G	180	-	2.26	2.0
43	45.0	trans-Sinapaldehyde	S	208	1.73	-	-
		SUM (L + H + G + S)			13.3	64.7	30.5

C = carbohydrate type structure; B = benzene type structure; L = non-specific lignin [37]; Pp = polyphenolic structure [38]; H = hydroxyphenyl type lignin; G = guaiacyl type lignin; S = syringyl type lignin; MW = molecular weight.

^aConventional Alkaline Extracted Lignin: Alkali lignin isolated from flax shives using 5% NaOH at 80 °C for 5 h;

^bPLPW Extracted Lignin: Lignin in flax shives isolated with 0.47 M NaOH-180 °C PLPW extraction.

Flax shives: (FS).